Tectonophysics 500 (2011) 20–33

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Tectonophysics

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Multiscale magmatic cyclicity, duration of pluton construction, and the paradoxicalrelationship between tectonism and plutonism in continental arcs

Michel de Saint Blanquat a,⁎, Eric Horsman b,1, Guillaume Habert a,2, Sven Morgan c, Olivier Vanderhaeghe d,Richard Law e, Basil Tikoff b

a CNRS – University of Toulouse, LMTG, 14 Avenue Edouard-Belin 31400 Toulouse, Franceb Dept. of Geology and Geophysics, Univ. of Wisconsin – Madison, 1215 W Dayton St., 53706, Madison, WI, USAc Department of Geology, Central Michigan University, Mount Pleasant, MI, 48859, USAd G2R, Géologie et Gestion des Ressources Minérales et Energétiques, BP 239, 54506 Vandoeuvre-les-Nancy, Francee Dept. of Geological Sciences, Virginia Tech. Institute, Virginia, 24061 Blacksburg, USA

⁎ Corresponding author.E-mail addresses: michel@lmtg.obs-mip.fr (M. de Sa

olivier.vanderhaeghe@g2r.uhp-nancy.fr (O. Vanderhaeg1 Now at: Dept. of Geological Sciences, East Carolina2 Now at: Laboratoire Central des Ponts et Chaussées

0040-1951/$ – see front matter © 2010 Elsevier B.V. Adoi:10.1016/j.tecto.2009.12.009

a b s t r a c t

a r t i c l e i n f o

Article history:Received 31 January 2009Received in revised form 7 December 2009Accepted 20 December 2009Available online 4 January 2010

Keywords:PlutonMagmaPulseTectonicsFabricPluton emplacement

The close relationship between crustal magmatism, an expression of heat dissipation, and tectonics, anexpression of stress dissipation, leads to the question of their mutual relationships. Indeed, the low viscosity ofmagmas and the large viscosity contrast between magmas and surrounding rocks favor strain localization inmagmas, and thenpossible “magmatic” initiation of structures at awide range of scales. However, newdata about3-d pluton shape and duration of pluton construction perturb this simple geological image, and indicate someindependence between magmatism and tectonics. In some cases we observe a direct genetic link and strongarguments for physical interactions between magmas and tectonics. In other cases, we observe an absence ofthese interactions and it is unclear how magma transfer and emplacement are related to lithospheric-platedynamics. A simple explanation of this complexity follows directly from the pulsed, incremental assembly ofplutons and its spatial and temporal characteristics. The size of each pluton is related to amagmatic pulsation at aparticular time scale, and each of these coupled time/space scales is related to a specific process: in small plutons,we can observe the incremental process, the building block of plutons; in larger plutons, the incremental processis lost, and the pulsation, which consists of a cycle of injections at different timescales, must be related to thecomposition and thermal regime of the source region, itself driving magmatic processes (melting, segregation,and transfer) that interact with tectonic boundary conditions. The dynamics of pulsed magmatism observed inplutonic systems is then a proxy for deep lithospheric and magmatic processes. From our data and a review ofpublished work, we find a positive corelation between volume and duration of pluton construction. The larger apluton, the longer its construction time. Large/fast or small/slow plutons have not been identified to date. Oneconsequence of this observation is that plutonic magmatic fluxes seem to be comparable from one geodynamicsetting to another and alsoover various geologic time spans. A secondconsequenceof this correlation is that smallplutons, which are constructed in a geologically short length of time, commonly record little about tectonicconditions, and result only from the interference between magma dynamics and the local geologic setting.The fast rate ofmagma transfer in the crust (on the order of cm/s) relative to tectonic rates (on the order of cm/yr)explain why the incremental process of pluton construction is independent of – but not insensitive to – thetectonic setting. However, in large plutonic bodies, which correspond to longer duration magmatic events,regional deformation has time to interact with the growing pluton and can be recorded within the pluton-wallrock structure.Magma transfer operates at a very short timescale (comparable to volcanic timescales),which canbe sustainedover variableperiods, dependingon the fertility of themagma source region and its ability to feed thesystem. The fast operation of magmatic processes relative to crustal tectonic processes ensures that the formercontrol the system from below.

int Blanquat), horsmane@ecu.edu (E. Horsman), guillaumhe), rdlaw@vt.edu (R. Law), basil@geology.wisc.edu (B. TUniversity, 101 Graham Building, Greenville, NC, 27858,, 58Bd Lefebvre, 75732 Paris Cedex 15, France.

ll rights reserved.

© 2010 Elsevier B.V. All rights reserved.

e.habert@lcpc.fr (G. Habert), morga1ss@cmich.edu (S. Morgan),ikoff).USA.

21M. de Saint Blanquat et al. / Tectonophysics 500 (2011) 20–33

1. Introduction

At the plate scale,magmatism (i.e. all processes associatedwith theformation, evolution, and transfer of magma) is directly controlled bylithospheric-plate dynamics, in the sense that plate divergence andconvergence are responsible for the modification of the P, T, and Xconditions leading to partial melting. This relationship is exemplifiedby the production of oceanic crust associated with basaltic tholeiiticmagmatism at divergent plate boundaries and by the production anddifferentiation of continental crust linked to calc-alkaline andperaluminous magmatism at convergent plate boundaries. At theregional scale, numerous studies on plutons of various ages haveshown that their location and internal structure are correlated withsurrounding regional structures, and consequently seem to becontrolled by tectonics (i.e. regional-scale deformation in responseto lithospheric plate motion). Consequently, granitic plutons arecommonly used in tectonic studies to reconstruct the geodynamicevolution of continental crust. The principal source of information isthe structure of pluton–wallrock systems, whose evolution iscontrolled by the regional stress regime, the local geologic setting(geometry and thermal structure), and the dynamics of magmainfilling. The structure of pluton–wallrock systems then allows us tostudy the interactions and the individual characteristics of bothtectonic and magmatic processes during emplacement.

This close relationship between crustal magmatism, an expressionof heat dissipation, and tectonics, an expression of stress dissipation,leads to the question of their mutual relationships. Indeed, the lowviscosity of magmas, and consequently the sharp viscosity contrastbetween magmas and surrounding rocks, favor strain localization inmagmas, and thus the possible “magmatic” initiation of structures at awide range of scales (Tikoff and Saint Blanquat, 1997; Bons et al.,2008).

However, somenewdata and ideas challenge this simple geologicalimage, and indicate some independence between magmatism andtectonics. For example, analysis of the 3-d shape of plutons fromvarious tectonic settings has shown that the majority are tabular tofunnel-shaped and that their shape evolves according to a power–lawrelationship, typical of systems exhibiting scale-invariant behaviour(McCaffrey and Petford, 1997; Cruden, 1998; Petford et al., 2000). Aconsequence is that the construction of plutons is controlled by a selforganization process of magmatic origin, irrespective of the tectoniccontext. Another example is provided by recent data on duration andrate of pluton construction, which show that some plutons areconstructed in less than 100,000 years (Saint Blanquat et al., 2001;Saint Blanquat et al., 2006; Michel et al., 2008), a duration whichprecludes any significant intervention and recording of syn-plutonicregional deformation during pluton construction. Thus, on the onehand we observe a direct genetic link, and some strong arguments forphysical interactions betweenmagmas and tectonics. Yet, on the otherhand,we also observe an absence of these interactions, as it is not clearhow magma transfer and emplacement are related to lithospheric-plate dynamics. In this paper,we describe how the recently recognizedpulsed, or incremental, growth of plutons will help us resolve thisapparent paradox.

