Preliminary Investigation of the Geometry and Kinematics of The

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2014 Preliminary Investigation of the Geometry and Kinematics of the Bangong-Nujiang Suture at the Basu Metamorphic Massif, SE Tibet Chase Michael Billeaudeau Louisiana State University and Agricultural and Mechanical College, [email protected]

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Recommended Citation Billeaudeau, Chase Michael, "Preliminary Investigation of the Geometry and Kinematics of the Bangong-Nujiang Suture at the Basu Metamorphic Massif, SE Tibet" (2014). LSU Master's Theses. 4249. https://digitalcommons.lsu.edu/gradschool_theses/4249

This Thesis is brought to you for free and open access by the Graduate School at LSU Digital Commons. It has been accepted for inclusion in LSU Master's Theses by an authorized graduate school editor of LSU Digital Commons. For more information, please contact [email protected]. PRELIMINARY INVESTIGATION OF THE GEOMETRY AND KINEMATICS OF THE BANGONG-NUJIANG SUTURE AT THE BASU METAMORPHIC MASSIF, SE TIBET

A Thesis

Submitted to the Graduate Faculty of the Louisiana State University and Agricultural and Mechanical College in partial fulfillment of the requirements for the degree of Master of Geology

The Department of Geology and Geophysics

by Chase Michael Billeaudeau B.S., Louisiana State University, 2012 December 2014

ACKNOWLEDGEMENTS

I am grateful to all the wonderful people who have contributed to the completion of this project. I would like to give special thanks to Dr. Alexander Webb for his valuable advice and project guidance. My committee members, Dr. Peter Clift and Dr. Amy Luther, have provided much appreciated feedback. I would like to thank Clayton Campbell, Ryan Boucher, John

Anthony, Suhib Al-massmoum, Eric Orphys, and Patrick Baudoin for their contributions leading to the mineral separates. I also want to thank my friends at the University of Frieberg, including

Dr. Lothar Ratchsbacher, Joerg Pfaender, and Blanka Sperner for their strenuous work in the field and for their contributions to the thermochronologic data.

Most importantly, I would like to thank my wife, Amelia, for all of her support and sacrifices.

TABLE OF CONTENTS

ACKNOWLEDGMENTS ...... ii

ABSTRACT ...... iv

INTRODUCTION ...... 1

GEOLOGIC BACKGROUND ...... 6

FIELD MAPPING ...... 10

PETROGRAPHY ...... 19

ADDITIONAL PETROGRAPHY...... 26

GEOTHERMOBAROMETRY ...... 29

THERMOCHRONOLOGY ...... 37

DISCUSSION ...... 44

CONCLUSIONS...... 50

REFERENCES ...... 51

APPENDIX I: AMPHIBOLE EMPA DATA ...... 61

APPENDIX II: GARNET EMPA DATA...... 62

APPENDIX III: BIOTITE EMPA DATA ...... 66

APPENDIX IV: PLAGIOCLASE EMPA DATA ...... 68

APPENDIX V: MINERAL STANDARDS...... 70

VITA ...... 71

iii

ABSTRACT

There are many uncertainties associated with the development and deformation of the

Tibetan Plateau. The Basu Massif, located along the eastern Bangong-Nujiang Suture Zone, is an ideal locality to help provide constraints to resolve the geologic evolution of the Tibetan

Plateau. The Basu Massif is characterized by high pressure-ultra high pressure (HP-UHP) metamorphic rocks, syn- and post-collisional granites, and a central Upper Paleozoic unit bounded by discontinuous belts of serpentinite. Field data suggests that the carbonates of the central Upper Paleozoic unit, serpentinites, granites and metasedimentary rocks are part of an isoclinally folded shear zone that may have been thrust from the Bangong-Nujiang Suture. New

40Ar/39Ar muscovite thermochronologic data from an augen gneiss, granite gneiss, and pegmatite are reported. The tight ages yielded (ca. 174 Ma) by the three samples are of significance and help resolve the timing of exhumation of the Basu Massif. Thermobarometric data from a retrogressed eclogite, amphibolite, granite, and mylonitic gneiss yield medium to high pressures and high temperatures. Exhumation of the metamorphic rocks would have likely been driven by slab breakoff due to the dominance of the Jurassic age granites in the area. There is no indication that, following the Cenozoic Indo-Asian collision, the Basu Massif behaved ductiley.

Instead, our evidence suggests that the Basu Massif moved as a discrete crustal block.

INTRODUCTION

With an average elevation of over 5 km, the Tibetan Plateau is the largest elevated region on Earth, consisting of an assemblage of several individual crustal fragments that were accreted onto the southern margin of Laurasia through a series of progressive northward collisions during

Paleozoic and Mesozoic time (Allegre et al., 1984; Dewey et al., 1988; Yin and Harrison, 2000).

These crustal fragments, separated by extensive, semi-continuous east-west trending oceanic sutures, are young (<1.4 Ga) (Dewey et al., 1988; Guynn et al., 2006; Hu et al., 2004a; Gehrels et al., 2003, 2011) and contain records of significant pre-Cenozoic deformation (Murphy et al.,

1997; Kapp et al., 2003; Guynn et al., 2006; Guynn et al., 2013) as well as deformation as a result of the Cenozoic Indo-Asian collision (Taylor et al., 2003; Tapponnier et al., 2001; Yin and

Taylor, 2011; Ratschbacher et al., 2011). Deformation of the plateau is consistent with north- south shortening and east-west extension, with much of the crustal material being extruded towards the South China Sea via north-trending normal faulting and strike-slip faulting

(Tapponnier et al., 2001; Murphy et al., 2010; Yin and Taylor et al., 2011). The growth of the

Tibetan Plateau has been largely attributed to the Indo-Asian collision; however, the pre-

Cenozoic tectonics of these crustal fragments must also be considered to understand their role in the style and extent of Tibetan deformation through time. By investigating the internal sutures, particularly the Bangong-Nujiang Suture Zone (BNSZ) which separates the Lhasa and Qiangtang terranes (Figure 1), the geologic evolution of Tibet can be better constrained.

During the Cenozoic Indo-Asian collision, the BNSZ was reactivated and experienced both contractional and strike-slip deformation, and active deformation along the suture zone still occurs today (Wang et al., 2001). Fault system geometry along the BNSZ has been inferred to represent a trailing extensional imbricate fan or, alternatively, a group of crustal tears, in which

1 both imply north-south shortening and east-west extension as a result of conjugate faulting within the Tibetan Plateau’s interior (Murphy et al., 2010; Yin and Taylor et al., 2011). If these interpretations are correct, deformation in the form of east-west extension is at a maximum centered on the BNSZ (Murphy et al., 2010).

Figure 1: Simplified geologic map of the Bangong-Nujiang Suture Zone (dotted black lines). The Basu Massif and Amdo terranes are HP-UHP metamorphosed basement rock exposures situated along the BNSZ. The field area is located within the Basu Massif which is outlined in black.

Multiple hypotheses have been developed to explain how the Tibetan lithosphere responds to continental collision, and each of these models predict unique outcomes along the

BNSZ. These models include: (1) Thin viscous sheet (England and Houseman, 1986), (2) microplate tectonics (Tapponnier et al., 2001), (3) lower crustal channel flow (Clark and Royden,

2000), and (4) coherent crustal flow (Flesch et al. 2005; Sol et al., 2007; Yin and Taylor et al.,

2011).

A soft Tibet model was proposed by England and Houseman (1986) in which the Tibetan lithosphere, both crust and mantle, is assumed to have thickened as a thin viscous sheet in response to continental convergence by broadly, distributed shortening during the Indo-Asian collision approximately ~45-55 Ma (England and Houseman, 1986; Tapponnier et al., 2001;

Molnar et al., 2009). The uplift and subsequent collapse of the plateau is attributed to a fluid-like behavior of the weak lithosphere, where the mid-crustal region is thought to be partially molten

(England and Houseman, 19888; Clark and Royden, 2000; Kapp et al., 2004). According to the soft Tibet model, the development of contractional structures would be distributed throughout the collision zone and multiple short-lived, small-scale faults with low magnitudes of slip and slip rates would form due to the ductile nature of the lithosphere (England and Houseman, 1986;

England and Molnar, 2005). Tapponnier et al. (2001) challenges this idea by instead suggesting that the lithospheric system is much stronger, consisting of a mosaic of rigid blocks, and a significant portion of the strain is accommodated through large-scale, strike-slip and thrust faults that cut through the entire lithosphere. In this microplate tectonic model, sutures that were originally formed during the Mesozoic accretion of terranes became reactivated in the Cenozoic as India collided with Asia (Tapponnier et al., 2001). In contrast to the implications of the soft

Tibet model, microplate tectonics predicts larger faults with longer life-spans and greater magnitudes of slip, where slip rates may approach several cm/yr (Peltzer and Tapponnier, 1988;

Tapponnier et. al., 2001).

Additional models include lower crustal channel flow (Clark and Royden, 2000) and a hybrid of the thin viscous sheet model (Flesch et al., 2005; Sol et al., 2007; Yin and Taylor,

2011). The buildup of East Tibet by lower crustal channel flow was proposed by Clark and

Royden (2000). Here, it is assumed that the eastward flow of material through East Tibet is

3 driven by a low-viscosity crustal layer as topographic loading occurs. This focused flow of material is channeled to the surface through erosional processes at the surface, such as by precipitation (Clark and Royden, 2000). Essentially, the lower crustal channel flow hypothesis follows the “jelly sandwich” model, predicting two strong lithologies, a strong brittle-elastic upper crust and an elastic-ductile lithospheric mantle, bounding a weak lower crust in between

(Clark and Royden, 2000). During deformation, there is complete decoupling between the seismogenic crust and the upper mantle (Clark and Royden, 2000; Flesh et al., 2007). Flesch et al. (2005), however, proposes a geodynamic model that requires mechanical coupling between the crust and upper mantle where there is vertically coherent crustal flow. The dominant dry olivine rheology within the upper mantle absorbs a major portion of the lateral strain variations, and the seismogenic crust responds passively to the motions below (Flesh et al., 2007). The inference of this hypothesis is based on a compilation of shear wave splitting measurements throughout eastern Tibet and adjacent regions. The major difference between the lower crustal channel flow and vertically coherent crustal flow models lie in how the topography is compensated.

While the four models above address deformation following the Indo-Asian collision, we must also consider the role of the pre-Cenozoic tectonics of the Lhasa and Qiangtang terranes.

The tectonic transition of central Tibet between the Middle Jurassic-Early Cretaceous Lhasa-

Qiangtang collision and the Late Cretaceous-Early Cenozoic Indo-Asian collision is poorly understood, and there are several contrasting views regarding this period in time. The controversy lies in the timing of when the Tibetan Plateau had reached its high elevation. The

Mesozoic suturing of Lhasa and Qiangtang terranes have been proposed to either have resulted as a major event in central-southern Tibet prior to the ~3-4 km of uplift since ca. 99 Ma due to

4 crustal shortening (Murphy et al., 1997; Yin and Harrison, 2000; Kapp et al., 2005b, 2007;

Guynn et al., 2006; Zhang et al., 2008) or the collision of these two crustal fragments may be relatively insignificant, where it is advocated that the uplift of southern Tibet is only a Cenozoic episode, which implies that subsequent to the Indo-Asian collision, there was a thinned continental crust (Xu, 1981; Coward et al., 1988; Dewey et al., 1988; Harris et al., 1990; Zhang et al., 2002, 2004).

To gain further insight into the pre- and post-Cenozoic models, we must first establish the geometry of the BNSZ and surrounding crustal fragments and resolve the kinematics of this system. An area within the Basu Massif, located in East Tibet along the BNSZ, was selected for fieldwork where we conducted field mapping and petrographic, petrologic and thermochronologic studies (Figure 1). The aim of these studies is to place constraints on the evolution of the BNSZ, which in turn, allows us to test the models presented above.

