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Doctoral Thesis

Physical properties of plagioclase- and bubble bearing magmas

Author(s): Tripoli, Barbara Andrea

Publication Date: 2016

Permanent Link: https://doi.org/10.3929/ethz-a-010691444

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DISS. ETH NO. 22938

PHYSICAL PROPERTIES OF

PLAGIOCLASE- AND BUBBLE-

BEARING MAGMAS

A thesis submitted to attain the degree of

DOCTOR OF SCIENCES of ETH ZURICH

(Dr. sc. ETH Zurich)

Presented by

BARBARA ANDREA TRIPOLI

Master in Earth Sciences, ETH Zürich, Switzerland

born on January 22, 1983

citizen of Valais, Switzerland

Accepted on the recommendation of

Prof. Dr. Peter Ulmer ETH Zürich Examiner

Prof. Dr. Jean-Pierre Burg ETH Zürich Co-Examiner

Dr. Alison Rust University of Bristol Co-Examiner

2016

ii

iii

" Dans la vie, rien n’est à craindre, tout est à comprendre. "

Marie Curie

A ma famille, A celle qu’on m’a donnée,

A celle que je construis.

Abstract

IV

Abstract

V

ABSTRACT

Seismic tomography of potentially hazardous volcanoes is a prime tool to assess the dimensions of magmatic

reservoirs and the possible modes and pathways of magma ascent. Magma rheology and volcanic eruptive style

are to a first order controlled by processes occurring within the conduit or in the magma chamber, such as

crystallization and bubble exsolution. Seismic velocities are strongly affected by these processes, but the

limited number of constrained measurements does not allow yet establishing a firm link between seismic

tomography and the textural and hence rheologic state of a particular volcanic system. Elastic parameters of

vapor-saturated, partially molten systems are thus providing fundamental information for the identification of

such reservoirs under active and seemingly dormant volcanoes.

In this PhD thesis, we investigated a chemically simplified melt analogous to andesite and trachyte, in the

system CaO-Na2O-Al2O3-SiO2-H2O-CO2, which undergoes plagioclase crystallization and bubble exsolution. A

Paterson-type internally-heated gas pressure apparatus was employed to measure the ultrasonic velocities at a

constant pressure of 250 MPa and at a frequency of 0.1 MHz. Samples were first heated at 850 °C for 30

minutes. Subsequently, the temperature was decreased at a rate of 0.5 or 0.1 °C/min to 700 °C and velocities

were recorded every 45 minutes. In order to characterize the microstructure evolution, series of cold-seal

experiments at identical pressure conditions but with rapid-quenching at each of the recorded temperatures

have been conducted in addition.

Magmatic processes such as crystallization, bubble nucleation and coalescence have been recognized

throughout the measurements of seismic velocities in the laboratory. Compression and shear wave velocities

increase non-linearly during crystallization. At crystal fractions exceeding 45 vol%, the formation of a crystal

network favors the propagation of seismic waves through magmatic liquids. However, bubble nucleation

induced by crystallization leads to an increase of magma compressibility resulting in a reduction of the wave

propagation velocities. These two processes occurring simultaneously have thus competing effects on the

seismic properties of magmas. In addition, when the bubble fraction is less than 10 vol%, the decrease in

seismic velocities is more pronounced than for higher bubble fractions. The effect of bubble coalescence on

elastic properties is thus lower than the effect of bubble nucleation.

In this study, the effect of increasing the amount of water dissolved in the melt is not taken into account in the

variation of seismic velocities, as no data at high pressure and high temperature are available in the current

literature. Consequently, velocities have been measured at high pressure and high temperature conditions in

hydrous phonolites from the Teide volcano, Canary Islands (Spain). At temperatures lower than the glass

transition, temperature derivatives of seismic velocities are independent of the dissolved water content. Upon

crossing the glass transition, temperature derivatives of both compression and shear wave velocities

significantly increase. This increase is accentuated by the addition of water following a trend previously

Abstract

VI

observed for melt viscosity. Indeed, the increase in temperature derivatives of seismic velocities is higher at

low water content. Glass transition temperatures estimated from the measured seismic velocities and

calculated relaxation times suggest that measurements in the liquid-like state have predominantly been

performed on relaxed samples.

Consequently, by continuously monitoring small seismic velocity perturbations in volcanic areas and by

combining these data with laboratory measurements of seismic velocities, evolution of the physical state of

magmatic reservoir could be assessed more precisely. In addition, a more accurate interpretation of available

seismic tomography images is possible and may permit a better assessment of potential volcanic hazards.

Another important aspect in volcanic hazards assessment is linked to the efficiency of the crystal-bearing melt

to release or withhold the volatile phase. We thus implemented the Paterson apparatus with a pore-fluid

system in order to explore the effect of crystallization on the extent of outgassing of bubble-bearing

haplotonalite melt.

The presence of crystals may favor or inhibit the outgassing. On one hand, the crystallization of anhydrous

minerals increases the water content dissolved in the melt. The induced decrease in viscosity leads to a higher

ascent velocity of bubbles, hence more extensive outgassing. In addition, a forced migration of bubbles due to

the growing plagioclase contributes to sustain the presence of large bubbles by coalescence and additionally

increases the outgassing rate. However, considering the same melt viscosity, the presence of crystals lowers

the outgassing rate by adding obstacles to the ascent path of bubbles. Crystallization of hydrous magma is thus

regulating the outgassing rate by (1) increasing the fraction and size of bubbles by exsolution and decreasing

the melt viscosity and (2) lowering their ascent velocity by increasing pathways length.

Consequently, the outgassing potential of a crystallizing magma chamber is high. In our experiments,

crystallization of more than 50 vol% of plagioclase in a melt containing initially 4.2 vol% of bubbles induced

outgassing of 4.6 to 6.6 vol% of bubbles over a rather limited time. Crystallization is thus only partially trapping

the magmatic volatiles into the system. Large bubbles produced in a hydrous melt are, thus, relatively free to

rise through a magmatic mush. These bubbles may ultimately rise to the surface through permeable networks

of fractures in the surrounding volcanic edifice or accumulate at the top of the magmatic reservoir and trigger

explosive eruptions.

Résumé

VII

RÉSUMÉ

La tomographie sismique effectuée sur des volcans potentiellement dangereux est un outil essentiel pour

l’identification et l’évaluation de la taille des chambres magmatiques. La rhéologie des magmas et le style

d’éruption volcanique sont principalement contrôlés par des processus se produisant dans le conduit ou dans la

chambre magmatique, tels que la cristallisation ou l’exsolution des phases gazeuses. Les vitesses sismiques

sont fortement affectées par ces processus, mais le nombre limité de mesures ne permet pas encore d’établir

un lien solide entre la tomographie sismique et l’état texturale et donc rhéologique d’un système volcanique.

Les paramètres élastiques des systèmes saturés en gaz et partiellement fondus peuvent donc fournir des

informations fondamentales dans l’identification des réservoirs magmatique de volcans actifs ou endormis.

Durant ce projet de thèse doctorale, nous avons étudié un liquide silicaté, chimiquement simplifié et analogue

aux andésites et trachytes, composé de CaO-Na2O-Al2O3-SiO2-H2O-CO2, qui cristallise des plagioclases tout en

formant des bulles. Une presse de type Paterson a été utilisée pour mesurer les vitesses ultrasoniques à haute

température, à une pression constante de 250 MPa et à une fréquence de vibration de 0.1 MHz. Les

échantillons ont d’abord été chauffés à 850°C pour une durée de 30 minutes. Par la suite, la température a été

descendue à un taux de 0.5 ou 0.1°C/min jusqu’à 700°C tout en mesurant les vitesses sismiques à intervalle de

45 minutes. Afin de caractériser l’évolution des microstructures, une série d’expériences dans une autoclave à

joint froid (Cold-Seal Vessel) a été réalisée à des pressions identiques mais en refroidissant rapidement

l’échantillon sur chaque palier de températures correspondant à la prise de mesures sismiques.

Les processus magmatiques, tels que la cristallisation, la nucléation et la coalescence des bulles ont été

reconnus au travers des mesures de vitesses sismiques en laboratoire. Les vitesses d’onde de compression et

de cisaillement augmentent de manière non-linéaire pendant la cristallisation. Lorsque le contenu en cristaux

est supérieur à 45% du volume, les cristaux forment un réseau continu ce qui favorise la propagation des ondes

sismiques dans les liquides magmatiques. Cependant, la nucléation des bulles induites par la cristallisation

produit une augmentation de la compressibilité ce qui réduit les vitesses de propagation des ondes. Ces deux

processus simultanés ont donc des effets contraires sur les propriétés sismiques des magmas. De plus, lorsque

le contenu en bulles est inférieur à 10% du volume, la diminution des vitesses sismiques est plus prononcée

que lorsque le contenu dépasse cette valeur. Il s’impose donc que la nucléation des bulles a un effet plus

important sur les vitesses sismiques que la coalescence des bulles.

Dans cette étude, l’augmentation du contenu en eau dissoute dans le liquide résiduel n’est pas prise en compte

dans les variations des vitesses sismiques, car aucune donnée à haute pression et haute température n’est

disponible dans la littérature. Par conséquent, les vitesses ont été mesurées à haute pression et à haute

température dans des phonolites hydratées du volcan Teide, situé à Tenerife (Espagne). A des températures

plus basses que la transition vitreuse, les dérivées des vitesses sismiques en fonction de la température sont

Résumé

VIII

indépendantes du contenu en eau dissoute. Lorsque la température dépasse celle de la transition vitreuse, les

dérivées des vitesses d’onde de compression et de cisaillement augmentent de manière significative en

fonction de la température. Cette augmentation est accentuée par l’ajout d’eau et suit une tendance

précédemment observée dans les études de la viscosité des liquides silicatés hydratés. En effet, l’augmentation

des dérivées des vitesses sismiques selon la température est plus importante pour des contenus en eau

inférieur à 1% pds. Les mesures de température de transitions vitreuses estimées par les vitesses sismiques et

les calculs de temps de relaxation suggèrent que les mesures dans l’état liquide ont été faites sur des

échantillons relaxés.

Par conséquent, en surveillant les petites perturbations des vitesses sismiques dans les zones volcaniques et en

combinant ces données aux mesures faites en laboratoire, l’évolution d’un réservoir magmatique peut être

estimée plus précisément. De plus, une interprétation plus précise des images de tomographie sismique est

possible et peut permettre une meilleure évaluation des risques potentiels liés aux volcans.

Un autre aspect important pour l’évaluation des risques volcaniques est lié à la capacité des liquides silicatés

contenant des cristaux à relâcher ou retenir la phase gazeuse. Nous avons donc implémenté dans la presse

Paterson un système mesurant la pression de pores, afin d’explorer l’effet de la cristallisation sur le dégazage

dans les liquides haplotonalitiques contenant des cristaux.

La présence des cristaux peut favoriser ou inhiber le dégazage. D’un côté, la cristallisation de minéraux

anhydres augmente le contenu en eau dissoute dans le liquide silicaté. La diminution de la viscosité induite par

ce processus produit une augmentation de la vitesse d’ascension des bulles, ce qui augmente le dégazage. De

plus, une migration forcée due à la croissance des plagioclases contribue à maintenir la présence de larges

bulles par coalescence et augmente encore plus le taux de dégazage. Cependant, en considérant une viscosité

identique du liquide silicaté, la présence de cristaux diminue le taux de dégazage en ajoutant des obstacles au

trajet ascensionnel des bulles. La cristallisation de magma aqueux a donc pour effet de réguler le taux de

dégazage par (1) l’augmentation de la fraction et de la taille des bulles par exsolution et la diminution de la

viscosité du liquide résiduelle et (2) la diminution de la vitesse d’ascension en augmentant la longueur du

parcours effectué par les bulles.

Par conséquent, le potentiel de dégazage d’une chambre magmatique cristallisant des minéraux est grand. Lors

de nos expériences, la cristallisation de plus de 50% du volume de plagioclase contenant initialement 4.2% du

volume de bulles induit un dégazage de 4.6 à 6.6% du volume de bulles dans un temps relativement limité. La

cristallisation piège donc seulement partiellement la phase volatile dans le système. Les grandes bulles

produites dans les liquides silicatés aqueux sont donc relativement libres de traverser une chambre

magmatique partiellement cristallisée. Ces bulles peuvent finalement atteindre la surface en passant par un

réseau de fractures dans l’édifice volcanique ou s’accumuler dans la partie supérieure d’une chambre

magmatique ce qui peut entraîner une éruption de type explosif.

Table of Content

IX

TABLE OF CONTENTS Abstract .................................................................................................................................................................... v Résumé................................................................................................................................................................... vii 1 Introduction .................................................................................................................................................... 1

1.1 General Introduction ............................................................................................................................. 1 1.1.1 Seismic properties of magmas .......................................................................................................... 2 1.1.2 Outgassing of volatile phases ............................................................................................................ 3

1.2 Structure of the thesis ........................................................................................................................... 4 1.3 References ............................................................................................................................................. 5

2 Experimental and analytical techniques ........................................................................................................ 8 2.1 Starting Materials .................................................................................................................................. 8

2.1.1 Phase equilibria calculation ............................................................................................................... 9 2.1.2 Glass Synthesis ................................................................................................................................ 10

2.2 Seismic velocities measurements ........................................................................................................ 12 2.2.1 Sample preparation ......................................................................................................................... 12 2.2.2 Paterson apparatus ......................................................................................................................... 12 2.2.3 Up-date of the assembly ................................................................................................................. 14 2.2.4 Calibration of the assembly ............................................................................................................. 15 2.2.5 Measurements strategy .................................................................................................................. 15

2.3 Rapid quench experiments .................................................................................................................. 16 2.4 Degassing Measurements.................................................................................................................... 16

2.4.1 Sample preparation ......................................................................................................................... 16 2.4.2 Paterson apparatus ......................................................................................................................... 16 2.4.3 Measurements strategy .................................................................................................................. 17

2.5 Analytical techniques ........................................................................................................................... 18 2.5.1 Microstructure analysis (2D) ........................................................................................................... 18 2.5.2 Chemical composition ..................................................................................................................... 20 2.5.3 Density............................................................................................................................................. 20

2.6 References ........................................................................................................................................... 21 3 Effects of crystallization and bubble nucleation on the seismic properties of magmas ............................ 22

3.1 Abstract ............................................................................................................................................... 22 3.2 Introduction ......................................................................................................................................... 22 3.3 Methodology ....................................................................................................................................... 24 3.4 Experimental and analytical results ..................................................................................................... 27

3.4.1 Microstructure: Cooling rate of 0.5 °C/min ..................................................................................... 27 3.4.2 Microstructure: Cooling rate of 0.1 °C/min ..................................................................................... 27 3.4.3 Microstructure: Interpretation........................................................................................................ 30

3.5 Discussion ............................................................................................................................................ 31 3.5.1 Effect of crystallization .................................................................................................................... 31 3.5.2 Effect of bubble nucleation ............................................................................................................. 32 3.5.3 Effect of bubble coalescence ........................................................................................................... 34 3.5.4 Effect of outgassing ......................................................................................................................... 34

3.6 Summary and application to natural system ....................................................................................... 36 3.7 Tables ................................................................................................................................................... 38 3.8 References ........................................................................................................................................... 40

4 Laboratory measurements of seismic velocities at HT-HP conditions in hydrous phonolite from Teide volcano, Tenerife, Canary Islands ........................................................................................................................ 42

4.1 Abstract ............................................................................................................................................... 42 4.2 Introduction ......................................................................................................................................... 42

4.2.1 Phonolite at Teide volcano .............................................................................................................. 43 4.3 Methods .............................................................................................................................................. 44

4.3.1 Glass synthesis ................................................................................................................................ 44 4.3.2 Seismic velocity measurements ...................................................................................................... 45

4.4 Results ................................................................................................................................................. 46

Table of Content

X

4.4.1 Glass synthesis ................................................................................................................................ 46 4.4.2 Effect of temperature on seismic velocities .................................................................................... 47 4.4.3 Effect of water content on temperature derivatives ...................................................................... 47 4.4.4 Effect of pressure on seismic velocities .......................................................................................... 49

4.5 Discussion ............................................................................................................................................ 49 4.5.1 Glass transition ................................................................................................................................ 49 4.5.2 Density............................................................................................................................................. 51 4.5.3 Elastic properties ............................................................................................................................. 52 4.5.4 Application to the magmatic chamber of teide volcano ................................................................. 53

4.6 Conclusion ........................................................................................................................................... 56 4.7 Tables ................................................................................................................................................... 57 4.8 References ........................................................................................................................................... 61

5 Outgassing induced by crystallization: An experimental study .................................................................. 64 5.1 Abstract ............................................................................................................................................... 64 5.2 Introduction ......................................................................................................................................... 64 5.3 Methods .............................................................................................................................................. 66

5.3.1 Sample synthesis ............................................................................................................................. 66 5.3.2 Outgassing experiments .................................................................................................................. 67 5.3.3 Evaluation of the microstructural variations ................................................................................... 68

5.4 Experimental and analytical results ..................................................................................................... 68 5.4.1 Involved magmatic processes ......................................................................................................... 69 5.4.2 Composition of the melt pockets .................................................................................................... 70 5.4.3 Microstructures of the samples recovered from the outgassing experiments ............................... 71 5.4.4 Outgassing measurements .............................................................................................................. 72

5.5 Discussion ............................................................................................................................................ 73 5.5.1 Cooling rate of 0.1°C/min ................................................................................................................ 75 5.5.2 Cooling rate of 0.5°C/min ................................................................................................................ 77

5.6 Conclusion ........................................................................................................................................... 78 5.7 Tables ................................................................................................................................................... 79 5.8 References ........................................................................................................................................... 81

6 Conclusion..................................................................................................................................................... 83 6.1 Seismic properties ............................................................................................................................... 83 6.2 Outgassing properties.......................................................................................................................... 84 6.3 Suggestions for future research .......................................................................................................... 84

Acknowledgements ............................................................................................................................................... 86 Curriculum Vitae ................................................................................................................................................... 88 Appendix A List of synthetized samples ......................................................................................................... 90 Appendix B Lists of experiments .................................................................................................................... 92

B.1 Paterson apparatus 9 ........................................................................................................................... 92 B.2 MHC cold-sealed pressure vessel ........................................................................................................ 93 B.3 Paterson apparatus 6 ........................................................................................................................... 93

Appendix C List of measured densities .......................................................................................................... 94 Appendix D Lists of chemical analyses ........................................................................................................... 95

D.1 Karl Fisher Titration measurements .................................................................................................... 95 D.2 Electron Microprobe measurements ................................................................................................... 97

D.2.1 Haplotonalite ................................................................................................................................... 97 D.2.2 Lavas Negras .................................................................................................................................. 108

Chapter 1 Introduction

1

1 INTRODUCTION

1.1 GENERAL INTRODUCTION

Volcanoes characterized by intermediate composition span a wide range of eruptive style, from relatively

benign effusive flows to devastating explosive Plinian eruptions. This dynamic variety of volcanic activities is a

direct consequence of both the underground driving forces (Takeuchi, 2004; Allan et al., 2012) and the magma

rheological properties. Magma rheology is strongly dependent on the intrinsic parameters of the involved

magma, i.e. melt composition, volatile content and bubble and crystal fractions (Giordano et al, 2008; Pistone

et al., 2012; Champallier et al, 2008) and on extrinsic parameters, such as temperature and strain rate (Webb

and Dingwell, 1990; Carricchi et al., 2007).

However, the internal structure of magmatic reservoirs is continuously evolving through various processes,

including cooling, heating or decompression. Once emplaced in the crust, magma crystallizes due to cooling

induced by conductive heat loss to the wall of the magma chamber (Brandeis and Jaupart, 1986; Sparks et al.,

1993). As a consequence, the melt becomes oversaturated in water and bubbles exsolve. Potentially, magma

mingling/mixing induces thermal and chemical instabilities and may trigger eruptions (Sparks and Sigurdsson,

1977). Petrologic data, such as chemical zonation or reaction patterns, suggest local temperature increases

prior to eruption and are attributed either to a direct injection of mafic magma into a felsic body (Murphy et

al., 2000) or to the conductive heat transfer from an underlying mafic magma body (Couch et al., 2001).

In addition, degassing-induced crystallization (e.g. Cashman and Blundy, 2000) results in close interdependence

of melt composition, crystal and bubble contents. As magma undergoes decompression during ascent,

exsolution of volatile components must occur. This phenomenon increases the melt liquidus temperature, and

ultimately leads to microlite crystallization. As a consequence, the crystal fraction increases, leading to a melt

with a continuously decreasing volatile content, and a shift towards silica-rich compositions (Hammer et al.,

1999; D'Oriano et al., 2005; Platz et al., 2007; Blundy et al., 2006). These processes operating in subvolcanic

magma reservoirs and within the volcanic conduit result in increasing the magma viscosity by orders of

magnitude.

Seismic velocities are strongly affected by processes such as crystallization or degassing. However, the limited

number of constrained measurements does not allow yet establishing a firm link between seismic tomography

and the textural and hence rheologic state of a particular volcanic system. Elastic parameters of vapor-

saturated, partially molten systems are thus providing fundamental information for the identification of such

reservoirs under active and seemingly dormant volcanoes. This PhD thesis is, therefore, dedicated to the

measurements of seismic properties and outgassing efficiency of crystal- and bubble-bearing magmas.


2

1.1.1 SEISMIC PROPERTIES OF MAGMAS

Seismic tomography of potentially hazardous volcanoes is a prime tool to identify and determine the size and

location of subvolcanic magma reservoirs (e.g. Ohlendorf et al., 2014; Chouet, 2003). Estimated through the

inversion of first-arrival times from local earthquakes, volcanic plumbing systems are recognized at depth by

their lower seismic velocity. Attempts to determine the physical state of magma reservoirs, i.e. melt

proportion, are more and more often conducted by combining seismic tomography with available laboratory

data and numerical simulation (Lin et al., 2014; Paulatto et al., 2012; Annen et al., 2014). Indeed, these low-

velocity zones may correspond to eruptible magma or non-eruptible mush depending on their phase fractions.

In situ laboratory measurements of compression and shear wave propagation velocities of magmas are thus

providing fundamental information for the identification of such reservoirs.

Laboratory measurements of elastic parameters have been performed on melts and glasses of various

compositions (Askarpour et al., 1993; Schilling et al., 2003; Webb and Courtial, 1996). Seismic velocities

decrease continuously with increasing temperature until reaching the glass transition temperature. This

temperature range corresponds to a transition in the physical properties of the melt from a solid-like (low

temperature) to a liquid-like behavior (high temperature). By crossing this region, a marked increase of the

temperature derivative of the compressional wave propagation velocity is observed. This break is less

pronounced for shear waves.

Although both mafic and silicic magmas can contain up to at least 6 wt% of dissolved water at depth (e.g.

Sisson and Layne, 1993; Hervig et al., 1989), studies on the effect of water on the seismic properties of magmas

are scarce. Experiments using Brillouin scattering spectroscopy have been performed on glasses with variable

composition and dissolved water content at room temperature (Richet and Polian, 1998; Malfait et al., 2011;

Whittington et al., 2012). Compression and shear wave velocities decrease linearly with the addition of water

for rhyolitic and andesitic glasses but remain constant for basaltic glasses (Malfait et al., 2011). With increasing

alkalinity of the investigated glasses, the addition of water results in increasing seismic velocities (Whittington

et al., 2012). These studies have been performed at room conditions and data collected at temperature

ensuring the liquid-like behavior of silicate are lacking to date.

The variation in elastic properties at the glass transition temperature has also been reported for crystal-bearing

melt (Caricchi et al., 2008). However, the amplitude of this variation decreases with increasing crystal content.

Microstructure, such as crystal or bubble content, is as well a fundamental parameter in determining the elastic

properties (e.g. Mueller et al., 2003; Hier-Majumder, 2008; Schmeling, 1985; Mavko, 1980). The non-linear

increase of seismic wave velocities by increasing the crystal fraction is a direct result of the formation of a

continuous crystal network (Caricchi et al., 2008). In addition, the orientation of elongated melt pockets

influences the seismic anisotropy of partially molten rocks and may result in erroneous estimation of the melt

fraction from seismic velocities (e.g. Mainprice, 1997)


3

Experimental studies on the effect of bubbles are scarce (Caricchi et al., 2008; Bagdassarov et al., 1994) and

their role on the elastic properties of magmas is not well-defined. However, some insight is given by studies

involving bubbly water. The addition of gas bubble critically decreases the seismic properties of the mixtures in

a logarithmic fashion, i.e. over the first percent of bubble, 90% of the total decrease of the sound speed is

achieved (Gibson, 1970; Kieffer, 1977). The density variation is not sufficient to account for this large variation

in the sound speed and it is, thus, attributed to the large increase in compressibility (Temkin, 2005). In their

numerical model involving bubble-bearing basaltic melt, Marchetti et al. (2004) applied equations of seismic

velocities derived for low- viscosity liquids, i.e. bubbly water, in order to better estimate variations in physical

properties of magmas. However, increasing the confining pressure and increasing the melt viscosity (compared

to measurements made on water at 1 atm) prevent a strong decrease in seismic velocities (Kieffer, 1977;

Ichihara et al., 2004; Ichihara and Kameda, 2004).

1.1.2 OUTGASSING OF VOLATILE PHASES

Another important aspect in volcanic hazards assessment is linked to the efficiency of the crystal-bearing melt

to release or not the volatile phase. Indeed, when the ascent velocity of large bubbles in a volcanic conduit is

faster than the ascent rate of the surrounding magma, the volcanic activity is characterized by passive

outgassing potentially accompanied by lava flows (e.g. Slezin, 2003, Melnik et al., 2005). However, more

explosive eruptions occur when the gas phase cannot separate from the rapidly ascending magma (e.g. Melnik

et al., 2005; Jaupart and Allègre, 1993). In addition, when outgassing is inhibited, the volatile phase may

accumulate in the magma chamber leading to a decrease in the bulk density (e.g. Blake, 1984). The increased

magma buoyancy may thus generate an overpressure higher than the strength of the country rocks, i.e.

overpressure higher than 10-40 MPa (Jellinek and DePaolo, 2003), leading to highly explosive eruptions (Malfait

et al., 2014; Bachman and Bergantz, 2008; Caricchi et al., 2014). The efficiency of outgassing is thus an

important parameter in determining the eruption style.

Various studies focused on mechanisms favoring or impeding outgassing in volcanoes. Bubbles may rise

buoyantly into the magma chamber or the volcanic conduit or volcanic gas can escape through interconnected

bubbles (e.g. Gonnermann and Manga, 2007). Eichelberger et al. (1986) observed that vesicular obsidian

becomes permeable at a porosity higher than 60 % whereas Klug and Cashman (1996) measured permeability

between 10-14 and 10-12 m-2 at a porosity as low as 30 %. In addition, when vesicular magmas are subject to

shearing, the bubbles are elongated and their connectivity is promoted (e.g. Saar and Manga, 1999). Gas can

thus escape in magmas with a porosity lower than 30 % depending on bubble shape. The crystalline phase

contributes as well to the extent of degassing: Bubbles are restricted to the melt phase and a large amount of

crystals would thus contribute to increase the connectivity in the residual melt although the porosity remains

low (Sparks, 2003). On the other hand, the crystalline phase may reduce the extent of degassing by inhibiting

the ascent of small bubbles (Belien et al., 2010).


4

Magmas at depth become saturated with volatile by two processes. The “first boiling” occurs when hydrous

melts are ascending towards the surface. Due to decompression, the solubility of water decreases and bubbles

exsolve (e.g. Cashman and Blundy, 2000). The second process that causes the volatile exsolution from the

silicate melt is linked to crystallization at constant pressure. Known as “second boiling”, this process is activated

by a cooling magma chamber which leads to crystallization. As a consequence, the melt becomes oversaturated

in water and bubbles exsolve. In both cases, the produced gas phase could escape from the magma chamber

along fracture networks developed within the magma and the conduit walls (Jaupart, 1998; Rust et al., 2004).

The “first boiling” has been studied experimentally (e.g. Mangan and Sisson, 2000; Mourtada-Bonnefoi and

Laporte, 2004) and numerically (e.g. Lensky et al., 2003; Proussevitch and Sahagian, 1998). Recently, some

studies investigated the influence of decompression on the permeability of magma (Okomura et al., 2012,

Namiki and Manga, 2008). However, no studies on the potentiality of degassing by “second boiling” have been

performed.

The studies presented in this PhD thesis are aimed at a better understanding of the seismic properties and

outgassing efficiency of magmas during crystallization. Simplified hydrous tonalite in the ternary system quartz-

albite-anorthite (Qtz-Ab-An; e.g. Johannes and Holtz, 1996; Johannes, 1989) is prone to crystallize plagioclase

at temperature and pressure conditions obtainable in the internally-heated gas pressure Paterson rig of the

Rock Deformation Laboratory (ETHZ). In addition, the crystallization of an anhydrous phase infers an increase in

water content in the melt which ultimately results in additional bubble nucleation.

1.2 STRUCTURE OF THE THESIS

The chapters of this PhD thesis are written in the form of paper for future submission to international journals.

The structure is as follow:

Chapter 2 is dedicated to the methodology followed during this thesis. A detailed description of the glass

synthesis and of the experimental techniques used for the measurements of physical properties during

crystallization are provided. In addition, analytical techniques used for the compositional and microstructural

characterization of the samples are described.

Chapter 3 reports the results of in-situ measurements of seismic properties of crystallizing magmas. Through

the continuous measurements of compression and shear wave velocities, magmatic processes, such as

crystallization, bubble nucleation and coalescence, as well as outgassing have been recognized and quantified.

This study has been accepted for publication in Geochemistry, Geophysics, Geosystems in February 2016.

Chapter 4 provides information on the effect of water content on the elastic properties of a natural melt from

the Teide volcano, Tenerife Island, Spain. The obtained data are directly applied to available seismic

tomography of the Teide volcano to infer the structure of the magmatic plumbing system.


5

Chapter 5 is dedicated to a study investigating the outgassing induced by crystallization. In-situ measurements

of the volume of gas lost from the sample with or without crystallization give some insight into gas migration in

magmatic chamber.

A series of Appendices are located at the end of this thesis. Tables containing all synthetized samples, all

performed experiments and all analytical measurements are available in this section.

1.3 REFERENCES

Annen, C., Paulatto, M., Sparks, R., Minshull, T., & Kiddle, E. (2014). Quantification of the intrusive magma fluxes during magma chamber growth at Soufrière Hills volcano (Montserrat, Lesser Antilles). Journal of petrology, 55(3), 529-548.

Askarpour, V., Manghnani, M. H., & Richet, P. (1993). Elastic properties of diopside, anorthite, and grossular glasses and liquids: a Brillouin scattering study up to 1400 K. Journal of Geophysical Research: Solid Earth (1978–2012), 98(B10), 17683-17689.

Bachmann, O., & Bergantz, G. (2008). The magma reservoirs that feed supereruptions. Elements, 4(1), 17-21. Bagdassarov, N., Dingwell, D. B., & Webb, S. L. (1994). Viscoelasticity of crystal-and bubble-bearing rhyolite

melts. Physics of the earth and planetary interiors, 83(2), 83-99. Belien, I. B., Cashman, K. V., & Rempel, A. W. (2010). Gas accumulation in particle-rich suspensions and

implications for bubble populations in crystal-rich magma. Earth and Planetary Science Letters, 297(1), 133-140.

Blake, S. (1984). Volatile oversaturation during the evolution of silicic magma chambers as an eruption trigger. Journal of Geophysical Research: Solid Earth (1978–2012), 89(B10), 8237-8244.

Blundy, J., Cashman, K., & Humphreys, M. (2006). Magma heating by decompression-driven crystallization beneath andesite volcanoes. Nature, 443(7107), 76-80.

Brandeis, G., & Jaupart, C. (1986). On the interaction between convection and crystallization in cooling magma chambers. Earth and Planetary Science Letters, 77(3), 345-361.

Caricchi, L., Annen, C., Blundy, J., Simpson, G., & Pinel, V. (2014). Frequency and magnitude of volcanic eruptions controlled by magma injection and buoyancy. Nature Geoscience, 7(2), 126-130.

Caricchi, L., Burlini, L., & Ulmer, P. (2008). Propagation of P and S-waves in magmas with different crystal contents: Insights into the crystallinity of magmatic reservoirs. Journal of volcanology and geothermal research, 178(4), 740-750.

Caricchi, L., Burlini, L., Ulmer, P., Gerya, T., Vassalli, M., & Papale, P. (2007). Non-Newtonian rheology of crystal-bearing magmas and implications for magma ascent dynamics. Earth and Planetary Science Letters, 264(3–4), 402-419. doi: http://dx.doi.org/10.1016/j.epsl.2007.09.032

Cashman, K., & Blundy, J. (2000). Degassing and crystallization of ascending andesite and dacite. Philosophical Transactions of the Royal Society of London A: Mathematical, Physical and Engineering Sciences, 358(1770), 1487-1513.

Champallier, R., Bystricky, M., & Arbaret, L. (2008). Experimental investigation of magma rheology at 300 MPa: From pure hydrous melt to 76 vol.% of crystals. Earth and Planetary Science Letters, 267(3), 571-583.