The origins of ideas developed in our paper include: (1) pioneeringwork demonstrating that magma intrusion and tectonic rates donot operate at the same time scales (e.g., Paterson and Tobisch,1992; Nyman et al., 1995); (2) the observation that some plutonsmay have an internal record which is only interpretable in terms ofemplacement-related processes injection and magma chamberprocesses) and has nothing to do with external regional deformationduring construction (Sylvester et al., 1978; Cruden et al., 1999;McNulty et al., 2000; Saint Blanquat et al., 2001; Harper et al., 2004;Barbey et al., 2008); and (3) work showing that pluton shapes seem tobe controlled by internal processes which are independent ofchemical composition and crustal tectonic regime (McCaffrey and

Petford, 1997; Cruden, 1998; Petford et al., 2000; Cruden andMcCaffrey, 2001).

In this paper, we first briefly summarize and then compare a seriesof petrostructural studies we have conducted on plutons of varioussizes, constructed in various tectonic settings, but all related to thesame geodynamic setting of arcmagmatism. These intrusions include:(1) the Black Mesa pluton in the Henry Mountains, Utah, of Oligoceneage and with no associated regional deformation; (2) the Mono Creekand Papoose Flat plutons, and Tuolumne intrusive suite in the SierraNevada andWhite-Inyos Mtns of California of late Cretaceous age andtranspressional setting; and (3) the Tinos pluton in the Cycladicislands, Greece, of Miocene age and extensional setting. Based onthese comparisons, we discuss the relations between the nature of thestructural record and the tectonic setting of the studied plutons. Weconclude that the incremental process of pluton construction is thesame for all these plutons, with similar characteristics irrespective oftheir tectonic setting, age, and composition. We also show that thefirst parameter to check before interpreting the nature of the plutonicrecord is the total duration of pluton construction, which is itselfdirectly related to the final pluton volume.

2. The plutonic structural record, a definition

The structural development of plutons is classically described asbeing recorded by the internal layering and fabrics. Layering can bedefined as “the combination at any scale of layers differing bycomposition or texture” (Barbey, 2009). Fabric is formed by theshape preferred orientation (SPO) of minerals, and is defined by itsorientation, shape, and intensity. Following Barbey (2009), threeprocesses are involved in the formation and evolution of the structuralrecord within a growing pluton: (1) injection processes (incrementalgrowth, magma channelized flow, mingling, mixing, etc…); (2)magma chamber processes (hydrodynamic processes, crystal settling,etc…); and (3) tectonic processes (forces applied to the boundaries ofthe magmatic bodies inducing a deformation). In other words, anystructural plutonic record can be interpreted as: (1) a record ofdeformation, either related to emplacement dynamics (injection) or toregional deformation, and/or (2) a magmatic record related tomagmadifferentiation during cooling of magma pulses.

3. The construction of plutons, historical perspective

The classical view of pluton construction consists of a dichotomybetween “forceful” or “active” type, including doming, diapirism andballooning, versus “passive” or “permitted” type, including stoping,cauldron subsidence and associated sheeting. Permitted types wereconsidered to characterize magma emplacement in the upper crust, incontrast with forceful types that were considered to work at greaterdepths (Pitcher, 1979). In addition, although the presence of astructural control on magma transfer and emplacement has longbeen recognized, this was primarily based on observed relationshipsbetween pre-existing structures and magma ascent, rather than oninteraction between evolving tectonic structures and magma transfer.Hutton (1988) first questioned the interaction betweenmagmatic andtectonic forces by hypothesizing that ‘active’ emplacement occurswhen the magma infilling rate is greater than the rate of tectonicopening, and ‘passive’ emplacement when it is less, and examining alltypes of tectonic setting, including transcurrent, extensional, andcontractional. Hutton proposed that the combination of these twoprocesses could generate the variety of emplacement mechanismsobserved in different plutons. A consequence is that most plutonscould be considered syntectonic. This idea was addressed in adiscussion on the so-called syntectonic paradigm by Karlstrom(1989), who stated that all granitoids are syntectonic in a broadsense, as they are emplaced into crust experiencing regionaldeformation, and that many and perhaps most of the granitoids are

Fig. 1. Graphic representation of the incremental process of pluton construction; seetext for explanation. Top: the incremental mechanism of pluton construction. Bottom:different intrusion histories for the same pluton thickness, showing that one plutoncould correspond to very contrasting intrusion histories, and that one averaged rate ofconstruction could correspond to many and very different intrusion histories.

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syntectonic in a strict sense, because there is melt present duringregional deformation. Paterson (1989) challenged this view with thesuggestion that only a small percentage of plutons are syntectonic inthe strictest sense, citing as evidence the contrasting rates of plutonemplacement, cooling and regional deformation, and arguing for amore rigorous use of the term syntectonic.

Since the 1980–1990s, with the help of the development of newmethods of fabric quantification (Ellwood and Whitney, 1980;Bouchez, 1997; Launeau and Robin, 2005; Gaillot et al., 2006), andafter the theoretical and experimental validation of the dike model formagma transport (Lagarde et al., 1990; Clemens and Mawer, 1992;Petford et al., 1993; Clemens, 1998; Menand, 2011), a large numberof publications have studied at various scales the nature of the linkbetween pluton construction and tectonics. These studies considermagmatism–tectonic links ranging from the plate scale (e.g., Glazner,1991; Grocott et al., 1994; Brown and Solar, 1998; Saint Blanquat et al.,1998 and Benn et al., 2001 among many others), through the regionalscale(e.g. Brun and Pons, 1981; Bussel and Pitcher, 1985; Castro, 1987;Brun et al., 1990; Hutton and Reavy, 1992; D'Lemos et al., 1992;Vigneresse, 1995; Druguet and Hutton, 1998; Gleizes et al., 1997;Tikoff and Saint Blanquat, 1997; Archanjo et al., 1999; Brownand Solar,1999; Vigneresse et al., 1999 and Grocott and Taylor, 2002 amongmany others), to the pluton scale (Hutton, 1988; Paterson and Tobisch,1988; Gapais, 1989; Hutton et al., 1990; Hutton and Ingram, 1992;Tikoff and Teyssier, 1992; Karlstrom et al., 1993; Cruden, 1998;Barroset al, 2001;Weinberg et al., 2004, and Grocott et al., 2009 amongmanyothers). One important consequence of these studies was therecognition that magmatism and pluton construction can stronglyinfluence the rheological behaviour of the lithosphere (see forexample Hollister and Crawford, 1986; Davidson et al., 1992, 1994;Klepeis et al., 2003). The question of the ultimate control on thetectono-magmatic systems then arrived with work on plutons andshear zones in northeast Brazil (shear zone-controlled magmaemplacement or magma-assisted nucleation of shear zones; Neveset al., 1996), and in the Mesozoic Sierra Nevada Batholith of California(see below, and Saint Blanquat et al., 1998). The “room problem” ofhow space is made in the crust for large volumes of intruding magmawas also largely resolved by rethinking old ideas about emplacement(magmas pushing their wallrocks, laterally, upward —roof uplift, ordownward—floor depression; Cruden, 1998; Acocella, 2000; Crudenand McCaffrey, 2001), and taking into account all the components ofthe regional and local displacement/deformation fields, includingtranslation, which is not recorded by rock internal strain (Tikoff et al.,1999). The analysis of 3-d pluton shape by McCaffrey and Petford(1997) and Petford et al. (2000) has shown that the observed tabularshape of many plutons is best explained by a self organization process,irrespective of the tectonic context or composition of magmasinvolved. This period ended with the recognition of the essential roleof deformation at all stages of magmatism (melting, segregation,transport, and emplacement), and the promotion of a new image ofgranitemagmatism as a rapid and dynamic process that can operate attimescales of less than 105 years, irrespective of tectonic setting(Petford et al., 2000).

