P-T ESTIMATES OF GARNET BEARING AMPHIBOLITE AT GETTERÖN, SOUTH WESTERN

SWEDEN

Natalie Gorne, University of Gothenburg, Department of Earth Sciences; Geology, Box 460, SE-405 30

Göteborg

Sammanfattning

En granatförande amfibolitisk bergart vid Getterön lokal, nära Varberg i Sydvästra Sverige uppvisar

mineralogiska och texturella indikationer av eklogitfaciesförhållanden tillsammans med riklig utbredning av

hornblände och möjlig retrograd plagioklas coronas på granat. Dessa samtidiga faser och texturer är tvetydiga i

meningen om att ha ett gemensamt tryck– och temperurföhållande och antyder en historia av åtminstone två

metamorfa händelser. Området är en del av det Östra Segmentet som har drabbats av metamorfos orsakat av

den Hallandiska och den Svekonorvegiska orogenesen. Mineral analyser gjordes med ett sveptunnelmikroskop

(SEM-EDS); dessa användes till geokemi och termobarometrisk modellering. Fyra mineralparageneser

användes till de termobarometriska uträkningarna för att undersöka den senaste metamorfa händelsen och för

att söka efter spår av högre tryck från äldre händelser arkiverat i granaternas inklusioner. Den

termobarometriska modelleringen gjordes med mjukvarona TWQ och HbPl samt GPT excelblad. TWQ angav

temperaturer omkring 800°C för grt-cpx-pl (qz) och 8.2 kbar vid 677°C till 10.4 kbar vid 801°C för grt-hbl-pl

(qz). Homogeniteten i mineralen antyder en jämviktsomställning (reequilibration) som kan ha skett under

avkylning av berget. Petrografiska indikationer för retrograd metamorfos stöds av analyser av kärna-rim

profiler i granater. Publicerad data från Ullared och Borås lokaler i Östra Segmentet bevisar att

Svekonorvegisk eklogitfaciesförhållanden följdes av retrograd metamorfos.

Det är troligt att tillskriva den Svekonorvegiska händelsen som orsakande för de dekomprimerade granaterna

och kanske för bildningen av granaterna vid högre tryck och temperaturförhållanden under äldre händelser.

Den Hallandiska metamorfosen har påverkat Varbergsregionen under amfibolit– till granulitfaciesförhållanden

vilka är överensstämmande med tryck och temperaturresultaten från denna studie. Dock gör de mineralogiska

och texturella föhållandena det tveksamt att den Hallandiska orogenesen ensamt skulle vara orsaken till den

metamorfa historia som har drabbat denna del av berget.

Nyckelord: tryck– och temperaturuppskattningar, mineralparagenes, retrograd, jämvikt, zonering, inklusion,

corona rim.

ISSN1400-3831 B683 2012

PT- ESTIMATES OF GARNET BEARING AMPHIBOLITE AT GETTERÖN, SOUTH WESTERN

SWEDEN

Natalie Gorne, University of Gothenburg, Department of Earth Sciences; Geology, Box 460, SE-405 30

Göteborg

Abstract

Garnet bearing amphibolitic rock at Getterön locality, near Varberg town in south western Sweden exhibits

mineralogical and textural indications of eclogite facies conditions, together with large abundances of

hornblende and possible retrograde plagioclase coronas on garnet. These coexisting phases and textures are

ambiguous in the sense of having one common metamorphic condition and points to a history of at least two

metamorphic events. The area is part of the Eastern Segment and has suffered metamorphose caused by the

Sveconorwegian and Hallandian orogenies. Mineral analysis was done using a scanning electron microscope

(SEM-EDS); these were used for geochemistry and thermobarometric modeling. Four mineral assemblages

were used for the thermobarometric calculations, to investigate the last metamorphic event and to search for

traces of higher pressures during an earlier event recorded in the inclusions of the garnets. The

thermobarometric modeling was done using TWQ and HbPl softwares and GPT spread sheet. TWQ gave

temperatures around 800°C for grt-cpx-pl (qz) and 8.2 kbar at 677°C to 10.4 kbar at 801°C for grt-hbl-pl (qz).

The homogeneity of the minerals suggests a reequilibration that might have taken place during cooling of the

rock. Petrographic indication of retrograde metamorphism is supported by analysis of core-rim profiles in

garnets. Published data from the Ullared and Borås localities in the Eastern Segment prove that

Sveconorewegian eclogite facies conditions were followed by retrograde metamorphism.

It is plausible to attribute the Sveconorwegian event as being responsible for the decompressed garnets and

probably for the formation of the garnets at higher P-T conditions during earlier events. The Hallandian

metamorphism has affected the Varberg region at amphibolitic to granulitic facies conditions which is

concordant with the P-T results from this study. However the mineralogical and textural relationships make it

doubtful that the Hallandian metamorphic event alone could be responsible for the metamorphic history that

has affected this rock.

Keywords: P-T estimates, mineral assemblage, retrograde, equilibrium, zonation, inclusion, corona rim.

ISSN1400-3831 B683 2012

Table of contents

1. Introduction 1

1.1 Objectives of the project 1

1.2 Regional geology 1

1.3 The Eastern Segment 1

1.4 Geological setting at Varberg 3

1.5 Sampling area 3

1.6 Thermodynamics 8

1.7 Element partitioning 8

2. Methods 9

2.1 Electron microanalysis 9

2.2 Thermobarometric modeling 10

3. Results 10

3.1 Petrography 10

3.1.1 Dc0305 10

3.1.2 Dc0308 12

3.2 Geochemistry 12

3.3 Termobarometric modeling 14

3.3.1TWQ 14

3.3.2 Hornblende-Plagioclase 15

3.3.3 Garnet-Ilmenite 16

3.3.4 Inclusions 16

3.4 Metmorphic facies 17

4. Discussion 18

5. Conclusions 20

6. Acknowledgements 20

7. References 21

1

1. Introduction

1.1 Objectives of the project

The main objective of this project is to analyze the geochemistry of the main minerals in a garnet

bearing amphibolite at Getterön (near Varberg) in order to investigate the pressure and temperature

of the last metamorphic event. A further objective is to search for earlier pressure and temperature

events recorded in the mineral chemistry of the rock. The most suitable objects for this aim are the

garnets and their inclusions. An interesting question is if the results will contribute to an

interpretation that is in concordant with the metamorphic history of the region. Field relationships

infer involvement of fluid movement and so this study will search for mineralogical evidence for this

assumption.

1.2 Regional Geology

The Sveconorwegian Province is the western part of the Baltic shield (Fig. 1) and consists of bedrock

that either formed or was deformed or metamorphosed during the 1.15-0.9 Ga Sveconorwegian

orogeny (Lindström, Lundqvist & Lundqvist, 2000). The Sveconorwegian province comprises a ~500

km wide belt situated in the south east of the Caledonian front that is bounded to the west and north

by the sea or Calendonian nappes and the Protogene Zone in the east. The Protogenee Zone marks a

limit between Sveconorwegian Province and the Transscandinavian Igneous Belt, it is also regarded

as a Sveconorwegian metamorphic discontinuity with high grade rocks to the west and low grade

rocks to the east (Hegardt & Cornell, 2010).

Approximately 40 kilometers east of the Protogene Zone the Sveconorwegian Frontal Deformation

Zone (SFDZ) delimits the area affected by Sveconorwegian deformation; here the deformation is

most obvious in N-S trending shear zones with dextral component. In Sweden the Sveconorwegian

province is made up of two tectonic units called Eastern and Western Segment. The Eastern segment

is regarded as a parautochthonous unit directly linked to the Fennoscandian foreland while the

Western Segment has been transported remarkably by the Sveconorwegian orogeny (Bingen,

Nordgulen, & Viola, 2008).

1.3 The Eastern Segment

The Eastern Segment is located between the Protogene and Mylonite Zones (Fig.1). The first

deformation and metamorphic event occurred around 1420-1460 Ma and is named the Hallandian

Orogeny (Johansson & Engroth, 2012). Sveconorwegian alteration and deformation affected the

rocks a second time at 970-960 Ma as the Western Segment was thrust over the Eastern Segment

along the Mylonite Zone, which increased pressure and temperature.