Chouet, B. (2003). Volcano seismology. Pure and Applied Geophysics, 160(3-4), 739-788. Couch, S., Sparks, R., & Carroll, M. (2001). Mineral disequilibrium in lavas explained by convective self-mixing in

open magma chambers. Nature, 411(6841), 1037-1039. D’Oriano, C., Poggianti, E., Bertagnini, A., Cioni, R., Landi, P., Polacci, M., & Rosi, M. (2005). Changes in eruptive

style during the AD 1538 Monte Nuovo eruption (Phlegrean Fields, Italy): the role of syn-eruptive crystallization. Bulletin of Volcanology, 67(7), 601-621.

Eichelberger, J., Carrigan, C., Westrich, H., & Price, R. (1986). Non-explosive silicic volcanism. Nature, 323(6089), 598-602.

Gibson, F. W. (1970). Measurement of the effect of air bubbles on the speed of sound in water. The Journal of the Acoustical Society of America, 48(5B), 1195-1197.

Giordano, D., Russell, J. K., & Dingwell, D. B. (2008). Viscosity of magmatic liquids: a model. Earth and Planetary Science Letters, 271(1), 123-134.

Gonnermann, H. M., & Manga, M. (2007). The fluid mechanics inside a volcano. Annu. Rev. Fluid Mech., 39,


6

321-356. Hammer, J., Cashman, K., Hoblitt, R., & Newman, S. (1999). Degassing and microlite crystallization during pre-

climactic events of the 1991 eruption of Mt. Pinatubo, Philippines. Bulletin of Volcanology, 60(5), 355-380.

Hervig, R. L., Dunbar, N., Westrich, H. R., & Kyle, P. R. (1989). Pre-eruptive water content of rhyolitic magmas as determined by ion microprobe analyses of melt inclusions in phenocrysts. Journal of volcanology and geothermal research, 36(4), 293-302.

Hier‐Majumder, S. (2008). Influence of contiguity on seismic velocities of partially molten aggregates. Journal of Geophysical Research: Solid Earth (1978–2012), 113(B12).

Ichihara, M., & Kameda, M. (2004). Propagation of acoustic waves in a visco-elastic two-phase system: influences of the liquid viscosity and the internal diffusion. Journal of volcanology and geothermal research, 137(1), 73-91.

Ichihara, M., Ohkunitani, H., Ida, Y., & Kameda, M. (2004). Dynamics of bubble oscillation and wave propagation in viscoelastic liquids. Journal of volcanology and geothermal research, 129(1), 37-60.

Jaupart, C. (1998). Gas loss from magmas through conduit walls during eruption. Geological Society, London, Special Publications, 145(1), 73-90.

Jaupart, C., & Allègre, C. J. (1991). Gas content, eruption rate and instabilities of eruption regime in silicic volcanoes. Earth and Planetary Science Letters, 102(3), 413-429.

Jellinek, A. M., & DePaolo, D. J. (2003). A model for the origin of large silicic magma chambers: precursors of caldera-forming eruptions. Bulletin of Volcanology, 65(5), 363-381.

Johannes, W. (1989). Melting of plagioclase-quartz assemblages at 2 kbar water pressure. Contributions to Mineralogy and Petrology, 103(3), 270-276.

Johannes, W., & Holtz, F. (1996). Petrogenesis and experimental petrology of granitic rocks (Vol. 335): Springer Berlin.

Kieffer, S. W. (1977). Sound speed in liquid‐gas mixtures: Water‐air and water‐steam. Journal of Geophysical research, 82(20), 2895-2904.

Klug, C., & Cashman, K. V. (1996). Permeability development in vesiculating magmas: implications for fragmentation. Bulletin of Volcanology, 58(2-3), 87-100.

Lensky, N., Navon, O., & Lyakhovsky, V. (2004). Bubble growth during decompression of magma: experimental and theoretical investigation. Journal of volcanology and geothermal research, 129(1), 7-22.

Lin, G., Amelung, F., Lavallée, Y., & Okubo, P. G. (2014). Seismic evidence for a crustal magma reservoir beneath the upper east rift zone of Kilauea volcano, Hawaii. Geology, 42(3), 187-190.

Mainprice, D. (1997). Modelling the anisotropic seismic properties of partially molten rocks found at mid-ocean ridges. Tectonophysics, 279(1), 161-179.

Malfait, W. J., Sanchez-Valle, C., Ardia, P., Médard, E., & Lerch, P. (2011). Amorphous Materials: Properties, Structure, and Durability Compositional dependent compressibility of dissolved water in silicate glasses. American Mineralogist, 96(8-9), 1402-1409.

Malfait, W. J., Seifert, R., Petitgirard, S., Perrillat, J.-P., Mezouar, M., Ota, T., . . . Sanchez-Valle, C. (2014). Supervolcano eruptions driven by melt buoyancy in large silicic magma chambers. Nature Geoscience, 7(2), 122-125.

Mangan, M., & Sisson, T. (2000). Delayed, disequilibrium degassing in rhyolite magma: decompression experiments and implications for explosive volcanism. Earth and Planetary Science Letters, 183(3), 441-455.

Marchetti, E., Ichihara, M., & Ripepe, M. (2004). Propagation of acoustic waves in a viscoelastic two-phase system: influence of gas bubble concentration. Journal of volcanology and geothermal research, 137(1), 93-108.

Mavko, G. M. (1980). Velocity and attenuation in partially molten rocks. Journal of Geophysical Research: Solid Earth (1978–2012), 85(B10), 5173-5189.

Melnik, O., Barmin, A., & Sparks, R. (2005). Dynamics of magma flow inside volcanic conduits with bubble overpressure buildup and gas loss through permeable magma. Journal of volcanology and geothermal research, 143(1), 53-68.

Mourtada-Bonnefoi, C. C., & Laporte, D. (2004). Kinetics of bubble nucleation in a rhyolitic melt: an experimental study of the effect of ascent rate. Earth and Planetary Science Letters, 218(3), 521-537.

Müller, K., Bagdassarov, N., James, M., Schmeling, H., & Deubener, J. (2003). Internal friction spectroscopy in Li2O–2SiO2 partially crystallised glasses. Journal of non-crystalline solids, 319(1), 44-56.


7

Murphy, M., Sparks, R., Barclay, J., Carroll, M., & Brewer, T. (2000). Remobilization of andesite magma by intrusion of mafic magma at the Soufriere Hills Volcano, Montserrat, West Indies. Journal of petrology, 41(1), 21-42.

Namiki, A., & Manga, M. (2008). Transition between fragmentation and permeable outgassing of low viscosity magmas. Journal of volcanology and geothermal research, 169(1), 48-60.

Ohlendorf, S. J., Thurber, C. H., Pesicek, J. D., & Prejean, S. G. (2014). Seismicity and seismic structure at Okmok Volcano, Alaska. Journal of volcanology and geothermal research, 278, 103-119.

Okumura, S., Nakamura, M., Nakano, T., Uesugi, K., & Tsuchiyama, A. (2012). Experimental constraints on permeable gas transport in crystalline silicic magmas. Contributions to Mineralogy and Petrology, 164(3), 493-504.

Paulatto, M., Annen, C., Henstock, T. J., Kiddle, E., Minshull, T. A., Sparks, R., & Voight, B. (2012). Magma chamber properties from integrated seismic tomography and thermal modeling at Montserrat. Geochemistry, Geophysics, Geosystems, 13(1).

Pistone, M., Caricchi, L., Ulmer, P., Burlini, L., Ardia, P., Reusser, E., . . . Arbaret, L. (2012). Deformation experiments of bubble‐and crystal‐bearing magmas: Rheological and microstructural analysis. Journal of Geophysical Research: Solid Earth (1978–2012), 117(B5).

Platz, T., Cronin, S. J., Cashman, K. V., Stewart, R. B., & Smith, I. E. (2007). Transition from effusive to explosive phases in andesite eruptions—A case-study from the AD1655 eruption of Mt. Taranaki, New Zealand. Journal of volcanology and geothermal research, 161(1), 15-34.

Proussevitch, A., & Sahagian, D. (1998). Dynamics and energetics of bubble growth in magmas: analytical formulation and numerical modeling. Journal of Geophysical Research: Solid Earth (1978–2012), 103(B8), 18223-18251.

Richet, P., & Polian, A. (1998). Water as a dense icelike component in silicate glasses. Science, 281(5375), 396-398.

Rust, A., Cashman, K., & Wallace, P. (2004). Magma degassing buffered by vapor flow through brecciated conduit margins. Geology, 32(4), 349-352.

Saar, M. O., & Manga, M. (1999). Permeability‐porosity relationship in vesicular basalts. Geophysical Research Letters, 26(1), 111-114.

Schilling, F. R., Sinogeikin, S. V., Hauser, M., & Bass, J. D. (2003). Elastic properties of model basaltic melt compositions at high temperatures. Journal of Geophysical Research: Solid Earth (1978–2012), 108(B6).

Sisson, T., & Layne, G. (1993). H 2 O in basalt and basaltic andesite glass inclusions from four subduction-related volcanoes. Earth and Planetary Science Letters, 117(3), 619-635.

Slezin, Y. B. (2003). The mechanism of volcanic eruptions (a steady state approach). Journal of volcanology and geothermal research, 122(1), 7-50.

Sparks, R. (2003). Dynamics of magma degassing. Geological Society, London, Special Publications, 213(1), 5-22. Sparks, R. S., Huppert, H. E., Koyaguchi, T., & Hallworth, M. A. (1993). Origin of modal and rhythmic igneous

layering by sedimentation in a convecting magma chamber. Nature, 361(6409), 246-249. Sparks, S. R., & Sigurdsson, H. (1977). Magma mixing: a mechanism for triggering acid explosive eruptions.

Nature, 267, 315-318. Takeuchi, S. (2004). Precursory dike propagation control of viscous magma eruptions. Geology, 32(11), 1001-

1004. Takeuchi, S. (2004). Precursory dike propagation control of viscous magma eruptions. Geology, 32(11), 1001-

1004. Temkin, S. (2005). Suspension acoustics: An introduction to the physics of suspensions: Cambridge University

Press. Webb, S., & Courtial, P. (1996). Compressibility of melts in the CaO-Al2O3-SiO2 system. Geochimica et

cosmochimica acta, 60(1), 75-86. Webb, S. L., & Dingwell, D. B. (1990). The onset of non-Newtonian rheology of silicate melts. Physics and

Chemistry of Minerals, 17(2), 125-132. Whittington, A. G., Richet, P., & Polian, A. (2012). Water and the compressibility of silicate glasses: A Brillouin

spectroscopic study. American Mineralogist, 97(2-3), 455-467.

Chapter 2 Experimental and Analytical Techniques

8

2 EXPERIMENTAL AND ANALYTICAL TECHNIQUES

2.1 STARTING MATERIALS

Studying the seismic and/or degassing properties of magmas requires a composition that crystallizes phases

relevant for volcanology in the P-T range achievable with the available apparatus. The simplified hydrous

tonalite system has been intensively studied in the ternary system quartz-albite-anorthite (Qtz-Ab-An; e.g.

Johannes and Holtz, 1996; Johannes, 1989) and has the advantage to either crystallize quartz and plagioclase or

a cotectic mixture of the two at low temperature and high pressure conditions (Figure 2.1).

Figure 2.1: (a) Ternary diagram of the simplified tonalite system quartz-albite-anorthite displaying variation in the cotectic line separating the plagioclase and quartz primary phase field as a function of pressure. (b) Liquidus surfaces from (a) at 5 kbar as cross-sections drawn from the Qz apex to the albite-anorthite join (Johannes and Holtz, 1996).

However, for this study, the crystallization of a single phase (plagioclase) was chosen in order to facilitate the

interpretation of the acquired physical properties data. We have chosen the same composition as Picard et al.

(2011) used for studying rheological properties of plagioclase-bearing melt (see Table 2.1). Their starting

material has been obtained by crystallization of plagioclase from a tonalite melt at 300 MPa and 800°C for a

duration of 7 days. This method has the advantage to produce a suspension of anisotropic, chemically (nearly)

homogeneous, euhedral and regularly distributed crystals.


9

Table 2.1: Compositions of the starting material containing 2.8 wt% H2O measured by electron microprobe in wt%. The nominal composition corresponds to the composition of the powder before the HIP. Water and CO2 contents have been measured by KFT and by coulometry respectively. The CO2 contained in the starting mix is contained in the coexisting bubbles in the synthetic glass (“measured composition”).

Sample SiO2 Al2O3 CaO Na2O H2O CO2 Total

Nominal Composition 65.69 18.56 3.33 7.61 2.80 2.00 100

Measured Composition 65.26 18.81 3.49 7.51 2.75* 0.03 97.82

2.1.1 PHASE EQUILIBRIA CALCULATION

In this study we investigated a chemically simplified melt analogous to andesite and trachyte in the system

CaO-Na2O-Al2O3-SiO2-H2O-CO2 (Picard et al, 2011). This composition has the advantage of containing the

element naturally present in plagioclase and is thus prone to crystallize this phase. The addition of water to this

system lowered the liquidus temperature as well as the temperature of phase stability; the addition of carbon

dioxide insured the presence of bubble at the investigated pressure as the CO2 solubility in this silica-saturated

composition at the conditions of synthesis and the subsequent crystallization experiments is very low. We

computed the phase equilibria of the considered system (Figure 2.2) for various pressure, temperature and

water contents using Perple_X (Connolly and Kerrick, 2002; Connolly, 2009). The water content dissolved in the

melt influences the position of various boundary curves: a) at 200 MPa, the liquidus temperature is 1171 °C for

2.8 wt% H2O, 1201 °C for 2 wt% H2O and 1255 °C for 1 wt% H2O; b) at temperature higher than the solidus,

water exsolution is shifted to higher pressure with increasing water content; and c) the stability of quartz

increases at the expense of plagioclase with decreasing water content (the plagioclase liquidus is suppressed

more effectively than the quartz liquidus).

Figure 2.2: P-T-Phase diagram of a simplified tonalite containing various amount of water.


10

Based on these (computed) phase diagrams, we decided to synthetize bubble-bearing glasses with various

water contents (Figure 2.2) at the highest pressure and temperature achievable with the Hot Isostatic Press, i.e.

1200 °C (1473 K) and 200 MPa (2000 bars).

2.1.2 GLASS SYNTHESIS

2.1.2.1 BUBBLE-BEARING GLASS

In order to produce large quantities of chemically homogeneous, hydrated glasses, oxide, hydroxide and

carbonate powders were mixed to obtain the desired compositions. These mixtures were subsequently cold

pressed into stainless steel canisters with a uniaxial pressure of 200 MPa. Molybdenum foils lining the border

of the canister avoided contamination from the container wall. Subsequently, these mechanical mixtures have

been thermally equilibrated in a Hot Isostatic Press (HIP) at 1200 °C and 200 MPa for 24 hours (see Figure 2.3).

The vessel was then rapidly cooled to 550 °C in order to quench the samples. This temperature corresponds to

the glass transition temperature of the least hydrated sample, i.e. containing 1 Wt% H2O, calculated using the

model of Giordano et al. (2008) and assuming a viscosity of 1012 Pa*s. From 550°C to room temperature, a

cooling rate of 0.6°C/min was applied to allow for thermal relaxation of the glass.

Figure 2.3: Pressure and temperature path applied in the Hot Isostatic Press (HIP) during the synthesis of glasses. The dark grey line represents the pressure and the light grey line the temperature. After technical upgrade of the HIP, the pressure could be maintained to 200 MPa (± 10 MPa) during the fast cooling (dashed line).

Samples containing less than 2 wt% H2O crystallized large and euhedral plagioclase rich in anorthite. A minor

amount of spherulitic albite (less than 1 vol%) crystallized in the sample containing more than 2 wt% H2O.

However, the resulting hydrated glasses are chemically homogeneous and their compositions correspond to

the nominal values within 1 % (Table 2.1). CO2-rich bubbles (4.2 vol%) have a number density of 167 [1/mm2]

and their sizes have a narrow distribution located around 6 µm (see Figure 2.4). The sample containing 2.8 wt%

H2O was finally selected for the experiments.


11

Figure 2.4: SEM image (A) of the bubble-bearing glass synthetized in the HIP and its bubble-size distribution (B).

As the sample containing less than 2 wt% H2O crystallized more than 20 vol% of anorthite, we decided to use

natural phonolite glass to study the effect of dissolved water on the seismic properties of melt.

2.1.2.2 PHONOLITE GLASS

For the synthesis of hydrated phonolite glass, we used the same P-T path in the HIP. However, the hydration of

a natural sample needs to be done through the addition of distilled water. The samples collected in the Lavas

Negras (Teide volcano, Spain) were first melted in air at 1600 °C. The resulting glass was crushed and mixed

with various amount of distilled water, i.e. 0.1, 0.5, 1.0, 2.0 and 3.0 wt% H20. The procedure for cold-pressing

these mixtures into stainless steel canisters was identical with the procedure used for the bubble-bearing glass.

Table 2.2: Composition in [wt%] of the hydrous phonolite from Lavas Negras (Tenerife, Spain) measured by electron microprobe. *The water content was measured by Karl Fisher Titration.

LN5 LN4 LN3 LN2 LN1

SiO2 60.16 60.23 60.65 60.24 60.39

Al2O3 18.33 18.52 18.66 18.56 18.58

FeO (tot) 3.04 3.36 3.37 3.40 3.44

TiO2 0.63 0.67 0.68 0.67 0.68

MnO 0.19 0.19 0.20 0.20 0.21

MgO 0.32 0.35 0.37 0.37 0.36

CaO 0.73 0.72 0.71 0.72 0.72

Na2O 8.74 9.05 9.19 9.33 9.24

K2O 4.72 4.75 4.84 4.85 4.85

H2O* 1.87 1.37 0.56 0.32 0.36

Nominal H2O 3.00 2.00 1.00 0.50 0.10

Total 98.74 99.21 99.23 98.66 98.84

After synthesis in the HIP, the water content of the glasses were measured by Karl Fisher Titration (KFT). The

sample containing nominally 0.1 wt% H20, i.e. LN1, has a water content higher than expected whereas samples


12

containing nominally more than 0.5 wt% H20 lost some water. All glasses are chemically homogeneous except

for LN4 and LN5 that contain 1.4 and 3.5 vol% of iron oxides, respectively. In order to quantify the influence of

these microlites on the seismic properties, we calculated the Voigt-Reuss-Hill average VVRH by using these

equations:

𝑉𝑉𝑅𝐻 = 𝑉𝑉 + 𝑉𝑅

2

𝑉𝑉 = ∑ 𝛷𝑖 ∗ 𝑉𝑖

𝑁

𝑖=1

1

𝑉𝑅

= ∑𝛷𝑖

𝑉𝑖

𝑁

𝑖=1

where VV is the Voigt upper bound, VR is the Reuss lower bound, Φi is the fraction of the ith component and Vi

is the seismic velocity (shear or compression waves) of the ith component (Mavko et al., 2009). Assuming a

compression wave velocity Vp of 6.04 km/s for the phonolite glass (Seifert et al., 2013) and 7.35 km/s for the

iron oxides (data for a magnetite crystal taken from Ji et al., 2002), the Voigt-Reuss-Hill average is 6.06 and 6.08

km/s for a crystal content of 1.4 and 3.5 vol%, respectively. Concerning the shear wave velocity Vs, we assumed

a velocity of 3.59 km/s for the phonolite glass (Seifert et al., 2013) and 4.2 km/s (Ji et al., 2002) for magnetite.

The calculated velocities are 3.60 and 3.61 km/s for a crystal content of 1.4 and 3.5 vol%, respectively.

Based on these calculations, we decided to measure the seismic properties of all phonolite glasses synthetized

in the HIP. The error induced by the presence of Fe-oxide microlite is effectively within the error of the

measurements, i.e. 0.1 km/s for Vp and 0.4 km/s for Vs.

2.2 SEISMIC VELOCITIES MEASUREMENTS

2.2.1 SAMPLE PREPARATION

Glasses synthetized in the HIP were drilled into cores of 22 mm diameter for the measurements of pressure

and temperature derivatives and 15 diameter mm for determination of the effect of crystallization on the

seismic and degassing properties of magmas. The cores were cut to a length of 30 mm and double polished to

obtain parallel faces. Bubble-free samples were dried at 110 °C for 24 hours prior to measurements whereas

bubble-bearing samples were dried at 40 °C for 24 hours. Higher temperature provoked the fracture of the

cored glasses due to the expansion of gas in the bubbles.

2.2.2 PATERSON APPARATUS

Absolute velocities as well as changes in seismic properties of crystallizing magmas have been measured in a

Paterson-type internally-heated gas pressure apparatus (Paterson and Olgaard, 2000). Piezoelectric

transducers placed at both extremities of the assembly (see Figure 2.5A) permit the in-situ measurement of


13

compression wave velocities using the pulse transmission technique (Birch, 1960). Electric waves with known

frequency, pulse width and repetition rate are generated using a pulser (PC-plug-in thoneburst card controlled

by the software Matec). The generated pulses (see Figure 2.5B) are sent to a piezoelectric transducer, which

converts them into elastic ultrasound waves, i.e. when an electric field is applied, the transducers expand and

produce compressional waves. The vibrational frequency applied to the transducers ranges from 0.1 to 3 MHz.

After traveling through the sample, the signals are converted back into electric waves by a second transducer

placed on the opposite side of the assembly and they are finally displayed on an oscilloscope (see Figure 2.5C).

The time required for the wave to travel through the sample can be deduced from the oscilloscope

measurement. Knowing the length of the core, the velocity can finally be calculated. For each measurements,

we recorded waveforms averaged over 1000 received signal. The picking of the first arrival was done after the

experiments through a code written in Matlab.

Figure 2.5: (A) Schematic drawing of the HP-HT Paterson apparatus implemented with the setup to measure seismic velocities. (B) Electronic signal emitted by the pulser. The frequency is 1 MHz, the pulse width is 2 µs and the repetition rate is 5 ms. (C) Electronic signal received by the oscilloscope. This waveform has been recorded while the assembly was at 310 MPa and ambient temperature.

As the piezoelectric transducers are inefficient at high temperature, alumina rods placed between the

transducers and the sample are used to obtain pulse generation and recording at considerably lower

temperature (less than 100°C). However, considering the length of the sample, i.e. 30 mm, we had to insure

that the furnace was producing a constant temperature all along the sample. The furnace was thus calibrated

using an assembly made of alumina rods having a 2 mm diameter hole. This hole permits the insertion of an R-


14

type thermocouple. In order to constrain the temperature during the experiments, two thermocouples are

inserted in the assembly, i.e. one at the bottom and one at the top of the sample. The temperature difference

between these two thermocouples never exceeded 5 °C.

In order to have hydrostatic condition, the system uses argon gas as confining medium. The assembly is

isolated from the argon by an iron jacket of 0.2 mm wall thickness.

2.2.3 UP-DATE OF THE ASSEMBLY

In order to obtain the elastic properties of a crystallizing melt, both compressional and shear wave velocities

need to be measured simultaneously. The assemblies for high temperature measurements previously

employed in the Rock Deformation laboratory are suitable for samples that do not significantly change their

physical state as they contain only one piezoelectric transducer. This is not the case for our synthetic samples

as crystal and bubble contents change during the experiment.

Based on the work of the previous head of the laboratory, PD Dr. Luigi Burlini, two different types of

piezoelectric transducers, producing vertical or horizontal motions, have been introduced in the high

temperature assembly (see Figure 2.6). In order to avoid the simultaneous excitation of the transducers, a disk

of pyrophillite is separating them. This assembly is placed at the end of the alumina spacers in order to avoid

the high temperature plateau in the center of the sample assembly.

Figure 2.6: Drawing of the Vp/Vs transducers assembly designed for high temperature measurements.

In order to calibrate this new transducers assembly, an isotropic standard was used instead of the commonly

employed anisotropic sapphire used for compression wave velocities measurements. This new standard had to

fulfill several specific conditions: high melting temperature, isotropic physical properties, low compressibility

and low thermal expansion. In addition, the pressure and temperature derivatives of at least two elastic

constants should be known. The most suitable standard resulted to be fused quartz glass.


15

2.2.4 CALIBRATION OF THE ASSEMBLY

The time delay caused by the stack of alumina rods have been measured at various pressures and

temperatures using a sapphire crystal cut parallel to [0001] for compression wave velocity. The formula used to

determine the travel time through the standard is:

𝑉𝑝,𝑠𝑡𝑟𝑑 = 11.356 + 5.4 ∗ 10−5 ∗ 𝑃 − 3.986 ∗ 10−4 ∗ 𝑇

where P is the confining pressure in MPa and T is the temperature in K. For the calibration of the time delay

when shear waves are travelling through the assembly, we used a glass of fused quartz manufactured by

Goodfellow. The formula for calculating the travel time is an average of data collected in various studies

(Peselnick et al., 1967; Manghnani, 1974; Gerlich and Kennedy, 1978; Polian et al., 2002; Spinner, 1956; Gieske

and Frost, 1991; Bucaro and Dardy, 1974):

𝑉𝑠,𝑠𝑡𝑟𝑑 = 3.7251 + 2.0641 ∗ 10−4 ∗ 𝑇

where T is the temperature in °C and P is set constant at 250 MPa.

The error on the measurements is mainly linked to the picking of the first arrival and reaches 0.1 km/s for

compression wave velocity and 0.2 km/s for shear wave velocity.

2.2.5 MEASUREMENTS STRATEGY

2.2.5.1 PRESSURE AND TEMPERATURE DERIVATIVES

The arrival times were recorded first at room temperature and various pressures in order to determine the

pressure derivative of shear and compression waves. Then, the pressure was maintained at 250 MPa and the

temperature was increased to the maximum temperature planned for the experiment. Ultrasonic velocities has

been recorded each 20 to 50 °C while decreasing the temperature at a rate of 10 °C/min. In order to allow the

sample and the assembly to equilibrate to the new thermal condition, constant temperature was maintained

during a minimum of 20 minutes.

2.2.5.2 CRYSTALLIZATION AND BUBBLE NUCLEATION

We performed the experiments at a constant pressure of 250 MPa. Samples were first heated at a rate of

30°C/min to 850°C. This temperature was maintained constant for 30 minutes. Subsequently, the temperature

was decreased to 700°C at a cooling rate of 0.5 or 0.1°C/min. Seismic velocities were recorded every 45

minutes. At 700°C, the temperature was decrease to room temperature at a rate of 30°C/min.


16

2.3 RAPID QUENCH EXPERIMENTS

In order to determine the evolution of the microstructure during the seismic property measurement

experiments, the P-T conditions applied in the Paterson apparatus were reproduced in a rapid-quench

molybdenum-hafnium-carbide (MHC) cold-seal pressure vessel. Placed on a rotary table, this externally heated

pressure vessel permits dropping the sample into the cold steel extremity linked to the MHC part by a water-

cooled nut. This setup allows rapid quench of the sample at a rate of about 100°C/s, which allows preserving

the microstructure formed at run pressure and temperature. The temperature gradient in the hot MHC

extremity never exceeded 5°C over the sample length. Cores of 4 mm in length and in diameter drilled from the

starting glass were contained in Au capsules that were welded shut using a W-electrode arc-welder. Runs were

quenched under pressure at identical time steps, and thus identical temperatures, as the seismic velocities

measurements were performed.

Figure 2.7: Schematic drawing of the Molybdenum-Hafnium-Carbide (MHC) cold-seal vessel.

2.4 DEGASSING MEASUREMENTS

2.4.1 SAMPLE PREPARATION

The bubble-bearing glasses were prepared with the same method as for the seismic velocity measurements,

except for their length. We double polished the samples to a length of approximatively 10 mm.

2.4.2 PATERSON APPARATUS

The extent of degassing during plagioclase crystallization was determined using a Paterson apparatus

implemented with a volumometer and upstream and downstream pore-fluid connections (see Figure 2.8). The

volumometer has a confined diameter of 7 mm and a length of 50 mm, which permits to achieve an accuracy of

the pore pressure (argon gas) of 0.1 MPa. Pressure sensors are placed in the upstream and downstream pore-

fluid connections. A Schaevitz LVDT placed on the axis of the actuator measures the displacement of the

volumometer piston with a resolution of 0.01 mm.


17

Figure 2.8: Schematic drawing of the Paterson apparatus implemented with a pore-fluid system (Violay et al., 2015).

The assembly is composed of zirconia and alumina rods with a 2 mm hole drilled in the center for the insertion

of the pore-fluid and the thermocouple. The sample is isolated from the pore fluid pressure at the bottom by

an alumina disc. Bubbles can thus escape from the sample only through the porous top mullite disc.

2.4.3 MEASUREMENTS STRATEGY

The temperature paths were identical to the seismic experiments, i.e. maintained during 30 minutes at 850 °C

and then cooled down to 700 °C at a rate of 0.5 and 0.1 °C/min respectively. The confining pressure was kept

constant at 250 MPa. As the precision of the volumometer is better at higher pressure, the pore-fluid pressure

was initially set to 5 MPa. A gradient of 5 MPa was therefore present within the sample; The alumina discs

placed at the bottom of the sample was at a pressure equal to the confining pressure (Pc) and the porous

mullite disc placed at the top of the sample was subjected to a pressure that is equal to Pc – Pf, i.e. the top part

of the sample was at 245 MPa.

During the experiments, the position of the volumometer piston was kept constant. The number of mole

degassed from the sample was calculated from the variation of pore pressure assuming ideal gas behavior:

𝑃 ∗ 𝑉 = 𝑛 ∗ 𝑅 ∗ 𝑇

where P is the variation of pressure measured in the volumometer in Pa, V is the volume of the pore fluid

system (assembly, pipes and volumometer) in m3, n is the number of moles degassed from the sample in mol, R

is the gas constant (8.3144621 J/(mol*K)) and T is the temperature in the volumometer in K. Although the

sample is degassing a mixture of H2O and CO2, we used the ideal gas law as more than 90 % of the gas in the

system at the end of the experiments is argon.


18

As the temperature was decreased during the experiments, the pore-fluid pressure was additionally corrected

for the variation of temperature:

𝑃 = 𝑃𝑚𝑒𝑎𝑠 −𝑑𝑃

𝑑𝑇∗ 𝑇

where Pmeas is the pore-fluid pressure measured during the experiments in MPa, T is the temperature of the

sample in °C and dP/dT is the calibrated variation of pressure as function of temperature changes. The

calibration has been done prior to the experiments using an alumina rod instead of the sample in the assembly.

2.5 ANALYTICAL TECHNIQUES

2.5.1 MICROSTRUCTURE ANALYSIS (2D)

Microstructures (phase fraction, bubble number density, bubble size distribution, spherulite number density

and spherulite diameter) have been determined by evaluation of BSE (back-scattered electron) images of the

starting material (synthetized in the HIP), the final sample (crystallized in the Paterson apparatus) and the

rapidly quenched samples (crystallized in the MHC cold-sealed vessel). Images were taken at a magnification of

200x over 1 cm2 for the starting and final samples and over the entire capsules (16 mm2) for the quenched

samples.

The phase fractions were determined by grayscale dissociation using the software ImageJ. The images were

first hand-corrected for bubbles that didn’t appear in black (see Figure 2.9A and B) and for the cracks that

appeared during the fast quench in the cold-sealed apparatus. We manually adjusted the threshold of each

image to separate individual phases (see Figure 2.9C, E and F). ImageJ was then used to calculate the total area

occupied by melt, crystals and bubbles respectively.


19

Figure 2.9: Example of the image processing using ImageJ. (A) Original BSE (back-scattered electron) image taken by SEM. (B) Image with enhanced contrast and corrected for bubbles and cracks. The scale bar has been removed. (C) Binary image of the bubble fraction. (D) Outlines of the bubbles from image (C). (E) Binary image of the melt fraction. (F) Binary image of the crystal fraction.

Another function in ImageJ permits to count and measure the size of each particles (see Figure 2.9D). The SEM

images were thus assembled and bubble number density and bubble size distribution were calculated for the

entire area covered by the image. Bubbles smaller than 3 pixel units, i.e. with a diameter smaller than 1.5 µm,

have been excluded from the bubble characterization. The diameters of irregular bubbles in the crystallized

samples were calculated assuming a spherical shape.


20

Spherulite number density and spherulite diameters were determined by manually drawing the limits of each

spherulite aggregate. The resulting drawing was then used in ImageJ for the spherulite characterization.

2.5.2 CHEMICAL COMPOSITION

2.5.2.1 MAJOR ELEMENTS

Melt compositions were measured with a JEOL JXA-8200 electron probe micro-analyzer (EPMA) employing a 20

µm beam diameter, 10 kV acceleration voltage and 20 nA beam current. The beam diameter was set to 3 µm

for the measurements of plagioclase composition. In order to minimize alkali loss, the counting time was set to

20 s for each elements and 10 s for the background. The standardization for the measurements of the tonalite

glass was done on a natural albite crystal (internal standard name: H021) for Na and Si and on a natural

anorthite (H103) for Al and Ca. The standardization for the measurements of the composition of the hydrous

phonolite was done on a natural wollastonite (H055) for Si and Ca, on a natural albite (H021) for Na, on an

natural orthoclase (H011) for K, on a synthetic corundum (D006) for Al, on a synthetic periclase (D044) for Mg,

on a synthetic rutile (D015) for Ti, on a natural hematite (D014) for Fe and on a synthetic pyrolusite (D023) for

Mn. The compositions given in this thesis are the average of more than 20 measurements.

2.5.2.2 WATER CONTENT

Water content in the samples before and after the experiments were measured by Karl Fisher Titration (KFT).