Much recentworkhas focused on examining the discontinuous andepisodic growth of plutons.While this subject is not a new idea (see forexample Pitcher and Berger, 1972; Hardee, 1982;Wiebe, 1988;Wiebeand Collins, 1998), recent field and theoretical work has appreciablyimproved our understanding of these processes by documenting thespatial and temporal scales of the incremental assembly of batholithsand individual plutons (Cruden and McCaffrey, 2001; Saint Blanquatet al., 2001; Saint Blanquat et al., 2006; de Silva and Gosnold, 2007;

Fig. 2. Synthesis of previously obtained data; explanation and references are in the text. All sof the plutons. (B) Maps: mineralogical zonation at pluton scale; stereos: poles of magmaticthe maps for clarity but gradual on the field. (D) Maps of the AMS lineation trajectories; stepoles.

Lipman, 2007; Menand, 2008; Bartley et al., 2008; Vigneresse, 2008;Horsman et al., 2009; Miller et al., 2011). Combined with considerableimprovement in knowledge about the timescales of magmaticprocesses due to radiogenic isotope techniques and chemical diffusionmethods (Coleman et al., 2004; Matzel et al., 2006; Miller et al., 2007;Walker et al., 2007; Turner and Costa, 2007; Michel et al., 2008; Costa,2008), the new data initiated vigorous debate on upper crustalplutonic systems, the relation between magma chamber and plutondynamics, and the relation between plutonism and volcanism(Glazner et al., 2004; Bachmann et al., 2007; Annen, 2009; Annen,2011). Additionally, important questions were raised about theentire system at the crustal scale, particularly themechanisms and rateof crustal growth (Ducea, 2001; Kemp et al., 2006; Hawkesworth andKemp, 2006; Kemp et al., 2007; DeCelles et al., 2009).

In Fig. 1, we present a model of howmany plutons are constructed,with – to recall the active/forceful versus passive/permitted terminol-ogy – an ‘active’ part of emplacement (magma pulse intrusion) and a‘passive’part duringwhich the previously intrudedmagmapulsesmaybe deformed at geologically ‘normal’ strain rates during cooling.Whenconsidering rates of pluton construction, it is essential to recognize thedifference between the instantaneous construction rate, that is the rateof magma infilling during the injection of one pulse, and the averagedconstruction rate,which is the simple ratio between pluton volume andtotal duration of pluton construction. This averaged rate takes intoaccount all the repose times between injections.Major challenges nowin the study of the plutonic processes are: (1) to identify andcharacterize the geologic marker(s) allowing reconstruction of thegrowth history of a pluton, and (2) to better quantify the rates ofpluton construction.

tereograms are equal area, lower hemisphere, Kamb contour (2σ). (A) Real relative sizelayering. (C) Map of microstructures; transition from one type to another are sharp onreos: AMS lineation. (E) Maps of the AMS foliation trajectories; stereos: AMS foliation

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With the help of previously completed petrostructural studies ofplutons of different sizes located in various tectonic settings, the aims ofthis paper is to present relevant data and ideas about these challenges,and to explore the geological implications of the observed episodicgrowth of many plutons.

4. The dataset

Wepresent below summaries of some of our previouswork, sortedby increasing pluton volume. These petro-structural studies areprimarily based on fieldwork, anisotropy of magnetic susceptibility(AMS) analysis, microstructural observations, and preliminary petro-logical and geochemical analyses. The detailed geology of the studiedplutons can be found in the cited references, and a synthesis ofstructural and microstructural data is given in Fig. 2.

Black Mesa pluton (Habert and Saint Blanquat, 2004; de SaintBlanquat et al., 2006; Horsman et al., 2009): the small Black Mesapluton is a satellite of the larger Mount Hillers intrusion in the HenryMtns (Utah, USA) on the Colorado Plateau. No regional deformationwas active during construction of this Oligocene pluton at 3 kmdepth. The pluton is a porphyritic microdiorite and has a volume ofapproximately 0.6 km3. The intrusion is broadly cylindrical in shape,but important details provide evidence of its construction history. Thewestern margin of the intrusion is laccolithic, with upward rotatedbedding. The eastern margin, where the horizontal wall rocks aredisplaced upward ∼200 m by a syn-magmatic vertical fault, is abysmalith, or fault-bounded, piston-like inflated laccolith. The internalstructure of the Black Mesa pluton is characterized by sub-horizontalmagmatic layering, defined by sharp variation in the diorite texture.Internal contacts are sub-horizontal, with compositional layeringmainly recognized in vertical magnetic susceptibility profiles, a weakvertical zonation in the content of someminor and trace elements, andsub-horizontal internal structures. The combination of these featuressuggests that the internal contacts are primary, and due to discontin-uous construction of the pluton, and not due to secondary in-situprocesses. Consequently, we infer that the pluton was constructed bythe amalgamation of sequentially injected horizontal sheet-likemagma pulses. The foliation is sub-horizontal except along themargins where it is concordant to the steeply dipping pluton contacts.The controlling factor for the foliation orientation is then the evolving3-d geometry of the pluton. Themineral lineations at the upper contactare orthogonal to lineations throughout the exposed interior of theintrusion. We suggest that the fabric at the contacts is a record of thestrain due to the relative displacement between the intruding magmaandwallrock, while the fabric away from the contacts is a record of thestrain within the flowing magma during infilling. Both in the field andin thin section, magmatic textures are observed everywhere in thepluton, except in the outermost few centimetres of the diorite at thepluton-host rock contact, where cataclastic deformation is observed.All the structural, textural and petrologic data (1) argue for a shortduration between intrusion of the earliest and latest magma batches,and (2) a short duration between the initial intrusion and the fullcrystallisation of the pluton, but (3) preclude the presence of anymagma chamber process such as crystal settling at the level ofemplacement. One-dimensional thermal modeling of the pluton,constrained by texture observations, suggests that emplacement ofthe pluton was a very rapid event, with a maximum duration on theorder of 100 years, which requires a minimum upward verticaldisplacement rate of the wall rocks immediately above the pluton onthe order of 1 m per year.