Syenitic intrusions and mafic intrusions in the central and southern parts were formed at 1230-1180

Ma as a result of early Sveconorwegian crustal extension. Metamorphic grade in the central parts

reached upper amphibolites facies with 750˚C and 9 kbar in the Ulricehamn area. There are

uncertainties about the influences of the pre-Sveconorwegian thermal and deformal events in these

parts of the Eastern Segment where pre-1.55 Ga (Gothian) has been the interpreted time of the main

tectonothermal reworking in the area. The problem is that no metamorphic ages older than 1.55 Ga

have been found in this area (Möller, 1998).

2

In the southern parts, upper amphibolite to high-pressure granulite facies affected most rocks at 680-

800 ˚C and 8-12 kbar. Isotopic studies of titanite from granulite facies rocks have given ages of 940-

880 Ma that are in accordance with U-Pb ages from metamorphic zircons (Möller, 1998). The

southern part is sometimes referred to as the Southwest Swedish Granulite Region (SGR),

dominating rocks are pervasively gneissic veined and locally migmatitic. These orthogneisses are

dated to 1.7-1.6 Ga and have intermediate-granitic compositions (Andersson, Söderlund, Cornell,

Johansson & Möller, 1999). The high pressure amphibolite facies conditions in the Eastern Segment

indicate a thickening of the crust, since the pressures represent depths up to 30-40 km. Such

thickening can be formed by continental plate collision (Lindström et al., 2000).

Even higher pressures (>15 kbar) are encountered in decompressed eclogites and garnet-pyroxenites

in Ullared area, located in the central parts of the Eastern Segment. The garnet-pyroxenites show

mineral assemblages indicative of eclogite facies like omphacite, pyrope and kyanite. These rocks

have been retrogressed to amphibolite facies and the whole alteration sequences from eclogite to

amphibolite facies are dated to 0.97 and 0.95 Ga (Lindström et al., 2000). Parts of the Eastern

Segment have thus been subjected to more than 15 kbar which corresponds to a depth of

approximatly 55 km. This is further evidenced in a study of a mafic intrusion in Borås (Mohammed,

Cornell, Danielsson, Hegardt, Anczkiewic, 2011) where garnet inclusions have original mineral

assemblages that give P-T conditions 22.3-24.5 kbar and 600°C. The minerals are of eclogite facies

assemblage and were isolated in an early stage from the whole rock. One of the inclusions that led to

the conclusion was Mg-rich staurolite which was formed at second stage during exhumation as

pressure decreases. The P-T conditions estimated by Mohammad et al. (2011) corresponds to depths

Fig. 1. Geological map of

Southwestern Sweden. (Modified from

Hegardt and Cornell, 2010)

3

of minimum 75-83 km which give evidence for a subduction and exhumation cycle in this part of the

Eastern Segment and the event is interpreted as part of the Sveconorwegian orogeny.

The retrogression in the Eastern Segment is thought to be caused by the tectonic event between 960

and 955 Ma when the Western Segment started to move back to its former position which in turn

resulted in a relief in pressure and temperature in the Eastern Segment, thus retrograde conditions

were attained. The preservation of high grade minerals in the Eastern Segment indicates that this

movement was relatively rapid since such minerals did not completely alter to lower grade minerals

(Möller et al., 1999).

1.4 Geological Setting at Varberg

Varberg town is located in south eastern Sweden (Halland) and is a part of the Eastern Segment. The

dominant rock type is granodiorite with gneissic structure. There are also high abundances of gneissic

granite and charnockite (see Fig. 2) which is a nearly anhydrous granitic rock containing

orthopyroxene, commonly hypersthene (Winter, 2010). The different rock types commonly merge

into each other and sharp contacts are only shown in a few places.

Different lithological units groups of the gneissic complex of the Varberg region are proposed by

Hubbard (1975). In some parts the regional amphibolite facies gneisses are overprinted by granulite

facies and the dominant granitic gneisses partially transformed to charnockites in situ which are

included in the Charnockite-granite association (Constable & Hubbard, 1981). The intrusive age of

rocks from the this group is ~1.37 Ga and it includes units like the Varberg Charnockite, Torpa

Granite and Tjärnesjö Granite (Lindström et al,. 2000). Granulite facies rocks from the Charnockite-

Granite Association (except the Varberg Charnockite) show Sveconorwegian isochron ages (Åhäll,

Samulelsson, Persson, 1997). The Sveconorwegian age is 970 Ma in this area (Lundquist & Kero,

2008). Mafic igneous activity is not seen as a primary feature in the region but metamorphic

derivatives in form of pyribolite and amphibolite bodies of magmatic origin are found and indicate

the former existence of mafic intrusions. Pyribolite is a high-grade metamorphic rock composed of

plagioclase, hornblende, clinopyroxene, orthopyroxene and garnet, hornblende and pyroxene are

present in approximately equal amounts (Coutinho, Kräutner, Sassi, Schmid & Sen, 2007).

In the field relationships three cycles of mafic igneous activity are recorded: 1. An older volcano-

hypabyssal stage related to the primary development of the Varberg granulite series; 2. A younger

stage, also volcano-hypabyssal was related to the pre-metamorphic stages of Bua Gneiss Series. This

was marked by extensive sheet and sill development; 3. An intrusive episode during the Varberg

granulite formation that was related to the Charnockite-Granite Association plutonism, this latter

stage occurs as cross-cutting bodies of pyribolite (Hubbard, 1975).

1.5 Sampling area

Getterön is situated approximately 2 km northwest of Varberg town. The most abundant rock type is

charnockite, there are also large occurrences of granodiorite and granite (see Fig. 3). Garnetiferous

amphibolite, metamafite (with hypersthene), xenoliths of metavolcanic rocks and gneissic granitoids

are encountered in lesser amounts. In places, the granodiorites are altered to veined gneisses.

4

Fig. 2. Geological map of the north western part of the Varberg region.

(Modified from SGU map sheet K 105, 2008)

Legend for Fig.2 and Fig. 3.

Fig. 3. Enlargement of Getterön in Fig. 2. Legend for Fig.2 and Fig. 3.

5

Garnetiferious amphibolite is found at several localities around the Varberg region. At Getterön, two

other occurrences of this rock (described by Lundquist and Kero, 2008) are very similar to the one

sampled in this study. It forms elongated, fairly small bodies with orientation NW-SE and NE-SW.

The protolith is magmatic with a basaltic composition and the different bodies show different degrees

of deformation and alteration which suggests that there have been several events of intrusion.

Because most of the amphibolites seem to have suffered granulite facies metamorphism which

occurred between 1460 and 1420 Ma, it is probable that they are older than 1400 Ma although there

are occurrences that seem to be younger (Lundquist & Kero, 2008). The most abundant minerals (in

decreasing order) in the garnet bearing amphibolite are hornblende, garnet, pyroxene (mainly

diopside) and plagioclase. The amphibolite in this study shares these mineral proportions. There is

also quartz, biotite and opaque minerals in minor amounts. The garnets are polycrystalline, cracked

with varying grain size (~1mm to 4 cm). At Obbhult approximately 20 km east of Getterön, garnet-

amphibolites contain coarse grained bands of minerals representing high pressure granulite facies like

primary orthopyroxene and kyanite. Zircons from these formations have given U-Pb-ages of 1400

Ma (Lundquist & Kero, 2008).

Field relationships of the sampling area show veins of two types, one with smaller garnet (≤0.5 cm),

clinopyroxene and plagioclase (decreasing order) and another that mainly consists of clinopyroxene

grains (see Fig. 4-7). The latter could be related to fluid movement with the hypothesis that

hornblende existed before clinopyroxene which became stable due to decreased water pressure (high

temperatures) when CO2 entered the system by fluids (Cornell personal communication, 2011).

Supporting evidence for CO2 rich fluids would be abundance of calcite in the samples. The veins

have somewhat N-S orientation but it is not consistent. The plagioclases exhibit pressure shadow that

seems to be related to a later stress event than the veins. Abundance of both hornblende and such

large garnets is most likely reflecting different events of metamorphism, the garnets and

clinopyroxene are indicative of eclogite facies (Fig. 8).

Fig. 4. Outcrop of sampling area at Getterön. Veins of garnet and clinopyroxene with

minor amounts of plagioclase.

6

Fig. 5. Outcrop of sampling area at Getterön. The most abundant mineral in the matrix is

hornblende. Clinopyroxene and garnet compose large veins.