The samples were first crushed and dried for 24 hours at 110°C prior to analysis. 20 to 30 mg of sample were

placed in a platinum crucible and transferred to the heating chamber. Exsolution of water from the sample was

promoted by heating the chamber to 1250°C, i.e. above the liquidus temperature of the respective

compositions. Pure argon gas (Ar 6.0, PanGas AG) flowing through the chamber transported the water

molecules an oxidation furnace. A network of quartz and CuO was heated to 450°C which promoted oxidation

of hydrogen or hydrocarbons. Finally, the water was further transported to the titration cell, where it was

quantified by a CA-100 Moisture meter (Mitsubishi Chemical Corporation).

As the samples are crushed and well mixed, this method gives only the bulk water content of the samples. The

maximum uncertainty of this method is ± 0.15 wt% (Behrens et al., 1996).

2.5.3 DENSITY

Density was measured on the cored samples before and after the experiments performed in the Paterson

apparatus with a Micromeritics Accupyc pycnometer. A gas displacement pycnometer measures the density of

a sample using gas pressure changes. It utilizes helium gas that is first inserted in the cell chamber, which holds

the sample, and then in the expansion chamber, which has been previously calibrated. Using Boyle’s law, which

relates gas pressure to volume, this laboratory device automatically calculates the volume of the sample with a

precision of 0.0001 cm3. The weight was measured with a precision of 0.001 g.


21

2.6 REFERENCES

Behrens, H., Romano, C., Nowak, M., Holtz, F., & Dingwell, D. B. (1996). Near-infrared spectroscopic determination

of water species in glasses of the system MAlSi 3 O 8 (M= Li, Na, K): an interlaboratory study. Chemical

geology, 128(1), 41-63.

Bucaro, J., & Dardy, H. (1974). High‐temperature Brillouin scattering in fused quartz. Journal of Applied Physics,

45(12), 5324-5329.

Connolly, J. (2009). The geodynamic equation of state: what and how. Geochemistry, Geophysics, Geosystems,

10(10).

Connolly, J., & Kerrick, D. (2002). Metamorphic controls on seismic velocity of subducted oceanic crust at 100–250

km depth. Earth and Planetary Science Letters, 204(1), 61-74.

Gerlich, D., & Kennedy, G. C. (1978). Second pressure derivatives of the elastic moduli of fused quartz. Journal of

Physics and Chemistry of Solids, 39(11), 1189-1191.

Gieske, J. H., & Frost III, H. M. (1991). Technique for measuring ultrasonic velocity and attenuation changes in

attenuative materials at temperature such as during sintering processes. Review of scientific instruments,

62(12), 3056-3060.

Giordano, D., Russell, J. K., & Dingwell, D. B. (2008). Viscosity of magmatic liquids: a model. Earth and Planetary

Science Letters, 271(1), 123-134.

Ji, S., Wang, Q., & Xia, B. (2002). Handbook of seismic properties of minerals, rocks and ores: Presses inter

Polytechnique.

Johannes, W. (1989). Melting of plagioclase-quartz assemblages at 2 kbar water pressure. Contributions to

Mineralogy and Petrology, 103(3), 270-276.

Johannes, W., & Holtz, F. (1996). Petrogenesis and experimental petrology of granitic rocks (Vol. 335): Springer

Berlin.

Manghnani, M. H. (1974). Pressure and Temperature Studies of Glass Properties Related to Vibrational Spectra:

DTIC Document.

Mavko, G., Mukerji, T., & Dvorkin, J. (2009). The rock physics handbook: Tools for seismic analysis of porous media:

Cambridge university press.

Paterson, M., & Olgaard, D. (2000). Rock deformation tests to large shear strains in torsion. Journal of Structural

Geology, 22(9), 1341-1358.

Peselnick, L., Meister, R., & Wilson, W. H. (1967). Pressure derivatives of elastic moduli of fused quartz to 10 kb.

Journal of Physics and Chemistry of Solids, 28(4), 635-639.

Picard, D., Arbaret, L., Pichavant, M., Champallier, R., & Launeau, P. (2011). Rheology and microstructure of

experimentally deformed plagioclase suspensions. Geology, 39(8), 747-750.

Polian, A., Vo-Thanh, D., & Richet, P. (2002). Elastic properties of a-SiO2 up to 2300 K from Brillouin scattering

measurements. EPL (Europhysics Letters), 57(3), 375.

Seifert, R., Malfait, W. J., Lerch, P., & Sanchez-Valle, C. (2013). Partial molar volume and compressibility of dissolved

CO 2 in glasses with magmatic compositions. Chemical geology, 358, 119-130.

Spinner, S. (1956). Elastic moduli of glasses at elevated temperatures by a dynamic method. Journal of the

American Ceramic Society, 39(3), 113-118.

Chapter 3 Seismic Properties of Crystallizing Magmas

22

3 EFFECTS OF CRYSTALLIZATION AND BUBBLE NUCLEATION ON THE SEISMIC

PROPERTIES OF MAGMAS

Accepted for publication in Geochemistry, Geophysics, Geosystems in February 2016.

Tripoli Barbara1, Cordonnier Benoit2, Zappone Alba3, Ulmer Peter1

1 Institute of Geochemistry and Petrology, Earth Sciences Department, ETH Zurich

2 No Affiliation

3 Geological Institute, Earth Sciences Department, ETH Zurich

3.1 ABSTRACT

Seismic tomography of potentially hazardous volcanoes is a prime tool to assess the location and dimensions of

magmatic reservoirs. Seismic velocities are strongly affected by processes occurring within the conduit or in the

magma chamber, such as crystallization and bubble exsolution. However, the limited number of constrained

measurements does not allow yet to link seismic tomography and the textural state of a particular volcanic

system. In this study, we investigated a chemically simplified melt in the system CaO-Na2O-Al2O3-SiO2-H2O-CO2,

which undergoes plagioclase crystallization and bubble exsolution. A Paterson-type internally-heated gas

pressure apparatus was employed to measure ultrasonic velocities at a constant pressure of 250 MPa and at

temperature from 850 to 700 °C. Magmatic processes such as crystallization, bubble nucleation and

coalescence have been recognized throughout the measurements of seismic velocities in the laboratory.

Compression and shear wave velocities increase non-linearly during crystallization. At a crystal fraction

exceeding 0.45, the formation of a crystal network favors the propagation of seismic waves through magmatic

liquids. However, bubble nucleation induced by crystallization leads to an increase of magma compressibility

resulting in a lowering of the wave propagation velocities. These two processes occur simultaneously and have

a competing influence on the seismic properties of magmas. In addition, as already observed by previous

authors, when the bubble fraction is less than 0.10, the decrease in seismic velocities is more pronounced than

for higher bubble fractions. The effect of bubble coalescence on elastic properties is thus lower than the effect

of bubble nucleation.

3.2 INTRODUCTION

Seismic tomography of potentially hazardous volcanoes is a prime tool to identify and determine the size and

location of subvolcanic magma reservoirs (e.g. Ohlendorf et al., 2014, Chouet, 2003). Recent progresses in data

acquisition and processing led to higher precision and resolution (e.g. Nagaoka et al., 2012). In addition,


23

attempts to determine the physical state of magma reservoirs, e.g. melt proportion, are more and more often

conducted by combining tomographic data with available laboratory data and numerical simulation (e.g. Lin et

al., 2014; Paulatto et al., 2012).

Laboratory measurements of elastic parameters have been performed on melts of various compositions at a

large range of temperatures (e.g. Rivers and Carmichael, 1987; Askarpour et al., 1993; Schilling et al., 2003;

Webb and Courtial, 1996). Due to the temperature-dependence of the elastic moduli, seismic velocities

decrease continuously with increasing temperature until the glass transition temperature is reached (e.g.

Schilling et al., 2003). This temperature range corresponds to a transition in the physical properties of the melt

from a solid-like (below the glass transition temperature) to a liquid-like behavior (above the glass transition

temperature) (e.g. Webb and Dingwell, 1990). By crossing this region, a marked increase of the temperature

derivative of the compressional wave propagation velocity is observed (e.g. Askarpour et al., 1993). This break

is less pronounced for shear waves (e.g. Caricchi et al., 2008). This variation in elastic properties at the glass

transition temperature has also been reported for crystal-bearing melt (Caricchi et al., 2008). However, the

amplitude of this variation decreases with increasing crystal content. Microstructure is as well a fundamental

parameter in determining the elastic properties (e.g. Mueller et al., 2003; Hier-Majumder, 2008; Schmeling,

1985; Mavko, 1980). The non-linear increase of seismic wave velocities by increasing the crystal fraction is a

direct result of the formation of a continuous crystal network (Caricchi et al., 2008).

Figure 3.1 : Phase diagram of an haplotonalite containing 2.8 wt% of water calculated with Perple_X (Connolly, 2009). The blue polygon corresponds to the P-T conditions used for the glass synthesis. The starting condition for the crystal and bubble growth experiments is shown by the yellow star.

The internal structure of magmatic reservoirs and conduits is continuously evolving through various processes.

Degassing-induced crystallization (e.g. Cashman and Blundy, 2000) reveals the close interdependence of melt

composition, crystal and bubble contents. Caricchi et al. (2008) and Bagdassarov et al. (1994) shows that the


24

presence of bubbles in crystal-bearing magmas tends to decrease their elastic properties. However, the effect

of bubbles on seismic velocities is not well defined. In addition, processes occurring within the conduit or in the

magma chamber, such as crystallization and bubble exsolution, control the magma rheology, hence the style of

volcanic eruption (Cordonnier et al., 2009; Gonnerman and Manga, 2013; Pistone et al., 2013). Here we present

a new set of compression and shear wave velocity laboratory data at high pressure and temperature on a

chemically simplified melt analogous to andesite and trachyte, in the system CaO-Na2O-Al2O3-SiO2-H2O-CO2.

This melt composition undergoes plagioclase crystallization and bubble exsolution closely simulating the

evolution of natural magmas crystallizing and decompressing in magma reservoirs and within volcanic conduits.

3.3 METHODOLOGY

In order to study the effect of crystallization and bubble nucleation on the seismic properties of magmas we

synthetized a chemically simplified tonalite melt (Table 3.1), which is prone to crystallize plagioclase (Picard et

al., 2011). First, oxide and hydroxide powders were mixed to obtain the desired compositions (Table 3.1). The

mixtures have been cold pressed into stainless steel canisters with a uniaxial pressure of 200 MPa.

Molybdenum foils lining the border of the canister avoid contamination from the wall. Subsequently, the

mixtures have been thermally equilibrated in a Hot Isostatic Press (HIP) at 1200 °C and 200 MPa for 24 hours. In

the phase diagram calculated using Perple_X (Connolly, 2009), this P-T condition corresponds to superliquidus

conditions (Figure 3.1). The resulting hydrated glasses are chemically homogeneous and their compositions

correspond to the nominal values within 1% (Table 3.1). The hydrated glass contains a bubble fraction of 0.04.

These CO2-rich bubbles have a number density of 167 mm-2 and their sizes exhibit a narrow distribution

situated around 6 µm (Figure 3.2A and Figure 3.5E and 3.5F). In addition to bubbles, the glass contains less than

0.01 fraction of spherulitic plagioclase, with a mean size of 150 µm (Figure 3.5). This bubble-bearing glass has

been drilled into cores of 30 mm length and 15 mm diameter to perform seismic velocities measurements.

Figure 3.2: SEM images of (A) the bubble-bearing glass synthetized in the HIP apparatus (starting material) and (B) the plagioclase- and bubble-bearing glass crystallized in the Paterson apparatus (experiment cooled at 0.1 °C/min). Lath shaped crystals are plagioclase (spherulites), darker grey interstitial patches is glass (quenched melt), black holes correspond to former bubbles.


25

Changes in seismic properties of crystallizing magmas have been measured in a Paterson-type internally-heated

gas pressure apparatus (Paterson and Olgaard, 2000). Piezoelectric transducers placed at both extremities of

the assembly (Figure 3.3) permit direct measurement at high pressure and high temperature of compression

wave velocities using the pulse transmission technique (Birch, 1960). The vibration frequency applied to the

transducers was 0.1 MHz and the input voltage was 300 V peak to peak. The alumina rods in the assembly have

a 2 mm diameter hole that permits the insertion of thermocouples at the bottom and at the top of the sample.

The temperature difference over the entire length of the sample never exceeded 5 °C. The temperature was

controlled by a Eurotherm controller connected to the thermocouple placed at the bottom of the sample. In

situ pressure conditions are simulated by hydrostatically confining the assembly in the pressure vessel with

argon. The assembly is isolated from the gas pressure medium by an iron jacket of 0.2 mm wall thickness.

Figure 3.3: Drawing of the HP-HT Paterson apparatus implemented with the setup to measure seismic velocities.

The stack of alumina rods in the assembly produces a time delay in the measurements of the P- and S-waves

arrival time. This delay has been determined at various pressure and temperature using a well-known sapphire

crystal cut parallel to (0001) for calibration of the compression wave velocity (see Burlini et al. (2005), Ferri et

al. (2007) Caricchi et al. (2008) for additional details on the experimental procedure) and a glass rod of fused

quartz for calibration of the shear wave velocity. Experiments were performed at a constant confining pressure

of 250 MPa. This pressure has been selected for the higher quality of the received seismic signal. Samples were

first heated to 850°C at a rate of 30°C/min. This temperature was maintained constant for 30 minutes.

Subsequently, the temperature was continuously decreased to 700°C at a cooling rate of 0.5 or 0.1°C/min.


26

Seismic velocities were recorded every 45 minutes. The error on the measurements is mainly linked to picking

of the first arrival (for additional details on data processing, see Caricchi et al. (2008)) and reaches 0.1 km/s for

compression wave velocity and 0.2 km/s for shear wave velocity.

In order to determine the evolution of the microstructure during the experiments, the P-T conditions applied in

the Paterson apparatus have been reproduced in a rapid-quench molybdenum-hafnium-carbide (MHC) cold-

sealed pressure vessel. Placed on a rotary system, this externally heated pressure vessel permits dropping the

sample into the cold steel extremity linked to the MHC part by a water-cooled nut. This setup results in a rapid

quench of the sample at a rate exceeding 100°C/s, which allows preservation of the microstructure formed at

high temperature. The temperature gradient in the hot MHC extremity never exceeded 5 °C over the length of

the sample. Cores of 4 mm in length and in diameter, previously drilled from the starting glass and placed into

Au capsules that were welded shut, have been quenched under pressure at identical time steps as the seismic

velocities measurements were obtained.


and spherulite diameter) have been determined by evaluation of SEM images of the starting material

(synthetized in the HIP), the final sample (crystallized in the Paterson apparatus) and the quenched samples

(crystallized in the MHC cold-sealed vessel). Images were taken at a magnification of 200x over 1 cm2 for the

starting and final samples and over the entire capsules (16 mm2) for the quenched samples. The phase

fractions have been determined by grayscale dissociation using the open source software ImageJ (Schneider et

al., 2012). Bubbles smaller than 3 pixel units, i.e. with a diameter smaller than 1.5 µm, have been excluded

from the bubble characterization. Melt and plagioclase compositions have been measured with a JEOL JXA-

8200 electron microprobe employing a 20 and 3 µm beam diameter respectively, 10 kV acceleration voltage

and 20 nA beam current.

Figure 3.4: Compression (Vp, in green) and shear (Vs, in purple) wave velocities as a function of temperature measured on the sample cooled at 0.5 °C/min (CR05, triangle symbols) and on the sample cooled at 0.1°C/min (CR01, circle symbols).


27

3.4 EXPERIMENTAL AND ANALYTICAL RESULTS

The evolution of seismic velocities through time is cooling rate-dependent (Figure 3.4). The sample cooled at

0.5°C/min (CR05) reveals a smooth variation of its seismic properties whereas sharp changes and an overall

larger variation of the seismic velocities are observed in the measurements conducted at lower cooling rate,

i.e. 0.1°C/min (CR01). This discrepancy highlights the transient dynamics of the observed microstructures and

thus the involved magmatic processes.

3.4.1 MICROSTRUCTURE: COOLING RATE OF 0.5 °C/MIN

By decreasing the temperature (T) from 850 to 830°C at a rate of 0.5°C/min, the compression wave velocity (Vp)

measured in the bubble-bearing tonalite melt increases from 5.01 to 5.16 km/s and the shear wave velocity (Vs)

increases from 2.88 to 2.94 km/s (Figure 3.5A and Table 3.2). Crystallization of spherulitic plagioclase is clearly

documented by the increase of the crystal fraction to 0.4 and a concomitant increase in the mean diameter of

spherulites to 350 µm (Figure 3.5B and 3.5C). As expected for closed system crystallization of plagioclase, the

Na, Ca and Al contents of the melt decrease while the Si content increases (Table 3.1). Bubble nucleation

occurs and is evidenced by a shift to smaller diameters in the bubble size distribution (Figure 3.5F) and by an

increase of the bubble number density (Figure 3.5E). After this initial increase, the bubble number density

decreases continuously in the interval between 810°C (t=120 minutes) and 790°C (t=165 minutes) (Figure 3.5E)

while the bubble fraction increases to 0.13 (Figure 3.5B). Although the crystal fraction increases in this interval

to 0.54 at 790°C (t=165 minutes), Vp reaches a plateau at 5.30 km/s and Vs only slightly increase from 2.99 to

3.00 km/s (Figure 3.5A). At 770°C (t=210 minutes), the acquired microstructure is similar to the final one at

690°C (Figure 3.5B). The interstitial rhyolite melt (Table 3.1) contains a plagioclase fraction of 0.54 and a bubble

fraction of 0.13. Vp continuously increases from 770°C to 690°C (from t=210 to t=390 min) to 5.47 km/s at a

mean rate of -2.2 (±0.2) × 10-3 km/s/°C. The relative evolution of Vs mimics the one of Vp although its absolute

change in amplitude is considerably lower (Figure 3.5A). Indeed, the difference in velocities at the beginning

and at the end of the experiment is higher for compression wave velocity (ΔVp=0.46 km/s) than for shear wave

velocity (ΔVs=0.16 km/s).


28

Figure 3.5: Evolution of seismic properties of the sample cooled at 0.5 °C/min and its associated microstructure. (A) Compression (green circle) and shear (purple circle) wave velocities measured during the crystallization of the bubble-bearing haplotonalite melt. The trends have been divided into three intervals: (CR05a) crystallization and bubble nucleation; (CR05b) crystallization and bubble coalescence; (CR05c) temperature derivative of the bubble- and crystal-bearing melt. (B) Temporal evolution of the crystal (square), melt (cross) and bubble (triangle) fractions. (C) Temporal evolution of the spherulite number density. (D) Temporal evolution of the spherulite diameter. The orange stars correspond to the average value for one specific time. (E) Temporal evolution of the bubble number density. (F) Evolution of the bubble size distribution (normalized bubble fraction as a function of bubble diameter) for various time steps. Each curve has been normalized to the highest number of bubbles measured for a specific time.


29

Figure 3.6: Evolution of seismic properties of the sample cooled at 0.1 °C/min and its associated microstructure. (A) Compression (green circle) and shear (purple circle) wave velocities measured during the crystallization of the bubble-bearing haplotonalite melt. The trends have been divided into four intervals: (CR01a) temperature derivative of the bubble-bearing melt and outgassing; (CR01b) crystallization and bubble nucleation; (CR01c) bubble coalescence; (CR01b) temperature derivative of the bubble- and crystal-bearing melt and textural maturation. (B) Temporal evolution of the crystal (square), melt (cross) and bubble (triangle) fractions. (C) Temporal Evolution of the spherulite number density. (D) Temporal evolution of the spherulite diameter. The orange stars correspond to the average value for one specific time. (E) Temporal evolution of the bubble number density. (F) Evolution of the bubble size distribution (normalized bubble fraction as a function of bubble diameter) for various time steps. Each curve has been normalized to the highest number of bubbles measured for a specific time.


30

3.4.2 MICROSTRUCTURE: COOLING RATE OF 0.1 °C/MIN

From 850°C to 795°C, i.e. during the first 525 minutes of the experiment cooled at a rate of 0.1 °C/min,

compression and shear wave velocities slowly increase with a mean rate of -4.0 (±0.1) × 10-3 and -1.8 (±0.2)

×10-3 km/s/°C , respectively (Figure 3.6A and Table 3.3). The bubble size distribution (dominant peak around 6

µm) and the bubble fraction, i.e. 0.04 (±0.02), remain constant during this interval and are basically identical to

the initial conditions (Figure 3.6F and 3.6B, respectively). Substantial crystallization of plagioclase initiates 570

minutes after the beginning of the experiment at T= 790 °C (Figure 3.6B). From 790°C down to 770°C (between

t=570 and t=750 minutes), seismic velocities increase from 5.20 to 5.71 km/s for Vp and from 2.98 to 3.08 km/s

for Vs (Figure 3.6A). During this interval, the crystal and bubble fractions increase up to 0.58 and 0.09,

respectively (Figure 3.6B). The bubble number density first increases from 142 to 1510 mm-2 between 790 and

785°C (between t=570 and t=615 minutes) and subsequently slowly decreases to 905 mm-2 at T=770°C and

t=750 minutes (Figure 3.6E). By decreasing the temperature from 770°C to 750°C (t=750 and 930 minutes), we

observe a decrease in the compression wave velocities down to 5.66 km/s (Figure 3.6A), although the crystal

and bubble contents remain nearly constant (Figure 3.6B). The spherulite number density amounts to 1.71 mm-

2 and the bubble number density is 1010 mm-2 at 755°C (t=885 minutes) (Figure 3.6C and 3.6E). From 750°C

(t=930 minutes) to the end of the experiment (at t=1335 minutes and T=700°C), Vp and Vs are increasing

linearly at a mean rate of -6.9 (±0.3) × 10-3 and -1.82 (±0.07) × 10-3 km/s/°C, respectively (Figure 3.6A). The only

microstructural parameter changing during this period is the spherulite number density, which increases to 5

mm-2 (Figure 3.6C).

3.4.3 MICROSTRUCTURE: INTERPRETATION

The seismic velocity trends measured for the sample cooled at 0.5 °C/min can be divided into three intervals.

The first interval (interval CR05a in Figure 3.5A) lasts 120 minutes, i.e. down to 810°C, and is dominated by

crystallization and bubble nucleation of tonalitic melt. The compression wave velocity increases by 5 % at a

mean rate of -6.5 (±0.8) × 10-3 km/s/°C during this first interval. The second interval between 810°C and 770°C

(interval CR05b in Figure 3.5A)) is characterized by a constant Vp value of 5.30 km/s that most likely results

from bubble coalescence which attenuates the increase due to crystallization and temperature decrease. The

final increase in compression wave velocity cannot be directly linked to any major changes in the

microstructure and is, thus, attributed to the temperature decrease. This third interval, i.e. interval CR05c in

Figure 3.5A, is characterized by a temperature derivative of the compression wave velocity of the final bubble-

and plagioclase-bearing rhyolite melt of -2.2 (±0.2) × 10-3 km/s/°C.

Upon cooling of the bubble-bearing tonalite melt at a rate of 0.1 °C/min, the measured Vp and Vs significantly

change. We divided the measured seismic velocity trend into four intervals. From 850 to 790°C, (interval CR01a

in Figure 3.6A), no crystallization occurs. However, inspection of the microstructures reveals that the largest

bubbles could have outgassed during this first interval. The second interval (from 790 to 770°C) is dominated by

the crystallization of ~60 vol% of spherulitic plagioclase generating an increase of 9 % in the compression wave


31

velocities at a mean rate of -2.4 (±0.3) × 10-2 km/s/°C. We attributed this continuous increase in Vp to be due to

a continuous increase of crystal content. However, the sample quenched at t=615 minutes (T=785°C) is

characterized by a large crystal and bubble fractions, as well as a large spherulite and bubble number densities.

This microstructure could be generated during the quench process due to a large degree of super-saturation.

During the second interval (interval CR01b in Figure 3.6A), the bubble number density increase suggests bubble

nucleation induced by crystallization. Coalescence of these newly formed bubbles characterizes the third

interval (interval CR01c in Figure 3.6A) and induces a decrease of Vp of 0.7 % at a mean rate of 2.5 (±0.2) × 10-3

km/s/°C. The last interval, i.e. interval CR01d in Figure 3.6A, is characterized by a textural maturation of the

plagioclase spherulites, which tends to decrease their sizes. This phenomenon may favor additional outgassing

of the sample thereby contributing to the recorded velocity increase at a rate of -6.9 (±0.3) × 10-3 km/s/°C.

3.5 DISCUSSION

The observed microstructures demonstrate the occurrence of crystallization, bubble nucleation and

coalescence and correlate with the seismic velocity measurements. In order to better understand the relation

between each of these processes and the seismic properties of magmas, we first estimated the seismic

velocities characterizing them as a suspension of solid grains in a fluid using the Reuss lower bound equation

(e.g. Mavko et al., 2009). We then compare the results with the measured seismic velocities and separated the

effect of bubble nucleation and coalescence from crystallization.

The calculation of the Reuss lower bound VReuss involves the weighted mean of the seismic wave velocities of

each of the involved phases as follow:

1

Re( )plag plag

uss

plag melt

VV V

(1)

where Φplag is the crystal fraction comprised between 0 and 1, Vplag and Vmelt are the seismic velocities in km/s

of the crystal phase and the melt phase respectively. This approach requires an estimation of the seismic

velocities of each phase for every temperature. For the melt phase, we measured the temperature derivatives

of compression and shear waves velocities of the starting material (tonalitic melt + 0.04 bubble fraction).

Temperature was kept below 650 °C to avoid any crystallization but higher than 440 °C, above the glass

transition temperature, to ensure liquid-like behavior of the sample. The equations derived from the measured

Vp and Vs are:

3

( ) 1.75( 0.05) 10 6.43( 0.07)p meltV T (2)

3

( ) 1.31( 0.04) 10 3.92( 0.02)s meltV T (3)


32

where T is the temperature in °C and Vp(melt) and Vs(melt) are the compression and shear wave velocities in km/s.

For the crystalline phase, data on the seismic properties of albite aggregates at high pressure and high

temperature are not available. In order to estimate the contribution of plagioclase, we thus used the pressure

derivative of its sodic end-member, an albitite from Sylmar (USA) measured by Simmons (1964) and the

temperature derivative of its calcic end-member, an anorthosite from Tanaelv Belt (Norway/Finland) measured

by Kern et al. (1993). These two samples are aggregates of randomly oriented plagioclase and do not have any

significant seismic anisotropy. Combining the two provides a first order estimate of the bulk seismic velocities

of the crystalline phase in the form of:

4

(plag) 1.84( 0.06) 10 6.65( 0.01)pV T (4)

5

s(plag) 9.99( 0.04) 10 3.61( 0.01)V T (5)

Figure 3.7: Compression (green diamonds) and shear (purple circles) wave velocities as a function of the crystal fraction. Dark colored symbols represent measured values; light colored symbols represent values calculated using the Reuss lower bound equation. The dashed lines have been drawn for visual purposes only.

3.5.1 EFFECT OF CRYSTALLIZATION

By comparing the variation of the crystal content and the seismic velocities as a function of time (representing

decreasing temperature), we observe that the crystal content is the principal parameter influencing the seismic

properties of the investigated magmas. Crystallization is thus inducing an increase in both measured and

calculated compression and shear waves velocities. Caricchi et al. (2008) demonstrated that this increase is

non-linear. Indeed, the formation of a crystal network at crystal fractions higher than 0.5 produces a non-linear

increase of both Vp and Vs. This characteristic is observed in our experiments as well (Figure 3.7). At crystal

fractions lower than 0.45, the maximum increase observed for a total difference in crystal fraction of 0.41 is 4

% for Vp and 2 % for Vs. In contrast, at crystal fractions higher than 0.45, Vp increases by 8 % and Vs by 5 % for a


33

much smaller difference in crystal fraction of only 0.14. Crystallization has, therefore, the strongest influence

on the seismic properties of magma above a critical crystal fraction.

The Reuss lower bound is a good estimation of the seismic velocities characterizing a suspension of solid grains

in a fluid (e.g. Mavko et al., 2009). The difference observed between the calculated values and our

measurements (Figure 3.7) are, thus, attributed to the presence of bubbles in addition to crystals.

3.5.2 EFFECT OF BUBBLE NUCLEATION

In our experiments, bubble nucleation occurs by water exsolution induced by crystallization of anhydrous

phases (plagioclase). Its effect on the seismic velocities is thus best appreciated in the first time interval of the

experiment cooled at a rate of 0.5 °C/min (interval CR05a in Figure 3.5A) and in the second interval of the

experiment cooled at a rate of 0.1 °C/min (interval CR01b in Figure 3.6A). These intervals are characterized by

simultaneous crystallization and bubble nucleation. Therefore, the effect of crystallization has to be considered

and subtracted in a first step.

Figure 3.8: Seismic velocities of the sample cooled at 0.5 °C/min as a function of temperature. Dark colored diamonds represent measured values; light colored diamonds are calculated values using the Reuss lower bounds (equation 1). The red and blue lines are the temperature derivatives of the bubble-bearing melt (measured) and the plagioclase aggregates (from equations 4 and 5), respectively. (A) Compression wave velocities. (B) Shear wave velocities.

For a cooling rate of 0.5 °C/min, Vp increases by 5 % (from 5.01 to 5.27 km/s) and Vs by 3 % (from 2.88 to 2.97

km/s) between 850 and 810°C (Figure 3.8). Comparatively and for the same variation of crystal fraction (i.e. 13

to 47%), the theoretical Reuss lower bound would increase by 9 % (from 5.11 to 5.62 km/s) for Vp and by 8 %

(from 2.88 to 3.14 km/s) for Vs. If this calculated effect of crystallization is subtracted from our measurements,

bubble nucleation results in a decrease of 4 % in Vp and 5 % in Vs.

For a cooling rate of 0.1 °C/min, Vp increases by 10 % (from 5.15 to 5.71 km/s) and Vs by 4 % (from 2.96 to 3.08

km/s) between 795 and 770°C (Figure 3.9). For the same amount of crystallization, i.e. for a crystal fraction of

0.58, the Reuss lower bound increases by 13 % (from 5.04 to 5.82 km/s) for Vp and by 9 % (from 2.87 to 3.15


34

km/s) for Vs. Subtracting the effect of crystallization from our experimental results, we obtain a decrease

induced by bubble nucleation of 3 % in compression and 5 % in shear wave velocities respectively.

Figure 3.9: Seismic velocities of the sample cooled at 0.1 °C/min as a function of temperature. Dark colored diamonds represent measured values; light colored diamonds are calculated values using the Reuss lower bounds (equation 1). The red and blue lines are the temperature derivatives of the bubble-bearing melt (measured) and the plagioclase aggregates (calculated from equation 4 and 5), respectively. (A) Compression wave velocities. (B) Shear wave velocities.

Although the bubble fraction increases only by 0.01, the appearance of a large amount of small bubbles

produces a significant decrease in measured seismic velocities. Similar behavior, but with a larger magnitude,

has been observed in previous studies involving bubbly water. The addition of gas bubbles critically decreases

the seismic properties of the mixtures in a logarithmic fashion, i.e. over the first percent of bubbles, the sound

speed decreases by 90%, from ~1500 m/s for pure water to ~150 m/s for water containing 0.8 % of bubbles

(Gibson, 1970; Kieffer, 1977). The density variation is not sufficient to account for this large variation in the

sound speed and it is, thus, attributed to the large increase in compressibility (Temkin, 2005). In their numerical

model involving bubble-bearing basaltic melt, Marchetti et al. (2004) applied equations of seismic velocities

derived for low-viscosity liquids, i.e. bubbly water, in order to better estimate variations in physical properties

of magmas (Figure 3.10). In our experiments, we observed that the decrease in seismic velocities due to bubble

nucleation could be similarly linked to an increase of the compressibility in a bubble-bearing melt. However,

increasing the confining pressure and increasing the melt viscosity (compared to measurements made on water

at 1 atm) prevent a strong decrease in seismic velocities (Kieffer, 1977; Ichihara et al., 2004; Ichihara and

Kameda, 2004). Consequently, the addition of a large amount of small bubbles in melts at high pressure and

high temperature decreases the seismic wave velocities only up to 5 %.

3.5.3 EFFECT OF BUBBLE COALESCENCE

Bubble coalescence is observed in interval CR05b (Figure 3.5A) and in interval CR01c (Figure 3.6A). Interval

CR05b is characterized by a constant Vp value of 5.30 km/s and a slight increase of Vs from 2.99 to 3.00 km/s.

Interval CR01c displays a decrease of Vp of less than 1 % (from 5.71 to 5.66 km/s) and an increase of Vs of less

than 1 % (from 3.08 to 3.10 km/s).


35

Bubble coalescence is thus producing less significant variations in seismic velocities than bubble nucleation.

This phenomenon is additionally linked to the variation of compressibility as function of bubble fraction.

Compressibility calculated by Marchetti et al. (2004) is strongly increasing for low bubble fraction but this

increase is much less pronounced when the bubble fraction exceeds 0.1 (Figure 3.10). In our experiments, the

bubble fraction is significantly increasing prior to or during bubble coalescence. Following equations derived for

low viscosity bubble-bearing liquids (Gibson, 1970; Kieffer, 1977), the compressibility of our sample containing

0.12 bubble fraction would not increase enough to affect the measured wave propagation velocities.

Consequently, the increase in compressibility at relatively low density contrast leads to large decrease in

seismic properties during bubble nucleation and less or no variation during bubble coalescence.