Tinos pluton (St Blanquat et al. submitted): located in the Aegeansea in Greece, the Tinos massif is a composite granodioritic plutonemplaced in the Cycladic blueschist unit of Tinos island during themid-Miocene (14–15 Ma; Brichau et al, 2007) at 10–12 km depthduring protracted regional NE–SW extension. The pluton is a semi-elliptical body, with its long axis parallel to the NE–SW regional

stretching direction. The surface exposure is probably only the SWhalf of a larger pluton, its NE part being located beneath the AegeanSea due to late activity on NW–SE striking, NE–verging normalfaults. Thus, it is possible to examine a vertical cross section of themassif from its SW/bottom part to its NE/upper part. The totalminimum vertical exposure through the pluton is 530 m. The totalpluton thickness is not directly observable, but scaled cross sectionssuggest a total thickness of approximately 1–2 km. The total plutonvolume is then approximately 10–40 km3 (or 20–80 km3 includingthe submarine part). Microstructural analysis indicates the upperpart of the pluton was affected by ductile deformation, while thelower part remains “undeformed” and exhibits magmatic texture.The pluton displays internal contacts and layering marked by thejuxtaposition of granitic layers with different grain size and/ormineralogy, or by biotite-enriched layers. These features can betraced across large outcrops. Magmatic layering is typically subhorizontal and has a shallower dip than the foliation. The pluton wasmainly emplaced by pushing its wallrocks upward, as exemplified bywallrock deflection at the exposedmargin and by concentric internalfoliations. The lineation defines amagmatic NW–SE trending patternin the lower/SWmagmatic part of the pluton, and a NE–SW trendingpattern in its upper/NE ductilely deformed part. Our observationssuggest complex interactions between magma intrusion and theregional extensional deformation, and document the verticalmigration of the brittle/ductile transition during regional extension.However, some parts of the structural record, such as the NW–SEmagmatic lineation at the lowest exposed structural level of thepluton, are not compatible with the regional deformation and maymagma infilling. The duration of construction of the Tinos pluton isnot constrained to date.

Papoose Flat pluton (Law et al., 1992; Morgan et al., 1998; SaintBlanquat et al., 2001): located in the White-Inyo Range of California,east of the Sierra Nevada batholith, this pluton is commonly cited as aclassic example of a ‘forcibly’ emplaced pluton (Sylvester et al., 1978),although the relative importance attributed to magmatic versustectonic processes in controlling the structural evolution of the plutonhas been controversial (Paterson et al., 1991; Law et al., 1992). Re-examination of this Late Cretaceous (83 Ma) pluton has shown thatit is an inclined and internally zoned tabular structure, assembled bythe vertical stacking of successive magma sheets at a crustal depth ofabout 12 km. The pluton is exposed over a 16 km by 8 km area, andcharacterized by more than 1700 m of topographic relief and verticalexposure. In map view the pluton is roughly elliptical in shape, withthe long axis trending WNW–ESE. A narrow ‘tail’ or ‘apophysis’ ofgranite protrudes at the eastern end, and is topographically andstructurally located below the main body of the pluton. The totalvolume is estimated to be between 100 and 200 km3. The Papoose Flatpluton displays a compositional range from granite in the eastern partof the pluton to granodiorite in thewestern part. Systematic analysis ofthin sections reveals a ring-shaped distribution pattern of mineralogyand microstructures centered on the core of the pluton. Thepreservation of compositional zoning within minerals, together withthe presence of internal magmatic contacts within the pluton,indicates that these mineral and microstructural distribution patternsare syn-emplacement, and are not the result of in-situ sub-solidusreequilibration associated with metasomatism, and can therefore beinterpreted as evidence of incremental pluton assembly. A preliminaryexamination of mineral chemistry by microprobe analysis has shownonly slight variations in mineral composition across the pluton,possibly indicating a limited range in whole-rock chemistry, inagreement with petrographic field observations. The foliation definesan elongate WNW–ESE dome-shaped pattern trending sub-parallelto the pluton's long axis and which, in map view, is not alwaysconcordant with pluton margins. Lineations are sub-horizontal togently plunging and trend mainly NE–SW in the center of the pluton,and NNW–SSE in the westernmost third of the pluton. The

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microstructures define an elongate WNW–ESE trending concentricmap distribution with a domainal transition from magmatic micro-structures in the centre of the pluton to high temperature solid-statedeformation features everywhere else, except near the pluton'ssidewalls and roof where a thin rind of intense gneissification isrecorded. The center of the pluton with its magmatic microstructureslocally contains either a NE–SW or less commonly NNW–SSE trendinglineation that must be synchronous with magma emplacement. In thewestern third of the pluton the NNW–SSE trending lineation isubiquitously recorded in all threemicrostructural domains, suggestingthat lineations in the magmatic and solid-state domains are alsosynchronous. This lineation is parallel to the grain-shape stretchinglineation in the surrounding aureole rocks. These data indicate thatsolid-state fabrics near the pluton's sidewalls and roof (previouslysuggested to be associated with regional deformation; Paterson et al.,1991) cannot be chronologically separated from fabrics in the centre ofthe pluton which appear to be related to magma flow duringemplacement. Initial pluton formation involved magma ascent in avertical WNW-striking feeder dike, which was arrested at a strati-graphically controlled mechanical discontinuity in the overlyingCambrian metasedimentary rocks, leading to formation of a SW-dipping sill. Subsequent sill inflation, accompanied by horizontalinfilling from the feeder dike at the base of the sill, resulted indeformation and vertical translation of earliermagmapulses, and localraising of the sill roof, facilitated by thermalweakening as thewall rocktemperatures progressively rose during emplacement of successivemagma pulses. Cooling from the roof of the pluton downward resultedin cessation of vertical inflation on the W side of the pluton, andpromoted lateral expansion toward the NE and floor depression belowthe eastern part of the pluton. We have been unable to document anyregional scale structures (e.g. equivalent to similar age syn-plutonicstrike-slip shear zones in the Sierra Nevada Batholith to the W, seebelow) that may have controlled emplacement of the Papoose Flatpluton.However, this does not preclude the likelihood that the countryrocks were subjected to a regional deformation at this time, as shownby evidence of Late Cretaceous deformation on the White Mountainshear zone and Santa Rita shear system,which constitutes thewesternborder of theWhite-Inyo range (Bartley et al., 2007; Sullivan and Law,2007). Simple thermal modeling, constrained by microstructural andthermobarometric data (Nyman et al., 1995; Saint Blanquat et al.,2001), indicates that the total duration time for emplacement of thepluton was on the order of 100,000 years.

Mono Creek pluton (Saint Blanquat and Tikoff, 1997; Tikoff andSaint Blanquat, 1997; Saint Blanquat et al., 1998; Tikoff et al., 1999):the late Cretaceous (86 Ma; Coleman and Glazner, 1997) Mono Creekpluton is one of the youngest plutons within the Sierra Nevadabatholith. This porphyritic granodiorite / monzogranite covers anarea of ∼600 km2 and at least 1800 m of vertical relief, providing aminimum volume estimate of ∼1000 km3. The depth of emplacementis to date unconstrained, but hypo-volcanic textures found in thenorthern part of the pluton suggest an upper crustal depth (1–5 km?), confirmed by preliminary Al-in-hornblende geobarometry.Detailed thin section analysis shows that the pluton ismineralogicallyzoned, from biotite–hornblende–sphene in the border to biotite–hornblende to biotite only in the center of the pluton. One of themoststriking characteristics of the pluton is its textural homogeneity;except along the margins, where sheeted complexes and internalcontacts exist. No enclaves and no internal structures have beenobserved in the main central part of the pluton. Nevertheless, rareinternal contacts exist between the three mineralogical facies, andshow that the biotite-only facies (similar to the Johnson Porphyryfacies in the Tuolumne Intrusive suite, see below; Titus et al., 2005)constitutes the youngest magma pulse, and the biotite–hornblende–sphene facies the oldest. The observations of the sheeted complexalong the margins and successives mineral facies with sharpboundaries constitute field evidence for incremental assembly of

the Mono Creek pluton. Fabrics define a sigmoidal pattern of foliationand lineation consistent with syn to late magmatic dextral shearwithin the Rosy Finch Shear Zone, part the ∼200 km long LateCretaceous Sierra Crest Shear Zone system. We have observed acontinuous evolution between two end-member geometries: theinferred earliest fabrics, located along pluton margins, are character-ized by magmatic east–west sub-vertical foliations and sub-verticallineations, while the latest fabrics, in the center of the pluton, arecharacterized by a solid-state fabric with N–S sub-vertical foliationsand sub-horizontal lineations. The transition between these two end-member fabrics is always progressive. We propose this fabricevolution characterizes a progressive switch from emplacement-dominated strain to regional-deformation-dominated strain. The E–W foliation orientation of the first batches of magma occurs at a highangle to the inferred regional finite strain (the dominant NNW–SSEverticalfoliation suggests a principal shortening axis oriented WSW–