Fig. 6. Close up of the veins (outcrop of sampling area).

7

Fig.7. Large veines of mainly garnet (outcrop of sampling area).

Fig. 8. Garnet porphyroblasts in hornblende matrix with minor amounts of clinopyroxene

(brown-green) and plagioclase (white-yellow) that exhibit pressure shadow (outcrop of

sampling area).

8

1.6 Thermodynamics

Thermodynamics tells us about the conditions under which minerals or mineral assemblages will be

stable. When a mineralogical phase is created from another phase the change in Gibbs free energy

ΔGf describes the amount of energy that is released or consumed (Perkins, Koziol, Brady, 2012). Since

the formation or transformation of mineralogical phases is dependent on the energy in terms of

pressure and temperature, these parameters can be investigated based on ΔGf. If there are two phase

asemblages, it is always the one with the lowest total free energy that is the stable assemblage and the

other is metastable, based on thermodynamic laws (Bucher & Frey, 2002).

Metastable equilibrium occurs in assemblages when there are kinetic barriers that are not overcome.

This is the reason why there are high grade metamorphic rocks found at the surface and not only the

stable low grade rocks. Because reactions require energy to progress it is more reasonable to assume

that mineral assemblages maintain equilibrium during prograde metamorphism than during

retrograde metamorphism (Bucher & Frey, 2002). During retrograde metamorphism reaction rims

(e.g. plagioclase corona) can be formed which is an indication of disequilibrium due to the fact that

the reaction never runs through completely forming a mineral across the whole mineral instead of

only a rim on the outer part of a the crystal (Bucher & Frey, 2002).

Some tests can be used to prove that phases are not in equilibrium or with the opposite outcome,

expect that they are, for one can never prove that an assemblage is in equilibrium but can prove the

opposite. One test is to look for zonation within minerals (Spear & Peacock, 1989).

If a mineral is zoned it has no longer the same composition through the entire crystal. This implies

that the whole grain is not in equilibrium with the coexisting mineral(s) or more likely, only a certain

spot of the crystal is in equilibrium with corresponding spot of the other mineral. A common

mechanism which can create and modify zoning patterns is diffusion. Typically when garnet is zoned

it is critical to evaluate whether the rim, the interior or the core is in equilibrium with the right part of

the other mineral (Spear, 1995).

When applying thermobarometry it is of great importance to consider the mechanism of

requilibration that could occur during cooling conditions. Such mechanism implies that old

compositions in the minerals that once reflected peak metamorphic conditions could be reset so that

thermobarometric calculations from these would reflect retrogade conditions. Another crucial

requirement is to determine mineral assemblages and to evaluate whether coexisting minerals are in

chemical equilibrium (Spear & Peacock, 1989).

1.7 Element partitioning in minerals

The distribution of certain elements in a mineral is controlled by its crystal structure and prevailing

conditions in terms of pressure and temperature. This is because a certain ion size with a certain

charge is preferred in a particular crystal site which makes elements stay in or leave a mineral under

different conditions. The Fe2+

-Mg distribution between e.g. garnet and hornblende is temperature

dependant in that garnet tends to increase the Fe2+

/Mg ratio and its almandine component during

cooling conditions while hornblende gets more magnesium-rich and loses iron content (Spear, 1995).

Garnet tends to favor calcium at high pressures. When the pressure decreases and calcium is no

longer stable in the garnet, the rim breaks down to mainly Ca-plagioclase and the remaining parts are

left with lower calcium component (Bucher & Frey, 2002).

9

When applying thermobarometry using modeling applications, the partitioning of elements in the

minerals is essential for how reactions take place between these. The reactions are in turn the basis of

the calibrations of the applications. Temperature-sensitive reactions (thermometers) are exchange

reactions or solvus reactions. P-T diagrams show a steep slope when representing a temperature-

sensitive reaction (see red line in Fig. 9). Many pressure-sensitive reactions (barometers) are net

transfer reactions with a shallow slope on P-T diagrams (see red line in Fig. 9). They involve a

change in volume as one mineral phase transforms to another. A pressure-sensitive reaction can also

involve the concentration of an element in a certain mineral equilibrium with a particular assemblage.

There are also reactions that are indicative for both pressure and temperature (thermobarometers).

The thermodynamic application TWQ works with all three sorts of reactions (thermometers,

barometers and thermobarometers). TWQ uses an internally consistent thermodynamic database to

calculate pressures and temperatures while using “classical” geothermobarometry calibrations

published in the literature (Perkins et al., 2012).

2. Method

Two samples from the same locality were analyzed in this study. Optical studies were performed

using transmission and reflection microscopy. Areas where garnet is in contact with or close to

several other minerals with visible grain boundaries were chosen because these areas represent

different mineral assemblages with possible phase equilibria.

2.1 Electron Microanalysis

Mineral compositions were determined in thin sections using the Hitachi S-3400 N scanning electron

microscope (SEM) with an energy-dispersive X-ray spectrometer (EDS) at the University of

Gothenburg (Department of Earth Science), with an operating condition of 20 kV, working distance

Fig. 9. P-T diagram showing different reaction lines where red line is a

barometer, blue line a thermometer and purple line a thermobarometer.

P-T estimates in the figure are 8.4 kbar and 600°C.

10

10 mm and beam current 3.5 nA. The quantitative calibration was done using simple oxides and

checked with Smithsonian mineral standards. Backscattered electron (BSE) images were used to

distinguish the different minerals as the brightness in these images is proportional to the density of

each mineral. Samples were carbon-coated and interesting areas marked with carbon ink before being

analyzed.

Two or three sets of each mineral assemblage were studied, distributed in two or three areas of each

thin section. Equilibrium in these was tested by looking for zonation in core to rim multispot profiles

using 30 to 40 second counting livetimes. The analyses for thermobarometric calculations were taken

at the rims for the main part of the analysis; count time for these measurements was 100 sec.

2.2 Thermobarometric modeling

Three approaches was used to make quantitative estimates of metamorphic conditions for the

samples; the data used were mineral oxide compositions and number of ions, all from SEM-analyses.

Thermodynamic calculations were done using the programs Win TWQ by Berman (1991) and HbPl

1.2 by Holland and Blundy (1994). Since both samples contained hornblende, the version for TWQ

was 1.02 from Mäder (1994) with database June (1992). TWQ calculations were done including

metastable reactions. The GPT spreadsheet (Reche & Martinez, 1996) was used to calculate

temperatures for garnet-ilmenite.

Thermodynamic calculations were done using the programs Win TWQ by Berman (1991) and HbPl

1.2 by Holland and Blundy (1994). Since both samples contained hornblende, the version for TWQ

was 1.02 from Mäder (1994) with database June (1992). TWQ calculations were done including

metastable reactions. The GPT spreadsheet (Reche & Martinez, 1996) was used to calculate

temperatures for garnet-ilmenite.

3. Results

3.1 Petrography

In both samples, large garnet porphyroblasts (~5 mm) are found in a medium grained matrix of

hornblende, plagioclase, clinopyroxene, ilmenite, quartz and biotite. The minerals in the matrix are

generally subhedral to anhedral with inequigranular texture and show no preferred orientation. The

petrography shows no obvious disequilibria in general although some minerals seem to be in state of

reaction.

3.1.1 Sample DC0305

The modally dominating mineral is hornblende and occurs as the largest grains in the matrix (max 15

mm), see Fig. 10. It has equant but irregular edges and is generally distributed outside the area of

garnet and clinopyroxene. The garnets are anhedral to subhedral and have inclusions of rounded

quartz grains, plagioclase and hornblende. Plagioclase is most generally present in contact with or

near garnet but is also found further away in the groundmass. Some crystals seem to surround garnet

like a rim, it could possibly be interpreted as a corona rim. The abundance of clinopyroxene is greater

close to the garnets. Parts of it occur as clusters with intergrowths of plagioclase and quartz (Fig. 11).

Chloritization of clinopyroxene is also seen. Accessories are ilmenite, quartz and biotite.

11

Fig. 10. DC0305 showing hornblende and clinopyroxene. Hornblende crystals are

large with well defined edges in contrast to clinopyroxene in DC0305.

Fig. 11. Investigated minerals in DC0305. The elongated anhedral shape of

clinopyroxene (in this Fig) is typical for those that are found close to the garnets.