GEOLOGIC BACKGROUND

Located in the central Tibetan Plateau, the east-west trending Bangong-Nujiang Suture separates the Lhasa and Qiangtang terranes. Magmatic and detrital zircon ages suggest that the

Lhasa and Qiangtang terranes may have originated from the Yangtze block of South China before rifting apart during back-arc extension or Rodinia break-up and amalgamating to East

Gondwana during the early Paleozoic (Gehrels et al., 2011; Guynn et al., 2012). The Qiangtang and Amdo microcontinents, associated with the Indian Gondwana by the geochemical signatures of their magmatism, were positioned further west from Lhasa which is thought to have originated from the Australian Gondwana (Ferrari et al., 2008; Guynn et al., 2012; Zhu et al., 2009, 2010,

2013). Following the Late Permian-Late Triassic rifting of Gondwana (Pearce and Mei, 1988), the Lhasa and Qiangtang terranes, along with several other crustal fragments, progressively collided into the southern margin of Laurasia and led to the closure of numerous ocean basins and the formation of the Tibetan Plateau (Allegre et al., 1984; Dewey et al., 1988; Yin and

Harrison, 2000). Final terrane assemblage took place during the Middle Jurassic-Early

Cretaceous, with the collision of the Lhasa and Qiangtang terranes, forming the BNSZ (Chang and Zhen, 1973; Allegre et al., 1984; Yin and Harrison, 2000; Kapp et al., 2007). This major

Tethyan suture is ~1200 km long (Shi et al., 2008) and varies in width from 10-20 km to several hundreds of km, possibly indicating that BNSZ is a composite suture (Qu et al., 2012). The polarity of the BNSZ is largely debated. Some authors support that the Bangong-Nujiang

Tethyan Ocean subducted beneath Qiangtang during the Mesozoic (Yin and Harrison, 2000;

Kapp et al., 2007; Guynn et al., 2006; Zhu et al., 2013), while others believe Permian-Early

Cretaceous southward subduction beneath Lhasa had occurred (Hsu et al., 1995; Pan et al., 2006;

Zhu et al., 2006b).

The Qiangtang terrane, bounded by the Songpan Garze terrane to the north and the Lhasa terrane to the south, is a large, stratigraphically and structurally complex east-west trending crustal fragment that consists of metamorphosed Neoproterozoic-Paleozoic metasedimentary basement overlain by thick sequences of Carboniferous-Triassic marine rocks (Kapp et al., 2000,

2003, 2007; Zhang et al., 2006a; Pullen et al., 2008). Mesozoic and Cenozoic sedimentary cover is extensive, and a majority of the Mesozoic units are fault bounded (Burchfiel and Zhiliang,

2012). Within the Qiangtang terrane lies the Longmu Co-Shuanghu Suture (LSSZ) which separates the Qiangtang terrane into two distinct blocks (Li et al., 1995; Liu et al., 2011; Zhai et al., 2011a,b; Zhu et al., 2013). Volcanic rocks are widely distributed throughout the northern

Qiangtang terrane (Deng et al., 1998; Lai et al., 2006; Chi et al., 2005; Wang et al., 2008; Dong et al., 2008) and are considered to be a product of partial melting of a thickened or delaminated lower crust (Dong et al., 2008; Liu et al., 2008). In the southeastern portion of the Qiangtang terrane near the BNSZ, Mesozoic sedimentary rocks are intruded by scarce plutonic rocks

(Burchfiel and Zhiliang, 2012). These Mesozoic rocks include thick, well exposed successions of Upper Triassic non-marine to marine strata unconformably overlain by Jurassic strata, which consists of sandstone, shale, and fossil-bearing limestone (Burchfiel and Zhiliang, 2012).

South of the Qiangtang terrane, the Lhasa terrane is a 100-300 km wide and ~2000 km long (Zhang et al., 2014) assemblage of two discrete crustal fragments separated by the

Carboniferous-Permian Luobadui-Milashan Suture Zone (Yang et al., 2006, 2007, 2009; Zhu et al., 2012a). The northern portion of the Lhasa terrane consists of a juvenile crust and is dominated by widespread Mesozoic sedimentary strata with abundant early Cretaceous volcano- sedimentary sequences and Cretaceous granitoids (Pan et al., 2004; Zhu et al., 2011a; Zhang et al., 2012a; Sui et al., 2013; Chen et al., 2014). Here, Middle to Upper Triassic age slate,

7 sandstone, and radiolarian chert make up the oldest sedimentary cover, (Pan et al., 2004;

Nimaciern et al., 2005) which is overlain by Middle Jurassic coarse-grained clastic rocks and finer grained Upper Jurassic marine rocks (Nimaciren et al., 2005). Upper and Lower

Cretaceous sequences occur extensively along strike of the Lhasa terrane and include marine and terrigenous deposits (Pan et al., 2004; Kapp et al., 2007; Zhu et al., 2013). Partially metamorphosed Precambrian basement rocks are exposed in central Lhasa (Kapp et al., 2005;

Zhu et al., 2009; Zhang et al., 2010). These basement rock exposures are covered by abundant

Devonian through Permian sedimentary and metasedimentary rocks (Burchfiel and Zhiliang,

2012) as well as Middle to Late Mesozoic sedimentary strata with abundant volcanic rocks and limestone of Ordovician, Silurian, Devonian, and Triassic age (Pan et al., 2004). The southern

Lhasa terrane is dominated by the Cretaceous-Tertiary Gangdese batholiths and Paleogene volcanics and features a locally preserved exposure of Precambrian crystalline basement (Pan et al., 2004; Mo et al., 2008; Ji et al., 2009a; Zhu et al., 2011a).

The Basu Massif, like the Amdo Metamorphic Complex to the west, is an exposure of metamorphosed basement rocks and upper Paleozoic plutonic rocks situated along the BNSZ. Its origin remains unknown; however, the massif may be part of the Lhasa terrane (Burchfiel and

Zhiliang, 2012). Two belts of Jurassic mélange can be traced to the northwest and to the south- southeast. The former of these mélange belts contains a large exposure of an ophiolite body overlain by a thin unit of Middle Jurassic marine rocks characteristic of the Lhasa terrane

(Burchfiel and Zhiliang, 2012). The mélange continues to the southeast at which point it terminates and Triassic strata of the Qiangtang terrane is in fault contact with Devonian and

Carboniferous rocks to the south. The second belt of mélange begins adjacent to the southern margin of the massif directly south of where the northern belt becomes difficult to identify. Both

8 mélange belts are interpreted to have formed along the northern continental margin of Lhasa through the opening of the Bangong Ocean (Burchfiel and Zhiliang, 2012). Between the two mélange belts, at the center of the Basu Massif, lie fault-bounded Paleozoic metamorphic rocks which contain slivers of serpentinite and a fragment of fault-bounded Triassic-Jurassic strata

(Figure 2).

Figure 2: Map of field area located in the Basu Massif. Jurassic mélange is shown in the upper right-hand and lower left-hand portions of the map. Altered from Burchfiel and Zhiliang (2012).

FIELD MAPPING

Fieldwork encompasses an area of approximately 3000 km2 in the Basu Massif (Figure

2). The field area is characterized by a central Upper Paleozoic unit, medium to high pressure metamorphic rocks (Zhang et al., 2008; Zhang et al., 2010), and mostly syn- and post-collisional granites; however, northeast of Tongka, zircon from a granitic body was dated and yielded a U-

Pb age of ca. 507 Ma (Li et al., 2008c), suggesting that at least some granitic bodies were in place long before the Middle Jurassic-Early Cretaceous Lhasa-Qiangtang collision. A fault- bounded fragment of Jurassic or Triassic strata juxtaposes the Upper Paleozoic unit on its western end, and along either side of the Upper Paleozoic unit lie discontinues belts of serpentinite. Additional belts of serpentinite-bearing mélange appear both to the northeast and southwest of the field area and consist of sheared marine rocks. Multiple unconformities exist where the folded and faulted Upper Cretaceous red beds overlie the northern mélange belt, and the Upper Cretaceous red beds are then unconformably overlain by Paleogene rocks that are also folded and faulted (Burchfiel and Zhiliang, 2012). Other units include the marine Triassic and shallow-marine Jurassic units as well as the Quaternary deposits throughout the field area.

Repetition of strata was observed as well as a shear zone with opposing senses of shear across a transect through the Upper Paleozoic unit. In this section, we will show that the repetition of strata and shear zone with opposing shear senses are part of an isoclinally folded shear zone.

West of the valley, at the southern extent of the field area along the Nu Jiang River, outcrops of serpentinite were observed within oblique, dextral shear zones with normal offset

(Figure 3). The fault plane surface appears warped and is sub-vertical to steeply dipping in the

ENE direction with early fibers plunging 37° to the SSE and later fibers measuring to be sub- horizontal and trending to the north, possibly indicating rotational slip. Carbonaceous, mica-rich

Figure 3: Serpentinite outcrop displaying fibers and a fabric that indicates an oblique, normal, dextral sense of shear. sandstones and conglomerates are in contact with the serpentinite outcrop on its eastern side.

The serpentinite-sandstone contact is smooth and continuous, neither displaying an increase in strain nor brittle deformation. The serpentinite-conglomerate contact, however, appears to contain conformable or brittle faulting. Clast composition changes ~10 m away from the area.

Here, the clasts consist of foliated to nonfoliated quartz-rich granites, few quartz vein chunks, and quartzite. Some quartzites appear to be metasedimentary, while other quartzites may be igneous to meta-igneous. Approximately 100 m structurally west of the serpentinite- conglomerate contact, the clasts disappear and dark, quartz-rich sediments with mica sheen on the bedding surface appear. These rocks, which lightly fizz between cracks, are highly similar to the sandstone observed on the eastern side of the serpentinite. Tension gashes are filled with mostly quartz and brown carbonate and are interpreted to be synchronous with late top-E normal

11 faults that resemble overturned thrusts. Granite cuts into the metasedimentary rocks and has a foliation measured to be dipping 59° to the WNW. Also west of the serpentinite outcrops, we observed a schuppen zone with numerous boudinaged lithologies (Figure 4). The schuppen zone contains reidel shears and sigma boudins, approximately 0.5 cm to 1 m in size, with a matrix that appears to mostly consist of chlorite and quartz. A majority of the boudins show some oxidation and are either amphibole or pyroxene in composition, and less than 5% are carbonates. Some carbonate boudins appear ductile, while others are brecciated blocks warped into sigmoidal shapes. The main foliation of this area is moderately to steeply dipping in the NE direction with extensional crenulation cleavage measured to be dipping sub-vertically and striking to the north.

Further north, also west of the central valley, outcrops of weakly foliated to unfoliated granite were observed. East of this location is the granite margin which is highly brecciated and contains undeformed blocks of granite that are boudinaged in a sea of granite mylonite. Rocks here are highly weathered making S-C fabrics difficult to discern. The granite is broadly warped and appears to be tilted out of the dominant local strike trend, possibly indicating a tilted fault block. Locally, highly deformed garnet-bearing mylonitic gneiss moderately to steeply dips in the NE direction. Moving eastward, we observed poorly exposed undeformed granite and a ~2 m sliver of serpentinite with excellent dextral S-C fabric. This was succeeded by an 8 m thick, odd gray rock type with altered or weathered, fragmented serpentinite where additional dextral

S-C fabric was observed. The overall slip direction and shear sense here reasonably match the observations to the far south of the field area. To the ENE, the next 5 m of section is poorly exposed blue slate and carbonate schists with highly variable dip directions. A steeply NNE dipping, foliated, coarse quartz and white feldspar granite or coarse sandstone unit appears for

~15 m.

Figure 4: Schuppen zone featuring multiple sigmoidal boudinaged lithologies in a predominantly chlorite and quartz matrix. A1, A2) amphibole or pyroxene boudins. B1, B2) carbonate boudin. C1, C2) brecciated carbonate boudin. The boudinaged lithologies display a dextral sense of shear.