ENE and horizontal); this orientation could be due to over-pressuredmagma opening accommodation space for itself. Thus, the firstbatches of melt may have initiated the shear zones that parallel thepluton, rather than being intruded passively between them. Thisprovides a good example of how magmatically induced strike-slippartitioning may occur. Subsequently, the eastern bulge of the plutonforcefully intruded 8 km toward the NE, pushing aside older magmasand pre-existing wall rocks. This localized forceful intrusion wasapparently caused by an increase in the rate of magmatic infillingrelative to the steady-state rate of regional strike-slip motion. Finally,the presence and cooling of this NE bulge locked the northern shearzone and triggered initiation of the Rosy Finch Shear Zone (RFSZ)coeval with the last pulses of magma emplacement. The RFSZconnects the two original shear zones located on the sides of thepluton, facilitating continued dextral strike-slip movement duringthe solidification and cooling of the pluton. Magmatic foliation andlineation are rotated into parallelismwith the shear zone boundaries.The duration of pluton construction is estimated to be on the order of1–2 m.y., and is constrained with both geochronology and platekinematics (Tikoff and Saint Blanquat, 1997).

Tuolumne Intrusive Suite (Habert, 2004; Tikoff et al., 2005; Tituset al., 2005; unpublished data): located in the central part of the SierraNevada batholith, this spectacularly exposed plutonic complex hasbeen the subject of extensive debate (e.g. BatemanandChappell, 1979;Kistler et al., 1986; Bateman, 1992; Coleman et al, 2004; Glazner et al.,2004; Zak and Paterson, 2005; Burgess and Miller, 2008; Gray et al.,2008; Solgadi and Sawyer, 2009; and Johnson and Glazner, 2009,among others). Individual plutons within the Tuolumne IntrusiveSuite (TIS) are nested and characteristically elongated NNW in mapview, and range in composition from granodioritic older plutons toleucogranitic younger plutons. Based on Al-in-hornblende barometry,these plutonswere intruded at upper crustal depths (∼1–3 kbar; Agueand Brimhall, 1988). The suite is exposed over an area of about1200 km2, and its thickness is estimated at a minimum of 2 km(maximum vertical relief) and at a maximum 10 km (based on gravitydata; Oliver, 1977). The suite's volume is estimated at between 2400and 12,000 km3. The individual plutons constituting the suite are, fromolder to younger, the Kuna Crest granodiorite, the Half Domegranodiorite, the Cathedral Peak granite, and the Johnson porphyry,constitute approximately 15%, 30%, 50% and 5% of the total volumerespectively. The internal structure of the TIS is complex. Each plutonhas an internal structure which shares similar characteristics with theMono Creek pluton, including internal textural homogeneity, sheetedmargins and rare internal contacts locally crosscut by the fabric, whichis mainly magmatic except along some margins. Our field and AMSmeasurements document a vertical WNW–ESE magmatic foliation,with more NW–SE strike toward pluton contacts and a more E–Worientation in the pluton center, especially for the Cathedral Peakpluton. The magmatic lineation is steeply plunging toward the NW inthe western part and toward the SE in the eastern part of the suite. In

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the Cathedral Peak pluton, the fabric define a dextral sigmoid, likein the Mono Creek pluton (see above), but here the shear zones arelocated along the borders of the plutons and the tectonicallyoriented fabrics are along pluton margins, especially the easternmargin (see Tikoff et al., 2005), and not in the middle as observedin the Mono Creek. We propose that there is a transition in the TISbetween fabrics which record an emplacement-dominated strain(more E–W fabrics) and fabrics that record a regional-deformation-dominated strain (more NW–SE fabrics). The total duration ofconstruction of the TIS is about 8–10 m.y. (Coleman et al., 2004).Individual plutons within the suite have shorter durations ofconstruction, with a maximum of about 4 m.y. for the Half Domegranodiorite. The existence of a repose time without magmainjection is suggested by the presence of mapable gradual or sharpcontacts between individual plutons and also by textures suggest-ing the presence of remelting in rocks in the old/cold side of someinternal contacts, for example in the Half Dome close to the contactwith the Cathedral Peak (Habert, 2004). But these field-basedcriteria for a discontinuous magma injection are also questioned byrecent petrological and geochronological data (Coleman et al.,2004; Gray et al., 2008; Johnson and Glazner, 2009) suggesting apetrological continuum without significant time gap betweenindividual mapped “plutons”.

5. Significance of the plutonic record in the studied examples

We now use these plutons as a basis for generalizations about thenature of the plutonic record preserved across a wide range of spatialscales and in awide range of tectonic settings. This broad dataset allowsus to consider several topics. First, we evaluate whether the plutonicrecord effectively preserves evidence of tectonic setting. Second, weexamine relationships between the nature of the plutonic record andpluton volume. Finally, we use the conclusions of the two previousanalyses to consider the different types of information that can bereliably inferred from the plutonic record as pluton volume increases.

5.1. Relation between the plutonic record and tectonic setting

Several patterns emerge from examination of our data in the lightof the regional tectonic setting active during pluton construction.

In the case of transpression (TIS and MCP), the foliations arevertical, and define a sigmoidal pattern in the horizontal plane, ingeneral agreement with the transpressional context; but dependingon their location, foliations may be either concordant or discordantrelative to pluton–wallrock contacts and to the regional foliationtrend. The lineations show a progressive change in orientation fromvertical to horizontal, and a close relationship is recorded betweentheir plunge and their trend. The NNW–SSE lineations are subhor-izontal and parallel to the regional syn-magmatic deformation in thewallrocks. The map distribution of microstructures shows a correla-tion between microstructure and fabric orientation, with solid-statelineations parallel to the regional lineation, and a horizontal zonationof microstructures.

In the extensional case (TI), the foliations are sub-horizontal anddefineaflat dome. Because of the involvementof the top of thepluton ina regional detachment, they define a sigmoid in the vertical plane, andare either concordant or discordant depending on location. Thelineations are horizontal and show a bimodal orientation distributionwith no clear progressive transition between the NE–SW and NW–SEend members, although the main NE–SW trend is parallel to regionalsynplutonic deformation. Here also, the fabric pattern is only partiallycompatible with the regional context. The map distribution of micro-structures shows a correlation between microstructure and fabricorientation, with solid-state lineation parallel to the contemporaneousregional lineation, and a vertical microstructural zonation.