12

3.1.2 Sample DC0308

The modally dominating mineral is garnet which occurs as anhedral, cracked, generally coarse sized

(max 7 mm) grains containing inclusions of all the minerals in the matrix. Some garnets are medium

grained and contain no inclusions (Fig. 12) but the large ones contains large inclusions.

Clinopyroxene is the most abundant mineral in the matrix and the others are plagioclase, hornblende

and ilmenite (decreasing abundance). Plagioclase shows corona texture around garnets. Next to the

coronas and within these, there are worm-like shaped clinopyroxene grains (Fig. 12), these are

smaller in size than the ones further away from the garnets where they occur as medium grains in

contrast to the rest of the minerals in the groundmass which are fine grained (<1 mm). Accessory

minerals are quartz and biotite.

3.2 Geochemistry

Mineral compositions from SEM analyses were used to identify the minerals (Fig. 13) and to

investigate their homogeneity. The homogeneity within single crystals was studied for hornblende,

clinopyroxene and plagioclase by analyzing profiles from core to rim to see if the compositions were

Fig. 6. Smaller garnets (~1 mm) in DC0308.

Fig. 7. Backscattered

image of DC0308.

Plagioclase corona

rims around garnets

are distinct in this

sample, the figure

also shows the large

amount of inclusions

that are trapped

within the garnet.

Fig. 13. Backscattered image of

DC0308. Plagiclase corona rim

around garnets are distinct in this

sample, the figure also shows the

large amount of inclusions that

are trapped within the garnet.

Fig. 12. Medium sized

garnets porphyroblasts

(~1 mm) in Dc0308.

13

unchanged. Hornblende, clinopyroxene and plagioclase are all homogenous in both DC0305 and

DC0308 and show very little zonation. The homogeneity through crystals of hornblende and in

clinopyroxene can be seen in Fig.14, where representative profiles display the Fe/(Fe+Mg) for Hbl

and Ca/(Ca+Mg) for Cpx. Andesine is the dominating variety of plagioclase with An33-37 . In DC0305

there is a very subtle compositional distinction between plagioclase occurring as rims around garnets

which are slightly Ca-richer than plagioclase in the matrix (see Fig. 15).

The garnets are nearly homogenous with a slight increase of almandine and pyrope component and a

decrease in grossular at the rims. Some grains have the reverse pattern at the core but to a smaller

extent. There is neither common shape of the profiles for the small grains nor the large ones as a

group, they either show the same trend or they have linear profiles. The profile in Fig. 16 could be

interpreted as reflecting increased pressure at the core relative to the rim. The iron-magnesium ratio

is plotted for the same garnet profile in Fig.17 and suggests a decrease in temperature during growth

of the core, followed by an increase in temperature as the rest of the crystal grew. Fe/Mg increases

from the rim to the interior and decreases from point 15 towards the core. It is also possible that the

pattern displays two different scenarios, one close to the core that is a relict profile of growth zoning

and one related to diffusion towards the rim. The timing of zonation propagation is the reverse for the

two parts of the profile and is marked in the diagram.

0,660,68

0,70,720,740,760,78

0,8

0 3 6 9 12

Wt% Hbl , Cpx

Fe/(Fe+Mg)

(Ca/(Ca+Mg))

20

25

30

35

40

0 5 10

An (

%)

Plagioclase

Corona

Matrix

Fig. 14. Profiles from core (0) to rim

(10) of hornblende and

clinopyroxene displaying

Fe/(Fe+Mg) in Hbl and Ca/(Ca+Mg)

in Cpx from DC0305.

Fig. 15. Anorthite content in

plagioclase, each point represents one

crystal in DC0305. The compositions

are very similar, only the two last

minerals show a slight difference.

14

3.3 Thermobarometric modeling

3.3.1 TWQ

Five assemblages (in total) with garnet-clinopyroxene-plagioclase (qz) assemblages were analyzed

in samples DC0305 and DC0308. Reactions used for these mineral sets are:

1) 2Grs + 3aQz = 3Hd + 3An

2) 2Grs + Prp + 3aQz = 3 Di +3 An

3) Alm + 3 Di Prp + 3 Hd

0

10

20

30

40

50

60

70

0 5 10 15 20

alm

grs

prp

5

7

9

11

13

500 600 700 800 900

Pre

ssu

re (

kb

ar)

Temperature (C

)

Grt-Cpx-Pl (Qz)

Dc0305

Dc0308

Fig. 16.Garnet profile from

Dc0305 showing endmember

composition (%) from rim (0)

to core (19).

Fig. 17. Garnet profile from

Figure 16. displaying the

iron-magnesium ratio from

rim (0) to core (19).

Fig. 18. Reactions of Grt-Cpx-Pl

(Qz) in TWQ.

Fig. 19. P-T intersections from TWQ calculations. At 810°C and 9

kbar a point from Dc0305 is covered by another point.

15

Figure 18. represents thermobarometric calculations by Win TWQ software. Intersections from the

diagrams were calculated using Win INTERSX and are compiled in Fig. 19. Both samples show

nearly the same temperatures close to 800°C and pressures around 8.8 kbar except for one area in

DC0305 that reaches 12 kbar.

Garnet-hornblende-plagioclase (qz) was analyzed in five different areas in sample DC0305 and

DC0308. More reactions have been used for this assemblage to include ferric equivalents

to of amphibole endmembers (Fig. 20). The reactions are:

1) 2Grs + Prp + 18aQz + 3Prg = 3 Tr + 1) 2Grs + Prp + 18aQz + 3Prg = 3 Tr + 6An + 3Ab

2) 3Tr + 5 Alm = 5 Prp + 3 fTr

3) 4Grs + 2 Prp + 12aQz + 3Ts = 3Tr + 12An

4) 3Prg + 4Alm + 4Prp + 3fPrg

5) 3fPrg + 18 aQz + 2Grs + Alm = 3 An + 6An + 3fTr

Pressures and temperatures calculated from these range from 8.2 kbar and 677°C to 10.4 kbar and

801°C. Pressures and temperatures are on average 2.0 kbar and 62°C higher in DC0305 than in

DC0308 (see Fig. 21). This assemblage shows more scatter compared to grt-cpx-pl.

3.3.2 Hornblende-Plagioclase

The Hornblende-Plagioclase thermometer of Holland and Blundy (1994) was used to compare results

from reactions with Garnet-hornblende-plagioclase in TWQ (Fig. 13 and Fig 15/Table. 1 in

appendix). The exchange reaction used for the calibration of hornblende-plagioclase is:

Edenite + 4 Quartz = Albite + Tremolite

The precision of the thermometer is 40°C at 1-15 kbar (Holland & Blundy, 1994). Calculations were

done by HbPl 1.2 software and results are presented in Table. 1 where they are compared to the

results from TWQ. The pressure in the row for TWQ is an average of the five areas in DC0305 and

DC0308. Every temperature column represents the same spot of a sample with the same mineral

assemblage from where the analysis were taken (that were later used in both TWQ and HbPl

applications).

5

7

9

11

13

500 600 700 800 900

Pre

ssure

(kbar

)

Temperature (C

)

Grt-Hbl-Pl (Qz)

Dc0305

Dc0308

Fig. 21. P-T intersections from calculations using TWQ.

Fig. 20. Reactions of Grt-Hbl-

Pl (Qz) in TWQ.

16

HbPl gave various results related to different pressures, the ones for 10.0 kbar were closest to the

ones given by TWQ hence these are the temperatures presented in Table 1. The correspondence

between the two groups of results is good. Temperatures differ between the two applications by

9-54°C and the best estimate is 730-760°C.

Table.1. Results from HbPl and TWQ software’s. Each temperature column represents analyses from

the same spot in a sample using the same group (e.g. Grt5.1, Hbl5.1, Pl5.1 in TWQ) or pair (e.g.

Hbl5.1, Pl5.1 in HbPl) of minerals. Refrences in the Author column are sources of calibrations for the

thermometers/geothermobarometers.