Near the foliated granite or sandstone unit lie carbonates with large (~15 m) folds. The interlimbs of the folds measure 15-30° and display sub-vertical fold axes. The carbonates, some containing layers of chert, are steeply to near vertically (~73-84°) east-dipping and include deformational structures such as parasitic folds, tension gashes, and conjugate faults. The parasitic folds with E-W shortening indicate layer-parallel slip with verging shear senses.

At the center of the Upper Paleozoic unit is a weathered outcrop of weakly foliated granite. The granite dips moderately to steeply in the NE direction; however, much of the granite may not be in place. Further southeast, more foliated granite was observed with weak to moderate S-C fabrics and lineations (Figure 5). The lineations are defined by feldspar and chlorite after biotite and trend in the N-S direction, plunging shallowly at approximately 12°; however, white mica on the foliation surface is unlineated, possibly indicating that the lineations post-date shearing.

Figure 5: Granite displaying weak to moderate S-C fabric with sigmoids indicating top-NNE flow.

Limestone and quartzite, similar to the rocks observed along the east side of the right- lateral shear zone, appear on the opposite side of the valley. The internal deformation within the limestone is roughly consistent with what was seen on the west side of the valley as well.

Exposures of small boudins (~2 m) of undeformed serpentinite appear within blue carbonate to the east. Locally, we observed poorly exposed outcrops of green flysch and shale with sparse sinistral faults. Following the outcrops of shale are exposures of folded blue carbonate, weathered, foliated granite, and ENE-dipping shale with granite interlayers. The folded blue carbonates contain sinistral extensional crenulation cleavages and few tension gashes.

Moderately to steeply dipping late conjugate fractures and sinistral gray boudins were also observed in the area. Eastward, we approached a poorly exposed band of weakly foliated granite in an area of extensive cover. Beyond the cover, more weakly foliated to nonfoliated granite was observed. The foliation of the granite was measured to be dipping steeply in the ENE-ESE direction. To the northeast, high-strain, highly weathered granite with mica-quartz-tourmaline veins is poorly exposed. A 100-150 m section of sheared granite with late undeformed dikes outcrops locally. Sinistral, asymmetric boudinage observed within this locality displays both brittle and ductile deformation (Figure 6). Eastward, a large (~1.5x8 m), elongate lens of garnet amphibolite within granite was discovered as well as eclogite float and garnet-pyroxenite.

Further south, outcrops of carbonates, micaceous sandstone, conglomerates containing serpentinite clasts, granites, and gneiss were observed. A flanking fold with a sinistral sense of shear appears locally. Eastward, up-valley, west-dipping migmatite, sparse granites, amphibolite, and mylonitic rocks appear where we also found evidence of late faulting.

Northeast of the shear zone, carbonates feature S-C type boudins, isoclinal to open folds, tension gashes, ECC-type extensional boudinage, and possible late normal faults. The carbonates show no signs of lineation; however, they do show good foliation and dip approximately 66° in the ENE direction. Asymmetric folds and sigmas within the carbonate suggest that these are directly related to isoclinal folding with a steep, W-plunging fold axis. An

Figure 6: Foliated granitic boudinage showing sinistral displacement. Both brittle (A1, A2) and ductile (B1, B2) deformation can be observed. implication of this is that high grade shear textures in the carbonates appear to result from isoclinal folding or are modified by later isoclinal folding on the meso-scale (meters to 10’s of meters). Therefore, carbonate and closely associated rocks, deformed by carbonate folds, is not a reliable source for shear criteria on the mega-scale shear zone. Traveling further northwest, we observed late faults with both normal and reverse offsets, a well exposed fold axis in a tight fold, and thrust tectonics on its side (Figure 7). The geometry of these areas strongly suggests that these rocks are part of a sinistral-oblique thrust shear zone, implying a sinistral version of the asymmetric fold geometry seen at outcrop scale applies to the whole hillside. Weakly deformed, chloritized augen gneiss can be found outcropping to the northwest where its foliation measures

Figure 7: Thrust tectonics. The geometry outlined (A, A2, B, B2, C, C2) strongly suggest that these rocks are part of a sinistral-oblique thrust shear zone. to be dipping 54° to the WSW. Approximately 100 m west, well foliated granite was observed dipping steeply to the ESE followed by observations of a schuppen zone containing slates in a carbonate rock, slate, granite, and serpentinite. Structural field data is located in Figure 8.

Figure 8: Structural field data plotted on stereonets (lower hemisphere, equal area). Density stereonets are based on foliation measurements and indicate southeast-northwest shortening.

PETROGRAPHY

Methods

Using a petrographic microscope, 52 thin sections were analyzed in plane polarized light

(PPL) and cross polarized light (XPL) to determine a general sense of the mineral assemblages across the field area. An additional 25 samples were further examined for quartz grain boundary deformation using a systematic scheme developed by Stipp et al. (2002). According to Stipp et al. (2002), the following deformational processes occur under increasing temperature: bulging recrystallization (~250-400 °C), subgrain rotation (400-500 °C), and grain boundary migration

(500-700 °C). The spatial variations of these quartz deformation temperatures are important to investigate in order to understand and estimate strain rates for major orogenic events (Dunlap et al., 1997).

Results

A summary of the assemblages of the 52 samples are provided in Table 1. Most samples that were collected along or near the western and eastern shear zones show significant to moderate deformational textures, and many contain garnets (95014A, 95085A, 95091B, 95092B,

95123A, 95152B, 95162A, 95171A, 95173A-AX, 95191A, 95194A, 95194C), generally associated with high temperature and/or high pressure metamorphism. Within the central Upper

Paleozoic unit, a total of six samples were collected and made into thin sections. Five of these samples (95091A, 95091B, 95091C, 95091D, 95091E) were collected from a single location a few meters away from the western shear zone. These samples show very little, if any, deformational textures, except for the sandstone (95091B) and gneiss pebble (95091D) which display high grade textures. The sixth sample, 95155A, is a limestone with very fine (~2-8 μm)

Table 1 Summary of mineral assemblages Sample Rt Zrn Ttn Grt Ep Opx Cpx Tur Amp Sil Cal Ap Ms Bt Srp Chl Ser Kfs Pl Qz Gr 95014A x x x x x x x

95072B x x x x x x x x x

95077B x x x x x x x x x

95078A x x x x x x x x

95082A x x x x x x x x x

95083A x x x x

95083B x x x x x x x

95085A x x x x x x x x x x

95091A x

95091B x x? x? x x x x x x

95091C x x? x x x x x x

95091D x? x? x x x x x

95091E x x x x x x x

95092B x x x x? x? x x x x x x

95094A x x x x x

95094B x x x? x? x x x x x

95123A x x x x x x

95127A x x x x x x x x x x x x x

95131A x x x x x x x x x

95133A x x x x x x x x x x x x x x x

95142C x x x x x x x x x

95142E x x x x x x x x x

95143A x x x x x x x x x

95152B x x x x x x x x x x

95153A x x

95153B x? x? x x

95155A x? x x

Rt – rutile; Zrn – zircon; Ttn – titanite; Grt – garnet; Ol – olivine; Ep – epidote; Opx – orthopyroxene; Cpx – clinopyroxene; Tur – tourmaline; Amp – amphibole; Sil – silliminate; Cal – calcite; Ap – apatite; Ms – muscovite; Bt – biotite; Srp – serpentine; Chl – chlorite; Ser – sericite; Kfs – alkali feldspar; Pl – plagioclase; Qz – quartz; Hem – hematite; Gr – graphite.

(Table 1 continued) Sample Rt Zrn Ttn Grt Ep Opx Cpx Tur Amp Sil Cal Ap Ms Bt Srp Chl Ser Kfs Pl Qz Gr 95161A x x 95162A x x x x x x 95162? x x x x x x 95164A x x? x x x x x 95166A x x x 95167A x? x x x x x

95168A x x x

95171A x x x x x x x x

95171B x? x

95171C x x? x x x x x x

95171D x x? x x x x x x x

95171E x x x x x x x x x

95171F x x? x x x x x x x

95171G x x x x x

95171H x x? x? x x x x x x

95171I x x x x x x x

95173AX x x x x x x x x x

95177A x x x x x x x x x

95191A x x x x x x x

95192A x x x x

95194A x x x x x

95194C x x x x x

95202A x x? x x x x x x x x

95211A x x x x

95232A x x x x x x x

21 calcite grains. No deformational textures, other than the styolites generated through pressure dissolution, were observed (Figure 9).

Figure 9: Sample 95155A consists of fine (<10 μm) calcite grains and features few styolites.

The results of the quartz microstructure analysis are located in Table 2 and four examples spanning BLG-GBM are shown in Figure 10. A map displays the spatial distribution of samples analyzed near the central field area (Figure 11). Quartz grains analyzed from samples taken near the shear zone more or less exhibit deformational textures indicative of subgrain rotation to grain boundary migration. The samples collected along the shear zone west of the valley appear to exhibit quartz grains that were subjected to higher strain rates than those collected to the east.

Away from the isoclinally folded shear zone, bulging recrystallization textures become more prevalent; however, within the granitic body to the southwest, quartz grains analyzed from six samples show a variety of textures.

Table 2 Quartz Microstructure Analysis Sample No. Rock Type Null BLG SGR GBM 95072A Granite x

95077B Augen gneiss x x

95078A Shales/Quartzites x

95091A Limestone x

95091B Sandstone x

95091C Conglomerate x

95091D Gneiss x x

95091E Sandstone x

95092B Eclogite x

95094A Amphibolite x

95094B Amphibolite x

95123A Quartzite x

95127A Migmatite, granitic dyke x

95131A Amphibolite x

95133A Gneiss x

95142C Gneiss x

95142E Metasedimentary x

95143A Quartzite x

95152B Mica schist x

95153A Mixture zone (skarn?) x x

95155A Marble x

95161A Marble w/ chert x

95162A Foliated Granite x

95164A Foliated Granite x

95167A Shales mixed w/ foliated granite x x

95168A Serpentinite x

95171A Foliated Granite x

95171B Granite x

95171D Granite x

95171E Granite x

95171F Granite x

95171G Granite x

95171H Granite x

95171I Granite x x

95173A Migmatite, granitic dike x

95191A Garnet-amphibolite x

95192A Quartzite x

95194A Garnet schist x

95194C Garnet schist x

95202A Pegmatitic dyke x

95211A Granite x

Null – no recrystallization observed; BLG – bulging recrystallization; SGR – subgrain rotation no; GBM – grain boundary migration.

Figure 10: Photomicrographs of four samples collected from the field showing: A) bulging recrystallization (~250-400 °C), B) subgrain rotation (400-500 °C), C) subgrain rotation to grain boundary migration (~450-600 °C), and D, E) grain boundary migration (500-700 °C).

Figure 11: Zoom-in of field area near the isoclinally folded shear zone. Quartz microstructure analysis results are displayed as shaded diamonds.

ADDITIONAL PETROGRAPHY

Of the 52 samples previously analyzed, a retrogressed float eclogite (95092B), granite

(95072B), amphibolite (95131A), and mylonitic gneiss (95152B) were studied in further detail to define their textures, alterations, and complete mineral assemblages with modal amounts before conducting thermobarometric studies of the field area. The sample locations for these rocks are shown in Figure 2.

Results

Sample 95092B is classified as a retrogressed eclogite based on its observed mineral assemblage and corresponding modal amounts (Figure 12, A, A1): Gr (45%) + matrix of Ep +

Qz (40%) + Amp (5%) + Bt (5%) + Qz (2%) + Pl (2%) + Ilm (1%) with trace minerals including rutile, apatite, and chalcopyrite. Garnet grains, with prevalent inclusions of quartz and apatite, are highly fractured and show hypidioblastic textures. Surrounding the garnet grains are bands of xenoblastic amphibole and sagenitic biotite with few recrystallized quartz ribbons.