In the case of plutonism in the absence of regional tectonicdeformation (BM), and the case where timing relationships betweenplutonism and regional deformation are uncertain (PFP), the plutonfoliation pattern has a domal shape, and is subparallel to the contact.Foliations are concordant at the pluton scale but discordant at theregional scale. The lineation pattern is complex and heterogeneous atthe pluton scale, which we interpret as a record of the history ofinternal strain during pluton construction. The map distribution ofmicrostructures shows an absence of correlation between micro-structure and fabric orientation, and a systematic development ofsolid-state deformation at the pluton margins that becomes increas-ingly important with greater depth of emplacement.

When the fabric pattern and the microstructural zonation areparallel to the pluton margins (BM and PFP), the pluton structuralrecord is clearly linked to pluton construction and the pluton containsessentially no record of contemporaneous regional deformation. Thissituation may arise from an effective absence of regional deformationduring pluton construction, as found in theHenryMountains study. Analternative explanation is necessary when it is obvious from othergeologic arguments that the area is subjected to a regional deforma-tion during pluton growth, as in the case of the Papoose Flat plutonexample. One explanation is that the spatial distribution of tectonicdeformation and magmatism does not “exactly” coincide. Anotherexplanation is that the duration of themagmatic event is too short, andthe cooling rate of the magma too fast, to allow the recording of asignificant part of the regional deformationwithin the growing pluton.

An interaction between regional deformation and the constructionof a pluton can be indentified when the fabric pattern and micro-structural zonation are parallel or partly parallel to the contemporane-ous regional structural trend (TI, MCP, and TIS). However, the fact thatthe orientation of the fabric is not always compatible with the regionalsyn-magmatic deformation suggests that inmany cases, thefinal plutonstructure is not completely controlled by or transposed into the regionaldeformation. In fact, when a record of the syn-plutonic regional defor-mation is identifiablewithin the internal structure of a pluton, remnantsof construction processes such as infilling may also be present, asobserved in all studied plutons, including the largest ones.

5.2. Relation between the plutonic record and pluton volume

The previous analysis strongly suggests that one pertinent param-eter to examine when considering these data is the final volume of thepluton. We note that the smallest studied plutons (BM, TI, and PFP)show a domal shape and are mostly regionally discordant. In contrast,the largest plutons or suite of plutons (MCP and TIS) are commonlyelongate in map view and more or less regionally concordant. Theseobservations suggest that as pluton volume increases, the tectonichistory recorded within the pluton increases. In other words, a smallpluton has less possibility than a large pluton to record information onsyn-construction regional tectonic activity. Consequently, the internalrecord of pluton constructionmay be partly or totally erased, dependingon the location and intensity of the tectonic overprint, and also on thepresence and intensity of secondary magma chamber processes.

It could be argued that the concordant nature of the fabricobserved in large plutons is an artifact of sampling, as in small plutonswhere we have more samples per unit of surface area. Thus therelatively low density of data used for fabric analysis in a large plutonmay not record the heterogeneity that would be apparent with moredata. However, this argument is contradicted by studies demonstrat-ing that fabric orientation, from centimetre to kilometre scales, is nottypically scale dependant (see Olivier et al., 1997).

To summarize our observations, the 3-d shapes of the studiedplutons provide a better record of syn-plutonic regional deformation forlarge plutons. Accordingly, the spatial variability of the internalstructure increases as pluton volume decreases. In small plutons, thefabric is heterogeneous, and is due to the history of magma injection. In

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large plutons the fabric pattern ismore homogeneous, but shows only apartial tectonic control. Large plutons commonly have both magmaticand solid-state microstructures and the solid-state deformation may bethe result of regional deformationormagma injection, dependingon thecooling rate and the evolution of the thermal structure during plutonconstruction. Small plutons also show a transition between magmaticand solid-state microstructures, but the solid-state deformation isclearly the result of the cooling of the intrusion margins during plutongrowth. Emplacement mechanisms of large plutons contain evidencefor ‘active’ intrusion due to pulse injection, followed by ‘passive’straining due to regional deformation both between and during pulseinjection. In all plutons, the ‘active’ intrusion can produce a magmati-cally induced local ‘tectonic-like’ deformation, such as the spectacularmargin deformation on the west side of the PFP. Features like these arepreferentially preserved in small plutons.

5.3. Magmatic episodes during pluton construction

Such studies of the 3-d geometry, composition, internal structure,andmicrostructure allowus topropose amodel for thehistory ofmagmaintrusion within each studied pluton or group of associated plutons.

The Black Mesa pluton is very homogeneous, and we have foundno field evidence for separating the pluton into different intrusionepisodes. The successive magma injections have the same size and thesame composition, and the texture suggests a rapid cooling.

The Tinos pluton is a composite pluton with two main facies, acentral large granodiorite facies constructed by the amalgamation ofpetrographically similar magma pulses, that are surrounded by smallmarginal leucogranites, which are younger. This may indicate twomagmatic episodes with very different volumes.

Our model for construction of the Papoose Flat pluton involves twomain stageswith slightly different chemical composition, oneassociatedwith roof uplift and producing the spectacular deformation along thewesternmargin of the pluton, and one associatedwith lateral expansionand floor depression. This change in emplacement mechanism mayindicate the presence of two main episodes of magma intrusion,separated by a repose time, in order to account for cooling of the upperpart of the pluton which in turn induced locking of roof uplift.

The structural and compositional homogeneity of the Mono Creekpluton indicate protracted magma intrusion, in the form of successivepulses, as indicated by the mineralogical zonation and by sheetedcomplexes along plutonmargins. But the presence of a bulge on its NEside indicates that this process was interrupted by a phase of moreintense magmatic activity, either because of an increase in theinjection rate and/or an increase in the injection volume.

For the Tuolumne Intrusive Suite, the debate rests on the questionof the existence of a large and dynamic magma system during itsconstruction, and on the relationship between mapable magmaticunits and intrusive events (Coleman et al., 2004; Glazner et al., 2004;Zak and Paterson, 2005; Burgess and Miller, 2008; Gray et al., 2008;Solgadi and Sawyer, 2009; Johnson and Glazner, 2009). In a recentstudy, Gray et al., (2008) found that map units, i.e. the plutonsconstituting the suite, record parts of a single petrological continuumrather than distinct intrusive phases, and that the textural differencesthat define the units probably reflects thermal evolution of the systemduring cooling rather than distinct intrusive events. As the thermalevolution of this kind of arc system should be magmaticallycontrolled, we think the interpretation is sustainable that each plutonof the TIS corresponds to a period of protracted magmatic activity,with similar characteristics as the MCP, and separated by a reposetime. Therefore, the contact between two plutons may be either sharpor gradational, and have different relationshipwith the internal fabric,depending on the cooling rate during the repose time, which itselfdepends on the local 3-d geometry of all intrusions. However, in theTIS (and other large plutons), the size and initial 3-d geometry ofindividual injections are to date precisely unknown, as well as the

duration of repose times between the main injection episodes.Consequently, the definition of what we call “pluton” is still an openquestion, particularly in a batholithic setting.

In each of our case studies, the main space-making mechanism iswallrock translation, vertically toward the surface (roof uplift, allstudied plutons), or downwards toward the Moho (PFP), but alsolaterally (PFP,MCP, TIS). This deformation ismainly due tomagmapush,as clearly shown by the BM, TI and PFP cases. But the orientation of themagmatic fabric in the large ‘syntectonic’ MCP pluton and TIS suite,which is E–Wand vertical and also not compatiblewith or controlled bythe syn-plutonic regional strain, shows that this mechanism is presentin all plutons whatever the spatial and temporal scales.