Figure 3.10: Variation of (A) density, (B) compressibility and (C) longitudinal wave propagation velocity in function of the void fraction calculated for basaltic melts nucleating bubbles by decompression (modified from Marchetti et al. (2004)). The shaded area represents the variation of properties with the addition of a bubble fraction of 0.1.

3.5.4 EFFECT OF OUTGASSING

Depending on the cooling rate, post-mortem evaluation of samples from the experiments conducted with the

Paterson apparatus reveals that the samples contain different amounts of bubbles. The bubble fraction

amounts to 0.12 in the experiment cooled at 0.5 °C/min and to 0.04 in the experiment cooled at 0.1 °C/min.

This difference strongly suggests the occurrence of outgassing during the lower cooling rate experiments most

likely caused by the 3.5 times longer duration of the experiments. As the samples are sealed into Au capsules,

the setup of the MHC experiments prevents outgassing of the samples during run time as well as during rapid-

quench. Consequently, microstructure observations of these latter experiments corresponding to various time

steps in the Paterson apparatus did not support any outgassing evidence.

Additionally, by comparing the calculated and the measured seismic velocities of interval CR01a (Figure 3.9),

we observed that the temperature derivatives of Vp (-4.0 (±0.1) × 10-3 km/s/°C) and Vs (-1.8 (±0.2) ×10-3


36

km/s/°C) are slightly higher than the temperature derivatives of the starting material (-1.75 (±0.05) × 10-3

km/s/°C for Vp and -1.31 (±0.04) × 10-3 km/s/°C for Vs) measured at lower temperature. This shift is interpreted

to be due to the outgassing of large bubbles.

3.6 SUMMARY AND APPLICATION TO NATURAL SYSTEM

Magmatic processes occurring in (sub)volcanic environments have been recognized and identified through the

measurement of seismic velocities in the laboratory. Compression and shear wave velocities increase non-

linearly during crystallization. At crystal fractions higher than 0.45, the formation of a crystal network favors

the propagation of seismic waves through magmas. However, bubble nucleation induced by crystallization

produces an increase in magma compressibility thereby lowering the wave propagation velocities. These two

processes occurring simultaneously have thus competing effects on the seismic properties of magmas. In

addition, when the bubble fraction is less than 0.1, the decrease in seismic velocities is more pronounced than

for larger bubble fractions. The effect of bubble coalescence on elastic properties is distinctly lower than the

effect of bubble nucleation.

Processes linked to the formation and growth of bubbles are, thus, lowering the increase of seismic velocities

induced by crystallization. In our experiments, the difference in compression wave velocities between melts

containing crystal fraction from 0 to 0.51 is as low as 0.5 km/s due to the presence of bubbles. The detection of

these small variations in velocities could be possible but difficult for conventional methods used to determine

the location and size of magmatic chambers. For example, tomographic data inferred from the inversion of

first-arrival times from local earthquakes are highly dependent on the spatial sampling (Chouet, 2003). Thus, a

large number of earthquakes with a high magnitude and a random spatial distribution should be collected by a

dense seismometers network in order to achieve high resolution and precision. This configuration is highly

improbable over a long period of time. Small variation of seismic properties induced by crystallization and

bubble nucleation in magmatic chambers can hardly be estimated with these methods.

However, improvement in tomographic techniques involving ambient seismic noise can achieve a

measurements resolution on the order of 0.05 % with a minimum of only two seismic receivers (Duputel et al.,

2008). Brenguier et al. (2008) monitored the ambient seismic noise at Piton de la Fournaise (Reunion Island,

France) over a period of 18 months. Each eruption is preceded by a decrease in relative seismic velocities

changes of 0.05 to 0.1 %, which is interpreted as an inflation of the volcanic edifice due to the pressurization of

the magma chamber. Indeed, when the pressure in a magma chamber is high enough, the wall rocks may crack

due to the applied stress (e.g. Jellinek and DePaolo, 2003) and these newly formed cracks induce a decrease in

elastic moduli (e.g. Heap et al., 2010). In view of our results, the variation in velocity observed by Brenguier et

al. (2008) could be similarly linked to (1) an increase in the melt fraction or (2) to bubble nucleation induced by

crystallization. However, a more precise interpretation could be assessed only through laboratory

measurements at pressure and temperature conditions similar to the basaltic magma chambers of Piton de la

Fournaise. In addition, as seismic velocities in magmas are strongly frequency-dependent, these measurements


37

should be adequately scaled for frequency, as discussed previously by Caricchi et al. (2008). Consequently, by

continuously monitoring small seismic velocity perturbations and by combining these data with laboratory

measurements of seismic velocities, evolution of the physical state of magmatic reservoir could be assessed

more precisely.

3.7 ACKNOWLEDGMENTS

This research was supported by Swiss National Foundation (grant 200020_140578 and 200020_132878). We

wish to thank: Robert Hoffmann for his precious technical support and Marie Violay for her scientific support at

the Rock Deformation Laboratory of ETH Zurich. In addition, we would like to thank Mike Heap, an anonymous

reviewer and the editor Ulrich Faul for their detailed and constructive comments that helped improving this

paper. We note that there no data sharing issues since all of the numerical information is provided in the

figures produced by solving the equations in the paper. The raw data are stored in the Rock Deformation

Laboratory at ETH, Zurich, and are available upon request ([email protected]).


38

3.8 TABLES

Table 3.1 : Compositions in wt% of the starting material, the interstitial glass and the plagioclase measured by electron microprobe. *The nominal composition corresponds to the composition of the powder before the HIP. **Water and CO2 contents have been measured by KFT and by coulometry respectively.

Sample SiO2 Al2O3 CaO Na2O H2O CO2

Total

HIP: Nominal Composition* 65.69 18.56 3.33 7.61 2.80 2.00

100

HIP: Measured Composition 64.96 18.78 3.49 7.46 2.78** 0.03**

97.47

Exp. 0.5°C/min: t=75 min (melt) 65.35 16.96 2.47 7.05 - -

91.83


90.08


91.59


89.48

Exp. 0.5°C/min: t=75 min (plag.) 61.86 23.74 5.38 8.08 - -

99.05


98.20


99.80


99.14


89.40


89.18


94.10


90.10


90.65

Exp. 0.1°C/min: t=603 min (plag) 61.20 24.32 5.57 8.09 - -

99.18


99.05


99.91


99.70


100.09


39

Table 3.2: Summary of measured seismic velocities and microstructures at a cooling rate of 0.5 °C/min.

T [°C] t [min] Vp [km/s] Vs [km/s] Φcrystal [n.u.]

Φmelt [n.u.]

Φbubble [n.u.]]

SND [1/mm2]

BND [1/mm2]

850 30 5.01 2.88 0.13 0.79 0.06 0.60 157

830 75 5.16 2.94 0.40 0.52 0.06 2.50 985

810 120 5.27 2.97 0.42 0.42 0.05 2.50 880

790 165 5.29 2.99 0.52 0.33 0.11 2.18 725

770 210 5.30 3.00 0.54 0.36 0.10 1.92 823

750 255 5.34 3.04

730 300 5.39 3.05

710 345 5.44 3.06

690 390 5.47 3.04 0.51 0.33 0.12 1.52 917

Table 3.3: Summary of measured seismic velocities and microstructures at a cooling rate of 0.1 °C/min.

T [°C] t [min] Vp [km/s] Vs [km/s] Φcrystal [vol%]

Φmelt [vol%]

Φbubble [vol%]

SND [1/mm2]

BND [1/mm2]

850 30 4.94 2.86

845 75 4.95 2.87 0.0 0.95 0.05 0.00 136

840 120 4.96 2.88

835 165 5.00 2.91

830 210 5.01 2.91

825 255 5.03 2.92

820 300 5.06 2.93

815 345 5.07 2.94 0.00 0.97 0.03 0.00 177

810 390 5.09 2.95

805 435 5.12 2.95 0.00 0.95 0.05 0.00 149

800 480 5.14 2.94

795 525 5.15 2.96 0.00 0.97 0.03 0.00 142

790 570 5.20 2.98

785 615 5.30 3.00 0.54 0.34 0.10 2.17 1506

780 660 5.39 3.06

775 705 5.47 3.07 0.50 0.40 0.10 1.65 1284

770 750 5.71 3.08 0.58 0.31 0.09 1.94 905

765 795 5.70 3.08

760 840 5.68 3.08 0.57 0.30 0.10 1.71 1014

755 885 5.67 3.09

750 930 5.66 3.10 0.59 0.30 0.09 4.95 908

745 975 5.69 3.10

740 1020 5.71 3.11

735 1065 5.76 3.12 0.61 0.27 0.09 5.90 2219

730 1110 5.79 3.13

725 1155 5.81 3.15

720 1200 5.85 3.15

715 1245 5.87 3.16

710 1290 5.94 3.17

700 1335 6.01 3.18 0.60 0.34 0.04 4.47 918


40

3.9 REFERENCES


Bagdassarov, N., Dingwell, D. B., & Webb, S. L. (1994). Viscoelasticity of crystal-and bubble-bearing rhyolite melts. Physics of the earth and planetary interiors, 83(2), 83-99.

Birch, F. (1960). The velocity of compressional waves in rocks to 10 kilobars: 1. Journal of Geophysical Research, 65(4), 1083-1102.

Brenguier, F., Shapiro, N. M., Campillo, M., Ferrazzini, V., Duputel, Z., Coutant, O., & Nercessian, A. (2008). Towards forecasting volcanic eruptions using seismic noise. Nature Geoscience, 1(2), 126-130.

Burlini, L., Arbaret, L., Zeilinger, G., & Burg, J.-P. (2005). High-temperature and pressure seismic properties of a lower crustal prograde shear zone from the Kohistan Arc, Pakistan. Geological Society, London, Special Publications, 245(1), 187-202.

Caricchi, L., Burlini, L., & Ulmer, P. (2008). Propagation of P and S-waves in magmas with different crystal contents: Insights into the crystallinity of magmatic reservoirs. Journal of volcanology and geothermal research, 178(4), 740-750.

Cashman, K., & Blundy, J. (2000). Degassing and crystallization of ascending andesite and dacite. Philosophical Transactions of the Royal Society of London A: Mathematical, Physical and Engineering Sciences, 358(1770), 1487-1513.

Chouet, B. (2003). Volcano seismology. Pure and Applied Geophysics, 160(3-4), 739-788. Connolly, J. (2009). The geodynamic equation of state: what and how. Geochemistry, Geophysics, Geosystems,

10(10). Cordonnier, B., Hess, K. U., Lavallee, Y., & Dingwell, D. B. (2009). Rheological properties of dome lavas: Case

study of Unzen volcano. Earth and Planetary Science Letters, 279(3–4), 263-272. doi: http://dx.doi.org/10.1016/j.epsl.2009.01.014

Duputel, Z., Ferrazzini, V., Brenguier, F., Shapiro, N., Campillo, M., & Nercessian, A. (2009). Real time monitoring of relative velocity changes using ambient seismic noise at the Piton de la Fournaise volcano (La Réunion) from January 2006 to June 2007. Journal of volcanology and geothermal research, 184(1), 164-173.

Ferri, F., Burlini, L., Cesare, B., & Sassi, R. (2007). Seismic properties of lower crustal xenoliths from El Hoyazo (SE Spain): Experimental evidence up to partial melting. Earth and Planetary Science Letters, 253(1), 239-253.

Gibson, F. W. (1970). Measurement of the effect of air bubbles on the speed of sound in water. The Journal of the Acoustical Society of America, 48(5B), 1195-1197.

Gonnermann, H.M., and M. Manga (2013), Magma ascent in the volcanic conduit, in Modeling volcanic processes: The physics and mathematics of volcanism, edited by S.A. Fagents, T.K.P. Gregg, and R.C. Lopez, Cambridge Univ Press, pages 55-84.

Heap, M. J., S. Vinciguerra, and P. G. Meredith (2009), The evolution of elastic moduli with increasing crack damage during cyclic stressing of a basalt from Mt. Etna volcano. Tectonophysics, 471(1), 153-160.

Hier‐Majumder, S. (2008). Influence of contiguity on seismic velocities of partially molten aggregates. Journal of Geophysical Research: Solid Earth (1978–2012), 113(B12).

Ichihara, M., & Kameda, M. (2004). Propagation of acoustic waves in a visco-elastic two-phase system: influences of the liquid viscosity and the internal diffusion. Journal of volcanology and geothermal research, 137(1), 73-91.



Jellinek, A. M., and D. J. DePaolo, (2003). A model for the origin of large silicic magma chambers: precursors of caldera-forming eruptions. Bulletin of Volcanology, 65(5), 363-381.

Kern, H., Walther, C., Flüh, E., & Marker, M. (1993). Seismic properties of rocks exposed in the POLAR profile region—constraints on the interpretation of the refraction data. Precambrian research, 64(1), 169-187.

Kieffer, S. W. (1977). Sound speed in liquid‐gas mixtures: Water‐air and water‐steam. Journal of Geophysical


41

Research, 82(20), 2895-2904. Lin, G., Amelung, F., Lavallée, Y., & Okubo, P. G. (2014). Seismic evidence for a crustal magma reservoir beneath

the upper east rift zone of Kilauea volcano, Hawaii. Geology, 42(3), 187-190. Marchetti, E., Ichihara, M., & Ripepe, M. (2004). Propagation of acoustic waves in a viscoelastic two-phase

system: influence of gas bubble concentration. Journal of volcanology and geothermal research, 137(1), 93-108.

Mavko, G., Mukerji, T., & Dvorkin, J. (2009). The rock physics handbook: Tools for seismic analysis of porous media: Cambridge university press.

Mavko, G. M. (1980). Velocity and attenuation in partially molten rocks. Journal of Geophysical Research: Solid Earth (1978–2012), 85(B10), 5173-5189.

Müller, K., Bagdassarov, N., James, M., Schmeling, H., & Deubener, J. (2003). Internal friction spectroscopy in Li 2 O–2SiO 2 partially crystallised glasses. Journal of non-crystalline solids, 319(1), 44-56.

Nagaoka, Y., K. Nishida, Y. Aoki, M. Takeo, and T. Ohminato (2012), Seismic imaging of magma chamber beneath an active volcano. Earth and Planetary Science Letters, 333, 1-8.

Ohlendorf, S. J., Thurber, C. H., Pesicek, J. D., & Prejean, S. G. (2014). Seismicity and seismic structure at Okmok Volcano, Alaska. Journal of volcanology and geothermal research, 278, 103-119.

Paterson, M., & Olgaard, D. (2000). Rock deformation tests to large shear strains in torsion. Journal of Structural Geology, 22(9), 1341-1358.

Paulatto, M., Annen, C., Henstock, T. J., Kiddle, E., Minshull, T. A., Sparks, R., & Voight, B. (2012). Magma chamber properties from integrated seismic tomography and thermal modeling at Montserrat. Geochemistry, Geophysics, Geosystems, 13(1).

Picard, D., Arbaret, L., Pichavant, M., Champallier, R., & Launeau, P. (2011). Rheology and microstructure of experimentally deformed plagioclase suspensions. Geology, 39(8), 747-750.

Pistone, M., Caricchi, L., Ulmer, P., Reusser, E., & Ardia, P. (2013). Rheology of volatile-bearing crystal mushes: mobilization vs. viscous death. Chemical Geology, 345, 16-39.

Schilling, F. R., Sinogeikin, S. V., Hauser, M., & Bass, J. D. (2003). Elastic properties of model basaltic melt compositions at high temperatures. Journal of Geophysical Research: Solid Earth (1978–2012), 108(B6).

Schmeling, H. (1985). Numerical models on the influence of partial melt on elastic, anelastic and electric properties of rocks. Part I: elasticity and anelasticity. Physics of the earth and planetary interiors, 41(1), 34-57.

Schneider, C. A., Rasband, W. S., & Eliceiri, K. W. (2012). NIH Image to ImageJ: 25 years of image analysis. Nature methods, 9(7), 671-675.

Simmons, G. (1964). Velocity of shear waves in rocks to 10 kilobars, 1. Journal of Geophysical Research, 69(6), 1123-1130.

Temkin, S. (2005). Suspension acoustics: An introduction to the physics of suspensions: Cambridge University Press.

Webb, S., and D. Dingwell (1990), The onset of non-newtonian rheology of silicate melts: a fiber elongation study, Physics and Chemistry of Minerals, 17(2), 125-132.

Webb, S., & Courtial, P. (1996). Compressibility of melts in the CaO-Al 2 O 3-SiO 2 system. Geochimica et cosmochimica acta, 60(1), 75-86.

Chapter 4 Seismic Properties of Hydrous Phonolite

42

4 LABORATORY MEASUREMENTS OF SEISMIC VELOCITIES AT HT-HP

CONDITIONS IN HYDROUS PHONOLITE FROM TEIDE VOLCANO, TENERIFE, CANARY ISLANDS

Tripoli Barbara1, Giordano Daniele2, Cordonnier Benoit3, Ulmer Peter1


2 Earth Sciences Department, Università degli Studi di Torino

3 No Affiliation

4.1 ABSTRACT

Seismic tomography performed under active volcanoes usually reveal low velocity zones interpreted as magma

chambers feeding volcanic eruptions. However, some volcanoes, such as Teide in Tenerife, Canary Islands, lack

evidences of a large magmatic reservoir. Measurements of seismic velocities at high pressure and high

temperature performed on hydrous melt are fundamental for a better understanding of seismic tomography

images. In order to better constrain the magmatic system at Teide volcano, new laboratory measurements of

seismic velocities of natural hydrous phonolite have been performed at pressure from 150 to 300 MPa and

temperature from 100 to 550°C. The temperature derivatives of seismic velocities are constant at temperature

lower than the glass transition. In the region characterized by liquid-like behavior, compression and shear wave

velocities vary significantly in function of the dissolved water content. The increase in temperature derivatives

of phonolite liquid is higher at water content lower than 1 wt%.

The data recorded in the region characterized by liquid-like behavior have been extrapolated to magmatic

temperatures (850 to 950°C) and combined to calculated seismic properties of prominent phenocrysts in the

investigated phonolite. The resulting seismic velocities vary between 4.4 and 5.0 km/s for a magma chamber

containing 30 to 40 vol% crystals. Various hypotheses concerning the magmatic plumbing system of Teide may

be related to the higher velocities observed in the currently available seismic tomography images (García-

Yeguas et al., 2012). These hypotheses include (1) the absence of a large eruptible magmatic reservoir, (2) a

magma chamber smaller than 3 km thickness, (3) a network of sills and dykes producing small magma pockets,

or (4) a cooling magma chamber containing more than 60 vol% crystals.

4.2 INTRODUCTION

Knowledge on the physical properties of magmas at high pressure and high temperature is prerequisite for a

better and more fundamental understanding of the magmatic plumbing system ultimately feeding volcanic

edifices. Indeed, parameters such as seismic velocities are fundamental for an accurate interpretation of


43

seismic tomography performed in volcanic environments. Laboratory measurements of elastic parameters

have been performed on melt of various compositions (Askarpour et al., 1993; Schilling et al., 2003; Webb and

Courtial, 1996). Seismic velocities decrease continuously with increasing temperature until the glass transition

temperature is attained. This temperature range corresponds to a transition in the physical properties of the

melt from a solid-like (low temperature) to a liquid-like behavior (high temperature). By crossing this region, a

marked increase of the temperature derivative of the compressional wave propagation velocity is observed.

This discontinuity is distinctly less pronounced for shear waves.

Although both mafic and silicic magmas can contain up to at least 6 wt% of dissolved water at depth (e.g.

Sisson and Layne, 1993; Hervig et al., 1989), studies on the effect of water on the seismic properties of magmas

are scarce. Experiments using Brillouin scattering spectroscopy have been performed on glasses with variable

composition and dissolved water content at room temperature (Richet and Polian, 1998; Malfait et al., 2011;

Whittington et al., 2012). Compression and shear wave velocities decrease linearly with the addition of water

for rhyolitic and andesitic glasses but remain relatively constant for depolymerized basaltic glasses (Malfait et

al., 2011). With increasing alkalinity of the investigated glasses, the addition of water results in increasing

seismic velocities (Whittington et al., 2012).

The studies mentioned above investigated the effect of water on the seismic properties of glasses at room

conditions. Data collected at temperature ensuring the liquid-like behavior of silicate are lacking to date. In this

study, compression and shear wave velocities have been measured at high pressure and high temperature on

hydrated phonolite collected in Tenerife, Canary Islands.

4.2.1 PHONOLITE AT TEIDE VOLCANO

The volcanic activity in Tenerife, Canary Islands, can be divided into three main phases: (1) a mafic alkaline

shield that forms about 90% of the island (e.g. Ancochea et al., 1990); (2) a Central complex subdivided into a

Lower Group dominated by mafic to intermediate compositions, and an Upper Group dominated by felsic

compositions. This volcanic cycle is characterized by explosive eruptions and triggered three caldera collapses

(e.g. Martí and Gudmundsson, 2000); (3) the active Teide and Pico Viejo stratovolcanoes which erupted a

significant volume of phonolitic magmas, and the volumetrically smaller basaltic rifts (e.g. Ablay and Martí,

2000).

Phonolites produced during the third volcanic cycle contain variable amount of crystals. The Roques Blancos

eruption (1714 BP) is characterized by a crystal content of approximatively 14 vol%, being mainly anorthoclase

(13.7 vol%) and to a lower extent biotite, magnetite, diopside and ilmenite. In order to determine the storage

conditions prior to the eruption, Andújar et al. (2013) compared the mineral compositions and fractions in

natural samples and in hydrous samples synthetized at various pressure and temperatures in the laboratory.

They concluded that the Roques Blancos phonolite was stored at 900 ± 15 °C, 50 ± 15 MPa, with about 2.2 wt%

H2O dissolved in the melt. In contrast, prior Teide phonolites as the products of the Montañas Blancas eruption

(2020 BP) are nearly aphyric and contain 1 to 4 vol% of crystals of anorthoclase, biotite, clinopyroxene,


44

magnetite/ilmenite and apatite (Andújar and Scaillet, 2012). Phase equilibrium experiments suggests that the

magma chamber was at 850 ± 15 °C, 50 ± 20 MPa with melt containing 2.5 ± 0·5 wt% H2O. Higher temperature

and pressure conditions have been inferred from the same type of experiments for the storage conditions of

the most recent Lavas Negras (1150 BP), i.e. 900 ± 20 °C, 150 ± 50 MPa, with 3 ± 0.5 wt% dissolved H2O in the

melt (Andújar et al., 2010). The product of this eruption contains up to 37 vol% phenocrysts (anorthoclase: 32

vol%, clinopyroxene: 2 vol%, magnetite: 3 vol%).

Although the crystal content varies considerably, these phonolites are chemically similar (Andújar and Scaillet,

2012). Interestingly, phonolitic eruptions at Teide are characterized by a wide range of eruptions styles, ranging

from effusion of thick lava flows to sustained explosive eruptions generating thick and widespread fallout

deposits (e.g. García et al., 2012). Phase equilibrium experiments revealed the importance of pre-eruptive

conditions, such as pressure and water content dissolved in the melt, on the dynamics and on the location, i.e.

summital (e.g. Lavas Negras) versus flank vents (e.g. Montañas Blancas; Roques Blancos), of the eruptions

(Andújar and Scaillet, 2012; Andújar et al., 2013). The identification of subvolcanic magma reservoirs at Teide

volcano would thus help to assess future volcanic activity. However, recent seismic tomography images lack

evidences of a low velocity zone common marker of magmatic chambers (García-Yeguas et al., 2012; Barros et

al., 2012).

In order to better constrain the magmatic system at Teide volcano, new laboratory measurements of seismic

velocities of natural hydrous phonolite have been performed at pressure from 150 to 300 MPa and

temperature from 100 to 550°C. We first emphasize the effect of water on the elastic properties of phonolite at

HP-HT. Extrapolation of these results to magmatic conditions are combined with seismic properties of mineral

assemblage characteristic of these phonolite.

4.3 METHODS


Natural samples from the Lavas Negras lava flows (Teide, Tenerife) were melted in air at 1600°C for 24 hours

and quenched. The recovered glass was crushed and subsequently mixed with the desired amount of distilled

water in order to obtain several hydrous phonolitic glasses, i.e. 0.1, 1.0, 2.0 and 3.0 wt% H20. The mixtures

were cold pressed into stainless steel canisters with a uniaxial pressure of 200 MPa. Molybdenum foils lining

the border of the canister avoided contamination from the wall. Glass synthesis was performed in a Hot

Isostatic Press (HIP) at 1200 °C and 200 MPa for 24 hours. In order to obtain crystal-free samples, the glass-

bearing canisters were first cooled at a rate of 60°C/min to 650°C. This temperature corresponds to a

temperature higher than the glass transition temperature of 613°C of the sample containing nominally 0.1 wt%

H2O (Giordano et al., 2008). The temperature was ultimately decreased to room temperature at a rate of

0.6°C/min to prevent thermally induced cracks. Drill cores of 30 mm length and 22 mm diameter were

extracted from the glasses to perform elastic property measurements.


45

Karl Fisher Titration has been used on all glasses before and after experiments to assess the bulk water content

(Table 4.1). The data presented represent averages of at least 3 individual analyses. We determined the major

element composition of the recovered experimental samples with a JEOL JXA-8200 electron microprobe

employing a 20 µm beam diameter, 10 kV acceleration voltage and 20 nA beam current. The homogeneity of

the samples was assessed by measuring the composition at various locations (Table 4.1). The data presented

are the average of at least 10 analyses.

Figure 4.1: Schematic drawing of the HP-HT Paterson apparatus implemented with the setup to measure seismic velocities.

4.3.2 SEISMIC VELOCITY MEASUREMENTS

Seismic velocities of the hydrous phonolites were measured in a Paterson-type internally-heated gas pressure

apparatus (Paterson and Olgaard, 2000). Piezoelectric transducers placed at both extremities of the assembly

permit the in-situ measurement of compression and shear wave velocities using the pulse transmission

technique (Birch, 1960). The vibration frequency applied to the transducers was 1 MHz. The alumina rods in the

assembly have a 2 mm diameter hole allowing insertion of thermocouples at the bottom and top of the sample

(Figure 4.1). The temperature difference between these two thermocouples never exceeded 5°C. The assembly

is isolated from the gas pressure medium (argon) by an iron jacket of 0.2 mm wall thickness. The time delay

caused by the stack of alumina rods was determined at various pressure and temperature conditions

employing a fused silica glass rod. Most seismic property measurement experiments were performed at a

constant pressure of 250 MPa. Some additional measurements were obtained at 150, 200 and 300 MPa on the

more hydrated samples to assess the effect of pressure. Samples were first heated at a rate of 10°C/min to the

highest temperature (between 500 and 550°C depending on the water content). Ultrasonic velocities were


46

recorded every 20 to 50 °C while decreasing the temperature at a rate of 10 °C/min. In order to allow the

sample and the assembly to equilibrate at the new thermal condition, constant temperature was maintained

during a minimum of 20 minutes prior to recording the arrival times and waveforms. The error on the

measurements is dominated by the picking of the first arrival (for additional details on data processing, see

Caricchi et al., 2008) and reaches 0.1 km/s for compression wave velocity and 0.2 km/s for shear wave velocity.

After the termination of the experiments, the density of the core samples was determined by measuring their

volume with a helium pycnometer and by weighing them with a high precision balance. The error on the

measured density amounts to 0.001 kg/cm3.

4.4 RESULTS


After synthesis in the HIP, the water content of the glass was determined by Karl Fisher Titration (KFT). The

sample containing nominally 0.1 wt% H20, i.e. LN1, resulted in water contents higher than expected, whereas

samples containing nominally more than 1 wt% H20 lost some water (Table 4.1). All glasses are compositionally

homogeneous and do not contain any crystals except for LN4 and LN5 that contain 1.4 and 3.5 vol% of iron

oxides, respectively. In order to quantify the influence of these microlites on the seismic properties, we

calculated the Voigt-Reuss-Hill average VVRH using the following equations:

𝑉𝑉𝑅𝐻 = 𝑉𝑉𝑜𝑖𝑔𝑡+𝑉𝑅𝑒𝑢𝑠𝑠

2 (1)

𝑉𝑉𝑜𝑖𝑔𝑡 = ∑ 𝛷𝑖 ∗ 𝑉𝑖𝑁𝑖=1 (2)

1

𝑉𝑅𝑒𝑢𝑠𝑠= ∑

𝛷𝑖

𝑉𝑖

𝑁𝑖=1 (3)

where VVoigt is the Voigt upper bound, VReuss is the Reuss lower bound, Φi is the fraction of the ith component

and Vi is the seismic velocity (of shear or compression waves) of the ith component (e.g. Mavko et al., 2009).

Assuming a compression wave velocity Vp of 6.04 km/s for the phonolite glass (Seifert et al., 2013) and 7.35

km/s for the iron oxides (data for a magnetite crystal taken from Ji et al., 2002), the Voigt-Reuss-Hill average is

6.06 and 6.08 km/s for a crystal content of 1.4 and 3.5 vol%, respectively. Concerning the shear wave velocity

Vs, we adopted a velocity of 3.59 km/s for the phonolite glass (Seifert et al., 2013) and 4.2 km/s (Ji et al., 2002)

for the magnetite. The calculated velocities are 3.60 and 3.61 km/s for a crystal content of 1.4 and 3.5 vol%,

respectively. The error induced by the presence of microlites is within the error of the measurements, i.e. 0.1

km/s for Vp and 0.2 km/s for Vs.


47

4.4.2 EFFECT OF TEMPERATURE ON SEISMIC VELOCITIES

While increasing temperature, the seismic velocities of the phonolite samples display the behavior previously

observed for silicate melts (Askarpour et al., 1993; Schilling et al., 2003; Webb and Courtial, 1996).

Compression and shear wave velocities continuously decrease with increasing temperature until a critical

temperature Tc (Figure 4.2). This temperature corresponds to a transition in the physical properties from a

solid-like (low temperature) to a liquid-like behavior (high temperature). Above this temperature, the

temperature derivative of wave propagation velocity becomes significantly steeper.

Figure 4.2: Compression (A) and shear (B) wave velocities measured in phonolite containing different amount of H2O. The glass transition temperature has been determined for each sample as the intersection between linear regressions obtained for the liquid-like (dashed lines) and the solid-like behavior (full lines).

4.4.3 EFFECT OF WATER CONTENT ON TEMPERATURE DERIVATIVES

Although the seismic velocities generally decrease with the addition of dissolved water (Figure 4.2), the four

hydrous phonolite display identical temperature derivatives of the compression wave velocities dVp/dT of -5.10

(±0.02) *10-4 km/s/°C at temperatures less than Tc (Figure 4.3). The temperature derivative of shear wave

velocities dVs/dT in the region characterized by solid-like behavior are slightly increasing with decreasing water

content. Above Tc, variable water content result in much larger variations in the temperature derivatives

(Figure 4.3). The LN5 (1.87 Wt.% H2O) super-cooled liquid displays a dVp/dT of -3.03*10-3 km/s/°C whereas LN1

(0.36 Wt.% H2O) results a dVp/dT of -1.71*10-3 km/s/°C for LN1. This difference in temperature derivatives is

lower for shear wave velocities ranging from -2.02*10-3 km/s/°C for LN5 to -1.27*10-3 km/s/°C for LN1.


48

Figure 4.3: Variation of the temperature derivatives of compression (dark symbols) and shear (light symbols) wave velocities as a function of the water content above (green squares) and below (purple circles) the glass transition temperature.

The critical temperature Tc is as well dependent on the water content. Calculated as the intersection between

the linear regressions of the solid-like and the liquid-like seismic velocities, Tc differs slightly for regressions

done for Vs and Vp measurements (Table 4.2). The difference does not exceed 8 °C for samples containing more

than 0.5 wt% H2O, i.e. LN5, LN4 and LN3, but reaches 13 °C for LN1. However, Tc derived from both Vp and Vs

varies non-linearly with the addition of dissolved water (Figure 4.4).

Figure 4.4: Glass transition temperatures Tg as a function of water concentration dissolved in the melt. The seismic Tg (crosses) were obtained from the intersections of the temperature dependence of compression wave velocities of solid-like and liquid-like behavior (Figure 4.2). Solid lines represent Tg at various cooling rates calculated with equations 4 and 5.


49

4.4.4 EFFECT OF PRESSURE ON SEISMIC VELOCITIES

Temperature derivatives of sample LN5 (1.87 Wt.% H2O) have been determined at 150, 200, 250 and 300 MPa.

Below Tc, compression wave velocities Vp are slightly higher at lower pressure but converge to the same values

above Tc (Figure 4.5A). Shear wave velocities displays the inverse pattern, i.e. Vs collected at lower pressure are

slightly lower at temperature above Tc (Figure 4.5B). Although some variations in the seismic velocities can be

observed, the data collected at various pressures are within the error of the measurements. We thus assumed

that Vp and Vs are not pressure-dependent over the range of investigated pressures.

Figure 4.5: Compression (A) and shear (B) wave velocities of samples containing 1.87 wt% H2O at various pressures. The variation of velocities at pressures from 150 to 300 MPa are within the error of the measurements.