Plagioclase is easily identifiable due to the presence of albite twinning. The matrix is formed through the vermicular intergrowth of quartz and epidote. Alterations within the sample have been observed. These alterations include chloritization of biotite, sericitization of plagioclase, rutile altering to ilmenite, and alterations of ilmenite to leucoxene.

With a main mineral assemblage of Kfs (35%) + Qz (30%) + Bt (25%) + Pl (7%) + Amp

(3%), sample 95072B can be classified as a granite (Figure 12, B, B1). Observable trace minerals include zircon, apatite, and ilmenite. Mineral grains do not show preferred orientation.

Textures include porphyroblasts of orthoclase with exsolution lamellae and sagenitic biotite and amphiboles. Pleochroic halos within biotite grains are abundant. Heavy chloritization of biotite

Figure 12: Photomicrographs of four samples in PPL (left) and XPL (right). A, A1) retrogressed eclogite (95092B), B, B1) granite (95072B), C, C1) amphibolite (95131A), D, D1) mylonitic gneiss (95152B).

(76%) and minor sericitization (14%), mostly confined between fractures of the plagioclase grains, was observed.

Sample 95131A can be classified as an amphibolite (Figure 12, C, C1). It has a main mineral assemblage of Amp (45%) + Pl (40%) + Qz (10%) + Pyx (5%) with trace minerals including zircon, ilmenite, titanite, hematite, and apatite. The amphibolite displays a granoblastic texture with alternating hydrated (amphibole + plagioclase) and dehydrated

(pyroxene + plagioclase + quartz) gneissic bands. Xenoblastic pyroxenes are prevalent and are concentrated within the dehydrated bands of the amphibolite along with hypidioblastic titanite grains. Within the titanite grains are ilmenite cores. Sericitization of plagioclase is most concentrated in the dehydrated bands.

The observed mineral assemblage of sample 95152B is Qz (32%) + Bt (19%) + Pl (14%)

+ Ser (12%) + Grt (12%) + Sil (8%) + Hem (2%). This sample can be classified as a sillimanite- garnet-plagioclase-biotite gneiss (Figure 12, D, D1). Trace minerals include zircon, hematite, and unidentified opaques. Textures include irregular quartz grains and fibrous sillimanite

(fibrolite). Garnet is highly included with quartz. Intergrowths of quartz and plagioclase, creating vermicular textures, are present but uncommon. Biotite and sillimanite display a preferred orientation and commonly appear in bands. Alterations include abundant sericitization of plagioclase, chloritization of biotite, and alteration of garnet to hematite, specifically in fractures.

GEOTHERMOBAROMETRY

Methods

Thin sections of samples 95092B, 95072B, 95131A, and 95152B were carbon-coated and placed into the chamber of Louisiana State University Department of Geology and Geophysics’ scanning electron microscope (SEM) JEOL JSM-840-A using an accelerating voltage of 15 kV and beam current of 6 nA. In order to identify evidence of zoning, backscatter electron images

(BSE) as well as secondary electron images (SEI) were acquired. Unknown grains and inclusions were identified through wavelength dispersive spectroscopy (WDS). Furthermore, microanalytical electron microprobe analyses (EMPA) were obtained using the JEOL

Superprobe 733 at Louisiana State University with an accelerating voltage of 15 kV, a beam current of 10 nA, and variable beam sizes for the minerals analyzed (1 μm for garnet and 3 μm for amphibole, biotite, and plagioclase). The machine was standardized before and after every analysis.

Amphibole, garnet, biotite, and plagioclase were the four targeted minerals for EMPA analysis for the retrogressed eclogite float (95092B). The amphibole analysis consisted of taking five points across a single grain. Three garnet grains were analyzed as well. The first garnet grain consisted of a traverse of nineteen points, twenty points crossing a second grain, and forty- one points traversing a third grain. For biotite analysis, one grain was traversed with eight points, and a single point on a second grain was analyzed to check for chemical equilibrium.

Plagioclase analysis was conducted by completing a point analysis in three separate locations.

The granite (95072B) was analyzed for amphibole, biotite, and plagioclase. Ten points were taken from a single amphibole grain, and two biotite grains consisting of a traverse of five points

29 were completed as well. For the analysis of plagioclase, a traverse of twenty points was taken.

Two amphibole grains and one plagioclase grain was analyzed from the amphibolite (95131A).

The first of the amphibole grains consisted of a traverse of four points, while the second grain was analyzed in two points. The plagioclase analysis consisted of a single grain with a traverse of ten points. Lastly, EMPA analysis conducted on the mylonitic gneiss (95152B) targeted garnet, biotite, and plagioclase. Garnet analysis was completed on two grains, with the first grain consisting of spot analysis of four points, and the second grain consisting of a traverse of five points. Three biotite grains were analyzed. Two spot analyses were completed within the core of the first biotite grain and one along the rim. The second biotite grain consists of two spot analyses along the rim and one in the core. The last biotite grain had one spot analysis in both core and rim. Only one plagioclase grain was analyzed from the mylonitic gneiss. Of the seven analyses, five of the points were chosen within the plagioclase core and two points near the rim.

Figure 13 details the locations of the analyses for each grain.

EMPA data was collected and normalization procedures were used to correct the data within 10% of the standard oxide values. Corrected data was normalized based on the number of oxides in amphibole (23), garnet (12), biotite (22), and plagioclase (8).

The hornblende-plagioclase thermobarometer of Holland and Blundy (1994) was used to attain a series of pressures and temperatures for samples 95092B, 95072B, and 95131A. The thermometry of these calculations, with an assumed absolute error of ± 40 °C, was based on arbitrary pressures dependent on sample mineral assemblage. Pressure and temperature calculations were further constrained by using the average weight percentage of Al2O3 and TiO2 values acquired from the sample points of the amphiboles and plotting the averaged values on a diagram by Ernst and Liu (1998) that uses Al2O3 and TiO2 found in amphibole to approximate

Figure 13: Backscatter images (BSE) of four samples: a) retrogressed eclogite (95092B), granite (95072B), amphibolite (95131A), and mylonitic gneiss (95152B). Blue lines and points indicate traverses and point analyses taken for EMPA. pressure and temperature. For sample 95152B, molar amounts for garnet end-members as well as plagioclase end-members were calculated by using the averaged normalized cation values for each grain. The averaged normalized cation values obtained for the garnets (Gt 1 and Gt 2) as well as the biotites (Bt 1, Bt 2, and Bt 3) were used in a garnet-biotite thermometer program that uses several calibrations (Thompson, 1976; Holdaway and Lee, 1977; Ferry and Spear, 1978;

Perchuk and Lavrent’eva, 1983; Dasgupta et al., 1991; Bhattacharya et al., 1992). An arbitrary reference pressure of 7.98 kbar was assumed. Furthermore, a garnet-aluminosilicate-silica- plagioclase (GASP) geobarometer by Holland and Powell (1995) was used to calculate pressure whose formulation normalized cations of Si, Ti, Al, Fe, Mn, Mg, Ca, Na, and K.

Results

WDS taken at several points from the core to rim of the garnet grains in the eclogite

(95092B) reveal magnesium depleted rims, indicating that there is possible minor compositional

31 zoning within these garnets. Five in situ analyses traversing the amphibole grain gave average

TiO2 and Al2O3 values of 1.5 wt% and 14.11 wt%, respectively, and these grains do not show any significant variations from rim to rim. An average XMg = 0.50 was calculated for the amphibole, classifying it as either a hastingsite or magnesiohastingsite as it borders the two

(Figure 14; Leake et al., 2003). Plagioclase is classified as andesine due to having anorthite compositions ranging between An32.96 – An35.33 (Figure 15).

Figure 14: Classification of amphiboles. Data points correspond to samples 95092B (green), 95072B (blue), and 95131A (orange). Charts modified from Leake et al. (2003).

For the granite (95072B), reported averaged TiO2 and Al2O3 values from the amphibole grain are 0.89 wt% and 7.5 wt%, respectively. Again, no significant compositional variation was observed. The amphibole can be classified as a magnesiohornblende due to the average XMg =

0.57 (Figure 14; Leake et al., 2003). Plagioclase within the granite can also be classified as andesine due to having a composition ranging from An43.12 – An53.9 (Figure 15).

Figure 15: Average feldspar compositions obtained from EMPA analyses of samples 95092B (green), 95072B (blue), 95131A (orange), and 95152B (red) are plotted on the ternary diagram.

For the EMPA analysis of the amphibolite (95131A), several points taken from the amphiboles resulted in anomalous H2O values; thus, these points were not used in any calculations. TiO2 calculations revealed an average wt% of 0.84, and Al2O3 was calculated to be

11.48 wt%. The calculated average of XMg = 0.55 classifies this amphibole as a magnesiohastingsite (Figure 14; Leake et al., 2003). The plagioclase grain, with a composition ranging from An42.68 – An49.04, can be classified as andesine (Figure 15).

Backscatter imaging shows that there is no observable compositional zoning in any of the analyzed grains from the mylonitic gneiss (95152B). Grt 1 features large quartz inclusions within the center of the grain, so only four points were analyzed along the rims. The Grt 1 grain was calculated to have an average composition Alm71.40Prp16.39Grs7.26Sps4.95. The less included

Grt 2 grain has an average composition calculated to be Alm71.56Prp17.48Grs6.37Sps4.59, which is

33 similar to Grt 1’s composition. Three biotite (Bt1, Bt2, and Bt3) and two plagioclase grains (Pl 1 and Pl 2) were analyzed near Grt 1. All three biotite grains have similar compositions ranging from Mg/(Mg+Fe) = 0.31 to Mg/(Mg+Fe) = 0.34 and low Ti (~0.02). These biotite grains most resemble annite in composition. Plagioclase, with a molar average of Ab71.53 – Ab72.14, can be classified as anorthoclase (Figure 15).

Thermobarometry

Using the data attained through EMPA analyses conducted on amphiboles from samples

95092B, 95072B, and 95131A, we were able to plot the Al2O3 and TiO2 compositions onto an isopleth diagram by Ernst and Liu (1998) to estimate pressures and temperatures. The results of the Ernst and Liu (1998) thermobarometer calculations are as follows: 810 °C 13 at kbar for the eclogite, 680 °C at 3 kbar for granite, and 690 °C at 11.5 kbar for the amphibolite (Figure 16).

Figure 16: Thermobarometer of Ernst and Liu (1988) showing isopleths of Al2O3 and TiO2 in weight percentage. Retrogressed eclogite (95092B), granite (95072B), and amphibolite (95131A) are plotted on the diagram.

The same data points used for the Ernst and Liu (1998) thermobarometer were also used in the plagioclase-hornblende thermobarometer of Holland and Blundy (1994) to compare results. The results are located in Table 3. These calculations were based on assumed pressures for all three samples. The Holland and Blundy (1994) plagioclase-hornblende thermobarometer was applied to the retrogressed eclogite (95092B) assuming pressures of 12 kb and 15 kb. At 12 kb, temperatures were calculated to be between 711-774 °C, while at 15 kb, temperatures range between 662-796 °C. Assumed pressures of 3 kb and 5 kb for the granite (95072B) were used, and temperatures were calculated to range from 670-744 °C and 674-723 °C, for 3 and 5 kb, respectively. For the amphibolite (95131A), assumed pressures of 8 kb and 12 kb were used to attain temperature estimates. Results from the temperatures calculated from Holland and Blundy

(1994) give 717-802 °C at 8 kb and 693-768 °C at 12 kb.