Software

Author

Temperature (C°)

Pressure

(kbar)

HbPl 1.2

Holland and Blundy (1994)

785

828

731

737

782

10.0

TWQ 1.02

Kohn and Spear (1989,1990),

Graham and Powel (1984)

759

801

677

728

747

9.2

3.3.3 Garnet-Ilmenite

The geothermometer of garnet-ilmenite is based on a system with simple chemistry where the

partitioning between Fe and Mn is used to calculate the temperature. One factor that contributes to

the reliability of the thermometer is that the partitioning between Fe and Mn is independent of

pressure (Pownceby, Wall, O'Neill, 1987). The exchange reaction used in the calibration is:

1/3 Alm + Pph = 1/3 Sps + Ilm

Three areas were investigated in both samples for this mineral pair. The GPT spreadsheet was used

for the calculations of the thermometer. DC0305 gave the temperature 689°C and DC0308 gave

temperatures 707°C and 650°C.

3.3.4 Inclusions

Three mineral assemblages of garnet porphyroblasts and their inclusions were analyzed. Both garnet-

rim and garnet-core compositions were used with the inclusions because of the uncertainty about

whether the inclusions could be in equilibrium with the rim or the core of garnets. TWQ and GPT

spreadsheet were used to calculate the results which are mainly temperatures; these are compiled in

Table 2. For assemblages garnet-ilmenite and garnet-clinopyroxene-plagioclase, the same reactions

were used for the calculations as the ones used for the minerals in the matrix. Reactions for

calculations of Garnet-hornblende are number 2 and 4 of the reactions listed for garnet-hornblende-

plagiclase among the TWQ results of the minerals in the matrix.

Table. 2 shows that calculations with garnet rims give higher temperatures than those with garnet

core. The pressure of garnet core-clinopyroxene-plagioclase is 0.8 kbar higher than the pressure

calculated from garnet rim composition. The temperatures from the inclusions and garnet rims are

close to the temperatures from the matrix minerals, inclusions of garnet-hornblende and garnet-

clinopyroxene-plagioclase gave 40°C and 20°C lower than the matrix minerals in the same area of

DC0308. Garnet core-ilmenite gave at most 100°C lower temperature than calculations of garnet rim

and ilmenites from the matrix.

17

Table. 2. Results of thermobarometric calculations (by TWQ) of garnet and garnet-inclusions.

Mineral

assemblage

Temp. (C°) Grt-rim

Temp. (C°) Grt-core

Grt-Ilm 574 434

Grt-Ilm 650 521

Grt-Hbl 700 655

Grt-Cpx-Pl 767 726

Pressure (kbar)

Grt-Cpx-Pl 8.1 8.9

3.4 Metamorphic facies

The pressures and temperatures of samples DC0305 and DC0308 indicate a transition between

amphibolite facies and granulite facies and below the eclogite facies. Plotting the P-T conditions

obtained by TWQ in a P-T diagram it shows that these plot both on the granulite and the amphibolite

facies fields as on the border between the two (see Fig.22). The similar results by HbPl give the same

trend (not plotted in the figure). The mean pressure of all data from TWQ is 9.2 kbar which

corresponds to a depth of 31 km in the crust (Spear, 1995).

Fig. 22. P-T diagram of principal metamorphic facies.

Blue crosses represent results from TWQ calculations

of DC0305 and DC0308 (Modified from Spear, 1995).

18

4. Discussion

No calcite was found in neither of the samples which would contribute to the assumption of the

involment of fluid movement, inferred by field relationships.

Despite reaction rims represent nothing but an interrupted reaction and so are indicative for

disequilibrium, the plagioclases formed around the garnets were used for P-T calculations in TWQ.

The comparison between the composition of the plagioclase rims and those in the matrix shows that

it is fairly the same composition, thus using the composition from the retrograde plagioclases do not

give any different results than using the composition of a plagioclase from the matrix.

The chemical homogeneity of sample Dc0305 and Dc0308 is clear in the P-T results that are fairly

correlating between different sets of mineral assemblages, using different thermobarmetric

applications with different mineral databases. This is with exception of the results from the garnet-

ilmenite thermometer which differ with lower temperatures than the other mineral assemblages

(around 100-150°C). One probable reason for this is that the manganese content is quite low in both

the garnets and in the ilmenites. It is probable that this rock have paragenesis that are locally in

equilibrium (with garnet rim), thereby showing rather consistent P-T estimates although the extent of

this study with only two analyzed samples cannot conclude that this is the case in the rock as whole.

Based on the petrography it is suggested that this rock has undergone several metamorphic events.

This can be seen by the large garnet porphyroblasts that were possibly formed during the eclogite

facies, existing together with chlorite, hornblende and plagioclase reaction rims in the same sample.

However, results from the inclusions yielded no other P-T estimations than what is presented by the

matrix mineral assemblages and thus no traces of peak metamorphism is visible that could for

instance support eclogite facies as the pressure and temperature conditions for the formation of the

large garnets. This indicates that the investigated minerals probably have reequilibrated during the

last metamorphic event.

There are two possible scenarios for the minerals to fit in the metamorphic puzzle. One involves

increasing P-T conditions as the rock was subjected to greater depths. This would result in

breakdown of hornblende and produces garnet and sodic plagioclase (as Na is released from Hbl).

The second scenario is that the pressure and temperature were decreasing and so the last formed

minerals were hornblende and calcium rich plagioclase rims as a product of garnet breakdown (Cees-

Jan De Hoog, 2003).

The composition of plagioclase does not contribute to either sides of the hypothesis by Jan De Hoog

(2003), having end-member that is andesine with (approximately) An35. More albitic or anorthitic

compositions would give better indication of the direction of the last metamorphose. Petrography of

Dc0305 indicates that hornblende is the more stable phase in contrast to clinopyroxene that seems to

be in state of reaction (exhibiting worm-like texture and intergrowths) which in turn suggests that the

last metamorphic conditions were retrograde, with clinopyroxene as a former (stable) phase durig

earlier conditions and hornblende as the more stable, last formed phase at the last metamorphic

conditions. This is further supported by garnet profiles that shows a decrease in pressure and

temperature interpreted by the decreasing grossular component towards the rim and the increased

Fe/(Fe+Mg) through time. Based on the homogeneity of mineral compositions as inclusions and in

the matrix, it is not likely that there would be any relict traces left in the garnets. The profile in Fig.

19

16 is therefore regarded to be caused by diffusion alone, although it is not clear why the curve turns

by the last stage near the core.

According to the results from the modeling by TWQ the metamorphic facies of the rock is

somewhere between amphibolite and granulite facies (see Fig. 21). However presupposing the last

metamorphic event was retrograde with decreasing pressure, it must have progressed through the

ultimate granulite facies condition since neither orthopyroxene is apparent nor hornblende is absent

in the samples which could have proved that the conditions were strictly granulitic (Bucher & Frey,

2002). On the contrary there are large abundances of hornblende evident from field observations as in

sample Dc0305. This further supports the previous suggestion that the conditions were closer to the

amphibolitic than the granulitic facies. The boundary between the granulite and the amphibolite

facies is very uncertain (Bucher & Frey, 2002) thus it is not obvious whether conclude the conditions

as on the border between the two facies or as amphibolitic.

This part of the Eastern Segment has suffered two deformation and metamorphic events, the

Hallandian, 1400 Ma and the Sveconorwegian, 960 Ma (Lundvist & Kero, 2008). The retrograde

metamorphos of the amphibolite might be related to the Sveconorwegian time as the Western

Segment moved back to its former position between 960 and 955 Ma which caused decrease in

pressure and temperature. This is inferred by the appearance of decompressed eclogites from Ullared

area (32 km east of Getterön) which represent this event (Lindström et al., 2000). Another trace of

high pressure rocks close to the area is in Obbhult (18 km east of Getterön) where primary

orhopyroxene and kyanite are found in the bands of garnet bearing amphibolites (Lunqvist & Kero,

2008). The pressure at Obbhult never reached higher than upper-granulite facies and plagioclase were

thus stable. This implies that in the case of the amphibolite in this study, were the grossular

component has been altered to plagioclase coronas around the garnets, the pressure must have been

higher (before plagioclase was formed) than in this particular case. This concludes that we cannot

prove that the Hallandian event is was the only metamorphic event for this rock. It is therefore

plausible its metamporhic history involved additional events during later time.

Connecting single outcrops to regional metamorphic history is not an easy task. The extent of this

project can give a glimpse of the metamorphic history of the rock, however further studies needs to

be done to acquire a more complete picture.