6. Synthesis: multiscale magmatic cyclicity

In all settings and in plutons of all sizes we have observed aninternal textural homogeneity associated with a more or lesspronounced petrological zonation and/or internal contacts andmagmatic layering showing spatially rapid textural change, whichsometimes corresponds with associated mineralogical changes. Theseobservations strongly suggest pluton construction by successiveinjections of pulses of magma. The textural homogeneity may bedue to the emplacement of pulse n before the complete solidificationof pulse n-1. However, even if pulse n-1 has the time to completelycrystallize before the injection of pulse n, the texture could behomogeneous because of remelting or textural aging due to thenumerous heating and cooling cycles induced by this magma pulsing(Habert, 2004; Johnson and Glazner, 2009; Miller et al., 2011). Thecritical control is then the cooling condition of each pulse. Whenmappable, these geologic markers can be interpreted as evidence forcontacts between successive pulses of magma, more or less smoothedand transposed by younger intrusion, deformation events, or magmachamber processes. These features may not represent true ‘isochrons’,or ‘emplacement time-lines’, but they are probably not very far fromit. This process of successive magma pulse injection is thus thefundamental process underlying pluton construction.

Consideration of all the above data concerning pluton structuralrecord, pluton volume, and duration of pluton construction, and theirinterpretation in terms of relationships between the dynamics ofmagmatic and tectonic processes, leads to the conclusion that plutonsize is closely tied to the time required for pluton assembly (Fig. 3). Thisapparently trivial observation indicates that the incremental process ofpulse injectionhas roughly the same characteristics (frequency, volume,and rate) for all plutons in each setting. To date, in arcs, we do not knowany example of large and very rapidly emplaced plutons (more than∼1000 km3 in less than 100,000 years), or small and very slowlyemplaced plutons (less than ∼100 km3 in more than 100,000 years). Italso appears that each pluton size is related to magmatic pulsation at aparticular time scale independent of the regional tectonic context. Thus,the observed pulsation has a different significance at each time/spacescale. In small plutons, it is the incremental process, the building blockofplutons. In larger plutons, the incremental process is lost, and theobservedpulsation consists of a cycle of injections atdifferent timescales(the ‘episodicity’ of Pitcher, 1979). The origin of this pulsation overlonger periods of time must be related to lithology and thermal regimeof the upper mantle–lower crust region, itself driving magmaticprocesses (melting, segregation, and transfer) in interactions withtectonic boundary conditions (e.g. Cruden, 2006).

7. Discussion

7.1. Validity of our database and comparison with other plutons

The plutons described here are not exceptional cases and, in fact,we view each of them as representative of a certain type of pluton. Forexample, the PFP is representative of many other “ballooning” plutons

Fig. 3. Evolution of pluton construction with time, from geochronological data were available (Coleman et al., 2004 for the TIS), and from our petrostructural data and thermalmodelling (see text). This figure illustrates the multiscale cyclicity of plutonic activity, from the incremental process of pulsed injection in the smallest plutons (BM), to the longermagmatic episodes of the largest plutons and suites of plutons (PFP, MCP and TIS); see text for more explanation. The Tinos pluton is not represented in this figure because of theabsence of constraints on its duration of construction kc Kuna Crest pluton, hde equigranular Half Dome pluton, hdp porphyric Half DOme pluton, cp Cathedral Peak pluton, jpJohnson Porphyry; hb hornblende, sph sphene, bi biotite.

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(Sylvester et al., 1978; Paterson et al., 1991; Law et al., 1992; Nymanet al., 1995; Morgan et al., 1998; Saint Blanquat et al., 2001), likeFlamanville (Brun et al., 1990), Ardara (Vernon and Paterson, 1993;Morgan, 1995; Vernon and Paterson, 1995; Molyneux and Hutton,2000), and Cannibal Creek (Bateman, 1985a, 1985b; Davis, 1993,1994; Godin, 1994). The question asked by these different authors isthe same for all these plutons: what are the respective contributionsof magmatic and tectonic processes in the plutonic record? Theanswers we have arrived at for the PFP may be appropriate for theother plutons, but the determination of the duration of construction ofthese plutons are essential to interpret their plutonic record. Similarly,the large plutons or intrusive suites (MCP and TIS) share similarcharacteristics with many other arc-type large plutons, like otherCretaceous Sierran plutons (e.g., Dinkey Creek and Mount Givensplutons; Cruden et al., 1999; McNulty et al, 2000), the Panafricantranspressive plutons in Brazil (Archanjo et al., 1999) or Africa (Ferréet al., 1998), or Variscan transpressive plutons in western Europe(Gleizes et al., 1997). The unique aspect of the data we discuss isconsideration of plutons, such as the Henry Mountains examples,which were emplaced in the absence of regional deformation. Theseintrusions constitute key case studies that allow us to studymagmaticprocesses without tectonic interference, and document the initialstages of pluton growth (Horsman et al., 2009).

Exceptions to our assumption of the increasing tectonic nature ofthe plutonic record as pluton volume increases certainly exist. Forlarge granitic plutons in arc settings, these exceptions are commonly

due to the effective absence of regional deformation during plutonconstruction or the localization of the pluton in a quiet tectonic area,as in the case of the Jurassic Eureka–Joshua Flat–Beer Creek (EJB)pluton in eastern California (Morgan et al., in prep.) or the MountGivens granodiorite in the Sierra Nevada batholith (McNulty et al.,2000). For small plutons showing a significant tectonic control, likethe small plutons in the Dolbel batholith (Pons et al., 1995; Pupieret al., 2008), we must first ensure this inprint was acquired duringpluton construction. Then, maybe particular emplacement conditions(higher P and/or T) could explain a slower cooling rate and a longer“magmatic life” for the pluton.

7.2. The nature of the plutonic structural record

As stated in the beginning of this article, any plutonic recordmay beinterpreted in two ways: (1) as a record of deformation, either relatedto emplacement dynamics (injection) or to the regional deformation,and/or (2) as a magmatic record related to magma chamber processesacting during cooling of successive magma pulses.

A basic observation is that depending on the individual pluton, none,only one, or both types of record may be observed. The prominence ofone or another type of record is strongly dependent on the cooling rateof the system. Fast cooling rates favor preservation of the record ofinjection processes. In contrast, slow cooling rates allow deformation,transposition, or the complete ereasingof the injection record, and favorinitiation of magma chamber processes and interference between the

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growing “magmatic” pluton and the regional deformation, if present.The cooling rate itself is linked to the thermal structure of the crust,which, in magmatic arcs, is directly controlled by the geometry, thefrequency and the volume of magma batches (Barton and Hanson,1989). Cooling rate is therefore directly controlled by the history andgeometry ofmagma injection. Thedynamicsofmagma infilling,which issource-controlled,will thendetermine the nature of the plutonic record.This is in agreement with our general assumptions concerning theimportance of constraining the duration of construction in interpretingthe nature of the plutonic record. All things being equal, small/rapidlyconstructed plutons generally have faster cooling rates than large/moreslowly constructed plutons.