Finally, thermobarometric calculations were conducted for the mylonitic gneiss (95152B) using several garnet-biotite geothermometers (Thompson, 1976; Holdaway and Lee, 1977; Ferry and Spear, 1978; Hodges and Spear, 1982; Perchuk and Lavrent’eva, 1983; Dasgupta et al.,

1991; Bhattacharya et al., 1992) and one garnet-aluminum silicate-plagioclase-quartz (GASP) geobarometer by Holland and Powell (1995). Calculated temperatures range between 672-792

°C using a reference pressure of 7.98 kbar attained through a geobarometer calculation program using the formulation by Bhattcharya et al. (1992). However, using calibrations by Dasgupta et al. (1991) yielded outliers of 468-482 °C (Table 4).

Table 3 Plagioclase-hornblende thermometer results Rock Granite Granite Granite Amphibolite Amphibolite Amphibolite Eclogite Eclogite Eclogite 95072B 95072B 95072B 95131A 95131A 95131A 95092B 95092B 95092B Sample PTA1 PTA1 PTA1 PTA2 PTA2 PTA2 PTA2 PTA2 PTA2 Specimen pt1 pt4 pt8 am1 pt4 am2 pt1 am2 pt2 pt2 pt3 pt4 P kb (input) 3 3 3 8 8 8 12 12 12 T (C) HB1 '94 731 725 744 792 802 798 741 746 755 T (C) HB2 '94 680 670 694 759 745 717 756 735 774 T (C) BH '90 706 705 712 758 762 767 711 711 724

P kb (input) 5 5 5 12 12 12 15 15 15 T (C) HB1 '94 711 706 723 748 755 757 745 745 754 T (C) HB2 '94 684 674 696 768 755 729 780 756 796 T (C) BH '90 678 677 684 693 698 703 662 662 675 HB1’94 – Holland and Blundy (1994) thermometry calibration reaction edenite + 4 quartz = tremolite + albite; HB2’94 – Holland and Blundy (1994) thermometry calibration reaction edenite + albite = richterite +anorthite; BH’90 – Blundy and Holland (1990) thermometry calibration reaction edenite + 4 quartz = tremolite + albite.

Table 4 Garnet-biotite thermometry for sample 95152B Temperature (°C)

Sample Ref P, kbar B92-HW B92-GS Dasg91 FS78 HS82 PL83 T76 HL77 Grt 2 Bt 1 7.98 688 692 472 769 795 681 752 703 Grt 2 Bt 2 7.98 686 691 482 766 792 679 750 701 Grt 3 Bt 3 7.98 679 684 468 751 777 672 739 692 B92HW – Bhattacharya et al. (1992) using Hackler and Wood (1989) mixing parameters; B92-GS – Bhattacharya et al. (1992) using Ganguly and Saxena (1984) mixing parameters; Dasg91 – Dasgupta et al. (1991); FS78 – Ferry and Spear (1978); HS82 – Hodges and Spear (1982); PL83 – Perchuk and Lavrent’eva (1983); T76 – Thompson (1976); HL77 – Holdaway and Lee (1977).

THERMOCHRONOLOGY

Methods

Four samples (95077A, 95124A, 95163A-1, 95163A-2) were selected for muscovite

40Ar/39Ar dating. The spatial distribution of these samples is shown in Figure 2. 40Ar–39Ar geochronology was conducted at the Argon laboratory of the TU Bergakademie Freiberg (ALF;

Pfänder et al., 2014). The muscovites were liberated from the rock samples using the Freiberg high-voltage electrical-pulse fragmentation facility (SelFrag-Lab; Sperner et al., 2014) and handpicked under a binocular microscope. The minerals were then ultrasonicated in alcohol and repeatedly cleaned in deionized water, dried, and subsequently wrapped into Al foil. These sample packets were loaded in 5 × 5 mm wells on ~30 mm Al-disks for irradiation, which was done without Cd shielding at the LVR-15 research reactor in Rez, Czech Republic, at a thermal neutron fluence of ~4.8 × 1013 n/cm2 s and a thermal to fast neutron ratio of ~2.1. Stepwise heating was performed using a defocused (~1.5 mm diameter) 25 W CO2 laser operating at a wavelength of 10.6 μm. Gas purification was achieved within 10 min using two AP10N getter pumps, one at room temperature and one at 400 °C. Ar-isotope compositions were measured in static mode using a GV Instruments ARGUS noble gas mass spectrometer equipped with five

Faraday cups and 1012 Ω resistors on mass positions 36–39 and a 1011 Ω resistor on mass position 40. Typical blank levels are ~2.5 × 10−16 mol 40Ar and ~8.1 × 10−18 mol 36Ar. Mass bias was corrected assuming linear mass dependent fractionation and using an atmospheric 40Ar–

36Ar ratio of 295.5. For data handling and raw-data reduction an in-house developed

MATLAB® software package associated with a MySQL database system was used; isochron, inverse isochron, and plateau ages were calculated using ISOPLOT (Ludwig, 2012). All ages were calculated using Fish Canyon sanidine as a flux monitor (28.305 ±0.036 Ma; Renne et al.,

2010). Errors on ages are 1σ. Decay constants used are those given in Renne et al. (2010).

Corrections for interfering Ar isotopes were done using (36Ar/37Ar)Ca = 0.000245, (39Ar/37Ar)Ca

=0.000932, (38Ar/39Ar)K = 0.01211, and (40Ar/39Ar)K =0.00183 and by applying 5% uncertainty.

Results

Table 5 displays a synopsis of the ages obtained through 40Ar/39Ar dating of the muscovite samples and stepwise heating details are provided in Table 6. Sample 95077A was analyzed three times yielding weight mean averages (WMAs), calculated using the shaded steps, of 173.6 ± 2.5 (MSWD = 2.9), 172.4 ± 2.8 (MSWD = 2.3), and 176.2 ± 2.8 (MSWD = 0.016).

The three other muscovite samples yielded similar WMAs (Figure 17) of 173.9 ± 2.5 (sample

95124A, MSWD = 0.6), 176.2 ± 2.6 (sample 95163A-1, MSWD = 11), and 175.9 ± 2.4 (MSWD

= 1.7). The tight ages yielded by the samples (ca. 174) represent the time at which muscovite cooled through its closure temperature of ~400 ± 50 °C (Hames and Bowring, 1994). Thus, the obtained Late-Early to Middle Jurassic ages are interpreted as cooling ages and provide meaningful geologic constraints. The samples were collected from elevations between 4249-

4802 m, and the thermochronometric ages do not show any vertical trends.

Table 5 Summary of 40Ar/39Ar data. Isochron Sample Elevation (m) Mineral mg TGA (Ma) WMA (Ma) MSWD 40Ar/36Ar %Ar steps (inverse, Ma) 95077A 4249 Muscovite 10.4 173.56 ± 2.65 173.6 ± 2.5 174.7 ± 2.6 2.9 268 ± 22 79.1 6-27 (30) 172.4 ± 2.8 172.8 ± 2.8 2.3 294 ± 27 34.3 6-16 (30)

176.2 ± 2.8 177 ± 48 0.016 258 ± 250 44.8 17-26 (30)

95124A 4802 Muscovite 23.3 173.58 ± 0.32 173.9 ± 2.5 174.6 ± 2.3 0.6 290.9 ± 3.4 96.1 7-27 (27) 95163A-1 4296 Muscovite 50.2 175.76 ± 0.45 176.2 ± 2.6 176.1 ± 2.9 11 296.5 ± 5.5 100 1-13 (13) 95163A-2 4296 Muscovite 50.2 175.17 ± 0.41 175.9 ± 2.4 175.9 ± 2.4 1.7 291.8 ± 8.2 91.9 10-19 (19) TGA is total gas age. The weighted mean ages (WMA) and isochron are based on fraction of 39Ar and steps listed. MWSD is the mean square weighted deviation which defines how well data fits the isochron.

Table 6 40Ar/39Ar data and constants used in age calculation. All errors are 1σ. Sample Nr. Step 36Ar ±σ36 37Ar ±σ37 38Ar ±σ38 39Ar ±σ39 40Ar ±σ40 95077A

1 2.0% 0.00046 0.00004 0.00000 0.00007 0.00007 0.00006 0.00006 0.00006 0.14262 0.00188

2 3.0% 0.00647 0.00005 0.00000 0.00007 0.00127 0.00006 0.00076 0.00006 1.96528 0.00459

3 4.0% 0.00807 0.00005 0.00000 0.00007 0.00211 0.00005 0.05716 0.00015 4.07748 0.00813

4 5.0% 0.02610 0.00008 0.00002 0.00007 0.00665 0.00006 0.16032 0.00031 12.22554 0.02629

5 6.0% 0.00574 0.00005 0.00006 0.00006 0.00271 0.00006 0.15150 0.00033 5.98340 0.01245

6 6.8% 0.00369 0.00005 0.00008 0.00008 0.00243 0.00006 0.15747 0.00032 5.61443 0.01173

7 7.6% 0.00401 0.00005 0.00014 0.00008 0.00370 0.00007 0.26785 0.00050 8.96014 0.01576

8 8.3% 0.00423 0.00005 0.00022 0.00008 0.00558 0.00008 0.42154 0.00151 13.53315 0.04095 9 8.8% 0.00314 0.00005 0.00040 0.00008 0.00519 0.00007 0.40580 0.00096 12.50574 0.03013 10 9.2% 0.00315 0.00005 0.00042 0.00008 0.00510 0.00008 0.38852 0.00145 12.20760 0.03839 11 9.6% 0.00313 0.00005 0.00045 0.00007 0.00448 0.00008 0.35416 0.00119 11.10267 0.03114 12 10.0% 0.00293 0.00005 0.00021 0.00009 0.00441 0.00007 0.33346 0.00086 10.41658 0.02160 13 10.5% 0.00293 0.00005 0.00035 0.00008 0.00460 0.00007 0.34997 0.00068 10.91221 0.02031 14 11.1% 0.00367 0.00005 0.00047 0.00008 0.00586 0.00008 0.45543 0.00124 14.11309 0.03302 15 11.6% 0.00378 0.00005 0.00055 0.00008 0.00695 0.00008 0.53887 0.00128 16.61058 0.03897 Sample 95077A: Irradiation number FGA011P7H3 (End date: 2012-04-04 17:30:00.0); CO2-laser; J-value: 0.0035081; J-value error: 0.0000246; f-value 0.994942; f-value error 0.000270; fit model: automatic; Reference standard HDB1 – 24.180 ±0.090 Ma.