4.5 DISCUSSION

4.5.1 GLASS TRANSITION

The critical temperatures Tc defined in this paper as the intersection between temperature derivatives of

seismic velocities at low and high temperature have previously been attributed to the glass transition

temperature Tg (e.g. Schilling and Sinogeikin, 2003; Askarpour et al., 1993). The glass transition is associated

with the theory of visco-elasticity and the structural relaxation timescale of silicate melt (e.g. Dingwell and

Webb, 1989). When a stress is applied to a melt, two possible reactions are expected, either, (1) liquid-like and

entirely viscous (Newtonian) behavior revealing the relaxed state of the material; or (2) solid-like and entirely

elastic behavior at small strains but brittle under large strains (Dingwell, 1997). These two states are separated

by a viscoelastic region where non-Newtonian rheology can be observed (Webb and Dingwell, 1990). This

particular behavior describes the inability of the melt to relax on the timescale of the experiment (Dingwell,

1997). Being dependent on the kinetics, the glass transition temperature of silicate melts is thus a temperature

range rather than a single temperature. However, this transition is often observed through marked variations


50

in the temperature derivatives of physical properties, such as thermal expansion (e.g. Knoche et al., 1995),

seismic velocities (e.g. Askarpour et al., 1993) or specific heat capacity (e.g. Moynihan et al., 1974).

Giordano et al. (2005) estimated Tg of hydrous phonolite through the measurement of specific heat capacity by

Differential Scanning Calorimetry (DSC) at cooling rates varying from 5 to 20 °C/min. Their glass transition

temperatures are significantly higher than the values obtained in this study, i.e. approximatively 80 °C for a

cooling rate of 10°C/min (Table 4.2). There is, however, a significant difference between a cooling experiment

conducted in DSC and the seismic velocity measurements as conducted in this study. During our experiments,

the temperature was maintained constant for 20 minutes prior to measuring the seismic velocities. This dwell

time was required to allow for thermal equilibration of the entire assembly in order to obtain accurate velocity

measurement. The bulk cooling rate in our experiments, therefore, resulted to be 1.3°C/min, considerably

lower than 10°C/min on the temperature cooling segments alone.

In order to extrapolate the data of Giordano et al. (2005) to lower cooling rate, viscosity η of hydrous phonolite

was calculated for each Tg measured by DSC using an empirical Vogel-Fulcher-Tammann (VFT) equation

(Giordano et al., 2009):

𝑙𝑜𝑔10𝜂 = −4.55 + (10261 − 26.21(𝐻2𝑂))/(𝑇𝑔 − 263.8 + 257.8𝑙𝑜𝑔10(1 + (𝐻2𝑂))) (4)

where Tg is the glass transition temperature in K and H2O is the water content in wt%. As viscosity is linearly

proportional to cooling rate (Scherer, 1984; Gottsman et al., 2002; Stevenson et al., 1995), extrapolation to

lower cooling rates is obtained through a regression in the form of:

𝑙𝑜𝑔10(𝜂) = 𝑘 − 𝑙𝑜𝑔10(𝑞) (5)

where q is the cooling rate in °C/min and k is a composition dependent shift factor (Gottsman et al., 2002).

Linear regressions between the calculated viscosity at Tg and the cooling rate provided by Giordano et al.

(2005) have a slope lower than 1 ( Figure 4.6 and Table 4.3). For the precision of our calculation, we have thus

introduced a parameter A as the slope of the regressions. A and k are estimated for each water content (Table

4.3). Calculated Tg using equations 4 and 5 are plotted in Figure 4.4 as a function of water content for various

cooling rates. Glass transition temperatures derived from the temperature derivatives of compression and

shear wave velocities, i.e. elastic Tg, correspond to a cooling rate of 10-4 °C/min, except for LN3 which lies

outside the calculated trends. This cooling rate is much lower than the bulk cooling rate applied during our

experiments, i.e. approximatively 1.3 °C/min.

This discrepancy could be linked to the relaxation time τ of the sample, which is calculated using the simplified

Maxwell relationship:

𝜏 =𝜂

𝐺∞ (6)


51

where η is the viscosity in Pas and G∞ is the shear modulus at infinite frequency approximated to a constant

value of 10 GPa (Dingwell and Webb, 1990). ). The calculated relaxation time of the samples is less than 20

minutes at temperature above the seismic Tg (Table 4.4). These calculations reveal that the structure of the

super-cooled liquid had sufficient time to relax during the 20 minutes dwell time and appeared as thermally

stable before the seismic velocity measurements were taken. The shift between the Tg measured by Giordano

et al. (2005) and our seismic Tg can thus be explained by the difference in the structural relaxation state of the

investigated samples. Indeed, at constant cooling, magmas store the stress generated from the thermal

contraction and are in a visco-elastic unrelaxed condition. If enough time is given to release this stress, the

sample returns to a relaxed liquid state.

Figure 4.6: Linear dependence of the viscosity at the glass transition temperature as a function of the cooling rate applied to hydrous samples (data from Giordano et al., 2005).

4.5.2 DENSITY

Density has been measured on the post-experiment samples at room conditions using a gas displacement

pycnometer (Table 4.2). In order to assess the variation of density during our experiments, the volumes of

silicate liquids are calculated as a function of composition, pressure and temperature (Carroll and Holloway,

1994) using an equation in the form of:

𝑉𝑙𝑖𝑞 = ∑ 𝑋𝑖 [�̅�𝑖,𝑇𝑟𝑒𝑓,𝑃𝑟𝑒𝑓+

𝑑𝑉𝑖

𝑑𝑇∗ (𝑇 − 𝑇𝑟𝑒𝑓) +

𝑑𝑉𝑖

𝑑𝑃∗ (𝑃 − 𝑃𝑟𝑒𝑓)] (7)

where Xi is the mole fraction of the ith oxide component, T is the temperature, P is the pressure, V̅i is the

partial molar volume of the ith oxide component, dV̅i/dT is the temperature derivative of V̅i and dV̅i/dP is the

pressure derivative of V̅i (parameters are given in Table 4.5). Density of silicate melt ρliq is calculated using the

following relationship:


52

𝜌𝑙𝑖𝑞 =∑ 𝑋𝑖∗(𝑀.𝑊.)𝑖

𝑉𝑙𝑖𝑞 (8)

where (M.W.)i is the molecular weight of the ith oxide component. Figure 4.7 provides the results of the

density calculations as a function of water content for all samples investigated at a pressure of 250 MPa and a

temperature corresponding to the glass transition temperature estimated from the seismic velocities

measurements. Although the density measured by pycnometry is always somewhat lower than the calculated

density, the calculated and measured values are within the errors identical. The density variation induced by

the decrease of temperature and pressure in the solid-like state, i.e. glassy state, is thus lower than the errors.

This feature has been observed by Malfait et al. (2014) on glasses of various compositions quenched and

decompressed from HT-HP. By comparing their measurements of glasses and calculated properties of melts

using their equations of state, they observed that glasses preserve the configuration induced by pressure and

temperature at Tg. For the calculation of the elastic properties, we are thus assuming that the density at

temperature lower than Tg remains constant.

Figure 4.7: Density as a function of the dissolved water in the melt. Densities were determined on recovered experimental charges by He pycnometry and calculated using equations 7 and 8 at the P-T conditions corresponding to the seismic Tg.

4.5.3 ELASTIC PROPERTIES

Shear (G) and bulk (K) moduli (Table 4.4) have been calculated at various temperatures from the measured

seismic velocities (Vp, Vs) and from the calculated density (ρ) using the following relationships:

𝐺 = 𝑉𝑠2 ∗ 𝜌 (9)

𝐾 = 𝜌 ∗ (𝑉𝑝2 −

4

3∗ 𝑉𝑠

2) (10)


53

Elastic moduli of phonolitic glasses have previously been determined at room temperature by Whittington et

al. (2012). As observed by Malfait et al. (2014) for density, the measured elastic properties of their phonolite

reflect the properties frozen at the glass transition temperature. Their measurements of bulk and shear

modulus are compared to our measurements at the glass transition temperature in Figure 4.8. Although their

synthesis pressure was 300 MPa and their phonolite has a different composition, our measurements give

similar results and follow the same trend within error. Yet the addition of water in glasses slightly decreases the

elastic moduli.

Figure 4.8: Variation of bulk (green diamonds) and shear (purple circles) modulus as a function of water content. Our data (dark symbols) are calculated at the seismic Tg using equations 9 and 10. The data from Whittington et al. (2012) (light symbols) are plotted for comparison.

However, the temperature dependency of the elastic properties above Tg depends significantly on the

dissolved water content (Figure 4.9). For the same temperature difference, the bulk and shear moduli of the

sample containing more water decrease steeper than for the sample with the lowest water content. This

feature could be linked to the efficiency of water to depolymerize silicate melt. At constant temperature, the

addition of less than 1 wt% H2O in melts decreases the viscosity by orders of magnitudes (e.g. Dingwell et al.,

1996; Richet et al., 1996). This effect levels out when the water content is further increased (Ardia et al, 2008).

Temperature derivatives of elastic moduli, and thus seismic velocities, are similarly affected by water content

above Tg.

4.5.4 APPLICATION TO THE MAGMATIC CHAMBER OF TEIDE VOLCANO

The measured compression wave velocity of hydrous phonolite has been employed to evaluate the seismic

properties of a potential magma chamber under the Teide volcano. First, our results were fitted from a

regression analysis into:


54

𝑉𝑝(𝑚𝑒𝑙𝑡) = 7.00 − 𝑙𝑜𝑔10(1 + 𝐻2𝑂) ∗ 1.28 − 𝑇 ∗ 2.47 ∗ 10−3 (11)

where Vp(melt) is the compression wave velocity of the melt in Km/s, H2O is the water content in wt% and T is the

temperature in °C. This regression has been used to extrapolate the experimental data set to magmatic

temperature conditions. As the recorded seismic velocities in the liquid-like state were performed on fully

relaxed samples, we are confident about the temperature extrapolation up to 1000 °C. Pressure has not been

included into the calculation as we infer only insignificant changes in seismic velocities due to pressure

variation over the range 100-300 MPa.

Figure 4.9: Contour map of compression wave velocity in function of water content and temperature, calculated using equation 11.

The Teide phonolites contain up to 40 vol% crystals. Therefore the effect of crystals has to be considered and

was taken into account in our calculation by using the Voigt upper bound and the Reuss lower bound, which

are the best estimations of the highest and lowest expected seismic velocities of a suspension of solid grains in

a fluid (e.g. Mavko et al., 2009). The Voigt upper bound VVoigt and the Reuss lower bound VReuss were calculated

using equation 2 and 3, respectively. The seismic velocities of the crystals corresponding to the phenocrysts

contained in the Lavas Negras, i.e. anorthoclase, clinopyroxene and magnetite, have been calculated using

Perple_X (Connolly, 2009). This thermodynamic model permits computation of elastic properties of minerals

depending on their compositions. We thus selected mineral compositions similar to the Lavas Negras

phenocrysts (Table 4.6) and computed the seismic velocity of each crystal phase following an equation in the

form of:

𝑉𝑝(min) = 𝑉0(𝑚𝑖𝑛) +𝑑𝑉𝑝(𝑚𝑖𝑛)

𝑑𝑇∗ 𝑇 +

𝑑𝑉𝑝(𝑚𝑖𝑛)

𝑑𝑃∗ 𝑃 (12)

where P is the pressure in bar and V0(min), dVp(min)/dT and dVp(min)/dP are constants listed in Table 4.6. We

calculated the Voigt and Reuss bounds at conditions relevant for the Lavas Negras prior to eruption (Andújar et


55

al., 2010), i.e. at a pressure of 150 MPa for a melt containing initially 2 wt% water. The water content in the

melt is increasing as function of the crystal content in order to simulate the effect of close system

crystallization. The anorthoclase fraction increases from 0 to 35 vol%, the clinopyroxene fraction from 0 to 2

vol% and the magnetite fraction from 0 to 3 vol%.

The seismic velocity of the magma chamber containing the phonolitic Lavas Negras varies between 5 km/s

(Voigt upper bound in Figure 4.10A) and 4.4 km/s (Reuss lower bound in Figure 4.10B) depending on the

temperature and the total crystal content. In case a large magmatic chamber is currently present under the

Teide volcano, it should be observable in the seismic tomography images provided by García-Yeguas et al.

(2012). These images reveal close to the surface, i.e. in the first 2-3 km, zones having a velocity comprised

between 3.5 and 5 km/s and interpreted as volcaniclastic sediments and hydrothermal deposits. At higher

depth, compression wave velocities are increasing from ~5.5 km/s at 4 km depth to more than 7.0 km/s at 8 km

depth. Low velocity zones are not observed.

Figure 4.10: Contour maps of the Voigt upper bound (A) and Reuss lower bound (B) in km/s as a function of the total crystal content and temperature. The shaded area represents the inferred condition of the magma chamber feeding the Lavas Negras eruption (Andújar et al., 2010).

Consequently, four hypotheses are possible. The first involves the total absence of a magmatic chamber under

Teide volcano. However, this hypothesis is in contradiction with the seismic activity in 2004 suggesting

magmatic intrusion (Cerdeña et al., 2011; Almendros et al., 2007). The second hypothesis involves a magma

chamber too small to be detected by seismic tomography. Considering that one of the largest volume phonolite

eruption at Teide was about 1 km3 (Roques Blancos; Andújar et al., 2013), it is possible that the magma

chamber is smaller than the resolution of the tomography image provided by García-Yeguas et al. (2012), i.e. 3

km. It is as well possible that the magmatic system under Teide is not characterized by a unique magma

chamber but by a network of more isolated and thin dykes and sills leading to a value which tends towards the

country rock one. This third hypothesis has been previously raised by Barros et al. (2012) who identified

scattering structures probably related to a complex network of dykes and sills. Petrologic evidences actually


56

support a complex structure producing multiple small magmatic reservoirs (Andújar et al., 2013). Finally, the

crystal content could be much higher at depth than the erupted product. Indeed, the phonolite erupted at

Teide volcano may have been extracted from a ‘mushy’ zone and would thus reflect mainly the residual melt

(Dávila-Harris et al., 2013; Sliwinski et al., in review).

4.6 CONCLUSION

Seismic velocities have been measured at high pressure and high temperature conditions in hydrous phonolites

from the Teide volcano. At temperature lower than the glass transition, compression wave velocities vary

between 5.7 and 5.9 km/s and shear wave velocities vary between 3.3 and 3.6 km/s. Their temperature

derivatives are independent of the dissolved water content. Upon crossing the glass transition, temperature

derivatives of both, compression and shear wave velocities, significantly increase. This increase is accentuated

by the addition of water following a trend previously observed for melt viscosity. Indeed, the increase in

temperature derivatives of seismic velocities is higher at low water content. Measured seismic glass transition

temperatures and calculated relaxation times suggest that measurements in the liquid-like state have

predominantly been performed on relaxed samples.

Combining the experimental results of this study with calculated seismic properties of relevant mineral phases

forming prominent phenocrysts in the investigated phonolite provides insights into the magmatic system

potentially present beneath the Teide volcano. The resulting seismic velocities vary between 4.4 and 5.0 km/s

for a magma chamber at 850 to 950 °C and containing 30 to 40 vol% crystals. In the currently available seismic

tomography images of the area (García-Yeguas et al., 2012), higher velocities are observed, i.e. from ~5.5 km/s

at 4 km depth to more than 7.0 km/s at 8 km depth. The absence of a low velocity zone leads to hypotheses

involving (1) the absence of a large eruptible magmatic reservoir, (2) a magma chamber smaller than 3 km

thickness, (3) a network of sills and dykes producing small magma pockets, or (4) a cooling magma chamber

containing more than 60 vol% crystals.


57

4.7 TABLES

Table 4.1: Compositions of hydrous phonolite from Lavas Negras (Tenerife, Spain) in wt.%. Major elements are determined by electron microprobe. The water content was measured by Karl Fisher Titration. Td_ph - composition of phonolite from Montañas Blancas (Tenerife, Spain) used in the study of Giordano et al. (2005).

LN5 LN4 LN3 LN1 Td_ph

SiO2 60.16 60.23 60.65 60.39 60.46

Al2O3 18.33 18.52 18.66 18.58 18.81

FeO (tot) 3.04 3.36 3.37 3.44 3.31

TiO2 0.63 0.67 0.68 0.68 0.56

MnO 0.19 0.19 0.20 0.21 0.20

MgO 0.32 0.35 0.37 0.36 0.36

CaO 0.73 0.72 0.71 0.72 0.67

Na2O 8.74 9.05 9.19 9.24 9.76

K2O 4.72 4.75 4.84 4.85 5.45

P2O2 ---- ---- ---- ---- 0.06

H2O 1.87 1.37 0.56 0.36 ----

Nominal H2O 3.00 2.00 1.00 0.10 ----

Total 98.74 99.21 99.23 98.84 99.64

Table 4.2: Comparison of measured properties between sample containing different water contents. The calorimetric Tg are calculated from data of Giordano et al. (2005) and corresponds to the onset of Tg, i.e. the temperature where the specific heat capacity starts to deviate, at a cooling rate of 10 °C/min.

LN5 LN4 LN3 LN1

H2O [wt%]

1.87 1.37 0.56 0.36

Density [g/cm3]

2.459 2.475 2.487 2.500

Seismic Tg [°C] Vp 320 336 382 459

Vs 329 335 380 473

Calorimetric Tg [°C]

408 426 455 542

T. deriv. below Tg dVp/dT -5.12 -5.12 -5.10 -5.14 [10-4 km/s/°C]

dVs/dT -4.93 -3.81 -3.92 -3.24

T. deriv. above Tg dVp/dT -3.03 -2.67 -2.21 -1.71 [10-3 km/s/°C] dVs/dT -2.02 -1.89 -1.46 -1.27


58

Table 4.3: Glass transition temperatures of hydrous phonolite measured by DSC (Giordano et al., 2005) used to derive viscosity at Tg for various cooling rate using equation 4. Parameters A and B are calculated using equation 5.

Cooling rate [°C/min]

H2O content [wt%]

0.03 0.85 0.95 2.10 3.75

Tg [°C] 20 670 522 505 456 403 15 665 516 500 451 398 10 656 509 492 446 392 5 648 501 482 434 382 1

621

log10η [Pas] 20 10.31 10.46 10.65 10.33 10.52 15 10.41 10.59 10.76 10.44 10.63 10 10.61 10.75 10.94 10.55 10.76 5 10.79 10.93 11.18 10.82 10.99 1

11.44

Parameter A 0.860 0.773 0.887 0.790 0.766 Parameter K 11.432 11.493 11.809 11.359 11.524

Table 4.4: Summary of measured seismic velocities and calculated physical properties.

Sample T [°C] Vp [km/s] Vs [km/s] ρ [g/cm3] G [Gpa] K [GPa] log10η

[Pas]

τ [min]

LN5 500 5.14 2.97 2.441 21.57 35.81 9.59 0.001

480 5.19 3.01 2.445 22.14 36.45 9.99 0.02

460 5.25 3.04 2.448 22.62 37.33 10.41 0.04

440 5.31 3.08 2.452 23.23 38.22 10.85 0.12

420 5.37 3.12 2.455 23.90 39.07 11.31 0.34

400 5.44 3.16 2.459 24.60 40.08 11.81 1.08

380 5.51 3.21 2.463 25.41 40.76 12.34 3.66

350 5.59 3.27 2.468 26.43 41.81 13.20 26.62

300 5.68 3.32 2.474 27.27 43.35

250 5.72 3.35 2.474 27.73 44.03

200 5.76 3.37 2.474 28.15 44.53

150 5.77 3.41 2.474 28.73 43.96

100 5.78 3.41 2.474 28.82 44.28

LN4 560 5.14 2.94 2.455 21.19 36.57 8.96 0.002

530 5.22 2.98 2.460 21.85 38.00 9.51 0.01

500 5.30 3.04 2.465 22.76 38.88 10.11 0.02

450 5.45 3.13 2.474 24.25 41.06 11.22 0.28

420 5.52 3.20 2.479 25.32 41.79 11.97 1.57

390 5.59 3.25 2.484 26.23 42.68 12.80 10.53


59

Table 4.4: Continued

Sample T [°C] Vp [km/s] Vs [km/s] ρ [g/cm3] G [Gpa] K [GPa] log10η

[Pas]

τ [min]

LN4 360 5.67 3.31 2.489 27.27 43.67

330 5.75 3.35 2.493 27.91 45.09

300 5.76 3.37 2.493 28.36 44.89

250 5.78 3.38 2.493 28.43 45.28

200 5.82 3.43 2.493 29.32 45.27

150 5.83 3.43 2.493 29.39 45.59

100 5.87 3.43 2.493 29.36 46.71

LN3 550 5.37 3.17 2.487 24.98 38.52 10.51 0.05

520 5.44 3.21 2.491 25.69 39.41 11.20 0.26

490 5.50 3.25 2.495 26.39 40.36 11.95 1.49

460 5.57 3.30 2.500 27.24 41.32 12.78 10.10

430 5.63 3.35 2.504 28.08 41.88

400 5.68 3.38 2.509 28.67 42.59

350 5.74 3.43 2.511 29.61 43.35

300 5.79 3.45 2.511 29.98 44.27

250 5.82 3.50 2.511 30.82 44.04

200 5.84 3.50 2.511 30.71 44.58

150 5.87 3.51 2.511 31.00 45.25

100 5.87 3.50 2.511 30.70 45.61

LN1 550 5.57 3.31 2.496 27.37 40.87 11.17 0.25

510 5.64 3.37 2.501 28.33 41.87 12.20 2.62

480 5.69 3.40 2.506 28.97 42.40 13.05 18.91

440 5.74 3.42 2.509 29.33 43.57

390 5.76 3.44 2.509 29.65 43.62

340 5.81 3.46 2.509 29.96 44.63

300 5.83 3.48 2.509 30.36 44.74

250 5.84 3.49 2.509 30.55 44.76

200 5.85 3.50 2.509 30.73 44.75

150 5.89 3.51 2.509 30.94 45.69

100 5.89 3.52 2.509 31.16 45.64


60

Table 4.5: Partial molar volumes and their pressure and temperature derivatives used for the calculation of density at experimental conditions (equations 7). References are given in parenthesis: (a) Lange, 1997; (b) Lange and Carmichael, 1987; (c) Ochs and Lange, 1999; (c) Kress and Carmichael, 1991.

V(i,1673K,1bar) [10-5 m3/mol] dV/dT [10-9 m3/mol*K] dV/dP [10-6 m3/mol*Gpa]

Si02 2.69 (a) 0.00 (a) -1.89 (d)

TiO2 2.32 (b) 7.24 (b) -2.31 (d)

Al2O3 3.74 (a) 0.00 (a) -2.26 (d)

FeO 1.37 (b) 2.92 (b) -0.45 (d)

MgO 1.17 (a) 3.27 (a) 0.27 (d)

CaO 1.65 (a) 3.74 (a) 0.34 (d)

Na2O 2.89 (a) 7.68 (a) -2.4 (d)

K2O 4.61 (a) 12.1 (a) -6.75 (d)

H2O 2.67 (c) 9.55 (c) -3.2 (c)

Table 4.6: Compositions in [wt%] and fit parameters (equation 12) of minerals included in the calculation of the magma chamber seismic properties.

Feldspar Clinopyroxene Magnetite

SiO2 66.20 53.82 0.00

TiO2 0.00 0.00 19.17

Al2O3 20.07 1.58 0.00

FeO (tot) 0.00 7.72 79.11

MgO 0.00 12.50 1.72

CaO 1.11 23.45 0.00

Na2O 7.79 0.93 0.00

K2O 4.84 0.00 0.00

V0 [km/s] 6.39 8.27 8.07

dVp/dT [km/s/°C] -4.63E-04 -5.93E-04 -2.67E-04

dVp/dP [km/s/bar] 2.63E-05 1.21E-05 5.15E-06


61

4.8 REFERENCES

Ablay, G., & Martı, J. (2000). Stratigraphy, structure, and volcanic evolution of the Pico Teide–Pico Viejo formation, Tenerife, Canary Islands. Journal of Volcanology and Geothermal Research, 103(1), 175-208.

Almendros, J., Ibáñez, J. M., Carmona, E., & Zandomeneghi, D. (2007). Array analyses of volcanic earthquakes and tremor recorded at Las Cañadas caldera (Tenerife Island, Spain) during the 2004 seismic activation of Teide volcano. Journal of Volcanology and Geothermal Research, 160(3), 285-299.

Ancochea, E., Fuster, J., Ibarrola, E., Cendrero, A., Coello, J., Hernan, F., Jamond, C. (1990). Volcanic evolution of the island of Tenerife (Canary Islands) in the light of new K-Ar data. Journal of Volcanology and Geothermal Research, 44(3), 231-249.

Andújar, J., Costa, F., & Martí, J. (2010). Magma storage conditions of the last eruption of Teide volcano (Canary Islands, Spain). Bulletin of Volcanology, 72(4), 381-395.

Andújar, J., Costa, F., & Scaillet, B. (2013). Storage conditions and eruptive dynamics of central versus flank eruptions in volcanic islands: the case of Tenerife (Canary Islands, Spain). Journal of Volcanology and Geothermal Research, 260, 62-79.

Andújar, J., & Scaillet, B. (2012). Experimental constraints on parameters controlling the difference in the eruptive dynamics of phonolitic magmas: the case of Tenerife (Canary Islands). Journal of Petrology, egs033.

Ardia, P., Giordano, D., & Schmidt, M. W. (2008). A model for the viscosity of rhyolite as a function of H2O-content and pressure: a calibration based on centrifuge piston cylinder experiments. Geochimica et Cosmochimica Acta, 72(24), 6103-6123.


Caricchi, L., Burlini, L., & Ulmer, P. (2008). Propagation of P and S-waves in magmas with different crystal contents: Insights into the crystallinity of magmatic reservoirs. Journal of Volcanology and Geothermal Research, 178(4), 740-750.

Carroll, M. R., & Holloway, J. R. (1994). Volatiles in magmas (Vol. 30): Mineralogical Society of America. Cerdeña, I. D., Del Fresno, C., & Rivera, L. (2011). New insight on the increasing seismicity during Tenerife's

2004 volcanic reactivation. Journal of Volcanology and Geothermal Research, 206(1), 15-29. Connolly, J. (2009). The geodynamic equation of state: what and how. Geochemistry, Geophysics, Geosystems,

10(10). De Barros, L., Martini, F., Bean, C. J., Garcia‐Yeguas, A., & Ibáñez, J. (2012). Imaging magma storage below Teide

volcano (Tenerife) using scattered seismic wavefields. Geophysical Journal International, 191(2), 695-706.

Dingwell, D., Romano, C., & Hess, K.-U. (1996). The effect of water on the viscosity of a haplogranitic melt under PTX conditions relevant to silicic volcanism. Contributions to Mineralogy and Petrology, 124(1), 19-28.

Dingwell, D. B., & Webb, S. L. (1989). Structural relaxation in silicate melts and non-Newtonian melt rheology in geologic processes. Physics and Chemistry of Minerals, 16(5), 508-516.

Dingwell, D. B., & Webb, S. L. (1990). Relaxation in silicate melts. European Journal of Mineralogy(4), 427-449. García, O., Bonadonna, C., Martí, J., & Pioli, L. (2012). The 5,660 yBP Boquerón explosive eruption, Teide–Pico

Viejo complex, Tenerife. Bulletin of Volcanology, 74(9), 2037-2050. García‐Yeguas, A., Koulakov, I., Ibáñez, J. M., & Rietbrock, A. (2012). High resolution 3D P wave velocity

structure beneath Tenerife Island (Canary Islands, Spain) based on tomographic inversion of active‐source data. Journal of Geophysical Research: Solid Earth (1978–2012), 117(B9).

Giordano, D., Ardia, P., Romano, C., Dingwell, D., Di Muro, A., Schmidt, M., Hess, K.-U. (2009). The rheological evolution of alkaline Vesuvius magmas and comparison with alkaline series from the Phlegrean Fields, Etna, Stromboli and Teide. Geochimica et cosmochimica acta, 73(21), 6613-6630.

Giordano, D., Nichols, A. R., & Dingwell, D. B. (2005). Glass transition temperatures of natural hydrous melts: a relationship with shear viscosity and implications for the welding process. Journal of Volcanology and Geothermal Research, 142(1), 105-118.



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Gottsmann, J., Giordano, D., & Dingwell, D. B. (2002). Predicting shear viscosity during volcanic processes at the glass transition: a calorimetric calibration. Earth and Planetary Science Letters, 198(3), 417-427.

Hervig, R. L., Dunbar, N., Westrich, H. R., & Kyle, P. R. (1989). Pre-eruptive water content of rhyolitic magmas as determined by ion microprobe analyses of melt inclusions in phenocrysts. Journal of Volcanology and Geothermal Research, 36(4), 293-302.

Ji, S., Wang, Q., & Xia, B. (2002). Handbook of seismic properties of minerals, rocks and ores: Presses inter Polytechnique.

Kress, V. C., & Carmichael, I. S. (1991). The compressibility of silicate liquids containing Fe2O3 and the effect of composition, temperature, oxygen fugacity and pressure on their redox states. Contributions to Mineralogy and Petrology, 108(1-2), 82-92.

Lange, R. A. (1997). A revised model for the density and thermal expansivity of K2O-Na2O-CaO-MgO-Al2O3-SiO2 liquids from 700 to 1900 K: extension to crustal magmatic temperatures. Contributions to Mineralogy and Petrology, 130(1), 1-11.

Lange, R. A., & Carmichael, I. S. (1987). Densities of Na2O-K2O-MgO-MgO-FeO-Fe2O3-Al2O3-TiO2-SiO2 liquids: New measurements and derived partial molar properties. Geochimica et cosmochimica acta, 51(11), 2931-2946.

Malfait, W. J., Sanchez-Valle, C., Ardia, P., Médard, E., & Lerch, P. (2011). Amorphous Materials: Properties, Structure, and Durability Compositional dependent compressibility of dissolved water in silicate glasses. American Mineralogist, 96(8-9), 1402-1409.

Malfait, W. J., Seifert, R., & Sanchez-Valle, C. (2014). Letter. Densified glasses as structural proxies for high-pressure melts: Configurational compressibility of silicate melts retained in quenched and decompressed glasses. American Mineralogist, 99(10), 2142-2145.

Martí, J., & Gudmundsson, A. (2000). The Las Cañadas caldera (Tenerife, Canary Islands): an overlapping collapse caldera generated by magma-chamber migration. Journal of Volcanology and Geothermal Research, 103(1), 161-173.

Mavko, G., Mukerji, T., & Dvorkin, J. (2009). The rock physics handbook: Tools for seismic analysis of porous media: Cambridge university press.

Moynihan, C. T., Easteal, A. J., Wilder, J., & Tucker, J. (1974). Dependence of the glass transition temperature on heating and cooling rate. The Journal of Physical Chemistry, 78(26), 2673-2677.

Ochs, F. A., & Lange, R. A. (1999). The density of hydrous magmatic liquids. Science, 283(5406), 1314-1317. Paterson, M., & Olgaard, D. (2000). Rock deformation tests to large shear strains in torsion. Journal of

Structural Geology, 22(9), 1341-1358. Richet, P., Lejeune, A.-M., Holtz, F., & Roux, J. (1996). Water and the viscosity of andesite melts. Chemical

Geology, 128(1), 185-197. Richet, P., & Polian, A. (1998). Water as a dense icelike component in silicate glasses. Science, 281(5375), 396-

398. Scherer, G. W. (1984). Use of the Adam‐Gibbs Equation in the Analysis of Structural Relaxation. Journal of the

American Ceramic Society, 67(7), 504-511. Schilling, F. R., Sinogeikin, S. V., Hauser, M., & Bass, J. D. (2003). Elastic properties of model basaltic melt

compositions at high temperatures. Journal of Geophysical Research: Solid Earth (1978–2012), 108(B6).

Seifert, R., Malfait, W., Petitgirard, S., & Sanchez-Valle, C. (2013). Density of phonolitic magmas and time scales of crystal fractionation in magma chambers. Earth and Planetary Science Letters, 381, 12-20.

Sisson, T., & Layne, G. (1993). H 2 O in basalt and basaltic andesite glass inclusions from four subduction-related volcanoes. Earth and Planetary Science Letters, 117(3), 619-635.

Sliwinski, J.T.; Bachmann, O.; Ellis, B.S.; Davila-Harris, P.; Nelson, B.K.; Dufek, J. Eruption of shallow crystal cumulates during caldera-forming events on Tenerife, Canary Islands. Journal of petrology, In review.

Stevenson, R., Dingwell, D. B., Webb, S., & Bagdassarov, N. (1995). The equivalence of enthalpy and shear stress relaxation in rhyolitic obsidians and quantification of the liquid-glass transition in volcanic processes. Journal of Volcanology and Geothermal Research, 68(4), 297-306.

Webb, S., & Courtial, P. (1996). Compressibility of melts in the CaO-Al 2 O 3-SiO 2 system. Geochimica et cosmochimica acta, 60(1), 75-86.

Webb, S. L., & Dingwell, D. B. (1990). The onset of non-Newtonian rheology of silicate melts. Physics and Chemistry of Minerals, 17(2), 125-132.