Some remarks that limit the quality of the results in this study:

Few inclusions were analyzed and plagioclase was excluded because of total weight percent less than

98%, except for one analysis that also gave pressure estimation (assemblage grt-cpx-pl8.4, see Table.

6 in appendix). This resulted in modeling exclusively by temperature (since plagioclase is pressure

sensitive and needed for reactions that contribute to pressure estimates). No profiles were analyzed of

the inclusions to search for zonation in these.

The large number of plagioclase compositions that were investigated were mainly from DC0305,

fewer ones were analyzed in DC0308, also the spread (which was limited to two areas in the whole

sample) of investigated minerals in DC0305 could be better.

20

5. Conclusions

No calcite was found to support the hypothesis of CO2 rich fluids that could have lowered the

water pressure and made clinopyroxene stable (forming the veins in the field).

The different thermobarometric applications gave fairly coherent results; P-T estimates

suggest amphibolite to granulite facies conditions of around 800°C and 9 kbar. Local

equilibrium is most likely maintained between garnet rim and the other analyzed phases.

This rock has been subjected to even higher pressures and suffered retrograde metamorphic

conditions, supported by textural and geochemical results.

The retrograde requilibration eliminated most geochemical traces of a former metamorphic

event, which would give higher pressure other temperatures than what is seen by the results of

the inclusions.

It is possible that this retrograde event is related to the Sveconorwegian event similar to that

at the Ullared locality where decompressed eclogites have been found.

It is doubtful that the pressure of granulite facies of the Hallandian metamorphism could

explain the textural relationships in this rock, questioning if the pressure of granulite facies is

really sufficient for the formation of the large garnets that are indicative for eclogite facies.

Evidence that the Eastern Segment has been in the mantle is presented by garnet inclusions at

Borås locality, which in addition suggests an exhumation cycle with retrograde

metamorphism that is also interpreted as being connected to the Sveconorwegian event. This

supports the interpretation of a retrograde metamorphism for the studied amphibolite as the

last metamorphic event and makes the assumption of the large garnets as signs of earlier

eclogite facies plausible.

6. Acknowledgements

I would like to thank David Cornell for his help with the analysis and as a supervisor. I also

want to thank Linus Brander, Valby Schijndel and Axel Sjöqvist for help and support. Finally

I would like to thank I want to thank Stina Hallinder for supporting me during this project.

21

7. References

Åhäll, K.-I., Samulelsson, L., & Persson, P.-O. (1997). Geochronology and structural setting of the 1.38 Ga

Torpa granite; implications for charnocite formation in SW Sweden. GFF, 119 , 37-39.

Andersson, J., Söderlund, U., Cornell, D., Johansson, L., & Möller, C. (1999). Sveconorwegian (Grenvillian

deformation, metamorphism and leucosome formation in SW Sweden, SW Baltic Shield: constraints from a

Mesoproterozoic granite intrusion. Precambrian Research, 98 , 152-153.

Austin Hegardt, E., & Cornell, D.H. (2010). Pressure, Temparerature and Time Constraints on Teconic

Models for Southwestern Sweden: An exhumation model for the eclogite-bearing Eastern Segment in the

Sveconorwegian Province of the Baltic Shield. PhD thesis: University of Gothenburg, Department of Earth

Sciences.

Bingen, B., Nordgulen, O., & Viola, G. (2008). A four-phase model for the Sveconorwegian orogeny.

Norwegian Journal of Geology, 88 , 44.

Bucher, K., & Frey, M. (2002). Petrogenesis of Metamorphic Rocks. Berlin Heidelberg: Springer-Verlag.

Contstable, J. L., & Hubbard, F. H. (1981). U, Th, and K distribution in a differentioated charnockite-granite

intrusion and associated rocks from SW Sweden. Mineralogical Magazine ,44, 409-410.

Coutinho, J., Kräutner, H., Sassi, F., Schmid, R., & Sen, S. (2007). Recommendations by the IUGS

Subcommission on the Systematics of Metamorphic Rocks, Amphibolite and Granulite, SCMR. Retrieved

from http://www.bgs.ac.uk/scmr/docs/papers/paper_8.pdf 05/2/12

Johansson, L., & Eneroth, E. (2008). Metamorfos och deformation i SV Sverige -

påverkan på bergarters FeTi-mineralogi och magnetiska egenskaper Geologiska institutionen, Lunds

universitet. Retrieved from http://www.sgu.se/dokument/fou_extern/Johansson.pdf 4/20/12

Holland, T., & Blundy, J. (1994). Non-ideal interactions in calcic amphiboles and their bearing on amphibole-

plagioclase thermo. Contributions to Mineralogy and Petrology ,116, 433.

Hubbard, F. (1975). The Precambrian crystalline complex of south-western Sweden. The geology and

petrogenetic development of the Varberg Region. GFF, 97 , 223-236.

Kohn, M. J., & Spear, F. S. (1989). Empirical calibration of geobarometers for the assemblage garnet +

hornblende + plagioclase + quartz. American Mineralogist, 74 , 77-84.

Kohn, M. J., & Spear, F. S. (u.d.). Two new geobarometersfo r garnet amphibolitesow ith applications to

southeastern Vermont. American Mineralogist, 75 , 89-96.

Lidström, M., Lundqvist, J., & Lundqvist, T. (2000). Sveriges geologi från uttid till nutid. Lund:

Studentlitteratur.

Lundquist, I., & Kero, L., 2008: Beskrivning till berggrundskartan 5B Varberg NO, Sveriges Geologiska

Undersökning, K 105.

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Möller, C. (1998). Decompressed eclogites in the Sveconorwegian (-Grenvillian) orogen of SW Sweden:

petrology nd tectonic implications. Journal of metamophic Geology, 16 , 641-643.

Mohammed, Y.O., Cornell, D.H., Danielsson, E., Austin. Hegardt, E., & Anczkiewic, R. (2011). Mg-rich

staurolite and kyanite inclusions in metabasic garnet amphibolite. European. Journal of. Mineral, 23, 609-629.

Perkins, D., Koziol, A., Brady, J. (2012). Termodynamics, Science Education Resource Center (SERC),

Carleton College. Retrieved from http://serc.carleton.edu/research_education/equilibria/thermodynamics.html

03/3/12

Perkins, D., Koziol, A., Brady, J. (2012). Classical Thermobarometry, Science Education Resource Center

(SERC), Carleton College. Retrieved from

http://serc.carleton.edu/research_education/equilibria/classicalthermobarometry.html 27/5/12

Pownceby, M. I., Wall, V. J., & O'Neill, H. S. (1987). Fe-Mn partitioning between garnet and ilmenite:

experimental calibration and applications. Contributions to Mineralogy and Petrology, 97, 116-124.

Reche, J., & Martinez, F. J. (1996). GPT: An excel spreadsheet for thermobarometric calculations in

metapelitic rocks. Computers & Geosciences, 22, 775–784.

Spear, F. S. (1995). Metamorphic Phase Equilibria and Pressure-Temperature-Time Paths. Chelsea : Book

Crafters, Inc.

Spear, F. S., & Peacock, S. M. (1989). Metamorphic pressures-temmperature-time paths. Washington D.C:

The American Geophysical Union.

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23

Appendix

Appendix 1.

Table 1. P-T results of all thermobarometric applications used in this study. Numbers refer to mineral analyses in tables below.

Application Assemblage T (C°) P (kbar)

TWQ Grt-Cpx-Pl5.1 808 9,19

Grt-Cpx-Pl5.1 815 12,06

Grt-Cpx-Pl8.1 790 8,21

Grt-Cpx-Pl8.2 810 9,32

Grt-Cpx-Pl8.3 779 8,31

Grt-Cpx-Pl8.4 726 8,98 inclusions + Grt-core

Grt-Cpx-Pl8.5 767 8,11 inclusions + Grt-rim

Grt-Hbl-Pl8.11 759 9,52

Grt-Hbl-Pl5.22 801 10,44

Grt-Hbl-Pl8.11 677 8,27

Grt-Hbl-Pl8.22 728 9,05

Grt-Hbl-Pl8.33 747 8,03

Grt-Hbl8.44 665 inclusion + Grt-core

Grt-Hbl8.55 700 inclusion + Grt-rim

HbPl Grt-Hbl5.11 785

Grt-Hbl5.22 828

Grt-Hbl8.11 731

Grt-Hbl8.22 737

Grt-Hbl-8.33 782

LnKd

GPT spread sheet Grt-Ilm8.111 689 1,6

Grt-Ilm8.222 707 1,62

Grt-Ilm8.333 650 1,76

Grt-Ilm8.444 521 2,17 inclusion + Grt-core

Grt-Ilm8.555 650 1,77 inclusion + Grt-rim

Grt-Ilm5.111 434 2,53 inclusion + Grt-core

24

Appendix 2.