(Table 6 continued) Sample Nr. Step 36Ar ±σ36 37Ar ±σ37 38Ar ±σ38 39Ar ±σ39 40Ar ±σ40 95077A 16 12.0% 0.00178 0.00004 0.00062 0.00009 0.00590 0.00009 0.47581 0.00173 14.22673 0.04444

17 12.4% 0.00152 0.00004 0.00073 0.00010 0.00619 0.00010 0.49564 0.00183 14.95120 0.05071

18 12.8% 0.00142 0.00005 0.00064 0.00009 0.00521 0.00008 0.40858 0.00223 12.35899 0.06100

19 13.3% 0.00132 0.00005 0.00057 0.00009 0.00492 0.00010 0.38126 0.00272 11.52776 0.07371

20 14.0% 0.00130 0.00005 0.00070 0.00009 0.00602 0.00010 0.48625 0.00552 14.60415 0.17449

21 14.8% 0.00150 0.00006 0.00092 0.00009 0.00821 0.00011 0.67751 0.00540 20.22507 0.18287

22 15.5% 0.00121 0.00005 0.00017 0.00008 0.00847 0.00009 0.78769 0.00361 23.58763 0.11137

23 16.0% 0.00093 0.00006 0.00066 0.00009 0.00638 0.00010 0.53067 0.00233 15.84217 0.06260

24 16.5% 0.00147 0.00004 0.00108 0.00010 0.00845 0.00017 0.67227 0.00668 20.12559 0.20888

25 16.8% 0.00126 0.00005 0.00104 0.00011 0.00679 0.00015 0.51964 0.00520 15.57177 0.15824

26 17.1% 0.00115 0.00005 0.00093 0.00011 0.00622 0.00014 0.47106 0.00532 14.09662 0.15314

27 17.5% 0.00094 0.00007 0.00085 0.00010 0.00480 0.00022 0.40343 0.01644 12.07684 0.50804

28 18.2% 0.00110 0.00007 0.00097 0.00008 0.00645 0.00023 0.54599 0.02543 13.87912 0.81921

29 19.5% 0.00086 0.00012 0.00087 0.00012 0.00639 0.00069 0.56227 0.06059 16.89237 1.85782

30 22.0% 0.00088 0.00015 0.00062 0.00009 0.00833 0.00122 0.65309 0.07921 19.43603 2.49333

95124A 1 2.0% 0.00066 0.00006 0.00001 0.00007 0.00018 0.00007 0.00010 0.00007 0.20180 0.00065 2 3.0% 0.08709 0.00012 0.00004 0.00008 0.01766 0.00008 0.09044 0.00014 28.97893 0.02882 3 3.8% 0.00965 0.00007 0.00000 0.00007 0.00251 0.00007 0.06426 0.00011 4.76388 0.00282 4 4.6% 0.00602 0.00006 0.00000 0.00007 0.00152 0.00007 0.03630 0.00009 2.88921 0.00281 5 5.4% 0.00553 0.00006 0.00000 0.00008 0.00137 0.00008 0.02457 0.00008 2.39096 0.00177 6 6.2% 0.01551 0.00007 0.00000 0.00006 0.00311 0.00007 0.01732 0.00008 5.09301 0.00451 7 7.0% 0.00395 0.00006 0.00000 0.00006 0.00095 0.00006 0.02006 0.00008 1.78007 0.00256 8 8.0% 0.00486 0.00005 0.00000 0.00006 0.00225 0.00007 0.13229 0.00018 5.32800 0.00664 9 8.7% 0.00436 0.00006 0.00000 0.00007 0.00218 0.00007 0.13002 0.00020 5.11097 0.00759 10 9.2% 0.00190 0.00005 0.00000 0.00006 0.00199 0.00007 0.16124 0.00020 5.26341 0.00650 Sample 95077A: Irradiation number FGA011P7H3 (End date: 2012-04-04 17:30:00.0); CO2-laser; J-value: 0.0035081; J-value error: 0.0000246; f-value 0.994942; f-value error 0.000270; fit model: automatic; Reference standard HDB1 – 24.180 ±0.090 Ma. Sample 95124A: Irradiation number FGA011P7H4 (End date: 2012-04-04 17:30:00.0); CO2-laser; J-value: 0.0035081; J-value error: 0.0000246; f-value 0.994296; f-value error 0.000176; fit model: automatic; Reference standard HDB1 – 24.180 ±0.090 Ma.

(Table 6 continued) Sample Nr. Step 36Ar ±σ36 37Ar ±σ37 38Ar ±σ38 39Ar ±σ39 40Ar ±σ40 95124A 11 9.6% 0.00174 0.00006 0.00000 0.00007 0.00190 0.00006 0.15334 0.00014 4.98286 0.00326 12 10.0% 0.00807 0.00006 0.00000 0.00005 0.00333 0.00006 0.17591 0.00015 7.53745 0.00536 13 10.5% 0.00085 0.00005 0.00000 0.00006 0.00179 0.00006 0.16307 0.00018 5.00843 0.00509 14 11.1% 0.00178 0.00006 0.00000 0.00006 0.00182 0.00007 0.14850 0.00022 4.87263 0.00476 15 11.8% 0.00102 0.00005 0.00000 0.00006 0.00174 0.00007 0.15574 0.00013 4.83629 0.00320 16 12.7% 0.00551 0.00005 0.00000 0.00006 0.00299 0.00006 0.19092 0.00012 7.18522 0.00435 17 13.6% 0.00366 0.00005 0.00000 0.00006 0.00356 0.00006 0.28965 0.00029 9.56685 0.00943 18 14.5% 0.00249 0.00005 0.00000 0.00006 0.00628 0.00006 0.58459 0.00064 17.82467 0.02215 19 15.0% 0.00324 0.00006 0.00000 0.00007 0.00583 0.00006 0.52225 0.00038 16.24235 0.01220 20 15.4% 0.00104 0.00005 0.00000 0.00006 0.00404 0.00007 0.38402 0.00038 11.49937 0.01313 21 15.8% 0.00191 0.00006 0.00000 0.00006 0.00399 0.00007 0.35799 0.00019 11.03138 0.00589 22 16.3% 0.00176 0.00005 0.00000 0.00006 0.00373 0.00006 0.33576 0.00024 10.34819 0.00872 23 17.0% 0.00183 0.00005 0.00000 0.00006 0.00354 0.00007 0.31926 0.00019 9.89099 0.00682 24 17.9% 0.00047 0.00005 0.00000 0.00006 0.00294 0.00007 0.28909 0.00015 8.59253 0.00399 25 19.2% 0.00040 0.00005 0.00000 0.00006 0.00310 0.00006 0.30104 0.00018 8.91069 0.00484 26 21.0% 0.00117 0.00005 0.00000 0.00006 0.00358 0.00006 0.33781 0.00016 10.22631 0.00364 27 24.0% 0.00071 0.00006 0.00000 0.00006 0.00628 0.00006 0.61107 0.00022 18.06877 0.00461 95163A-1 1 2.0% 0.00113 0.00006 0.00000 0.00007 0.00016 0.00007 0.00019 0.00007 0.37786 0.00087 2 3.0% 0.00512 0.00006 0.00000 0.00007 0.00183 0.00007 0.08829 0.00009 4.20665 0.00079 3 4.0% 0.01049 0.00007 0.00000 0.00007 0.00323 0.00007 0.12518 0.00010 6.92283 0.00247 4 5.0% 0.00366 0.00006 0.00000 0.00007 0.00141 0.00007 0.07618 0.00010 3.40050 0.00204 5 6.0% 0.00506 0.00006 0.00000 0.00007 0.00178 0.00007 0.08928 0.00010 4.15729 0.00278 6 7.0% 0.00729 0.00006 0.00000 0.00006 0.00265 0.00007 0.13069 0.00013 6.11071 0.00480 7 8.0% 0.00970 0.00006 0.00000 0.00007 0.00364 0.00007 0.18376 0.00013 8.47309 0.00386 8 9.0% 0.00259 0.00006 0.00000 0.00007 0.00357 0.00007 0.31412 0.00016 10.08764 0.00464 Sample 95124A: Irradiation number FGA011P7H4 (End date: 2012-04-04 17:30:00.0); CO2-laser; J-value: 0.0035081; J-value error: 0.0000246; f-value 0.994296; f-value error 0.000176; fit model: automatic; Reference standard HDB1 – 24.180 ±0.090 Ma. Sample 95163A-1: Irradiation number FGA011P7H5 (End date: 2012-04-04 17:30:00.0); CO2-laser; J-value: 0.0035081; J-value error: 0.0000246; f-value 0.994296; f-value error 0.000176; fit model: automatic; Reference standard HDB1 – 24.180 ±0.090 Ma.

(Table 6 continued) Sample Nr. Step 36Ar ±σ36 37Ar ±σ37 38Ar ±σ38 39Ar ±σ39 40Ar ±σ40 95163A-1 9 9.7% 0.00100 0.00006 0.00000 0.00007 0.00195 0.00006 0.18124 0.00015 5.68068 0.00329 10 10.6% 0.00297 0.00006 0.00000 0.00007 0.00359 0.00007 0.31027 0.00013 10.10143 0.00232 11 11.5% 0.02252 0.00007 0.00000 0.00007 0.00989 0.00007 0.56157 0.00019 23.18514 0.00870 12 12.0% 0.05433 0.00007 0.00000 0.00007 0.01621 0.00007 0.56663 0.00019 33.19553 0.00778 13 12.3% 0.01420 0.00006 0.00000 0.00007 0.00601 0.00007 0.33726 0.00014 14.20655 0.00268 95163A-2 1 2.0% 0.00000 0.00007 0.00000 0.00008 0.00000 0.00007 0.00003 0.00007 0.00253 0.00020 2 3.0% 0.00005 0.00006 0.00000 0.00008 0.00004 0.00006 0.00008 0.00008 0.02090 0.00020 3 4.0% 0.00021 0.00007 0.00000 0.00008 0.00002 0.00007 0.00038 0.00008 0.07433 0.00024 4 5.0% 0.00195 0.00006 0.00000 0.00007 0.00043 0.00007 0.00446 0.00007 0.71168 0.00066 5 6.0% 0.00307 0.00006 0.00000 0.00008 0.00086 0.00007 0.03017 0.00009 1.77898 0.00214 6 7.0% 0.00544 0.00006 0.00000 0.00007 0.00174 0.00007 0.06663 0.00011 3.55941 0.00439 7 8.0% 0.00575 0.00006 0.00000 0.00008 0.00224 0.00007 0.10871 0.00017 4.87509 0.00701 8 9.0% 0.02453 0.00009 0.00000 0.00008 0.00647 0.00007 0.16548 0.00034 12.19503 0.02218 9 10.0% 0.01057 0.00006 0.00000 0.00007 0.00415 0.00007 0.21047 0.00027 9.30351 0.01161 10 11.0% 0.01349 0.00007 0.00004 0.00007 0.01147 0.00007 0.86204 0.00090 29.39519 0.03622 11 11.5% 0.01124 0.00006 0.00005 0.00007 0.01271 0.00007 1.03858 0.00125 33.77649 0.04399 12 11.7% 0.00256 0.00006 0.00003 0.00007 0.00814 0.00007 0.75277 0.00057 22.84054 0.01637 13 11.8% 0.00100 0.00006 0.00005 0.00007 0.00528 0.00006 0.49835 0.00043 14.92363 0.01398 14 11.9% 0.00156 0.00006 0.00004 0.00008 0.00496 0.00007 0.45628 0.00021 13.87427 0.00825 15 12.0% 0.00076 0.00006 0.00002 0.00008 0.00418 0.00007 0.39627 0.00024 11.88562 0.00883 16 12.2% 0.00259 0.00006 0.00003 0.00008 0.00532 0.00007 0.47471 0.00022 14.77073 0.00694 17 12.5% 0.00229 0.00006 0.00006 0.00008 0.00574 0.00007 0.52155 0.00020 16.04742 0.00414 18 13.0% 0.00188 0.00006 0.00006 0.00008 0.00806 0.00006 0.75726 0.00076 22.86268 0.02612 19 13.5% 0.00261 0.00006 0.00010 0.00008 0.00985 0.00008 0.92227 0.00267 27.95319 0.08786 Sample 95163A-1: Irradiation number FGA011P7H5 (End date: 2012-04-04 17:30:00.0); CO2-laser; J-value: 0.0035081; J-value error: 0.0000246; f-value 0.994296; f-value error 0.000176; fit model: automatic; Reference standard HDB1 – 24.180 ±0.090 Ma. Sample 95163A-2: Irradiation number FGA011P7H5 (End date: 2012-04-04 17:30:00.0); CO2-laser; J-value: 0.0035081; J-value error: 0.0000246; f-value 0.995145; f-value error 0.000264; fit model: automatic; Reference standard HDB1 – 24.180 ±0.090 Ma.

Figure 17: 40Ar/39Ar release spectra, K/Ca ratios, and inverse isochrons. Weighted mean ages (WMA) calculated using shaded steps. TGA (total gas age), MWSD (mean square weighted deviation), IIA (inverse isochron age).