Whittington, A. G., Richet, P., & Polian, A. (2012). Water and the compressibility of silicate glasses: A Brillouin


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spectroscopic study. American Mineralogist, 97(2-3), 455-467

Chapter 5 Outgassing Induced by Crystallization

64

5 OUTGASSING INDUCED BY CRYSTALLIZATION: AN EXPERIMENTAL STUDY

Tripoli Barbara1, Marie Violay2, Cordonnier Benoit3, Ulmer Peter1


2 Laboratoire de Mécanique des Roches, ENAC, EPF Lausanne

3 No Affiliation

5.1 ABSTRACT

Volcanic eruptions style is to a first order controlled by the ability of the gas phase to separate from the

crystallizing melt. Determining the outgassing potential of a crystallizing magma chamber is thus fundamental

to understand a wide range of volcanic phenomena, from quiescent emissions of gas at the surface to explosive

plinian eruptions. In this study, we explore the effect of crystallization on the extent of outgassing of a

synthetic bubble-bearing haplotonalite melt at high pressure and high temperature. A Paterson-type internally-

heated gas pressure apparatus implemented with a pore-fluid system was employed to measure in situ the

volume of outgassed volatile during plagioclase crystallization and bubble exsolution. Samples were first

heated at 850 °C for 30 minutes. Subsequently, the temperature was decreased at a rate of 0.5 or 0.1 °C/min to

700 °C. In order to characterize the microstructure evolution, series of cold-seal experiments at identical

pressure conditions but with rapid-quenching have been conducted in addition.

The rate and extent of outgassing is directly related to the evolution of the microstructures. If no crystallization

occurs, the measured outgassing rate is fully explained by the ascent of bubbles calculated using Stoke’s law.

The presence of crystals may favor or inhibit the outgassing by (1) increasing the fraction and size of bubbles by

exsolution and decreasing the melt viscosity and (2) lowering their ascent velocity by increasing pathways

length or by acting as barriers. In our experiments, crystallization of more than 50 vol% of plagioclase in a melt

containing initially 4.2 vol% of bubbles induced outgassing of 4.6 to 6.6 vol% of bubbles over a rather limited

time. Consequently, the outgassing potential of a crystallizing magma chamber is high.

5.2 INTRODUCTION

A better understanding of the transport of gas in volcanic environment is fundamental to constrain a wide

range of volcanic phenomena, from quiescent emissions of gas at the surface to explosive plinian eruptions.

Indeed, when the rise speed of large bubbles in a volcanic conduit is faster than the ascent rate of the

surrounding basaltic magma, the volcanic activity is characterized by passive outgassing potentially

accompanied by lava flows (e.g. Slezin, 2003, Melnik et al., 2005). In silicic volcanoes, explosive hazards is

reduced when magmatic volatiles outgas through a permeable network of fractures (e.g. Gonnermann and

Manga, 2003; Castro et al., 2012). However, more explosive eruptions occur when the gas phase cannot


65

separate from the rapidly ascending magma (e.g. Melnik et al., 2005; Jaupart and Allègre, 1991). In addition,

when outgassing is inhibited, the volatile phase may accumulate in the magma chamber leading to a decrease

in the bulk density (e.g. Blake, 1984). The increased magma buoyancy may thus generate an overpressure

higher than the strength of the country rocks, i.e. overpressure higher than 10-40 MPa (Jellinek and DePaolo,

2003), leading to highly explosive eruptions (Malfait et al., 2014; Bachman and Bergantz, 2008; Caricchi et al.,

2014). The efficiency of outgassing is thus an important parameter in determining the eruption style.

Various studies focused on mechanisms favoring or impeding outgassing in volcanoes. Bubbles may rise

buoyantly into the magma chamber or the volcanic conduit or volcanic gas can escape through interconnected

bubbles (e.g. Gonnermann and Manga, 2007). Eichelberger et al. (1986) observed that vesicular obsidian

becomes permeable at porosity higher than 60 % whereas Klug and Cashman (1996) measured permeability

between 10-14 and 10-12 m-2 at porosity as low as 30 %. In addition, when vesicular magmas are subject to

deformation, the bubbles are elongated (e.g. Rust et al., 2003) and their connectivity is promoted (e.g. Saar and

Manga, 1999). Gas can thus escape in magmas with porosity lower than 30 % depending on bubble shape. The

crystalline phase contributes as well to the extent of outgassing. Indeed, bubbles are restricted to the melt

phase and a large amount of crystals would thus contribute to an increase of the connectivity in the residual

melt although the porosity remains low (Sparks, 2003). On the other hand, the crystalline phase, acting as

barriers, may reduce the extent of outgassing by inhibiting the ascent of bubbles (Belien et al., 2010).

The exsolution of volatiles from magmas at depth is achieved through two processes. The “first boiling” occurs

when hydrous melts are ascending towards the surface. Due to the decompression, the solubility of water

decreases and bubbles exsolve (e.g. Cashman and Blundy, 2000). The second process that causes the volatile

exsolution from the silicate melt is due to crystallization at constant pressure. Known as “second boiling”, this

process is activated by a cooling magma chamber which leads to crystallization. As a consequence, the melt

becomes oversaturated in water and bubbles exsolve. In both cases, the produced gas phase could escape from

the magma chamber along fracture networks developed in the magma and in the conduit walls (Jaupart, 1998;

Rust et al., 2004).

The “first boiling” has been studied experimentally (e.g. Mangan and Sisson, 2000; Mourtada-Bonnefoi and

Laporte, 2004) and numerically (e.g. Lensky et al., 2004; Proussevitch and Sahagian, 1998). Recently, some

studies investigated the influence of decompression on the permeability of magma (Okomura et al., 2012,

Namiki and Manga, 2008). However, until now, no studies investigated the outgassing potential from “second

boiling”. Indeed, technical challenges related to pore fluid confinement impeded reproducing the pressure and

temperature conditions typical of volcanoes. We surpassed this limitation thanks to the technical

improvements of the Paterson apparatus at the Rock deformation laboratory of ETHZ, equipped with a

purpose-built pore pressure system (Violay et al., 2015). This allowed us to explore the effect of crystallization

on the extent of outgassing of a synthetic haplotonalite magma at high pressure and high temperature by

measuring in situ the volume of outgassed volatile.


66

5.3 METHODS

5.3.1 SAMPLE SYNTHESIS

In order to study the effect of crystallization on the extent of outgassing of magmas, we synthetized a

chemically simplified tonalite melt (Table 5.1), which is prone to crystallize plagioclase (Picard et al., 2011).

First, oxide and hydroxide powders were mixed to obtain the desired compositions (Table 5.1). The mixtures

have been cold pressed into stainless steel canisters with a uniaxial pressure of 200 MPa. Molybdenum foils

lining the inside of the canister avoid contamination of the melt by reaction with the wall. Subsequently, the

mixtures have been thermally equilibrated in a Hot Isostatic Press (HIP), installed in the Rock Deformation

Laboratory of ETHZ, at 1200 °C and 200 MPa for 24 hours. The vessel was then rapidly cooled at a rate of 60

°C/min to 550 °C in order to quench the samples. Subsequently, a cooling rate of 0.6°C/min was applied to

allow for thermal relaxation of the glass. The resulting hydrated glasses are chemically homogeneous and their

compositions correspond to the nominal values within 1% (Table 5.1). CO2-rich bubbles (4.2 vol%) have a

number density of 167 [1/mm2] and their sizes exhibit a narrow distribution situated around 6 µm (Figure 5.1).

The largest bubble measured is 643 µm. The glass contains less than 1 vol% of spherulitic plagioclase, with a

mean size of 150 µm. This bubble-bearing glass has been drilled into two cores of 10 mm length and 15 mm

diameter to perform measurements.

Figure 5.1: SEM image (a) of the bubble-bearing glass synthetized in the HIP and its bubble-size distribution (b).

The extent of outgassing during plagioclase crystallization was determined using a Paterson-type internally-

heated gas pressure apparatus (Paterson and Olgaard, 2000) implemented with a volumometer and upstream

and downstream pore-fluid connections. The volumometer piston has a diameter of 7 mm and a length of 50

mm, which permits to achieve an accuracy of the pore pressure (argon gas) of 0.1 MPa. Pressure sensors are

placed in the upstream and downstream pore-fluid connections. A Schaevitz LVDT placed on the axis of the

actuator measures the displacement of the volumometer piston with a resolution of 0.01 mm. The sample

assembly is composed of zirconia and alumina rods with a 2 mm hole drilled in the center for the insertion of

the pore-fluid and the thermocouple (Figure 5.2). The sample is isolated from the pore fluid pressure at the

bottom by an alumina disc. Bubbles can thus escape from the sample only through the porous top mullite disc.

This upper disc is made of Mullite C530 and has a connected porosity of 27 % and a young modulus of 60 GPa.


67

Figure 5.2: Schematic drawing of the assembly used in the outgassing experiments in the Paterson apparatus implemented with a pore-fluid system.

5.3.2 OUTGASSING EXPERIMENTS

We performed two different experiments. In both cases, samples were initially maintained during 30 minutes

at a constant temperature of 850 °C. Subsequently, the first sample was cooled down to 700 °C at a rate of 0.5

°C/min and the second sample down to 740 °C at a rate of 0.1 °C/min. The confining pressure was kept

constant at 250 MPa. As the precision of the volumometer is better at higher pressure, the pore-fluid pressure

Pf was initially set to 5 MPa. A gradient of 5 MPa was therefore present within the sample; The alumina discs

placed at the bottom of the sample was at a pressure equal to the confining pressure (Pc) and the porous

mullite disc placed at the top of the sample was subjected to a pressure that is equal to Pc – Pf, i.e. the top part

of the sample was at 245 MPa.

During the experiments, the position of the volumometer piston, i.e. the volume V, was kept constant. The

number of mole degassed from the sample was calculated from the variation of pore pressure assuming ideal

gas behavior:

𝑃𝑓 ∗ 𝑉 = 𝑛 ∗ 𝑅 ∗ 𝑇 (1)

where Pf is the variation of pressure measured in the volumometer in Pa, V is the volume of the pore fluid

system (assembly, pipes and volumometer) in m3, n is the number of moles degassed from the sample in mol, R

is the gas constant (8.3144621 J/(mol*K)) and T is the temperature in the volumometer in K. Although the

sample is outgassing a mixture of H2O and CO2, we used the ideal gas law as more than 90 % of the gas in the

system at the end of the experiments is argon.


68

As the temperature was decreased during the experiments, the pore-fluid pressure was additionally corrected

for the variation of temperature:

𝑃𝑓 = 𝑃𝑚𝑒𝑎𝑠 −𝑑𝑃𝑓

𝑑𝑇∗ 𝑇 (2)

where Pmeas is the pore-fluid pressure measured during the experiments in MPa, T is the temperature of the

sample in °C and dPf/dT is the calibrated variation of pressure as function of temperature changes. The

calibration has been done prior to the experiments using an alumina rod instead of the sample in the assembly

and resulted in a value of dPf/dT= 3.6119*104 [MPa/°C].

5.3.3 EVALUATION OF THE MICROSTRUCTURAL VARIATIONS

In order to determine the evolution of the microstructure during the experiments, the P-T conditions applied in

the Paterson apparatus have been reproduced in a rapid-quench molybdenum-hafnium-carbide (MHC) cold-

sealed pressure vessel. Placed on a rotary system, this externally heated pressure vessel permits dropping the

sample into the cold steel extremity linked to the MHC part by a water-cooled nut. This setup results in a rapid

quench of the sample at a rate exceeding 100°C/s, which allows preservation of the microstructure formed at

high temperature. The temperature gradient in the hot MHC extremity never exceeded 5 °C over the length of

the sample. Cores of 4 mm in length and in diameter, previously drilled from the starting glass and placed into

Au capsules that were welded shut, have been quenched under pressure at various time steps.


and spherulite diameter) have been determined by evaluation of SEM images of the starting material

(synthetized in the HIP), the final samples (crystallized in the Paterson apparatus) and the quenched samples

(crystallized in the MHC cold-sealed vessel). Images were taken at a magnification of 200x over the entire

length of the final samples and over the entire capsules (16 mm2) for the quenched samples. The phase

fractions have been determined by grayscale dissociation using ImageJ. Bubbles smaller than 3 pixel units, i.e.

with a diameter smaller than 1.5 m, have been excluded from the bubble characterization. Interstitial melt

compositions have been measured with a JEOL JXA-8200 electron microprobe employing a 20 µm beam

diameter, 10 kV acceleration voltage and 20 nA beam current.

5.4 EXPERIMENTAL AND ANALYTICAL RESULTS

The evolution of the microstructure determined from the quenched samples are cooling rate dependent and

are documented in chapter 3. The magmatic processes identified through these microstructures are

summarized for both cooling rates. Additionally, we report here measurements of major elements composition

performed across large melt pockets (more than 1 mm) and on small interstitial melts (size smaller than 30

µm). Microstructures of the recovered samples from the Paterson apparatus are then characterized from the

bottom to the top of the samples. Finally, the extent and the rate of outgassing, which is as well cooling-rate

dependent, is documented as a function of time.


69

Figure 5.3: Volume of gas lost over time from the sample cooled at 0.5 °C/min (in green) and from the sample cooled at 0.1°C/min (in red). Figures A and B display the data corrected for the decrease in temperature (see text). The steps in the recorded data are a consequence of the resolution of the sensor. Figure C and D displays the average of each steps as well as the intervals determined from the evolution of the microstructure. Each interval correspond to specific magmatic processes.

5.4.1 INVOLVED MAGMATIC PROCESSES

The evolution of the microstructure of the sample cooled at 0.5 °C/min (CR05) can be divided into three

intervals. The first interval (interval CR05a in Figure 5.3C) lasts 120 minutes and is dominated by the

crystallization of ~40 vol% of spherulitic plagioclase which induced bubble nucleation. The second interval,

between 120 and 210 minutes (interval CR05b in Figure 5.3C), is characterized by bubble coalescence. No

major crystallization process is observed during the third interval, i.e. interval CR05c in Figure 5.3C.

Upon cooling of the bubble-bearing tonalitic melt at a rate of 0.1 °C/min (CR01), the evolution of the observed

microstructures significantly changes. We divided the trend into four intervals. During the first 570 minutes

(interval CR01a in Figure 5.3D), no crystallization occurs. The second interval (from t=570 to t=750 minutes) is

characterized by the crystallization of ~60 vol% of spherulitic plagioclase and by bubble nucleation (interval

CR01b in Figure 5.3D). Coalescence of these newly formed bubbles is observed during the third interval (from

t=750 to t=930 minutes; interval CR01c in Figure 5.3D). The last interval, i.e. interval CR01d in Figure 5.3D, is

characterized by a textural maturation of the plagioclase spherulites, which tend to decrease their sizes.


70

Figure 5.4: (A) SEM image of the plagioclase- and bubble-bearing glass crystallized in the Paterson apparatus (CR01). (B) Evolution of the composition of the interstitial melts of CR01 (red circles) and CR05 (green circles).

5.4.2 COMPOSITION OF THE MELT POCKETS

All recovered samples from the quenched experiments present residual melts between or within the

spherulites (Figure 5.4A) which are smaller than 30 µm. As plagioclase crystallizes, the Na, Ca and Al contents of

these melts decrease while the Si content increases (Figure 5.4B). The observed trend is linked to the

crystallization of plagioclase in a closed system, i.e. the crystals are not physically separated from the melt.

Samples cooled at 0.5 °C/min present additionally larger melt pockets, up to mm-size (Figure 5.5A). In this

section, we present the compositional data on two melt pockets observed in the sample quenched at t=75

minutes. The composition in major elements of the smaller melt pocket, i.e. 1.3 mm-thickness, is constant

through the melt pockets and corresponds within analytical error to the analyses performed on the starting

material (Figure 5.5B-D and Table 5.1)). In the larger melt pockets (~1.8 mm-thickness), the content of Al, Na

and Ca is constant through the melt pockets whereas the content of Si is varying in the 400 µm next to the

spherulite (Figure 5.5B). Indeed, Si content increases from ~75.5 mol% in the center to ~76.5 mol% close to the

crystal-melt contact. In addition, the total of measured oxides in wt% (Na2O + CaO + Al2O3 + SiO2) are

significantly decreasing from the center of the pockets, i.e total of ~97 %, to the border of the spherulites, i.e.

total of ~93 % (Figure 5.5D). This decrease of the total measured oxides is attributed to increased dissolved

water content (not measurable with the electron microprobe). The shape of the bubbles are as well different

throughout the melt pockets (Figure 5.5A). In the center, they are spherical and become more elliptic close to

the spherulite, reaching an aspect ratio of 3. In addition, these bubbles are often elongated parallel to the

crystallization front.


71

Figure 5.5: (A) SEM picture of large melt pockets observed in the sample cooled at 0.5 °C/min. (B) Variation of Al (red squares), Na (green circles) and Ca (blue triangles) contents measured across two melt pockets and in interstitial melt in between the spherulites (black colors). The darker colors represent the composition across a small melt pocket (from on extremity to the other) and the light colors represent the composition across a larger melt pockets (from one extremity to the center of the pocket). (C) Variation of Si concentration across the melt pockets (purple diamonds) and in interstitial melt (black diamonds). (D) Variation of the total sum of oxides, i.e. SiO2 + Na2O + Al2O3 + CaO, measured across the melt pockets (brown stars) and in interstitial melt (black stars).

5.4.3 MICROSTRUCTURES OF THE SAMPLES RECOVERED FROM THE OUTGASSING EXPERIMENTS

The final samples are divided into three parts for the description of their microstructures: the bottom part,

which is next to the alumina disc (closed from the pore pressure inlet), the central part and the top part, which

is next to the porous mullite disc (connected to the pore pressure inlet).

The sample cooled at 0.5 °C/min has a crystal fraction decreasing from 57 vol% at the bottom to 52 vol% at the

top part (Table 5.2). The melt fraction remains constant with a value of 34 vol% at the bottom and at the center

and 33 vol% at the top. Higher variation are observed for the bubble fraction. Indeed, although the bottom and

the center parts have a bubble fraction close to 10 vol%, the top part is as high as 14 vol%. The number

densities of spherulites and bubbles are constant along the samples with values of 1.8 (±0.3) mm-2 and 1290

(±80) mm-2, respectively. However, it should be noticed that the lowest value of number densities is always


72

situated at the top of the sample. The bubble size distribution is as well constant along the samples, with a

unique peak situated at 2-3 µm. The largest bubble diameter measured is 244 µm at the bottom, 274 µm in the

center and 527 µm in the top part.

The crystal fraction is slightly varying along the sample cooled at 0.1 °C/min (Table 5.2). At the bottom, it

reaches the highest value of 61 vol% whereas in the center and at the top, it amounts to 58 vol%. Although the

melt fraction is slightly lower at the bottom (31 vol%), we consider the melt fraction as constant along the

sample, with a value of 32 (±1) vol%. The bubble fraction is increasing from 7 vol% at the bottom to 10 vol% at

the top. Concerning the bubble number density, the bottom and the top parts have values in a narrow range,

i.e. 987 and 977 mm-2 respectively, whereas the center part has a value of 852 mm-2. The spherulite number

density at the bottom and in the center parts have similar values of 1.8 and 1.7 mm-2 respectively. However,

the top part has a higher value of 3.0 mm-2. A unique peak at 2-3 µm characterizes the bubble size distributions

measured in all three parts of the sample. The largest bubble diameter measured is 241 µm in the bottom, 329

µm in the center and 671 µm in the top part.

5.4.4 OUTGASSING MEASUREMENTS

The recorded variation of pore pressure as a function of time is characterized by a discontinuous trend, i.e. step

function (Figure 5.3A-B). The accuracy of the pore pressure sensor of 0.1 MPa leads to an accuracy of ~0.4 vol%

of gas lost by the samples. The data presented here are the average of the volume percent and the time for

each recorded “step” or “plateau” (Figure 5.3A-B).

The extent of outgassing is dependent on the cooling rate applied to the samples (Figure 5.6). The total volume

of gas lost by the sample cooled at 0.5 °C/min (CR05) is 4.6 vol% whereas it reaches 6.6 vol% for the sample

cooled at 0.1 °C/min (CR01). In addition, the rate of outgassing varies as a function of time. Sample CR05

outgassed at a rate of 1.51*10-2 vol%/min during the first 180 minutes and then the value decreased to

9.27*10-3 vol%/min. This decrease in outgassing rate occurred close to the end of interval CR05b (Figure 5.3C),

i.e. the sample already crystallized ~50 vol% of plagioclase and bubbles were coalescing.

The outgassing trend of sample CR01 follows a parabolic shape characterized by an outgassing rate of 1.10*10-2

vol%/min for the first 230 min (Figure 5.6). It then decreases down to 5.76*10-3 vol%/min during the next 360

min, until reaching a rate of 4.46*10-3 vol%/min for the last 450 min of the experiment. These shifts in

outgassing rate can generally not be attributed to any crystallization processes recognized in the evolution of

the microstructures. However, the crystallization interval CR01b coincides with the last shift in outgassing rate.


73

Figure 5.6: Volume of gas lost by the samples measured in experiments with a cooling rate of 0.5 °C/min (green) and 0.1 °C/min (red). Numbers indicate the outgassing rates of selected intervals along the curves.

5.5 DISCUSSION

Although the shifts in outgassing rate are not always related to crystallization processes, the rate and extent of

outgassing should be related to the evolution of the microstructure, as they are both cooling rate dependent.

Indeed, the total difference of gas lost between CR01 and CR05 (ΔVOutgassing=2.0 vol%) and the difference

between the bubble fraction averaged over both samples (ΔΦBB=2.9 vol%) are in good agreement (Table 5.2).

The increase in bubble content and in the diameter of the largest bubble of both samples supports as well a

link between outgassing and microstructure.

At a time of 390 minutes, CR01 lost 3.2 vol % of gas whereas CR05 lost 4.6 vol% (Figure 5.6). This discrepancy

could be linked to the crystallization processes as CR01 did not contain any plagioclase yet (interval CR01a in

Figure 5.3D). Along the crystallization front, the observed elongated bubbles evidence a stress field most likely

generated by the growing spherulites. This forced migration of bubbles into the residual melt favored their

connectivity and the coalescence into larger bubbles was thus enhanced. Although not observed, small

channels may have formed and would provide an efficient mechanism for gas migration.

However, no abrupt change in the outgassing rate is observed after 570 minutes, i.e. when plagioclase starts to

crystallize in CR01. The absence of an increase in the outgassing rate could be linked to an evolution of the

bubble size distribution at the onset of crystallization. Indeed, during these 390 minutes, the largest bubbles

could have had time to rise through the sample. This hypothesis is tested by estimating the ascent velocity

uascent of the largest bubbles from Stoke’s law as follow:

𝑢𝑎𝑠𝑐𝑒𝑛𝑡 = −2∗(𝜌𝐵𝐵−𝜌𝑚)∗𝑔∗𝑟2

9∗𝜂 (3)

where ρBB and ρm are the densities, in g/m3, of the bubble and the melt respectively, g is the gravitational

acceleration in m/s2, r is the bubble radius in m and η is the viscosity of the melt in Pas. Although the bubbles


74

contain a mixture of CO2 and H2O, we calculated the bubble density assuming that only water is present and

using equation 1. In order to assess the melt density, the volume of silicate melt is first calculated as a function

of composition, pressure and temperature (Carroll and Holloway, 1994) using an equation in the form of:

𝑉𝑚 = ∑ 𝑋𝑖 [�̅�𝑖,𝑇𝑟𝑒𝑓,𝑃𝑟𝑒𝑓+

𝑑𝑉𝑖

𝑑𝑇∗ (𝑇 − 𝑇𝑟𝑒𝑓) +

𝑑𝑉𝑖

𝑑𝑃∗ (𝑃 − 𝑃𝑟𝑒𝑓)]

(4)

where Xi is the mole fraction of the ith oxide component, T is the temperature, P is the pressure, V̅i is the

partial molar volume of the ith oxide component, dV̅i/dT is the temperature derivative of V̅i and dV̅i/dP is the

pressure derivative of V̅i (parameters are given in Table 5.3). Density of silicate melt ρm is calculated using the

following relationship:

𝜌𝑚 =∑ 𝑋𝑖∗(𝑀.𝑊.)𝑖

𝑉𝑚 (5)

where (M.W.)i is the molecular weight of the ith oxide component. Finally, the viscosity η is calculated using a

Vogel-Fulcher-Tammann equation:

log 𝜂 = 𝐴𝑉𝐹𝑇 +𝐵𝑉𝐹𝑇

𝑇−𝐶𝑉𝐹𝑇 (6)

where T is the temperature in K and AVFT, BVFT and CVFT are the pre-exponential factor, the pseudo-activation

energy and the VFT temperature respectively. BVFT and CVFT are calculated using the model of Giordano et al.

(2008). As Pistone et al. (2012) observed a difference of 2 log units between viscosities measured in the

laboratory and calculated using this model, they modified the pre-exponential factor to -6.55. Indeed, the

model of Giordano et al. (2008) does not take into account the viscosity of chemically simplified non-natural

synthetic melts. In addition, the viscosity and the density of silicate melt are strongly dependent on the water

content (e.g. Dingwell et al., 1996; Ochs and Lange, 1999) which is known only for the starting material, i.e.

2.72 wt%. We thus estimated the variation of water content in residual melt as a function of crystal content by

mass balance calculation (Table 5.4). As the water content is limited by its solubility, we calculated the highest

amount of dissolved water by using the model of Papale et al. (2006). The solubility limit of water in our melt

composition is 5.9 wt%.

By simplifying the problem to non-interacting rising bubbles in a homogeneous media (diluted approximation),

we calculated the amount of outgassing in function of time using a numerical model written in Matlab. The

bubbles were placed randomly into the sample with a size distribution based on our measurements. This

bubble size distribution measured in 2D on the starting material was fitted into a Weibull distribution. We used

Monte Carlo simulations to test the influence of bubbles initial positions and small fluctuations in their bubble

size distribution with a control function to keep their fraction between 3 and 5 vol%.


75

Figure 5.7: Dependence of the calculated viscosity η in Pas (A) and density ρ in kg/m3 (B) of the melt as a function of temperature and water content. The red circles represent the variation of η and ρ of the melt cooled at a rate of 0.1 °C/min and the green circles represent the variation of the melt cooled at 0.5 °C/min.

5.5.1 COOLING RATE OF 0.1°C/MIN

Following this approach, we observe that the calculated viscosity and density of the melt vary non-linearly

along the experiments cooled at 0.1 °C/min (Figure 5.7). Before the onset of crystallization, the logarithm of the

melt viscosity of CR01 increased from 3.03 at t=75 minutes to 3.56 Pas at t=525 minutes and the melt density

had a near constant value of ~2310 kg/m3. This increase in viscosity due to the cooling of the sample strongly

affects and continuously decrease the rising velocity of bubble (Figure 5.8A). The calculation of the distance

covered by bubble during this time reveals that, at t=570 min, two third of the sample volume will be depleted

in bubble larger than 600 µm and that one third is depleted in bubble larger than 400 µm. Indeed, during the

first 200 minutes, the calculated rate of outgassing using the Monte Carlo simulations is similar to our

measurements (Figure 5.9A and B). The rate of outgassing at the beginning of the experiment is thus fully

explained by the rise of large bubbles. At t>200 minutes, the calculated and the measured rates are diverging.

During their ascent to the top of the sample, bubbles may have interacted and coalesced into larger bubbles.

Such interaction is not considered in our calculations (Figure 5.9A and B). In the measurements, the larger rate

of outgassing between 200 and 600 minutes might thus be linked to bubble coalescence. Indeed, larger

bubbles, having a higher buoyancy, rise faster and are thus contributing to a larger increase in the volume of

outgassing.

At the onset of crystallization, the rate of outgassing increased due to a lower melt viscosity. An increase of 0.5

to 1 vol% of gas lost is observed in the simulations between 570 and 800 minutes (Figure 5.9A and B). In our

measurements, a larger increase between discrete data at 600 and 650 minutes is found (arrow in Figure 5.3B).

Although the difference of 0.5 vol% is close to the resolution of the method, i.e. 0.4 vol%, the similarity in time

and amount of gas lost is noteworthy. After this increase, the rate of measured outgassing was constant and

higher than the calculated rate of outgassing. This difference may be linked to bubble exsolution and

coalescence driven by crystallization.


76

Figure 5.8: Travel distance of bubbles during the experiment cooled at 0.1 °C/min (A) and 0.5 °C/min (B) calculated using

equation 3. Numbers indicate the different bubble radius (in µm) used in the calculations. The sample length (10 mm) is

as well displayed.

The rate of outgassing is thus mainly dependent on the viscosity and on the evolution of bubble size

distribution along the experiment cooled at 0.1 °C/min. If the bubble size distribution slightly varies in the

Monte Carlo simulation, the trends of outgassing are similar but the total amount of outgassing may vary

between 2.8 and 4.6 vol% (Figure 5.9A). On the other hand, the position of bubbles in the sample does not

affect the rate of outgassing (Figure 5.9B). This behavior is as well observable when the sample is cooled at 0.5

°C/min (Figure 5.9C and D).


77

Figure 5.9: Evolution of the volume of gas lost calculated using a Monte Carlo simulation (light blue to dark areas) and measured with the Paterson apparatus (points). (A) and (B) are the results for a cooling rate of 0.1 °C/min and (C) and (D) are results for a cooling rate of 0.5 °C/min. The plots on the left hand side (A and C) displays simulations considering various bubble size distributions. The simulations displayed on the right hand side (B and D) considered various bubbles positions within the sample.

5.5.2 COOLING RATE OF 0.5°C/MIN

The logarithm of the melt viscosity of CR05 decreased from 2.73 Pas to a minimum of 2.08 Pas at t=165

minutes due to the increase in water content and then increased to 2.87 Pas due to the cooling of the sample

(Figure 5.7). The variation in melt density follows a similar trend by decreasing first from 2290 to 2220 kg/m3 at

t=210 and then increasing up to 2230 kg/m3. Including the evolution of viscosity and density in equation 3, we

observe that the ascent velocity of CR05 bubbles is higher than velocity of CR01 bubbles (Figure 5.8B). Indeed,

the sample is completely depleted in bubbles larger than 600 µm after 100 minutes and, after 200 minutes, in


78

bubbles larger than 400 µm. This loss in large bubbles is observable in the numerical simulation (Figure 5.9C

and D). During the first 100 minutes, the calculated outgassing reaches 2 to 3.5 vol%. However, the measured

volume of outgassed bubbles was 1.8 vol% at 110 minutes. The presence of crystals is thus lowering the ascent

velocity of large bubbles. Indeed, the distance that bubbles have to travel is larger in a crystal-bearing melt as

they have to move around the crystals. The larger bubbles may have been deformed to bypass these obstacles

but the smaller bubbles were probably trapped by the crystals as already observed by Belien et al. (2010).

After 200 minutes, the increase in viscosity induces a decrease in the ascent velocity of bubbles (Figure 5.8B).

Interestingly, the shift in the measured outgassing rate occurred at a similar time, i.e. 180 minutes (Figure 5.6).

However, the measured outgassing rate is larger than in the Monte Carlo simulation (Figure 5.9C and D). This

difference may be explained by the continuous presence of large bubbles. Indeed, in the numerical model, the

sample is depleted in larger bubbles whereas crystallization sustained bubble coalescence in the experiments.

By comparing both cooling rates, the crystallization of CR05 resulted in a higher rate of outgassing by

decreasing the melt viscosity. However, considering the same viscosity, the presence of crystals lowers the

outgassing rate.

5.6 CONCLUSION

The rate and extent of outgassing varies between crystallizing samples cooled at a rate of 0.1 and 0.5 °C/min.

These variations are related to timing and extent of crystallization and thus to the evolution of the

microstructures. At the beginning of the experiment cooled at a rate of 0.1°C/min, the measured outgassing

rate is fully explained by the ascent of bubbles following Stoke’s law. The subsequent deviation from the

calculation is most likely linked to bubble coalescence. The bubble size distribution is thus a fundamental

parameter controlling the rate of outgassing.

The presence of crystals may favor or inhibit the outgassing. On one hand, the crystallization of anhydrous

minerals increases the water content dissolved in the melt. The induced decrease in viscosity leads to a higher

ascent velocity of bubbles, hence more extensive outgassing. In addition, a forced migration of bubbles due to

the growing plagioclase contributes to sustain the presence of large bubbles by coalescence and additionally

increases the outgassing rate. However, considering the same melt viscosity, the presence of crystals lowers

the outgassing rate by adding obstacles to the ascent of bubbles. Crystallization of hydrous magma is thus

regulating the outgassing rate by (1) increasing the fraction and size of bubbles by exsolution and decreasing

the melt viscosity and (2) lowering their ascent velocity by increasing pathways length.






79


of fractures in the surrounding volcanic edifice (Jaupart, 1998; Rust et al., 2004) or accumulate at the top of the

magmatic reservoir and produce explosive eruptions (Malfait et al., 2014; Bachman and Bergantz, 2008).

5.7 TABLES

Table 5.1: Compositions of the starting material determined by electron microprobe. The nominal composition corresponds to the composition of the powder before the HIP. Water and CO2 contents have been measured by Karl Fisher and by coulometric titrations respectively.

Sample SiO2 Al2O3 CaO Na2O H2O CO2 Total

HIP: Nominal Composition 65.69 18.56 3.33 7.61 2.80 2.00 100

HIP: Measured Composition 65.26 18.81 3.49 7.51 2.75* 0.03 97.82

Table 5.2: Summary of the microstructures measured in the samples recovered after the outgassing measurements. CR01 = Cooling Rate 0.1 °C/min. CR05 = Cooling Rate of 0.5 °C/min.