Table 2. Mineral analysis of DC0305. Table 3. Mineral analysis of DC0308.

Grt-Cpx-Pl5.1

Site 44,1 41,2 43,2

Grt5.1 Cpx5.1 Pl5.1

Na2O 0,12 0,65 7,47

MgO 4,55 11,39 0

Al2O3 21,08 2,11 25

SiO2 37,54 51,02 59,31

K2O 0 0,03 0,4

CaO 7,16 21,95 6,61

TiO2 0,06 0,25 0

MnO 0,95 0,1 0

FeO 29,5 12,29 0,1

Totals 100,96 99,79 98,9

Grt-Cpx-Pl5.2

Site 7,1 72,1 11,1

Grt5.2 Cpx5.2 Pl5.2

Na2O 0,11 0,69 6,81

MgO 3,48 10,91 0

Al2O3 20,62 2,02 26

SiO2 36,68 50,14 56,98

K2O 0 0 0,39

CaO 11,78 21,46 8

TiO2 0,11 0,2 0

MnO 0,57 0,12 0

FeO 25 12,75 0,17

Totals 98,36 98,28 98,35

Grt-Cpx-Pl8.1

Site 40,2 34,2 36,2

Grt8.1 Cpx8.1 Pl8.1

Na2O 0,09 0,62 6,94

MgO 3,86 10,9 0

Al2O3 20,57 1,83 26,06

SiO2 36,39 50 57,92

K2O 0 0,03 0,18

CaO 7,23 21,38 7,8

TiO2 0 0,19 0

MnO 1,17 0,18 0

FeO 28,96 12,9 0,29

Totals 98,27 98,03 99,19

Grt-Cpx-Pl8.2

Site 20,3 16,3 45,3

Grt8.2 Cpx8.2 Pl8.2

Na2O 0,12 0,57 6,82

MgO 3,94 11,07 0

Al2O3 20,42 1,49 25,46

SiO2 36,27 50,33 57,97

K2O 0 0,03 0,22

CaO 8,22 21,47 7,45

TiO2 0 0,2 0,04

MnO 0,82 0,1 0

FeO 28,58 13,26 0,17

Totals 98,41 98,53 98,13

Grt-Cpx-Pl8.3

Site 3,1 1,1 4,1

Grt8.3 Cpx8.3 Pl8.3

Na2O 0,11 0,54 6,65

MgO 4,47 12,02 0

Al2O3 21,09 1,44 26,48

SiO2 37,55 52,26 57,92

K2O 0 0,03 0,26

CaO 7,59 22,3 8,31

TiO2 0 0,18 0,06

MnO 0,93 0,12 0

FeO 29,09 12,18 0,18

Totals 100,83 101,07 99,85

25

Grt-Hbl-Pl8.11

Site 44,2 44,2 61,2

Grt8.11 Hbl8.11 Pl8.11

Na2O 0,1 1,65 7,29

MgO 3,59 9,47 0,11

Al2O3 20,34 11,73 24,32

SiO2 36,13 41,59 60,63

K2O 0,04 0,75 0,67

CaO 7,07 11,03 5,82

TiO2 0,08 1,19 0,25

MnO 1,48 0,18 0

FeO 29,22 17,78 0,91

Totals 98,05 95,37 100

Grt-Hbl-Pl8.22

Site 10,3 14,3 11,3

Grt8.22 Hbl8.22 Pl8.22

Na2O 0,07 1,57 7,55

MgO 3,69 9,18 0

Al2O3 20,76 10,4 25,61

SiO2 36,2 41,72 59,84

K2O 0,02 1,04 0,91

CaO 7,93 11,33 5,7

TiO2 0 1,85 0,05

MnO 1,02 0,06 0,05

FeO 28,64 18,72 0,4

Totals 98,34 95,88 100,1

Grt-Hbl-Pl8.33

Site 16,1 13,1 14,1

Grt8.3 Hbl8.33 Pl8.33

Na2O 0,16 1,79 6,96

MgO 4,32 9,07 0

Al2O3 21,19 11,17 26,21

SiO2 37,76 41,5 58,73

K2O 0 1 0,2

CaO 7,58 11,53 7,95

TiO2 0 2,16 0

MnO 0,91 0,13 0

FeO 29,88 19,02 0,2

Totals 101,8 97,36 100,25

Grt-Hbl-Pl5.11

Site 22,1 4,1 9,1

Grt5.11 Hbl5.11 Pl5.11

Na2O 0,09 1,93 6,93

MgO 3,82 8,96 0,07

Al2O3 21,07 11,03 25,71

SiO2 37,71 40,9 58,73

K2O 0 1,03 0,35

CaO 9,66 11,08 7,27

TiO2 0,09 2,11 0

MnO 0,79 0 0

FeO 28,01 19,2 0,08

Totals 101,26 96,36 99,15

Grt-Hbl-Pl5.22

Site 7,1 13,1

Grt5.1 Hbl5.22 Pl5.2

Na2O 0,11 2,01 6,81

MgO 3,48 8,6 0

Al2O3 20,62 11,13 26

SiO2 36,68 40,74 56,98

K2O 0 1,21 0,39

CaO 11,78 11,62 8

TiO2 0,11 2,36 0

MnO 0,57 0,05 0

FeO 25 20,01 0,17

Totals 98,36 97,85 98,35

Table 4. Mineral analysis of DC0305. Table 5. Mineral analysis of DC0308

...fffrfffffffroffrDDC0305

26

Grt-Cpx-Pl8.4

Site 6,1 11,1 11,1

Grt8.3 Cpx8.4 Pl8.4

Na2O 0,08 0,55 6,69

MgO 3,35 11,9 0

Al2O3 21,28 1,92 26,1

SiO2 37,72 52,31 58,23

K2O 0 0 0,27

CaO 10,06 22,32 8,02

TiO2 0,06 0,2 0

MnO 1,27 0,13 0

FeO 27,99 12,58 0,24

Totals 101,82 101,91 99,57

Grt-Cpx-Pl8.5

Site 16,1 11,1 11,1

Grt8.3 Cpx8.4 Pl8.4

Na2O 0,16 0,55 6,69

MgO 4,32 11,9 0

Al2O3 21,19 1,92 26,1

SiO2 37,76 52,31 58,23

K2O 0 0 0,27

CaO 7,58 22,32 8,02

TiO2 0 0,2 0

MnO 0,91 0,13 0

FeO 29,88 12,58 0,24

Totals 101,8 101,91 99,57

Table 6. Mineral analysis of DC0308

representing inclusions and the

entrapping garnet. Grt-Cpx-Pl8.4

represents garnet gore and Grt-Cpx-Pl8.5

represent garnet rim

Table 7. Mineral analysis of DC0308

representing inclusions and the

entrapping garnet. Grt-Hbl-Pl8.4

represents garnet gore and Grt-Hbl-

Pl8.5 represent garnet rim

Grt-Hbl8.4

Site 6,1 9,1

Grt8.3 Hbl8.4

Na2O 0,08 1,75

MgO 3,35 9,82

Al2O3 21,28 11,17

SiO2 37,72 42,36

K2O 0 1,01

CaO 10,06 11,42

TiO2 0,06 1,92

MnO 1,27 0,08

FeO 27,99 18,06

Totals 101,82 97,6

Grt-Hbl8.5

Site 16,1 9,1

Grt8.33 Hbl8.4

Na2O 0,16 1,75

MgO 4,32 9,82

Al2O3 21,19 11,17

SiO2 37,76 42,36

K2O 0 1,01

CaO 7,58 11,42

TiO2 0 1,92

MnO 0,91 0,08

FeO 29,88 18,06

Totals 101,8 97,6

27

Ta

Table 8. Mineral analysis of DC0305 representing inclusions and the entrapping. Grt-

Ilm8.111 represents garnet core and Grt-Ilm8.222 represents garnet rim.