DISCUSSION

Summary of Results

Our field evidence suggests there is an isoclinally folded shear zone in the central portion of the Basu Massif (Figure 18). Large-scale folding, mostly to the east, and repetition of granites and metasedimentary rocks, discontinuous serpentinites, and carbonates can be observed on either side of the valley. East of the shear zone there is an array of rocks that indicate intense metamorphism, including eclogites, restites, and amphibolites. We did not venture far past the western shear zone; however, there are high-grade metamorphic assemblages present, such as the mylonitic gneiss mentioned above. Within the center of the shear zone of the Upper Paleozoic unit, generally lower grade metamorphic textures were observed in both the field and thin section; however, a sample taken from a sandstone within the Upper Paleozoic unit shows significant metamorphism as indicated by the presence of garnets and large (~180-270 μm) muscovite grains.

We interpret the area to be part of a fold-thrust belt. The collision of the Lhasa and

Qiangtang terranes would have led to compressional stresses that generated the south- to southwest-directed thrust faulting and folding, as seen in the field. The isoclinally folded shear zone may be the result of a fold-thrust sequence that displaced the belt of serpentinites from the

BNSZ to the north, or alternatively, the belt of serpentinites may have been thrust northward from the mélange belt to the south.

The thermobarometric and petrographic studies suggest regional HP to UHP metamorphism of the Basu Massif, similar to conditions reported in the Amdo Metamorphic

Complex (Guynn et al., 2006; Guynn et al., 2013). Our P-T estimates, using calibrations from

Holland and Blundy (1994) and Ernst and Liu (1988), indicate that the amphibolite sample

(95131A) falls within the upper amphibolite-lower granulite facies. The unusually high temperature range experienced by the amphibolite suggests that it may be a product of crustal thickening and was exhumed from mid-crustal regions to the surface. A retrograde metamorphic pathway was determined for the amphibolite, based on our observations of titanite in ilmenite cores. This alteration is mostly concentrated within the dehydrated, pyroxene-rich veins, and it is indicative of decreasing temperature, which occurs at temperatures less than ~600 °C to temperatures up to ~780 °C.

Figure 18: a) Map defining the isoclinally folded shear zone, b and c) field photos indicating repetition of strata, d) cross section of shear zone, e and f) orientation of the fold is unknown.

P-T estimates of the mylonitic gneiss (95152B) also fall into the upper amphibolite-lower granulite metamorphic facies. Because this sample was collected along the western shear zone

45 and is of upper amphibolite-lower granulite facies metamorphism, it is likely that the fibrolite examined in thin section is caused by retrogressive formation through fluid-assisted and deformation induced reactions (Vernon, 1979; Digel et al., 1998; Musumeci, 2002). The recorded P-T is consistent with the kyanite stability field, at least along or near the boundary, which is a higher metamorphic condition at which the fibrolite would have formed. Thus, isothermal decompression would have resulted in the formation of fibrolite.

The granite sample (95072B) displays retrograde textures, including distinctive sagenitic needles within the hornblende and biotite grains. These oriented rutile needles indicate a decrease in Ti concentration within hornblende and biotite, which suggests decreasing temperature (Henry et al., 2005). Using the calibrations of Holland and Blundy (1994) and Ernst and Liu (1988), we estimated a temperature range from 670-744 °C at ~3 kbar. Based on the petrographic analysis, the granite is most likely characteristic of an intermediate I-type granitic intrusion (Chappell and White, 1974); thus, this sample would have derived from source rocks of igneous composition and not derived from the remelting of the surrounding metasedimentary rocks.

The pressures and temperatures obtained for sample 95092B indicates lower eclogite- upper amphibolite facies metamorphism. The sagenitic textures of the biotite grains observed in thin section suggests a retrograde metamorphic pathway. Furthermore, alteration of rutile to ilmenite, which occurs approximately at 13-16 kbar, is common in thin section and indicates a decrease in pressure. Plagioclase represents just 2% modal amount within sample 95092B.

Earlier in the P-T path in the blueschist facies, plagioclase breaks down when Na is lost to sodic amphiboles or pyroxenes (Winter, 2010). With these textures, alterations, and assemblage, sample 95092B likely underwent a retrograde metamorphic path.

A similar eclogite to the sample above was reported by Zhang et al. (2008) ~7 km to the north; however, the retrograde metamorphism of this eclogite was evaluated based on the analysis of the garnet rims and pyroxene using the amphibole-plagioclase thermometer (Blundy and Holland, 1990) and garnet-hornblende-plagioclase-quartz and garnet-plagioclase- clinopyroxene-quartz barometers (Moecher et al., 1988; Powell and Holland, 1988; Kohn and

Spear, 1990) which yielded lower temperatures (520-620 °C) but similar pressures (10-14 kbar)

(Zhang et al., 2008). The peak metamorphic conditions of the eclogite studied by Zhang et al.

(2008) lies in the range of 930-1050 °C, based on the pyroxene solvus thermometer (Nickel and

Green, 1985; Brey and Kohler, 1990), and 35-45 kbar, based on an Al-exchange barometer for orthopyroxene and garnet (Nickel and Green, 1985; Brey and Kohler, 1990).

Due to the close sampling proximity of these two eclogites and the resemblance of their textures, it is likely that the float eclogite came from the same source. This source, suggested by

Zhang et al. (2008) appears to be continental crust that was subducted to depths >130 km, based on the relatively low Mg and Cr contents of the examined garnet grains and low Mg of clinopyroxene compared to mantle eclogites (Neal and Taylor, 1990; Beard et al., 1992).

Tectonic Implications

The perception that the Lhasa-Qiangtang collision was a relatively insignificant event leading to the development of the Tibetan Plateau (Xu, 1981; Coward et al., 1988; Dewey et al.,

1988; Harris et al., 1990; Zhang et al., 2004; Schneider et al., 2003stip) was driven by the lack of evidence of major mid-Mesozoic tectonism or the presence of a Jurassic arc. Our results, however, provide evidence for a significant tectonothermal event during the latest Early Jurassic- earliest Middle Jurassic time. Metamorphism of the Basu Massif would have been driven by

47 crustal thickening within an extensive contractional setting at approximately 195 Ma, based on stratigraphic data (Wang et al., 2002) and sparse geochronologic data (Guynn et al., 2006), as suggested by Zhang et al. (2009). Based on the results from our thermochronologic data in combination with our geothermobarometric data, we interpret that the Basu Massif was exhumed from lower- to mid-crustal regions to the upper crust during latest Early Jurassic-earliest Middle

Jurassic time. This timing closely resembles the 165 ± 5 Ma age range acquired from 40Ar/39Ar mica and potassium feldspar analyses from orthogneiss samples collected within the Amdo

Metamorphic Complex (Guynn et al., 2006). The syn-collisional and post-collisional magmatism experienced across the Amdo Metamorphic Complex (185-170 Ma; Guynn et al.,

2006), and possibly the Basu Massif, may be attributed to slab breakoff (Coulon et al., 2002; Xu et al., 2008; Zhu et al., 2009, 2011a), which would have driven exhumation. The alkali granitic intrusions seen in the Amdo Metamorphic Complex and Basu Massif may both reflect a time of extension at ca. 172 Ma (Guynn et al., 2006). If so, it is possible, as Burchfiel and Zhiliang

(2012) have suggested, the southern mélange belt represents a failed rift that had formed during the Jurassic.

The Basu Massif likely exists as an extension of the Lhasa terrane and not as a separate crustal fragment, based on shared Triassic and Jurassic strata similarities (Burchfiel and Zhiliang,

2012). If the Basu Massif does belong to the Lhasa terrane, then subduction must have occurred northward beneath the Qiangtang terrane to result in the HP to UHP rocks that have been observed. Thus, the Bangong-Nujiang Suture must certainly have a northward polarity.

Because our data is restricted to Middle Mesozoic time, it is difficult to examine the four initial Cenozoic models that address the Indo-Asian collision. However, what we do know is the

Basu Massif has not experienced much, if any, significant ductile deformation since the Lhasa-

Qiangtang collision. Therefore, during the Indo-Asian collision, the Basu Massif must have moved as a discrete block.

CONCLUSIONS

Our study of the development and deformation along the Bangong-Nujiang suture zone in the Basu Massif area demonstrates the following:

1) There is an isoclinally folded shear zone at the center of the Basu Massif as indicated by the repetition of strata and shear zones with opposing shear senses. This isoclinally folded shear zone may be linked to the BNSZ to the north.

2) The Basu Massif subducted northward beneath the Qiangtang terrane leading to intense metamorphism and the formation of HP-UHP rocks at ~190 Ma.

3) These basement rocks were exhumed, likely due to slab breakoff, and cooled below ~300°C at ca. 174 Ma.

4) The Basu Massif had moved as a discrete block during the Cenozoic Indo-Asian collision as there is no evidence suggesting ductile deformation at this time.

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APPENDIX I: AMPHIBOLE EMPA DATA wt% SiO2 TiO2 Al2O3 Cr2O3 FeO MnO MgO CaO Na2O K2O H2O Total 95092B Amp1 1 41.86 1.5404 14.74 0.0058 15.49 0.1377 11.31 12.05 2.3074 0.9538 0 100.3951 2 41.89 1.5272 14.45 0.0552 15.02 0.1456 11.24 11.38 2.3974 1.0416 0.8668 100.0138 3 41.47 1.5365 14.26 0.0261 15.27 0.1121 11.14 11.73 2.2252 1.0859 1.1496 100.0054 4 41.6 1.5006 14.2 0.061 15.18 0.0978 11.33 11.31 2.2192 1.0792 1.4337 100.0115 5 42.01 1.4544 13.53 0.0436 14.93 0.0872 11.64 11.98 2.1874 0.8919 1.2546 100.0091 95072A Amp1 1 46.44 0.9114 7.61 0.0147 16.74 0.5041 12.28 11.82 1.1666 0.8238 1.6827 99.9933 2 46.73 0.9224 7.64 0.05 16.07 0.5171 12.12 12.23 1.0855 0.8482 1.7902 100.0034 3 46.35 0.9177 7.58 0.0557 16.99 0.5268 12.14 11.78 1.1725 0.8532 1.631 99.9969 4 46.67 0.9199 7.74 0.0499 16.75 0.5504 12.13 12.08 1.139 0.8341 1.1411 100.0044 5 46.18 0.9368 7.57 0 16.83 0.5712 11.92 11.93 1.1451 0.8694 2.0414 99.9939 6 46.96 0.8678 7.39 0.0527 16.86 0.5308 12.33 12.2 1.1144 0.7756 0.9039 99.9852 7 47 0.9091 7.4 0.0147 16.67 0.4836 12.29 11.86 1.1369 0.7885 1.4482 100.001 8 47.03 0.8936 7.42 0.0439 16.89 0.5459 12.43 12.2 1.0952 0.7593 0.6804 99.9883 9 (error) 47.37 0.7894 6.75 0.0499 16.55 0.5978 12.58 11.87 1.0165 0.7597 1.665 99.9983 10 47.57 0.8133 7.15 0.0088 17.06 0.537 12.45 12.3 0.9655 0.7785 0.3679 100.001 95131A Amp1 1 (error) 40.31 0.7146 10.82 0.0571 12.43 0.1288 9.87 9.7 4.92 0.4686 10.57 99.9891 2 (error) 37.57 0.6512 10.31 0.0489 10.66 0.1426 10.78 9.57 1.634 0.6883 17.95 100.005 3 (error) 42.26 0.8275 11.05 0.0764 16.5 0.2023 11.37 12.32 1.7204 0.8359 2.8482 100.0107 4 42.4 0.8776 11.36 0.0967 16.7 0.2007 11.52 12.76 1.6926 0.8556 1.55 100.0132