CR01 CR05

Bottom Center Top Average Bottom Center Top Average

Crystal fraction [vol%] 61.0 58.2 57.6 58.9 56.8 54.5 52.1 54.5

Melt fraction [vol%] 30.9 31.5 32.0 31.5 33.5 34.2 33.1 33.6

Bubble fraction [vol%] 6.5 8.4 10.3 8.4 9.6 10.3 14.1 11.3

Spherulite number density

[1/mm2]

1.85 1.66 3.01 2.17 1.98 2.06 1.59 1.88

Bubble number density

[1/mm2]

987.27 851.98 976.72 938.66 1313.73 1370.94 1211.78 1298.82

Largest bubble diameter

[µm]

244 274 527 241 329 671


80

Table 5.3: Partial molar volumes and their pressure and temperature derivatives used for the calculation of melt density at experimental conditions (equation 4). References are given in parenthesis: (a) Lange, 1997; (b) Kress and Carmichael, 1991; (c) Ochs and Lange, 1999.

V(i,1673K,1bar) [10-5 m3/mol] dV/dT [10-9 m3/mol*K] dV/dP [10-6 m3/mol*Gpa]

Si02 2.69 (a) 0.00 (a) -1.89 (b)

Al2O3 3.74 (a) 0.00 (a) -2.26 (b)

CaO 1.65 (a) 3.74 (a) 0.34 (b)

Na2O 2.89 (a) 7.68 (a) -2.4 (b)

H2O 2.67 (c) 9.55 (c) -3.2 (c)

Table 5.4: Summary of the parameters used for the calculation of the ascent velocity of bubbles.

Temperature

[°C]

Time

[s]

Crystal

fraction [vol%]

H2O

[wt%]

log η

[Pas]

ρ melt

[kg/m3]

Δρ

[kg/m3]

CR05 850 30 13.2 3.14 2.73 2294 1808

830 75 40.0 4.54 2.21 2248 1752

810 120 42.4 4.73 2.30 2245 1740

790 165 52.2 5.70 2.08 2218 1702

770 210 53.9 5.91 2.18 2216 1690

700 390 54.5 5.90 2.88 2230 1667

CR01 845 75 0.0 2.72 3.03 2310 1823

815 345 0.0 2.72 3.34 2314 1814

805 405 0.0 2.72 3.45 2315 1810

795 525 0.0 2.72 3.56 2317 1807

790 570 12.4 3.52 3.21 2289 1778

785 615 24.8 4.31 2.85 2264 1749

780 660 37.2 5.11 2.49 2239 1720

775 705 49.6 5.90 2.14 2215 1691

770 750 57.6 5.90 2.18 2216 1690

760 840 57.3 5.90 2.28 2218 1687

750 930 59.2 5.90 2.37 2220 1684

740 1020 59.2 5.90 2.59 2222 1688


81

5.8 REFERENCES

Bachmann, O., & Bergantz, G. (2008). The magma reservoirs that feed supereruptions. Elements, 4(1), 17-21. Belien, I. B., Cashman, K. V., & Rempel, A. W. (2010). Gas accumulation in particle-rich suspensions and

implications for bubble populations in crystal-rich magma. Earth and Planetary Science Letters, 297(1), 133-140.

Blake, S. (1984). Volatile oversaturation during the evolution of silicic magma chambers as an eruption trigger. Journal of Geophysical Research: Solid Earth (1978–2012), 89(B10), 8237-8244.

Caricchi, L., Annen, C., Blundy, J., Simpson, G., & Pinel, V. (2014). Frequency and magnitude of volcanic eruptions controlled by magma injection and buoyancy. Nature Geoscience, 7(2), 126-130.

Carroll, M. R., & Holloway, J. R. (1994). Volatiles in magmas (Vol. 30): Mineralogical Society of America. Cashman, K., & Blundy, J. (2000). Degassing and crystallization of ascending andesite and dacite. Philosophical

Transactions of the Royal Society of London A: Mathematical, Physical and Engineering Sciences, 358(1770), 1487-1513.

Castro, J. M., Cordonnier, B., Tuffen, H., Tobin, M. J., Puskar, L., Martin, M. C., & Bechtel, H. A. (2012). The role of melt-fracture degassing in defusing explosive rhyolite eruptions at volcán Chaitén. Earth and Planetary Science Letters, 333, 63-69.

Dingwell, D., Romano, C., & Hess, K.-U. (1996). The effect of water on the viscosity of a haplogranitic melt under PTX conditions relevant to silicic volcanism. Contributions to Mineralogy and Petrology, 124(1), 19-28.

Eichelberger, J., Carrigan, C., Westrich, H., & Price, R. (1986). Non-explosive silicic volcanism. Nature, 323(6089), 598-602.


Gonnermann, H. M., & Manga, M. (2003). Explosive volcanism may not be an inevitable consequence of magma fragmentation. Nature, 426(6965), 432-435.

Gonnermann, H. M., & Manga, M. (2007). The fluid mechanics inside a volcano. Annu. Rev. Fluid Mech., 39, 321-356.

Jaupart, C. (1998). Gas loss from magmas through conduit walls during eruption. Geological Society, London, Special Publications, 145(1), 73-90.

Jaupart, C., & Allègre, C. J. (1991). Gas content, eruption rate and instabilities of eruption regime in silicic volcanoes. Earth and Planetary Science Letters, 102(3), 413-429.

Jellinek, A. M., & DePaolo, D. J. (2003). A model for the origin of large silicic magma chambers: precursors of caldera-forming eruptions. Bulletin of Volcanology, 65(5), 363-381.

Klug, C., & Cashman, K. V. (1996). Permeability development in vesiculating magmas: implications for fragmentation. Bulletin of Volcanology, 58(2-3), 87-100.

Lensky, N., Navon, O., & Lyakhovsky, V. (2004). Bubble growth during decompression of magma: experimental and theoretical investigation. Journal of Volcanology and Geothermal Research, 129(1), 7-22.

Malfait, W. J., Seifert, R., Petitgirard, S., Perrillat, J.-P., Mezouar, M., Ota, T., Sanchez-Valle, C. (2014). Supervolcano eruptions driven by melt buoyancy in large silicic magma chambers. Nature Geoscience, 7(2), 122-125.

Mangan, M., & Sisson, T. (2000). Delayed, disequilibrium degassing in rhyolite magma: decompression experiments and implications for explosive volcanism. Earth and Planetary Science Letters, 183(3), 441-455.

Melnik, O., Barmin, A., & Sparks, R. (2005). Dynamics of magma flow inside volcanic conduits with bubble overpressure buildup and gas loss through permeable magma. Journal of Volcanology and Geothermal Research, 143(1), 53-68.

Mourtada-Bonnefoi, C. C., & Laporte, D. (2004). Kinetics of bubble nucleation in a rhyolitic melt: an experimental study of the effect of ascent rate. Earth and Planetary Science Letters, 218(3), 521-537.

Namiki, A., & Manga, M. (2008). Transition between fragmentation and permeable outgassing of low viscosity magmas. Journal of Volcanology and Geothermal Research, 169(1), 48-60.

Ochs, F. A., & Lange, R. A. (1999). The density of hydrous magmatic liquids. Science, 283(5406), 1314-1317. Okumura, S., Nakamura, M., Nakano, T., Uesugi, K., & Tsuchiyama, A. (2012). Experimental constraints on

permeable gas transport in crystalline silicic magmas. Contributions to Mineralogy and Petrology, 164(3), 493-504.


82

Papale, P. (1999). Modeling of the solubility of a two-component H2O+ CO2 fluid in silicate liquids. American Mineralogist, 84(4), 477-492.

Paterson, M., & Olgaard, D. (2000). Rock deformation tests to large shear strains in torsion. Journal of Structural Geology, 22(9), 1341-1358.

Picard, D., Arbaret, L., Pichavant, M., Champallier, R., & Launeau, P. (2011). Rheology and microstructure of experimentally deformed plagioclase suspensions. Geology, 39(8), 747-750.

Pistone, M., Caricchi, L., Ulmer, P., Burlini, L., Ardia, P., Reusser, E., Arbaret, L. (2012). Deformation experiments of bubble‐ and crystal‐bearing magmas: Rheological and microstructural analysis. Journal of Geophysical Research: Solid Earth (1978–2012), 117(B5).

Proussevitch, A., & Sahagian, D. (1998). Dynamics and energetics of bubble growth in magmas: analytical formulation and numerical modeling. Journal of Geophysical Research: Solid Earth (1978–2012), 103(B8), 18223-18251.

Rust, A., Cashman, K., & Wallace, P. (2004). Magma degassing buffered by vapor flow through brecciated conduit margins. Geology, 32(4), 349-352.

Rust, A., Manga, M., & Cashman, K. V. (2003). Determining flow type, shear rate and shear stress in magmas from bubble shapes and orientations. Journal of Volcanology and Geothermal Research, 122(1), 111-132.

Saar, M. O., & Manga, M. (1999). Permeability‐porosity relationship in vesicular basalts. Geophysical Research Letters, 26(1), 111-114.

Slezin, Y. B. (2003). The mechanism of volcanic eruptions (a steady state approach). Journal of Volcanology and Geothermal Research, 122(1), 7-50.

Sparks, R. (2003). Dynamics of magma degassing. Geological Society, London, Special Publications, 213(1), 5-22.

Chapter 6 Conclusion

83

6 CONCLUSION

The main goal of this PhD thesis was to include dynamic magmatic processes, such as crystallization and bubble

nucleation, in the characterization of physical properties of magmas. These processes are fundamental in the

evolution of magmatic liquids in various plutonic and volcanic environments, from deep magma chambers to

lava flows at the surface. Their effects on the seismic properties and on the ability of outgassing have been

highlighted along this thesis by measuring their evolution in a chemically simplified tonalite crystallizing

plagioclase. The main results are summarized below.

6.1 SEISMIC PROPERTIES

Magmatic processes occurring in volcanic environments have been recognized and identified through the

measurement of seismic velocities using an internally heated gas pressure Paterson apparatus. During

crystallization processes, compression and shear wave velocities increase non-linearly. Indeed, the formation of

a crystal network at crystal fractions higher than 45 vol% favors the propagation of seismic waves through

magmatic liquids. Crystal content is the principal parameter influencing the seismic velocities. However, bubble

nucleation induced by crystallization produces an increase in magma compressibility thereby reducing the

wave propagation velocities. These two processes occurring simultaneously have thus competing effects on the

seismic properties of magmas. In addition, when the bubble fraction is less than 10 vol%, the decrease in

seismic velocities is more pronounced than for larger bubble fractions. Consequently, the increase in

compressibility at relatively low density contrast leads to large decrease in seismic properties during bubble

nucleation and less or no variation during bubble coalescence.

In conclusion, by continuously monitoring small seismic velocity perturbations in volcanic areas and by

combining these data with laboratory measurements of seismic velocities, evolution of the physical state of

magmatic reservoir could be assessed more precisely. In addition, a more accurate interpretation of available

seismic tomography images is possible and may permit a better assessment of potential volcanic hazards.

In this study, the dissolved water content as well as the major elements composition is continuously changing

in the melt. In order to assess the effect of water content in the elastic properties, velocities have been

measured at high pressure and high temperature conditions in hydrous phonolites from the Teide volcano. At

temperature lower than the glass transition, temperature derivatives of seismic velocities are independent of

the dissolved water content. However, temperature derivatives of both, compression and shear wave

velocities, significantly increase at temperature higher than the glass transition. This increase is accentuated by

the addition of water following a trend previously observed for melt viscosity, i.e. the increase is higher at

water content lower than 1 wt%. Glass transition temperatures estimated through our seismic velocity


84

measurements and calculated relaxation times suggest that measurements in the liquid-like state have

predominantly been performed on relaxed samples.

The seismic velocities measured on hydrous phonolite at temperature higher than the glass transition have

been extrapolated to magmatic temperature and combined to calculated seismic properties of prominent

phenocrysts in the Teide phonolite. The resulting seismic velocities vary between 4.4 and 5.0 km/s for a magma

chamber containing 30 to 40 vol% crystals. Despite these low values, the currently available seismic

tomography images lack evidences of a large magmatic reservoir. Based on these results, four hypotheses

concerning the magmatic plumbing system of Teide are possible: (1) the absence of a large eruptible magmatic

reservoir, (2) a magma chamber smaller than 3 km thickness, (3) a network of sills and dykes producing small

magma pockets, or (4) a cooling magma chamber containing more than 60 vol% crystals.

6.2 OUTGASSING PROPERTIES

During the experiments involving the crystallization of plagioclase in the Paterson apparatus, significant loss of

gas occurred. We thus implemented this apparatus with a pore-fluid system in order to explore the effect of

crystallization on the extent of outgassing of our bubble-bearing haplotonalite melt.

The presence of crystals may favor or inhibit the outgassing. On one hand, the water content dissolved in the

melt increases due to the crystallization of anhydrous minerals. The induced decrease in viscosity leads to a

higher ascent velocity of bubbles promoting a higher outgassing. In addition, a forced migration of bubbles due

to the growing plagioclase is evidenced by bubbles elongated along the crystallization front. This phenomenon

may contribute to sustain the presence of large bubbles by coalescence and additionally increase the

outgassing rate. However, considering the same melt viscosity, crystals act as barrier to the ascent of bubbles

and their presence reduces the outgassing rate. Crystallization of hydrous magma is thus regulating the

outgassing rate by (1) increasing the fraction and size of bubbles by exsolution and decreasing the melt

viscosity and (2) lowering their ascent velocity by increasing pathways length.






of fractures in the surrounding volcanic edifice or accumulate at the top of the magmatic reservoir and produce

explosive eruptions.

6.3 SUGGESTIONS FOR FUTURE RESEARCH

The outgassing occurring during the experiments performed in the Paterson apparatus impeded the presence

of more than 12 vol% of bubbles in the system. However, higher bubble content should be reached in order to


85

evaluate the effect of crystal and bubble content in the seismic properties of magmas and implement them

into semi-empirical equations. Consequently, future research should be realized in an apparatus ensuring gas-

tight enclosure of the sample during the experiment. In addition, bubble size distribution is an important

parameter influencing physical properties and may easily change along an experiment. Characterization of its

evolution through in-situ 3D tomography would permit a better understanding of physical properties linked to

exsolved volatiles in magmas.

The plagioclases crystallized in our experiments are spherulite, which is the expected shape at high

undercooling temperature. Higher experimental temperature required for euhedral plagioclase can be

achieved with the Paterson apparatus. However, the subsequent accumulation of heat at the position where

the piezoelectric transducers are placed impeded us to perform this kind of experiments. It would, thus, be

interesting to evaluate the effect of texture on the seismic properties of magmas. In addition, natural magmas

crystallize several mineral phases having varying liquidus/solidus and elastic properties. The resulting evolution

of seismic velocities during their crystallization should as well be evaluated

Acknowledgements

86

ACKNOWLEDGEMENTS

First of all, I would like to thank Peter Ulmer. In addition to be an excellent supervisor, he’s a great person who

was here when I really needed. I thank him as well to have let my creativity growing as much as I wanted during

this PhD. The second person who was really helpful was Benoit Cordonnier. I loved our (crazy) scientific

discussions and I hope we will have much more occasions to share ideas and work together. I would like to

thank as well Jean-Pierre Burg for nice talks at Friday beer and to have helped me whenever he could. I spent

quite a lot of excellent “afterwork beers” at the Hot Pasta with Erik Reusser but I mainly would like to thank

him for his patience and precious help at the microprobe. Thank you as well to Jamie Connolly, always smiling,

who helped me with some obscure thermodynamics and who always repeated when I was not getting what he

was saying (in case, I refer to his wonderful jokes!!). I would like to thank Max Schmidt as well for his magic

phone call, without which I would have to pass my PhD exam much later. Thank you to Lucie Tajcmanova who

chaired my PhD defense. I hope you will continue to bring the sunshine in Science.

During the last years, I have shared quite a lot of time with people in the Rock Deformation Lab. Marie Violay

arrived in a chaotic place and managed to be a great lab leader. Thank you for having taken care of this lab as

much as you could. Without you and your magic furnaces, it would have been hard to finish this PhD. A big

thank is as well given to Robert Hoffmann, who always did an excellent and fast job. I would like as well to

thank Alba Zappone, the mama of the lab. She was always here to give a hand and to listen. Although he’s not

here anymore, I would like as well to thank the papa of the lab. He was the person who pushed me and helped

me to start the PhD. Grazie Luigi Burlini! And I send some big thanks around the world to all the people I met in

this lab and who made me feel like home: Mattia, Bjarne, Rolf, Liza, Jacques, Sebastien, Michaela, Nicola,

Richard, Claudio, Shankar, Rita, Melchior…

I had the chance to have excellent people in my office with who I laughed a lot: Francesca, Shahrzad, Jakub,

Natalia, Giuliano, Shan, Rohit and Sonja. Maybe I should as well apologize to them for having shouted loudly in

French to my computer… I spent a lot of great time with all the remaining of the group and I thank you all for

that: Mareen, Anna, Jule, Nico, Steffi, Ingrid, Monica, Daniel, Dawid, Max, Lucas, Julia… Sorry if I forget some

people!

There are as well all the people that passed by ERDW and with who I felt like being with my family: Marion L.,

Marion C., Jessica, Pinar, Janne, Ulrik, Mathieu, Teo, Pietro, Mat, Thiebault, Magali, Greg, Luca, Pierre, Paola,

Daniela, Sasha, Masha, Rita and many other people with you I danced the whole evening at Friday beers! I

hope we will have some more occasions to meet all together.

J’aimerai également remercier ma famille et plus particulièrement mes parents. Ils m’ont toujours poussé à

faire de mon mieux et à atteindre mes objectifs. Merci d’avoir toujours cru en moi et de m’avoir aidé à

accomplir cette thèse. Je vous aime fort ! Un grand merci aussi pour mes amis de Baden qui n’ont pas

Acknowledgements

87

forcement eu conscience du bien qu’ils m’ont procuré pendant ces années. Malgré le fait que j’arrivais tard au

Mojo, ils ont toujours réussi à me relaxer de ma journée en me faisant penser à d’autres choses. Merci !!!

Et finalement, mes plus grands remerciements reviennent à l’homme qui partage ma vie et qui m’as donné

tout le soutien dont j’avais besoin pendant cette thèse, et plus encore. Jérôme, merci d’être comme tu es.

Curriculum Vitae

88

CURRICULUM VITAE

PERSONAL INFORMATION Name: Barbara Andrea Tripoli Birth date: 22/01/1983 Nationality: Swiss/Italian Email address: [email protected] [email protected]

RESEARCH INTERESTS Physical processes occurring in volcanoes by investigating morphology, geochemistry and

stratigraphy of volcanic deposits.

Seismic properties of crystalline and partially molten rocks at crustal conditions linked to microstructural anisotropy.

Internal physical processes occurring in volcanoes with focus on rheology of fully or partially molten rocks at high pressure and high temperature.

Crystallization kinetics and bubble nucleation in magmatic liquids.

EDUCATION AND DEGREES April 2011-Sept 2015 ETH Zurich, Doctoral studies in Earth Sciences

PhD Thesis: Physical properties of plagioclase- and bubble-bearing magmas.

Advisors: Prof. Dr. Peter ULMER Prof. Dr. Jean-Pierre BURG Sept. 2006 – Sept. 2008 ETH Zurich, Master in Earth Sciences Major in Geology & Geochemistry

Master’s thesis: Physical Volcanology of the Lake Natron-Engaruka Monogenetic Field, Northern Tanzania.

Advisor: Dr. Hannes MATTSSON Sept. 2003 – Aug. 2006 University of Geneva, Bachelor of Science in Earth Sciences Including Erasmus exchange with the University of Granada (2005-2006) Course grades available on request.

PROFESSIONAL EXPERIENCES Oct. 2008 - March 2011 ETH Zurich, Seismic velocities measurement In-situ measurement of Vp/Vs in crystalline materials at high pressure

and high temperature for the Swiss Atlas of Physical Properties of Rocks (Saphyr). Density measurement. Microstructure analysis. Aug. - Sept. 2005 University of Geneva Mineral separation from basaltic samples (Frantz magnetic separator).

ASSISTANTSHIP Since Feb. 2007 ETH Zurich, Teaching assistant

Demonstrator for optical mineralogy practical classes. Duties also included additional explanation of course material and help with exam preparation.

Curriculum Vitae

89

Assistant on numerous field courses.

Demonstrator for rock physics practical courses (seismic velocities measurements). Duties also included assistantships for external guests.

EXPERIENCES IN EXPERIMENTAL AND ANALYTICAL TECHNIQUES

HP-HT internally heated gas-pressure Paterson rig

HP oil-pressure rig

Hot Isostatic Press

HP-HT externally heated gas-pressure cold-seal apparatus

Gas pycnometer

Electron Microprobe

Scanning Electron Microscope

X-Ray Diffraction

Karl Fisher Titration

WORKSHOPS / SHORT COURSES Aug. 2008 Recent Developments in Explosive Volcanism University of Iceland (IAVCEI short course) June 2009 Melts, Glasses and Magmas Ludwig-Maximilians-Universität München, Germany Feb. 2010 Rheology and Physical Properties of Magmas: Controls on Dynamics of

Magma Transport, Storage and Eruption ETH Zurich, Switzerland Jan. 2014 The Dynamics of Volcanic Explosive Eruptions University of Geneva, Switzerland

LANGUAGES French : Mother tongue English : Good - C1 (european standard CEFR) Italian : Good - C1 (european standard CEFR) Spanish : Good - C1 (european standard CEFR) German : Good - B2 (european standard CEFR)

PUBLICATION Mattsson, H. B. and Tripoli, B.A. (2011). Depositional characteristics and volcanic landforms in the Lake Natron – Engaruka monogenetic field, northern Tanzania. Journal of Volcanology and Geothermal Research,203, 23-34.

Appendix

90

Appendix A LIST OF SYNTHETIZED SAMPLES

HIP session HIP condition Canister name Sample name H2O [wt%]

CO2 [wt%]

Comments

Lausannne T = 1100°C 1A Haplotonalite 2 2 Cores exploded in the oven…

P = 130 MPa 3A Haplotonalite 2 0

ZH H018 T = 1100°C 2.1A Haplotonalite 2 2 Canisters were deformed due to gas escape. Solution: smaller canister and higher pressure.

P = 130 MPa 2.1B Haplotonalite 2 2

2.1C Haplotonalite 2 2

2.2() Haplotonalite 3.4 2

2.2A Haplotonalite 3.4 2


2.5B Haplotonalite 2.8 2

2.6A Haplotonalite 2 4


ZH H019 T = 1200°C 3.1() Haplotonalite 2 2 -Samples placed at the bottom of the alumina container were fully crystallized. Thus the fast cooling was not correctly applied all along the vessel. Solution: Alumina container was replaced by a tube in alumina. -Large and angular pieces of alumina in the glasses. Solution: Use of pulverisette in agate for crushing the initial powder.

P = 200 MPa 3.3(A) Haplotonalite 2 0

3.3(B) Haplotonalite 2 0

3.3(C) Haplotonalite 2 0

3.9(A) Haplotonalite 1.5 0

3.9(B) Haplotonalite 1.5 0

3.10(A) Haplotonalite 1 0




ZH H020 T = 1200°C 4.1(A) Haplotonalite 2 2 Samples with low water content were crystallized. Solution: use another composition for water content effect on seismic velocity.

P = 180 MPa 4.1(B) Haplotonalite 2 2


4.1(D) Haplotonalite 2 2

4.1(E) Haplotonalite 2 2










Appendix

91


List of synthetized samples: Continued

HIP session HIP condition Canister name Sample name H2O [wt%]

CO2 [wt%]

Comments


4.9(C) Haplotonalite 1.5 0

4.9(D) Haplotonalite 1.5 0








4.11(C) Haplotonalite 1.5 2







ZH H021 T = 1000°C P = 200 MPa

LN5 Lavas Negras Mantle furnace not working. LN5 and LN1 canisters were open. Solution: Furnace repaired. LN5 was ok but not LN1 so all the others canisters have been re-hipped.

ZH H022 T = 1200°C PAN1 Pantelleria 1 0

P = 200 MPa PAN2 Pantelleria 2 0

Glass Recrushed Haplotonalite

2 0

LN1 Lavas Negras 0.1 0

LN2 Lavas Negras 0.5 0

LN3 Lavas Negras 1 0

LN4 Lavas Negras 2 0

G01 HPG8 (0.1%) 0.1 2

G03 HPG8 (0.3%) 0.3 2

G05 HPG8 (0.5%) 0.5 2

G1 HPG8 (1%) 1 2

G3 HPG8 (3%) 3 2

Appendix

92

Appendix B LISTS OF EXPERIMENTS

B.1 PATERSON APPARATUS 9

Experiments Sample name Diameter [mm]

Length [mm]

P max [MPa]

T max [°C]

Comments

PP952 Fused Quartz 22 30.06 310 25 Calibration: P derivative

PP954 Fused Quartz 22 30.06 250 600 Calibration: T derivative at 250 MPa

PP955 4.13B 22 30.95 300 650 P-T derivative / T cycle at 250 MPa



PP958 3.4 22 30.27 300 600 P-T derivative / T cycle at 250 MPa



PP961 Sapphire 15 30.04 310 850 Calibration: P-T derivative

PP962 4.13A-3.4-4.1A

15 24.82 250 850 Crystallization exp. test / T cycle at 250 MPa / Cooling rate of 1 °C/min

PP963 4.13A 15 29.61 300 850 Crystallization exp. / T cycle at 250 MPa / Cooling rate of 0.5 °C/min



PP974 Fused quartz 22 30.04 310 450 Calibration: P-T derivative + frequency dependence

PP975 LN5 22 33.63 310 500 P-T derivative + frequency dependence / T cycle at 250 MPa

PP976 LN5 22 33.63 150 500 T derivative / T cycle at 150 MPa

PP977 LN3 22 32.02 310 550 P-T derivative / T cycle at 250 MPa



PP980 LN2 22 29.11 310 550 P-T derivative / T cycle at 250 MPa

PP989 Fused quartz 15 30.02 250 450 Calibration: P-T derivative

PP990 LN1 15 250 550 T derivative / T cycle at 250 MPa

PP991 LN0 22 30.06 290 680 Failed: Unstable temperature


Appendix

93

B.2 MHC COLD-SEALED PRESSURE VESSEL

Experiments Sample name

Diameter [mm]

P max [MPa]

T max [°C]

Duration [min]

Cooling rate [°C/min]

Comments

CS1 4.5A 2 250 850 30 0.5 Failed: sample too small

CS2 4.13A 4 250 850 30 0.5 Failed: sample stuck; had to drill it out

CS3 4.13A 4 250 850 30 0.5

CS4 4.13A 4 250 850 75 0.5

CS5 4.13A 4 250 850 120 0.5 Failed: Fast decompression at HT

CS6 4.13A 4 250 850 165 0.5

CS7 4.13A 4 250 850 210 0.5

CS8 4.13A 4 250 850 120 0.5

CS9 4.13A 4 250 850 124 0.1 Failed: Leak during experiment

CS10 4.13A 4 250 850 345 0.1

CS11 4.13A 4 250 850 526 0.1 Failed: sample in hot zone from beginning

CS12 4.13A 4 250 850 546 0.1

CS13 4.13A 4 250 850 405 0.1

CS14 4.13A 4 250 850 72 0.1

CS15 4.13A 4 250 850 744 0.1

CS16 4.13A 4 250 850 861 0.1

CS17 4.13A 4 250 850 925 0.1 Failed: sample stuck, not placed in hot zone

CS18 4.13A 4 250 850 603 0.1

CS19 4.13A 4 250 850 701 0.1

CS20 4.13A 4 250 850 925 0.1

CS21 4.13A 4 250 850 1055 0.1

B.3 PATERSON APPARATUS 6

Experiments Sample name Diameter [mm]

Length [mm]

P max [MPa]

T max [°C]

Comments

P1771 Fused quartz 15 30.04 150 430 Thermal expansion of glass

P1772 LN3 15 30.02 150 430 Thermal expansion of glass

P18-- Crystallized haplotonalite

15 25 250 850 Degassing test failed: Porous alumina is causing leaks in the jacket

P1817 Mullite 15 20 100 100 Permeability

P1818 4.13A 15 8.07 250 850 Crystalization exp. / cooling rate of 0.5 °C/min

P1819 Alumina piston

15 20 200 750 Thermal expansion of pore pressure

P1820 4.13A 15 11.07 250 850 Crystalization exp. / cooling rate of 0.1 °C/min

Appendix

94

Appendix C LIST OF MEASURED DENSITIES

De

nsi

ty

[g/c

m3 ]

Bef

ore

exp

erim

ents

in P

ate

rso

n

2.4

63

2

2.4

70

0

2.4

85

3

2.4

83

1

2.4

74

7

2.4

48

4

2.3

20

8

2.3

08

4

2.3

49

0

2.3

03

8

Aft

er e

xper

imen

ts in

Pa

ters

on

2.5

19

2

2.5

00

3

2.4

89

0

2.4

87

1

2.4

74

6

2.4

58

6

2.4

83

1

2.4

84

5

Av.

Vo

lum

e

[cm

3 ]

1.6

92

1

5.0

25

8

5.8

25

8

1.4

99

2

10

.42

33

13

.67

76

4.7

21

9

3.8

68

3

2.3

90

3

4.1

09

5

7.9

61

9

4.2

86

9

11

.07

17

10

.93

19

6.2

41

7

7.4

57

1

2.3

42

6

2.0

09

7

4.7

24

2.3

9

4.1

09

4

4.2

88

9

1.5

00

2

4.7

22

3

3.8

68

9

2.3

90

3

4.1

10

5

4.2

88

7

2.3

41

4

2.0

08

7

5.8

25

4

1.4

98

9

4.7

22

7

3.8

7

2.3

89

3

4.1

10

6

4.2

88

2.3

43

4

2.0

10

7

5.8

24

6

1.4

99

4

4.7

21

3

3.8

70

7

2.3

91

5

4.1

09

3

4.2

85

6

2.3

42

8

2.0

08

4

1.6

92

1

5.0

25

2

5.8

25

2

1.5

10

.42

43

13

.67

74

4.7

20

7

3.8

67

5

2.3

91

3

4.1

09

8

4.2

85

1

11

.07

10

.93

22

6.2

41

7.4

58

2.3

43

1

2.0

10

5

1.6

91

5

5.0

25

8

5.8

26

2

1.5

00

5

10

.42

25

13

.67

73

4.7

23

2

3.8

67

2

2.3

89

5

4.1

08

7.9

62

4.2

85

4

11

.07

2

10

.93

07

6.2

43

3

7.4

55

3

2.3

42

6

2.0

08

8

1.6

92

1

5.0

26

4

5.8

27

1

1.5

00

3

10

.42

29

13

.67

79

4.7

2

3.8

67

6

2.3

89

6

4.1

09

8

7.9

61

9

4.2

86

5

11

.07

31

10

.93

18

6.2

41

7

7.4

57

2.3

42

1

2.0

11

7

1.6

91

9

5.0

26

5.8

27

1

1.4

98

1

10

.42

42

13

.67

79

4.7

22

8

3.8

67

9

2.3

9

4.1

08

1

7.9

61

4

4.2

88

11

.07

16

10

.93

18

6.2

41

5

7.4

56

3

2.3

42

2

2.0

1

Vo

lum

e

[cm

3 ]

1.6

92

9

5.0

25

7

5.8

25

1

1.4

97

8

10

.42

28

13

.67

75

4.7

20

2

3.8

66

9

2.3

91

6

4.1

10

5

7.9

62

3

4.2

86

7

11

.07

16

10

.93

28

6.2

41

1

7.4

58

8

2.3

42

9

2.0

08

7

We

igh

t

[g]

4.1

68

12

.41

4

14

.47

9

3.7

23

25

.79

5

33

.48

9

10

.95

9

8.9

3

5.6

15

9.4

68

20

.05

8

10

.71

9

27

.55

8

27

.18

9

15

.44

6

18

.33

4

5.8

17

4.9

93

Tem

pe

ratu

re

[°C

]

29

.8

29

.8

27

.9

28

29

.6

29

.4

28

28

.1

28

.4

28

.3

29

.6

27

.9

29

.5

29

.5

29

.7

29

.4

28

.1

28

.2

Sam

ple

LNO

LN1

LN2

LN3

LN4

LN5

4.1

3

3.4

4.3

b

3.3

c

LNO

LN1

LN2

LN3

LN4

LN5

PP

96

4

PP

96

5

Appendix

95

Appendix D LISTS OF CHEMICAL ANALYSES

D.1 KARL FISHER TITRATION MEASUREMENTS

Sample Weight [g]

H2O [ug]

Blank [ug]

Background [ug/s]

H2O [Wt%]

Average H2O [Wt%]

1A 0.02442 466.7 0 0.17 1.911

0.02310 407.1 0 0.28 1.762

0.02062 386.8 0 0.23 1.876

0.02116 319.2 0 0.29 1.509 1.764

3A 0.02158 404.1 0 0.34 1.873

0.02036 441.5 0 0.27 2.168

0.01931 429.1 0 0.26 2.222

0.02386 506.5 0 0.30 2.123

0.02072 405.7 0 0.27 1.958

0.02184 387.1 0 0.28 1.772

0.02043 340.6 0 0.33 1.667

0.02023 348.0 0 0.32 1.720 1.938

2.1A 0.01889 373.5 0 0.24 1.977

0.01920 379.0 0 0.24 1.974

0.01943 342.5 0 0.32 1.763 1.905

2.2A 0.02040 298.6 0 0.32 1.464

0.02213 334.5 0 0.27 1.512

0.02184 321.6 0 0.22 1.473 1.483

2.5A 0.02034 396.1 0 0.33 1.947

0.02109 479.3 0 0.26 2.273

0.01989 379.8 0 0.36 1.910 2.043

3.4 0.02283 639.1 0 0.32 2.799

0.02247 582.3 0 0.36 2.591

0.01985 566.1 0 0.28 2.852 2.748

3.3C 0.01864 326.0 0 0.37 1.749

0.01986 392.6 0 0.35 1.977

0.01967 358.7 0 0.34 1.824 1.850

3.3A 0.02006 312.3 0 0.38 1.557

0.02163 410.3 0 0.2 1.897

0.02096 366.8 0 0.32 1.750 1.735

4.13A 0.02065 547.8 0 0.1 2.653

0.02041 564.4 0 0.19 2.765

0.02342 683.5 0 0.13 2.918 2.779

LN1 (before) 0.01675 67.7 0 0.25 0.404

0.02240 63.9 0 0.27 0.285

0.02605 103.7 0 0.21 0.398 0.363

Appendix

96

Karl Fisher Titration measurements: Continued

Sample Weight [g]

H2O [ug]

Blank [ug]

Background [ug/s]

H2O [Wt%]

Average H2O [Wt%]

LN2 (before) 0.01834 59.8 0 0.24 0.326

0.02620 67.5 0 0.28 0.258

0.02151 44.9 0 0.24 0.209 0.264

LN2 (after) 0.02048 93.9 0 0.22 0.458

0.01830 39.3 0 0.23 0.215

0.02511 71.5 0 0.26 0.285 0.319

LN3 (before) 0.02158 179.4 0 0.25 0.831

0.01974 87.2 0 0.29 0.442

0.01808 95.0 0 0.27 0.525

0.01784 106.0 0 0.26 0.594 0.598

LN3 (after) 0.01987 102.9 0 0.31 0.518

0.02207 107.9 0 0.34 0.489

0.01977 112.9 0 0.2 0.571

0.02120 173.3 0 0.23 0.817

0.02288 95.8 0 0.32 0.419 0.563

LN4 (before) 0.01791 287.8 0 0.26 1.607

0.01776 251.4 0 0.3 1.416

0.01736 216.2 0 0.32 1.245

0.01758 247.9 0 0.28 1.410 1.419

LN4 (after) 0.01667 223.2 0 0.26 1.339

0.01748 255.9 0 0.24 1.464

0.01838 229.7 0 0.28 1.250

0.02473 350.6 0 0.28 1.418 1.368

LN5 (before) 0.01994 425.6 0 0.2 2.134

0.02076 496.2 0 0.17 2.390

0.02979 586.5 0 0.26 1.969

0.02006 398.8 0 0.19 1.988 2.120

LN5 (after) 0.02627 509.9 0 0.31 1.941

0.02256 422.0 0 0.28 1.871

0.01805 304.9 0 0.32 1.689

0.02071 409.2 0 0.25 1.976 1.869

Appendix

97

D.2 ELECTRON MICROPROBE MEASUREMENTS

All the data given in this section are in [wt%].