Grt-Ilm5.111 Grt-Ilm5.222

Site 119,2 115,2 Site 123, 2 115,2

Grt5.1 Ilm5.111 Grt5.1 Ilm5.111

Element Wt% No of ions Wt% No of ions Element Wt% No of ions Wt% No of ions

Na 0 0 0,1 0,01 Na 0,09 0,018 0,1 0,007

Mg 1,51 0,294 0,5 0,03 Mg 2,7 0,515 0,5 0,031

Al 11,22 1,965 0,16 0,01 Al 11,35 1,951 0,16 0,009

Si 17,54 2,951 0,04 0 Si 17,88 2,953 0,04 0,002

Ca 9,26 1,092 0 0 Ca 5,74 0,664 0 0,000

Ti 0,06 0,006 29,73 0,94 Ti 0,04 0,004 29,73 0,941

Mn 1,14 0,098 0,15 0 Mn 0,76 0,064 0,15 0,004

Fe 19,6 1,658 39,15 1,06 Fe 22,95 1,906 39,15 1,062

O 40,63 12 31,67 3 O 41,39 12 31,67 3,000

Totals 100,95 101,49 Totals 102,9 101,49

Grt-Ilm8.333

Site 31,2 25,2

Grt8.333 Ilm8.333

Element Wt% No of ions Wt% No of ions

Na 0,09 0,019 0,09 0,006

Mg 2,49 0,496 0,43 0,027

Al 10,91 1,956 0,03 0,002

Si 17,1 2,945 0,06 0,003

K 0 0,000 0 0,000

Ca 5,89 0,711 0,03 0,001

Ti 0,05 0,005 29,34 0,950

Mn 0,85 0,075 0,23 0,006

Fe 21,64 1,874 38 1,055

O 39,69 12,000 30,97 3

Totals 98,72 99,18

Grt-Ilm8.111 Grt-Ilm8.222

Site 37,2 36.2 Site 5,3 4,3

Grt8.111 Ilm8.111 Grt8.2 Ilm8.222

Element Wt% No of ions Wt% No of ions Element Wt% No of ionsWt% No of ions

Na 0,07 0,015 0,14 0,009 Na 0,06 0,012 0,15 0,010

Mg 1,9 0,375 0,28 0,017 Mg 2,44 0,478 0,28 0,018

Al 10,99 1,953 0,22 0,012 Al 11,23 1,981 0 0,000

Si 17,23 2,941 0,03 0,002 Si 17,34 2,939 0,06 0,003

K 0 0,000 0 0,000 K 0,03 0,004 0 0,000

Ca 8,79 1,051 0 0,000 Ca 6,71 0,797 0,02 0,001

Ti 0,06 0,006 30 0,948 Ti 0 0,000 29,8 0,946

Mn 0,65 0,057 0,21 0,006 Mn 0,74 0,064 0,24 0,007

Fe 19,64 1,686 38,97 1,055 Fe 21,13 1,801 39,39 1,072

O 40,05 12,000 31,74 3,000 O 40,33 12 31,57 3

Totals 99,38 101,59 Totals 100,02 101,51

Table 9. Mineral analysis of DC0308.

Table 10. Mineral analysis of DC0308.

28

Appendix 3

Cpx

All results in compound%

Site 73,1

Spectrum Na2O MgO Al2O3 SiO2 K2O CaO TiO2 MnO FeO Totals

1 0,66 11,37 1,65 50,6 0 21,39 0,17 0,08 12,3 98,22

2 0,71 11,44 1,76 50,58 0 21,21 0,21 0 12,86 98,77

3 0,67 11,12 1,78 50,49 0,05 21,55 0,22 0,09 13,21 99,18

4 0,74 11,21 1,9 50,61 0 21,25 0,2 0,14 12,93 98,98

5 0,66 11,03 2,13 50,2 0,06 21,15 0,12 0 13,08 98,44

6 0,72 11,14 2,03 50,1 0 21,3 0,29 0,12 13,14 98,84

7 0,72 11,18 1,8 50,41 0 21,74 0,21 0,21 12,71 98,97

8 0,75 11,1 2,03 50,5 0 21,1 0,28 0,17 12,95 98,88

9 0,63 11,05 1,98 50,53 0 21,45 0,19 0 12,98 98,81

10 0,66 11,31 2,01 51,73 0 21,16 0 0 13,75 100,61

Grt-Ilm8.444 Grt-Ilm8.555

Site 6,1 10,1 Site 16,1 10,1

Grt8.3 Ilm8.444 Grt8.3 Ilm8.444

Element Wt% No of ions Wt% No of ions Element Wt% No of ionsWt% No of ions

Na 0,06 0,012 0,07 0,005 Na 0,12 0,025 0,07 0,005

Mg 2,02 0,390 0,49 0,030 Mg 2,61 0,505 0,49 0,030

Al 11,26 1,960 0,06 0,003 Al 11,21 1,952 0,06 0,003

Si 17,63 2,949 0,06 0,003 Si 17,65 2,953 0,06 0,003

K 0 0,000 0 0,000 K 0 0,000 0 0,000

Ca 7,19 0,843 0,03 0,001 Ca 5,42 0,635 0,03 0,001

Ti 0,04 0,004 30,13 0,949 Ti 0 0,000 30,13 0,949

Mn 0,99 0,085 0,17 0,005 Mn 0,7 0,060 0,17 0,005

Fe 21,75 1,830 38,97 1,053 Fe 23,23 1,955 38,97 1,053

O 40,87 12,000 31,82 3,000 O 40,86 12,000 31,82 3,000

Totals 101,81 101,8 Totals 101,8 101,8

Table 11. Table 8. Mineral analysis of DC0308 representing inclusions and the entrapping. Grt-

Ilm8.444 represents garnet core and Grt-Ilm8.555 represents garnet rim.

Table 12. Mineral analysis of clinopyroxene profile (core-rim) in DC0305 (from Fig. 14).

29

All results in weight%

Hbl

Spectrum Na Mg Al Si K Ca Ti Mn Fe O Total

1 1,49 5,17 5,93 18,67 0,97 8,02 1,37 0,07 14,9 39,07 95,8

2 1,49 5,27 5,93 18,65 0,96 7,95 1,39 0 15,08 39,12 96,01

3 1,28 5,09 5,83 18,68 0,95 7,95 1,33 0,06 14,94 38,82 95,07

4 1,4 5,24 6,07 18,88 0,96 7,99 1,39 0 14,58 39,33 95,95

5 1,39 5,22 5,91 18,71 0,96 8,06 1,39 0,14 14,65 39,07 95,6

6 1,38 5,19 6,11 18,95 1 7,92 1,35 0 14,82 39,43 96,22

7 1,45 5,21 5,73 18,86 0,96 8,06 1,3 0 14,58 38,97 95,29

8 1,44 5,31 5,84 18,98 0,99 8,05 1,4 0,07 14,85 39,44 96,43

9 1,35 5,38 5,82 18,88 0,96 7,98 1,31 0,09 14,83 39,23 95,98

10 1,26 5,4 5,88 19,43 1,12 8,14 1,25 0,09 13,95 39,69 96,28

Grt

All results in weight%

Spectrum Mg Ca Mn Fe

1 2,36 5,6 0,73 22,54

2 2,31 6,56 0,53 22,24

3 2,25 7,02 0,64 21,43

4 2,16 7,63 0,58 20,62

5 2,04 8,3 0,56 20,08

6 2,03 8,8 0,49 19,69

7 1,96 8,98 0,55 19,2

8 2 9,02 0,54 19,66

9 1,91 9,2 0,59 19,21

10 1,94 9,13 0,51 19,26

11 1,87 9,23 0,59 19,43

12 1,81 9,26 0,56 19,39

13 1,76 9,39 0,65 19,38

14 1,74 9,32 0,62 19,41

15 1,94 9,13 0,51 19,26

16 1,87 9,23 0,59 19,43

17 1,81 9,26 0,56 19,39

18 1,76 9,39 0,65 19,38

19 1,74 9,32 0,62 19,41

Table 13. Mineral analysis of hornblende profile (core-rim) in DC0305 (from Fig. 14).

Table 14. Mineral analysis of garnet profile (rim-core) in DC0305 (from Fig. 16 and Fig. 17).

30