7.3. The timescales of pluton construction

Our studies have shown that the duration of pluton constructioncan vary by orders of magnitude during a single tectonic event, andthat the duration of construction is correlated at first order to plutonvolume. This is confirmed by the very precise geochronological dataobtained recently on the Tuolumne Intrusive suite (N2500 km3, 8 m.y.,

Fig. 4. Compilation of available data on duration and rates of pluton construction; see text foElba island (Rocchi et al, 2002), 3 - Papoose Flat (St-Blanquat et al, 2001), 4 - Emerald lake (Cal, 2002), 7 - Tuolumne intrusive suite (Coleman et al, 2002), 8 - Scuzzy (Brown & McClellanDinkey Creek (Petford et al, 2000), 12 -Mnt Givens (Petford et al, 2000) , 13 - SocorromagmaHualca Hualca volcano (Pritchard & Simons, 2002), 16 - Empereur Mnts (Shaw, 1985), 17 - UnGeysers plutonic complex (Schmitt et al, 2003), 20 - Bergell pluton (from Oberli et al, 2004),del Paine (Michel et al, 2008), 24 - APVC (de Silva and Gosnold, 2007), 25 - Aleutian Island(Matzel et al, 2006), 28 - Tenpeak (Matzel et al, 2006), 29 - Manaslu (Annen et al, 2006), 30 -32 - volcanism in a: oceanic arcs; b: continental arcs (White et al, 2006), 33 - Uturuncu vo

Coleman et al., 2004), the Mount Stuart (1200 km3, 5.5 m.y.) andTenpeak (400 km3, 2.6 m.y.) intrusions (Matzel et al., 2006), and theTorres del Paine granitic pluton (between 100 and 200 km3,90,000 years; Michel et al., 2008).

In order to compare our data with the published literature on thesame subject, we have made a compilation of all available data on theduration of pluton construction and compared these data withcorresponding data on pluton volume when available (Fig. 4). Wehave sorted the data based on tectonic setting, and have includedcurrently growing plutons detected by geophysical methods. Datacomparing ancient with currently growing volcanic systems are alsoshown. The primary observations from this compilation are as follows:

(1) We find a positive correlation between volume and duration ofpluton construction. As discussed previously, the larger a pluton,the longer its construction time. Big/fast or small/slow plutonshave not been identified to date. The direct consequence is thatplutonic magmatic fluxes seem to be comparable from onecontext to another and also over various geologic time spans. Thisis of fundamental importance and confirms that deep magmaticprocesses like melting and segregation, controlled both by mantle

r explanation; 1 - Black Mesa (Habert et St-Blanquat, 2004; St-Blanquat et al., 2006), 2 -oulson et al, 2002), 5 - Mono Creek (St-Blanquat et al, 1998), 6- Half Dome (Coleman etd, 2000), 9- Tinos (St-Blanquat et al, in prep), 10 - Bald Mtn (Petford et al, 2000) , 11 -body (Fialko et Simons, 2001), 14 - Syowa Sinzan (Minakami et al., 1951), 15 - Lazufre &zen volcano (Nakada &Motomura, 1999), 18 - Tenpeak pluton (Matzel et al, 2006), 19 -21 - Salmi complexes (Amelin et al, 1997), 22 - Lastarria (Froger et al, 2007), 23 - Torresarc (Jicha et al, 2006), 26 - Stuart Mtn batholith (Walker et al, 2007), 27 - Mnt StuartPX1 pluton (Allibon et al, this vol.), 31 - Southern Rocky Mtn volc. field (Lipman, 2007),lcano; a: long term; b: actual (Sparks et al., 2008).

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and crust fertility and boundary conditions (e.g. age and rate of thedowngoing oceanic plate in subduction systems), are the control-ling processes of pluton formation in the middle and upper crust.

(2) We observe an absence of correlation between duration andrate of pluton construction and the tectonic context, whichagain indicates that the elementary controlling process ismagmatic (pulse intrusion).

(3) We observe a weak tendency for time averaged constructionrates to be faster in small plutons than in large plutons. Asdiscussed above, this is linked to the existence of a characteristiccyclicity timescale that depends on pluton size. This cyclicitymay be due to the existence of magmatic episodes, which areseparated by longer repose times in large plutonic systems.

(4) In the available dataset, the range of time averaged plutonconstruction rates covers 3 orders of magnitude, from 10−1 to10−4 km3yr−1 (or approximately 1 to 10−3 m3 s−1). Thisvariation does not seem to be explained by the processesassociated with construction of plutons. Further work shouldexplore the interactions between magmatic and geodynamicprocesses located below the level of pluton emplacement, andparticularly the link(s) between themagmatic productivity andthe changes in the boundary condition of the system.

(5) A strong correlation exists between data on ancient andmodern plutonic systems, which validates our results andinterpretations.

(6) Finally, we note a similarity between plutonic and volcanicrates, in both ancient and currently active systems. This mustbe considered in the light of on-going debate concerning thelink between volcanism and plutonism, and whether largeopenmagma chambers exist or not, both at the present day andin the geologic past (e.g. Wiebe, 1988; Robinson and Miller,1999; Barnes et al., 2001; Miller and Miller, 2002; Wiebe et al.,2002; Metcalf, 2004; Glazner et al., 2004; Bachmann et al.,2007; Annen, 2009; Annen, 2011).

8. Conclusion

We find a positive correlation between volume and duration ofpluton construction. The larger a pluton, the longer its constructiontime. Large/fast or small/slow plutons have not been identified todate. The direct consequence is that plutonic magmatic fluxes seem tobe comparable from one geodynamic context to another and also overvarious geologic time spans. A consequence of this correlation is thatsmall plutons, which are constructed over short geological time at thegeologic time scales, commonly record little about tectonic conditionsduring their construction. In large plutonic bodies, which correspondto longer duration magmatic events, regional deformation has time tointeract with the growing pluton and can be recorded within thepluton–wallrock structure. In addition to other important parameterslike cooling rate, the structural record of an individual intrusiontherefore cannot be interpreted without information on the durationof its construction, which will determine the potential extent ofmechanical interaction between the magma and host rocks.

The pulsed nature of plutonism, that is the incremental assemblyof plutons and its spatial and temporal characteristics, offers a simpleexplanation of this complexity. Specifically, the fast rate of magmatransfer in the crust (on the order of cm/s) relative to normal tectonicrates (on the order of cm/yr) makes pluton construction independentof – but not insensitive to – the tectonic context. Each pluton size isrelated to a magmatic pulsation at a particular time scale, and each ofthese coupled time/space scales is related to a specific process: insmall plutons, we can observe the incremental process, the buildingblock of plutons; in larger plutons, the incremental process is lost, andthe pulsation, which consists of a cycle of injections at differenttimescales, must be related to the composition and thermal regime ofthe source region, itself driving magmatic processes (melting,

segregation, and transfer) interacting with tectonic boundary condi-tions. The fast operation of magmatic processes relative to crustaltectonic processes ensures that magmatic process control the systemfrom below.

Consequently, the dynamics of the pulsed magmatism observed inarc plutonic systems is a proxy for deep lithospheric and magmaticprocesses.

Acknowledgements

All our works cited in this paper were funded by CNRS/INSU grants(DBT 1992–1993, IT 2001–2002, DyETI 2003–2005, and 3F 2008–2009), NSF grants (EAR–9305262, EAR-0003574, EAR-0510893, EAR-9506525, and EAR-9018929), and CNRS/NSF grants (12971 and94N92/0049). Comments on drafts and revised versions of themanuscript by C. Annen and T. Menand, and critical and constructivereviews by A.R. Cruden and P. Barbey are gratefully acknowledged.

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