D.2.1 HAPLOTONALITE

D.2.1.1 INITIAL GLASS

Sample SiO2 Al2O3 CaO Na2O Total

4.5A 64.86 18.39 3.47 7.22 93.94

63.31 18.95 3.37 7.22 92.85

63.69 18.76 3.59 7.03 93.07

65.43 18.50 3.37 7.18 94.48

63.14 18.46 3.47 7.56 92.63

65.17 18.78 3.59 7.55 95.09

64.48 19.21 3.37 7.33 94.39

65.38 19.29 3.65 7.35 95.67

64.87 18.51 3.94 7.85 95.17

65.82 19.04 3.30 7.38 95.54

64.75 18.65 3.44 7.61 94.45

66.20 18.68 3.18 7.82 95.88

65.06 19.06 3.30 8.01 95.43

66.18 18.82 3.45 7.24 95.69

64.74 18.71 3.74 7.33 94.52

64.68 18.76 3.29 7.78 94.51

64.79 18.71 3.54 7.61 94.65

65.86 18.33 3.55 7.26 95.00

64.46 18.97 3.75 7.36 94.54

66.36 19.01 3.43 7.48 96.28

Average 64.96 18.78 3.49 7.46 94.69

StrDev 0.90 0.27 0.18 0.26 0.99

Appendix

98

D.2.1.2 INTERSTITIAL GLASS


CS4 64.03 17.31 2.87 7.04 91.25

64.30 17.79 2.76 7.29 92.14

63.65 18.01 2.99 7.36 92.01

64.72 17.83 2.74 7.12 92.41

64.99 17.40 2.59 7.19 92.17

64.95 17.53 2.57 7.25 92.30

65.42 17.00 2.39 7.15 91.96

65.67 15.97 2.01 6.86 90.51

67.30 15.68 2.02 6.51 91.51

68.50 15.03 1.75 6.72 92.00

Average 65.35 16.96 2.47 7.05 91.83

StrDev 1.50 1.03 0.42 0.27 0.58

CS6 72.20 12.23 1.01 5.97 91.41

73.83 12.39 1.28 5.92 93.42

73.69 12.04 1.08 5.54 92.35

71.14 12.26 1.11 5.28 89.79

74.49 11.68 0.92 5.77 92.86

72.02 12.17 0.97 5.93 91.09

73.22 12.31 1.20 5.59 92.32

74.61 11.53 0.98 5.83 92.95

71.00 11.96 0.99 5.99 89.94

70.44 12.36 1.11 5.99 89.90

Average 72.66 12.09 1.06 5.78 91.60

StrDev 1.51 0.29 0.11 0.24 1.38

CS8 71.56 12.44 1.26 6.25 91.51

71.14 12.53 1.16 5.16 89.99

69.59 13.47 1.16 6.27 90.49

72.33 11.91 1.18 5.65 91.07

70.50 12.12 1.05 5.88 89.55

71.55 12.82 1.19 6.05 91.61

68.29 14.78 1.91 6.53 91.51

71.07 12.63 1.25 6.29 91.24

71.59 13.41 1.75 3.67 90.42

70.64 13.37 1.44 5.01 90.46

Average 70.83 12.95 1.34 5.68 90.79

StrDev 1.16 0.84 0.28 0.86 0.71

PP964 76.38 8.74 0.51 4.82 90.45

76.35 9.57 0.62 4.82 91.36

77.52 8.89 0.43 3.67 90.51

72.08 10.06 1.04 4.83 88.01

Appendix

99

Interstitial glass: Continued


PP964 72.60 9.68 0.78 4.42 87.48

73.19 9.95 0.82 4.92 88.88

74.21 9.53 0.58 5.11 89.43

73.59 9.42 0.67 4.68 88.36

74.25 10.16 1.01 4.89 90.31

73.37 10.84 0.90 5.14 90.25

73.10 10.65 0.85 4.96 89.56

73.85 9.91 0.50 4.79 89.05

72.40 10.36 0.84 4.78 88.38

75.72 9.69 0.50 4.60 90.51

Average 74.19 9.82 0.72 4.75 89.47

StrDev 1.67 0.59 0.20 0.36 1.15

CS16 77.41 10.69 0.97 4.49 93.56

76.72 11.07 1.13 4.97 93.89

78.24 10.22 0.81 4.95 94.22

75.29 12.84 1.57 5.63 95.33

78.29 10.01 0.56 4.63 93.49

Average 77.19 10.97 1.01 4.93 94.10

StrDev 1.24 1.13 0.38 0.44 0.75

CS18 72.28 11.84 0.71 4.07 88.90

69.28 15.39 2.32 5.89 92.88

70.37 13.87 1.72 5.00 90.96

72.36 11.50 0.78 3.81 88.45

72.32 12.12 1.09 4.51 90.04

72.97 11.28 0.84 3.83 88.92

72.90 12.48 1.11 4.57 91.06

73.44 11.15 0.85 3.87 89.31

72.54 11.16 0.83 4.03 88.56

69.32 12.12 1.29 5.17 87.90

72.28 11.24 0.81 3.77 88.10

71.91 10.60 0.76 4.43 87.70

Average 71.83 12.06 1.09 4.41 89.40

StrDev 1.40 1.35 0.48 0.66 1.56

CS19 73.42 10.94 0.89 4.09 89.34

73.17 10.66 0.77 4.75 89.35

74.08 10.55 0.94 4.00 89.57

72.44 10.62 0.95 3.94 87.95

73.81 10.26 0.88 3.87 88.82

72.16 11.43 0.91 4.60 89.10

74.32 10.29 0.67 3.55 88.83

73.81 10.49 0.72 4.42 89.44

73.91 10.75 0.87 3.86 89.39

74.36 10.64 0.97 3.78 89.75

Appendix

100

Interstitial glass: Continued


CS19 74.46 9.92 0.97 4.05 89.40

Average 73.63 10.60 0.87 4.08 89.18

StrDev 0.77 0.39 0.10 0.36 0.50

CS20 74.02 10.45 1.22 3.04 88.73

75.20 9.48 1.22 3.58 89.48

73.56 11.29 1.31 4.41 90.57

73.35 11.91 1.51 4.80 91.57

73.55 11.44 1.48 4.18 90.65

75.29 9.88 1.07 2.93 89.17

73.32 11.29 1.43 4.17 90.21

72.53 11.67 1.53 4.71 90.44

Average 73.85 10.93 1.35 3.98 90.10

StrDev 0.95 0.88 0.17 0.72 0.92

PP965 75.89 9.94 1.29 3.64 90.76

75.76 10.36 1.30 4.50 91.92

73.30 11.43 1.61 4.40 90.74

74.84 10.12 1.50 3.98 90.44

75.80 9.94 0.64 3.75 90.13

76.54 9.80 0.84 3.81 90.99

75.10 9.42 1.59 3.83 89.94

76.99 9.13 1.30 3.61 91.03

74.41 10.13 1.14 3.62 89.30

75.64 9.79 1.48 3.61 90.52

75.89 10.07 1.29 3.81 91.06

75.24 9.80 1.18 4.00 90.22

75.67 10.44 1.50 3.79 91.40

Average 75.47 10.03 1.28 3.87 90.65

StrDev 0.93 0.55 0.29 0.29 0.68

D.2.1.3 PLAGIOCLASE


CS4 63.17 22.85 4.74 8.33 99.09

59.78 24.94 6.27 7.60 98.59

62.36 23.54 5.07 8.21 99.18

62.34 23.37 5.11 8.22 99.04

61.63 23.98 5.71 8.03 99.35

Average 61.86 23.74 5.38 8.08 99.05

StrDev 1.28 0.79 0.61 0.29 0.28

CS6 63.95 22.25 5.29 8.24 99.73

62.55 23.82 5.89 7.96 100.22

61.87 24.26 6.08 7.39 99.60

62.29 24.25 6.29 7.97 100.80

Appendix

101

Plagioclase: Continued


CS6 62.12 23.72 5.62 8.18 99.64

64.90 21.37 4.00 8.47 98.74

Average 62.95 23.28 5.53 8.04 91.79

StrDev 1.20 1.19 0.83 0.37 0.69

CS8 61.08 23.92 5.44 7.81 98.25

60.47 24.26 6.83 7.01 98.57

62.76 21.66 4.24 8.19 96.85

62.18 22.49 4.98 7.77 97.42

61.84 23.21 5.24 8.31 98.60

60.20 24.35 6.06 7.75 98.36

61.59 23.79 5.41 8.62 99.41

60.61 24.64 6.19 7.83 99.27

63.10 22.31 4.45 8.21 98.07

61.21 23.08 4.87 8.05 97.21

Average 61.50 23.37 5.37 7.96 98.20

StrDev 0.97 0.99 0.80 0.44 0.84

PP963 63.23 22.00 3.90 9.19 98.32

61.76 23.88 4.77 8.60 99.01

61.19 23.61 4.88 8.68 98.36

62.15 23.38 5.50 8.40 99.43

62.56 24.06 5.59 8.38 100.59

63.28 22.90 4.64 8.63 99.45

61.38 24.26 5.15 8.47 99.26

61.41 23.63 5.22 8.61 98.87

62.75 23.26 5.05 8.40 99.46

60.45 24.56 5.87 7.79 98.67

Average 62.02 23.55 5.06 8.52 99.14

StrDev 0.94 0.73 0.56 0.35 0.67

CS16 62.33 24.06 6.00 7.62 100.01

63.28 23.28 5.19 8.07 99.82

63.02 23.68 5.04 8.31 100.05

62.19 23.72 4.62 8.36 98.89

63.67 23.69 5.06 8.36 100.78

Average 62.90 23.69 5.18 8.14 99.91

StrDev 0.63 0.28 0.50 0.32 0.68

CS18 61.32 24.68 5.70 8.12 99.82

61.14 24.00 5.41 7.99 98.54

59.91 24.82 6.17 7.56 98.46

61.88 23.82 5.16 8.54 99.40

61.76 24.27 5.42 8.23 99.68

Average 61.20 24.32 5.57 8.09 99.18

StrDev 0.78 0.43 0.39 0.36 0.64

Appendix

102

Plagioclase: Continued


CS19 62.55 23.40 4.61 8.65 99.21

62.40 23.31 4.94 8.41 99.06

63.42 22.24 4.77 7.89 98.32

62.27 23.54 5.15 8.55 99.51

62.62 23.20 4.45 8.90 99.17

Average 62.65 23.14 4.78 8.48 99.05

StrDev 0.45 0.52 0.27 0.38 0.44

CS20 63.20 23.50 5.43 7.73 99.86

63.35 23.15 5.23 8.06 99.79

62.57 23.89 5.34 8.16 99.96

62.45 23.57 5.00 8.44 99.46

63.23 23.05 5.14 8.01 99.43

Average 62.96 23.43 5.23 8.08 99.70

StrDev 0.42 0.34 0.17 0.26 0.24

PP965 62.50 24.03 5.27 8.36 100.16

63.53 23.12 5.47 7.91 100.03

62.06 24.11 5.18 8.23 99.58

63.99 23.24 4.42 8.72 100.37

63.56 23.24 5.06 8.46 100.32

Average 63.13 23.55 5.08 8.34 100.09

StrDev 0.81 0.48 0.40 0.30 0.32

D.2.1.4 MELT POCKETS

Distance from spherulite border

[µm]

SiO2 Al2O3 CaO Na2O Total

Large melt pocket in CS4

20 76.34 12.33 3.36 7.97 91.33

40 76.24 12.05 4.06 7.65 92.86

60 76.61 12.06 3.51 7.81 91.73

80 76.01 12.17 3.60 8.22 92.63

100 76.17 12.19 3.68 7.96 92.36

120 76.00 12.16 3.98 7.86 93.43

140 75.86 12.15 3.99 8.01 94.03

160 76.27 12.21 3.71 7.81 92.57

180 75.78 12.32 4.13 7.77 92.35

200 75.94 12.13 3.90 8.03 92.44

220 75.80 12.43 3.96 7.80 93.16

240 75.74 12.21 3.83 8.23 93.30

260 75.25 12.42 4.08 8.24 94.06

280 76.33 12.42 3.42 7.82 93.21

300 75.80 12.33 3.90 7.97 93.27

320 75.99 12.19 3.80 8.02 92.61

Appendix

103

Melt pockets: Continued


[µm]



340 75.93 12.33 3.71 8.03 93.26

360 75.52 12.28 3.77 8.43 93.45

380 75.96 12.45 3.62 7.97 93.36

400 75.38 12.90 3.89 7.82 93.58

420 75.60 12.52 4.01 7.88 94.43

440 75.74 12.26 4.12 7.88 93.67

460 75.03 12.37 4.33 8.27 94.54

480 75.68 12.49 4.12 7.71 94.12

500 75.74 12.37 3.98 7.90 95.79

520 75.60 12.23 4.18 8.00 94.59

540 75.30 12.36 4.01 8.33 95.69

560 75.10 12.49 4.05 8.35 95.36

580 75.55 12.44 4.16 7.86 96.00

600 75.43 12.52 3.97 8.07 95.84

620 75.71 12.36 4.36 7.58 96.12

640 75.72 12.54 4.14 7.60 95.68

660 74.80 12.60 4.54 8.06 96.65

680 75.39 12.59 4.21 7.81 94.86

700 75.80 12.29 4.03 7.89 95.60

720 75.76 12.46 4.21 7.58 95.49

740 75.49 12.61 3.83 8.06 95.22

760 75.21 12.47 4.35 7.96 95.89

780 75.34 12.39 4.25 8.01 96.04

800 75.75 12.32 3.99 7.94 96.22

820 75.49 12.09 4.35 8.07 96.08

840 75.55 12.36 4.33 7.76 96.26

860 75.61 12.29 4.32 7.78 94.97

880 75.69 12.31 4.05 7.96 95.38

900 75.62 12.44 3.99 7.95 95.74

920 75.43 12.45 4.10 8.02 95.45

940 75.64 12.45 3.97 7.94 95.55

960 75.33 12.58 4.33 7.75 95.57

980 76.03 12.36 4.00 7.61 96.37

1000 75.75 12.26 4.21 7.78 96.35

1020 75.69 12.47 4.03 7.81 95.40

1040 75.66 12.27 4.23 7.84 94.88

1060 75.86 12.38 4.33 7.43 95.71

1080 75.68 12.22 3.99 8.10 95.54

1100 75.35 12.59 4.17 7.88 95.49

1120 75.14 12.59 4.20 8.08 96.34

1140 76.21 12.16 3.87 7.76 94.86

1160 75.37 12.45 4.06 8.12 94.96

Appendix

104



[µm]



1180 75.81 12.53 3.85 7.80 95.25

1200 75.81 12.40 3.82 7.97 95.12

1220 75.41 12.36 4.09 8.13 96.05

1240 75.84 12.60 3.71 7.85 95.50

1260 75.53 12.46 4.16 7.85 95.92

1280 75.87 12.39 3.95 7.78 95.14

1300 75.54 12.69 4.13 7.64 94.52

1320 74.98 12.50 4.40 8.12 95.77

Small melt pocket in CS4

20 75.05 12.49 4.42 8.05 93.07

40 75.48 12.48 3.90 8.13 93.18

60 74.88 12.39 4.24 8.49 92.45

80 74.78 12.69 4.21 8.33 93.72

100 75.49 12.57 3.97 7.97 92.39

120 75.23 12.60 3.86 8.31 92.05

140 75.20 12.60 3.97 8.23 93.27

160 75.34 12.41 4.13 8.12 93.93

180 75.40 12.45 3.74 8.41 93.11

200 75.34 12.35 4.03 8.29 93.36

220 75.63 12.44 3.78 8.15 92.99

240 75.41 12.30 3.75 8.55 93.73

260 75.70 12.41 3.66 8.22 93.42

280 75.53 12.58 3.83 8.07 93.82

300 74.76 12.70 4.11 8.43 94.27

320 75.65 12.49 4.00 7.85 94.89

340 75.65 12.50 3.87 7.98 94.86

360 75.61 12.60 3.97 7.82 95.15

380 75.21 12.67 4.21 7.91 95.49

400 75.68 12.19 4.33 7.80 95.18

420 75.26 12.60 4.04 8.10 95.17

440 74.93 12.40 4.45 8.22 94.88

460 75.39 12.43 4.18 8.00 94.58

480 75.82 12.41 4.11 7.66 94.76

500 74.96 12.73 4.42 7.89 95.34

520 74.87 12.42 4.30 8.40 96.01

540 75.40 12.22 4.29 8.08 95.88

560 74.92 12.48 4.42 8.18 96.16

580 75.15 12.58 4.00 8.27 95.88

600 75.63 12.45 3.90 8.01 96.11

620 75.18 12.65 3.99 8.17 96.02

640 75.37 12.21 4.55 7.87 96.28

660 75.78 12.37 4.02 7.84 96.21

680 75.39 12.25 4.08 8.28 95.47

Appendix

105



[µm]


Small melt pocket in CS4

700 75.83 12.35 4.06 7.76 95.39

720 75.37 12.40 4.44 7.79 96.23

740 75.41 12.45 4.09 8.04 95.54

760 75.08 12.57 4.24 8.12 95.97

780 75.78 12.28 4.02 7.92 95.24

800 75.18 12.35 4.48 7.98 95.46

820 75.16 12.53 4.29 8.02 95.94

840 75.78 12.41 4.05 7.76 94.31

860 75.62 12.20 4.26 7.92 96.89

880 75.71 12.35 3.82 8.11 95.26

900 75.15 12.62 4.00 8.23 95.93

920 75.52 12.41 4.21 7.87 95.96

940 75.55 12.46 3.88 8.11 94.76

960 75.76 12.72 3.84 7.68 93.74

980 74.87 12.76 4.28 8.09 94.82

1000 75.92 12.15 3.93 8.00 92.93

1020 75.94 12.31 3.98 7.77 95.09

1040 75.35 12.47 3.86 8.33 94.80

1060 75.56 12.34 3.99 8.11 94.68

1080 75.58 12.35 3.94 8.13 94.03

1100 75.52 12.43 3.82 8.24 94.00

1120 75.41 12.19 3.97 8.44 93.98

1140 75.64 12.31 3.93 8.12 93.47

1160 75.65 12.40 3.80 8.14 93.95

1180 75.14 12.31 4.65 7.89 93.19

1200 75.52 12.30 4.21 7.97 93.31

1220 75.21 12.46 4.16 8.17 93.73

1240 74.96 12.50 4.21 8.32 93.70

1260 75.10 12.39 4.20 8.30 93.86

1280 75.51 12.32 4.03 8.15 93.26

1300 75.29 12.39 4.27 8.06 92.49

1320 76.10 12.25 3.69 7.95 92.92

Appendix

106

D.2.1.5 ELEMENTS DISTRIBUTION MAPS

Figure D.1: Elements distribution map performed on the haplotonalite used for the crystallization experiments (4.13A).

Appendix

107

Figure D.2: SEM image and elements distribution maps of the haplotonalite cooled at 0.5°C/min in the Paterson apparatus. The contour of the plagioclase crystal are highlighted in black in the elements distribution maps.

Appendix

108

D.2.2 LAVAS NEGRAS

Sample SiO2 TiO2 Al2O3 FeO MnO MgO CaO Na2O K2O Total

LN1 60.50 0.67 18.52 3.44 0.19 0.36 0.72 9.43 4.86 98.69

60.14 0.68 18.44 3.44 0.20 0.37 0.74 9.36 4.83 98.19

60.18 0.69 18.47 3.43 0.23 0.36 0.72 9.29 4.92 98.28

59.88 0.69 18.43 3.44 0.19 0.38 0.72 9.29 4.85 97.87

60.88 0.66 18.65 3.42 0.23 0.35 0.70 9.19 4.88 98.95

60.35 0.69 18.48 3.42 0.19 0.35 0.74 9.25 4.85 98.33

60.17 0.69 18.44 3.45 0.23 0.37 0.73 9.34 4.83 98.26

59.90 0.67 18.37 3.47 0.19 0.36 0.70 9.10 4.84 97.60

60.70 0.66 18.70 3.47 0.20 0.37 0.74 9.30 4.82 98.97

60.29 0.66 18.50 3.46 0.20 0.37 0.74 9.24 4.86 98.31

60.17 0.70 18.43 3.46 0.20 0.39 0.75 9.29 4.83 98.22

60.11 0.69 18.43 3.48 0.20 0.35 0.74 9.26 4.84 98.10

60.09 0.68 18.38 3.43 0.20 0.37 0.72 9.24 4.82 97.93

60.00 0.69 18.42 3.43 0.21 0.35 0.70 9.26 4.84 97.90

60.14 0.67 18.47 3.44 0.22 0.36 0.71 9.23 4.86 98.10

60.24 0.69 18.45 3.39 0.19 0.36 0.73 9.25 4.85 98.15

60.40 0.67 18.62 3.43 0.21 0.37 0.71 9.21 4.86 98.48

60.40 0.69 18.66 3.39 0.22 0.38 0.72 9.02 4.81 98.29

60.57 0.67 18.55 3.45 0.21 0.38 0.73 9.18 4.84 98.58

60.43 0.68 18.64 3.49 0.21 0.37 0.72 9.23 4.86 98.64

60.44 0.69 18.48 3.47 0.20 0.35 0.71 9.35 4.84 98.52

60.16 0.66 18.50 3.44 0.20 0.37 0.72 9.15 4.87 98.07

61.35 0.67 18.73 3.41 0.17 0.38 0.75 9.21 4.82 99.49

60.93 0.68 18.85 3.36 0.20 0.38 0.74 9.30 4.90 99.34

61.00 0.67 18.67 3.42 0.22 0.38 0.71 9.22 4.84 99.12

61.06 0.68 18.86 3.44 0.21 0.35 0.71 9.23 4.87 99.42

60.76 0.68 18.63 3.45 0.20 0.37 0.74 9.11 4.79 98.73

60.48 0.66 18.65 3.41 0.20 0.35 0.73 9.24 4.83 98.54

60.54 0.70 18.65 3.51 0.21 0.37 0.73 9.32 4.85 98.88

60.54 0.66 18.62 3.43 0.21 0.36 0.72 9.23 4.84 98.61

60.53 0.68 18.61 3.50 0.21 0.34 0.71 9.27 4.84 98.69

60.44 0.67 18.68 3.40 0.20 0.39 0.73 9.18 4.82 98.51

60.59 0.67 18.79 3.48 0.21 0.36 0.73 9.28 4.82 98.93

60.32 0.68 18.75 3.49 0.21 0.35 0.72 9.30 4.81 98.63

60.32 0.68 18.78 3.44 0.18 0.37 0.71 9.32 4.85 98.66

60.16 0.69 18.70 3.49 0.20 0.34 0.73 9.21 4.91 98.43

60.34 0.67 18.56 3.43 0.23 0.36 0.71 9.21 4.89 98.40

60.13 0.70 18.47 3.41 0.21 0.36 0.72 9.17 4.91 98.08

59.78 0.70 18.49 3.41 0.17 0.36 0.72 9.28 4.89 97.80

60.61 0.68 18.75 3.36 0.22 0.36 0.72 9.25 4.86 98.82

Appendix

109

Lavas Negras: Continued


LN1 60.03 0.68 18.62 3.42 0.22 0.36 0.72 9.09 4.86 97.99

Average 60.39 0.68 18.58 3.44 0.21 0.36 0.72 9.24 4.85 98.48

StrDev 0.34 0.01 0.13 0.03 0.01 0.01 0.01 0.08 0.03 0.44

LN2 60.27 0.67 18.64 3.39 0.21 0.36 0.70 9.34 4.85 98.43

60.37 0.67 18.59 3.41 0.20 0.37 0.70 9.32 4.84 98.47

60.10 0.68 18.52 3.42 0.19 0.38 0.74 9.38 4.82 98.23

60.19 0.66 18.46 3.39 0.21 0.38 0.73 9.33 4.86 98.20

60.29 0.68 18.58 3.41 0.20 0.36 0.73 9.26 4.87 98.38

Average 60.24 0.67 18.56 3.40 0.20 0.37 0.72 9.33 4.85 98.34

StrDev 0.10 0.01 0.07 0.01 0.01 0.01 0.02 0.04 0.02 0.12

LN3 60.33 0.67 18.67 3.40 0.19 0.35 0.71 9.02 4.81 98.15

60.58 0.69 18.75 3.32 0.22 0.37 0.70 9.26 4.87 98.76

61.07 0.66 18.75 3.36 0.20 0.39 0.71 9.24 4.81 99.19

60.27 0.68 18.56 3.39 0.20 0.36 0.71 9.11 4.84 98.12

60.87 0.69 18.62 3.33 0.19 0.36 0.73 9.21 4.85 98.85

60.80 0.66 18.61 3.43 0.21 0.39 0.71 9.31 4.85 98.97

Average 60.65 0.68 18.66 3.37 0.20 0.37 0.71 9.19 4.84 98.67

StrDev 0.32 0.01 0.08 0.04 0.01 0.02 0.01 0.11 0.02 0.44

LN4 59.78 0.68 18.21 3.31 0.18 0.36 0.70 8.99 4.74 96.96

59.44 0.67 18.31 3.40 0.21 0.35 0.69 9.16 4.73 96.97

59.93 0.67 18.40 3.25 0.20 0.34 0.69 8.96 4.73 97.17

59.79 0.66 18.39 3.38 0.18 0.36 0.71 9.03 4.76 97.26

59.68 0.68 18.29 3.41 0.20 0.36 0.69 9.04 4.76 97.10

60.76 0.66 18.63 3.46 0.19 0.36 0.72 9.02 4.75 98.56

60.65 0.65 18.77 3.36 0.18 0.35 0.73 9.11 4.74 98.54

60.53 0.68 18.67 3.39 0.19 0.37 0.74 8.98 4.76 98.30

60.40 0.65 18.69 3.33 0.18 0.33 0.72 9.03 4.75 98.09

60.39 0.66 18.50 3.34 0.20 0.35 0.73 9.17 4.74 98.08

60.43 0.65 18.56 3.37 0.22 0.34 0.73 9.06 4.76 98.11

60.55 0.66 18.58 3.32 0.20 0.36 0.73 9.09 4.74 98.22

60.33 0.67 18.48 3.41 0.19 0.34 0.71 9.16 4.76 98.04

60.53 0.68 18.50 3.45 0.19 0.35 0.71 9.00 4.77 98.18

60.32 0.65 18.57 3.33 0.20 0.36 0.71 9.01 4.75 97.91

60.21 0.67 18.51 3.53 0.21 0.36 0.71 9.00 4.77 97.98

60.24 0.67 18.67 3.27 0.18 0.35 0.73 9.14 4.79 98.06

60.29 0.66 18.49 3.27 0.18 0.36 0.71 9.00 4.73 97.68

60.13 0.66 18.60 3.32 0.19 0.34 0.71 9.02 4.76 97.74

Average 60.23 0.67 18.52 3.36 0.19 0.35 0.72 9.05 4.75 97.84

StrDev 0.36 0.01 0.15 0.07 0.01 0.01 0.01 0.07 0.02 0.51

LN5 59.54 0.66 18.17 3.02 0.19 0.27 0.83 8.80 4.69 96.16

59.80 0.62 18.30 2.98 0.20 0.29 0.78 8.87 4.70 96.54

Appendix

110

Lavas Negras: Continued


LN5 59.59 0.64 18.39 3.30 0.20 0.38 0.68 8.76 4.72 96.65

58.98 0.63 18.08 3.18 0.20 0.35 0.71 8.73 4.70 95.56

58.59 0.64 18.04 3.15 0.20 0.34 0.74 8.68 4.79 95.17

59.40 0.66 18.16 3.10 0.19 0.33 0.75 8.23 4.76 95.58

59.69 0.66 18.41 3.19 0.20 0.39 0.73 8.58 4.77 96.62

60.88 0.57 18.52 2.54 0.18 0.16 0.74 8.66 4.70 96.94

60.10 0.57 18.49 3.05 0.20 0.37 0.61 8.87 4.75 97.01

59.99 0.66 18.18 2.98 0.20 0.32 0.80 8.81 4.70 96.65

59.55 0.64 18.08 3.12 0.17 0.32 0.74 8.63 4.75 96.00

60.30 0.64 18.49 3.15 0.18 0.35 0.74 8.65 4.75 97.26

60.58 0.66 18.44 3.07 0.21 0.30 0.74 8.98 4.71 97.70

60.44 0.62 18.32 2.82 0.17 0.27 0.81 8.77 4.66 96.88

60.63 0.62 18.46 2.82 0.19 0.25 0.81 8.68 4.76 97.22

60.44 0.60 18.28 2.79 0.18 0.26 0.70 8.75 4.77 96.76

61.18 0.51 18.62 2.80 0.15 0.34 0.58 8.91 4.69 97.78

60.85 0.65 18.31 2.99 0.19 0.29 0.77 8.77 4.72 97.53

60.53 0.64 18.29 2.81 0.19 0.26 0.85 8.74 4.71 97.02

60.84 0.63 18.42 2.91 0.18 0.39 0.66 8.68 4.65 97.36

60.64 0.64 18.33 3.17 0.19 0.32 0.78 8.66 4.70 97.43

60.33 0.65 18.31 2.98 0.19 0.29 0.80 8.81 4.66 97.02

60.70 0.63 18.47 2.83 0.20 0.24 0.75 8.81 4.75 97.38

60.16 0.61 18.28 3.34 0.21 0.48 0.59 8.65 4.78 97.09

60.69 0.66 18.47 3.25 0.17 0.27 0.64 8.86 4.66 97.68

59.54 0.69 18.30 3.57 0.21 0.59 0.64 8.71 4.77 97.01

60.10 0.65 18.25 3.07 0.17 0.33 0.77 8.76 4.71 96.81

59.84 0.67 18.27 3.16 0.19 0.32 0.75 8.86 4.71 96.77

60.68 0.68 18.37 2.97 0.20 0.27 0.80 8.89 4.74 97.58

Average 60.16 0.63 18.33 3.04 0.19 0.32 0.73 8.74 4.72 96.87

StrDev 0.62 0.04 0.14 0.21 0.01 0.08 0.07 0.14 0.04 0.66

Documents

In Copyright - Non-Commercial Use Permitted Rights ...49504/et… · performed on relaxed samples. Consequently, by continuously monitoring small seismic velocity perturbations in