APPENDIX II: GARNET EMPA DATA wt% SiO2 TiO2 Al2O3 Cr2O3 FeO MnO MgO CaO Total 95092B Grt1 1 38.2 0.0995 21.47 0.0563 23.07 0.5378 6 9.81 99.2436 2 38.81 0.966 21.62 0.0226 22.36 0.5089 6.54 10.03 100.8575 3 38.77 0.702 21.52 0 22.37 0.5012 6.8 10.07 100.7332 4 38.82 0.1109 21.54 0.0788 22.42 0.5005 6.58 10.07 100.1202 5 38.69 0.1088 21.27 0.0758 22.79 0.4658 6.37 9.93 99.7004 6 38.88 0.0661 21.52 0.1377 22.06 0.5851 6.5 10.09 99.8389 7 38.41 0.0789 21.32 0.07 22.14 0.532 6.58 9.99 99.1209 8 38.69 0.0876 21.56 0.0448 22.24 0.5123 6.73 10 99.8647 9 38.73 0.1043 21.56 0.0673 22.08 0.5308 6.79 10.09 99.9524 10 38.51 0.0785 21.57 0.028 22.19 0.4931 6.53 10.06 99.4596 11 38.52 0.0598 21.34 0.0084 22.22 0.5415 6.68 10.07 99.4397 12 38.49 0.0777 21.35 0.039 22.18 0.4989 6.63 9.84 99.1056 13 38.25 0.0886 21.26 0 22.2 0.4768 6.52 9.91 98.7054 14 38.75 0.091 21.52 0.0307 22.71 0.4717 6.52 9.92 100.0134 15 38.66 0.617 21.28 0.0643 22.86 0.502 6.16 10.02 100.1633 16 38.58 0.0868 20.89 0.0364 22.4 0.4329 6.65 9.55 98.6261 17 38.8 0.0711 21.33 0.0393 22.45 0.503 6.46 10.08 99.7334 18 38.91 0.0529 21.76 0.0449 22.92 0.508 6.44 9.85 100.4858 19 38.72 0.0821 21.39 0.0168 23.69 0.6198 5.75 9.99 100.2587 95092B Grt2 1 38.46 0.0861 21.33 0.0084 23.07 0.5279 5.95 10.04 99.4724 2 38.3 0.093 21.35 0.0197 22.84 0.5515 6.22 10.07 99.4442 3 38.4 0.0953 21.73 0 22.68 0.494 6.45 9.99 99.8393 4 38.53 0.0792 21.37 0.031 22.66 0.5193 6.48 10.21 99.8795 5 38.84 0.0735 21.57 0.0225 22.46 0.511 6.41 10.03 99.917 6 38.72 0.0795 21.6 0.0253 22.88 0.5106 6.34 10.04 100.1954

APPENDIX II: GARNET EMPA DATA, CONTINUED wt% SiO2 TiO2 Al2O3 Cr2O3 FeO MnO MgO CaO Total 7 38.82 0.096 21.56 0.0281 22.25 0.5577 6.39 10.06 99.7618 8 38.5 0.0803 21.21 0 22.36 0.5106 6.57 10.18 99.4109 9 38.7 0.0937 21.54 0.0197 22.48 0.4849 6.17 10.11 99.5983 10 38.47 0.0537 21.18 0.0169 22.25 0.5132 6.36 10.28 99.1238 11 38.67 0.067 21.53 0.0366 22.88 0.5108 6.54 10.26 100.4944 12 38.66 0.0861 21.47 0 22.69 0.5028 6.46 10.19 100.0589 13 39.04 0.1281 21.58 0 22.36 0.4926 6.43 10.02 100.0507 14 38.68 0.1155 21.68 0.0028 22.81 0.5113 6.49 10 100.2896 15 38.87 0.0969 21.51 0.0338 22.15 0.5067 6.55 10 99.7174 16 38.72 0.1128 21.64 0.0169 22.49 0.4711 6.51 9.95 99.9108 17 38.46 0.1268 21.83 0.0253 22.52 0.5354 6.29 9.92 99.7075 18 38.47 0.1609 21.51 0.0281 23.08 0.527 6.19 10.02 99.986 19 38.78 0.1532 21.83 0.0814 23.29 0.663 5.79 9.8 100.3876 20 41.69 0.3089 22.52 0.0197 22.69 1.052 3.99 8.62 100.8906 95092B Grt3 1 38.44 0.0655 21.49 0.0478 22.49 0.5076 6.25 9.98 99.2709 2 38.6 0.0915 21.4 0.0282 22.35 0.5022 6.51 9.78 99.2619 3 39.05 0.0875 21.77 0.0452 22.13 0.5548 6.55 9.92 100.1075 4 38.56 0.0894 21.56 0 21.97 0.536 6.61 9.91 99.2354 5 38.9 0.0497 21.62 0 22.25 0.5006 6.64 9.99 99.9503 6 38.52 0.0871 21.68 0 22.15 0.5123 6.6 10 99.5494 7 38.87 0.1257 21.74 0.0395 22.18 0.4746 6.67 9.88 99.9798 8 38.66 0.1115 21.59 0 22.33 0.5603 6.55 10.02 99.8218 9 38.8 0.1229 21.73 0.0085 22.47 0.4803 6.57 10.1 100.2817 10 38.78 0.1473 21.54 0.0649 22.35 0.5131 6.68 10.06 100.1353 11 39.22 0.1012 21.51 0 21.94 0.484 6.52 10.05 99.8252 12 38.52 0.1173 21.69 0.0085 22.06 0.5016 6.54 10.07 99.5074

APPENDIX II: GARNET EMPA DATA, CONTINUED wt% SiO2 TiO2 Al2O3 Cr2O3 FeO MnO MgO CaO Total 13 39.15 0.1136 21.78 0.0255 21.6 0.5067 6.52 10.07 99.7658 14 38.64 0.0852 21.82 0 22.46 0.4993 6.71 10.04 100.2545 15 38.99 0.1017 21.54 0.0057 21.93 0.4749 6.56 10.11 99.7123 16 38.63 0.0802 21.66 0 22.23 0.4889 6.61 9.97 99.6691 17 38.95 0.0955 21.89 0.0141 22.32 0.4653 6.71 10.02 100.4649 18 38.69 0.108 21.59 0.0226 22.56 0.5237 6.73 9.86 100.0843 19 38.91 0.0936 21.74 0 22.39 0.4521 6.74 10.12 100.4457 20 38.45 0.0922 21.57 0.079 22.38 0.472 6.54 9.88 99.4632 21 38.8 0.0938 21.67 0.0028 22.74 0.4731 6.56 9.75 100.0897 22 38.6 0.1358 21.66 0.0225 22.82 0.486 6.25 9.91 99.8843 23 38.73 0.1218 21.69 0.0423 22.28 0.4981 6.3 10.1 99.7622 24 38.6 0.0783 21.48 0.0028 22.62 0.4675 6.57 9.97 99.7886 25 39.17 0.0978 21.88 0 22.35 0.5029 6.73 10.01 100.7407 26 38.56 0.1123 21.79 0.0197 22.3 0.4756 6.59 10.05 99.8976 27 38.85 0.0775 21.6 0 22.42 0.5156 6.6 10.19 100.2531 28 39.73 0.0817 21.64 0.0395 22.39 0.492 6.66 10.05 101.0832 29 39.04 0.1024 21.7 0 21.52 0.4631 6.99 9.37 99.1855 30 38.82 0.097 21.57 0.0339 22.4 0.458 6.74 9.84 99.9589 31 39.21 0.0829 21.78 0.0254 22.19 0.5066 6.59 9.95 100.3349 32 38.61 0.0955 21.82 0.0932 22.34 0.5053 6.53 10.1 100.094 33 38.74 0.1024 21.85 0.0424 22.12 0.556 6.61 10.04 100.0608 34 32.36 0.0683 19.06 0.0224 20.94 0.3374 9.9 5.64 88.3281 35 38.97 0.0687 21.98 0.0226 22.31 0.5522 6.59 9.87 100.3635 36 38.68 0.0947 21.92 0.0677 22.57 0.4814 6.51 9.98 100.3038 37 38.82 0.0908 21.94 0.0761 22.42 0.5404 6.44 9.8 100.1273 38 38.82 0.0603 21.64 0.0451 22.98 0.506 6.1 10.04 100.1914 39 39.05 0.095 21.97 0 22.83 0.5508 6.25 10.01 100.7558

APPENDIX II: GARNET EMPA DATA, CONTINUED wt% SiO2 TiO2 Al2O3 Cr2O3 FeO MnO MgO CaO Total 40 38.81 0.0705 21.7 0.0197 23.04 0.5541 5.84 9.92 99.9543 41 38.95 0.0756 21.84 0.0141 22.85 0.6719 5.67 10.48 100.5516 95152B Grt1 1 37.79 0 21.55 0.03 32.39 2.18 4.11 2.46 100.51 2 37.23 0.02 21.48 0.03 31.2 1.63 4.52 2.91 99.02 3 37.22 0.04 21.54 0.03 32.02 2.4 3.87 2.68 99.8 4 37.85 0.03 21.1 0 33.1 2.57 4.01 2.12 100.78 95152B Grt 2 1 37.9 0.06 21.05 0.01 32.83 2.14 4.37 2.03 100.39 2 37.88 0.06 21.17 0 32.34 1.83 4.79 2.41 100.48 3 37.6 0.04 21.21 0 31.45 1.8 4.69 2.91 99.7 4 37.96 0.01 20.68 0 32.59 2.34 3.93 1.61 99.12 5 37.56 0 21.33 0 33.83 2.14 4.39 2.28 101.53

APPENDIX III: BIOTITE EMPA DATA wt% SiO2 TiO2 Al2O3 Cr2O3 FeO MnO MgO CaO BaO Na2O K2O Cl H2O Total 95072A Bt1 1 36.88 3.64 14.9 0.0828 19.43 0.2566 11.83 0.0119 0.2628 0.098 9.07 0.0571 3.49 100.0092 2 36.5 3.54 14.54 0.0513 19.47 0.2504 12.05 0.0123 0.3511 0.1267 9.11 0.051 3.96 100.0128 3 36.46 3.42 14.74 0.0541 19.72 0.2717 12.09 0 0.3341 0.0866 8.51 0.0741 4.25 100.0106 4 36.42 3.39 14.46 0.0571 19.4 0.2984 12.03 0.0258 0.0922 0.0602 9.05 0.025 4.69 99.9987 5 36.26 3.6 14.43 0.037 20.61 0.3041 11.33 0.0134 0.1137 0.1796 8.49 0.0401 4.6 100.0079 95072A Bt2 1 37.23 3.56 14.93 0.0656 19.92 0.2852 12.21 0.1188 0.1206 0.1682 8.99 0.0251 2.3853 100.0088 2 36.6 3.59 14.42 0.0544 19.78 0.2719 12.01 0.0943 0.1947 0.2139 8.39 0.0684 4.33 100.0176 3 36.31 3.53 14.62 0.0372 19.64 0.2729 12.05 0.0288 0.1578 0.1059 9.3 0.0412 3.92 100.0138 4 36.63 3.5 14.55 0.0542 20.42 0.3473 12.22 0.0923 0.134 0.1047 8.15 0.0352 3.77 100.0077 5 36.52 3.56 14.59 0.0315 19.98 0.3225 12.02 0.0569 0.1962 0 8.92 0.0472 3.76 100.0043 95092B Bt 1 1 35.5 2.7679 16.89 0.0374 18.39 0.0572 12.54 0.0937 0.2178 0.0085 8.22 0.0303 5.25 100.0028 2 36.09 3.21 16.55 0.0575 18.12 0.1248 12.72 0.0267 0.2629 0.1156 8.99 0.0252 3.71 100.0027 3 35.16 9.56 13.28 0.0528 14.25 0.0933 9.74 5.77 0.131 0.016 6.86 0.0259 5.08 100.019 4 35.62 2.9088 16.88 0.0144 17.62 0.0573 13.24 0.0305 0.1977 0.0655 8.26 0.0364 5.07 100.0006 5 36.37 3.47 16.02 0.0288 18.07 0.0512 13.04 0.033 0.2578 0.0918 8.65 0.0353 3.88 99.9979 6 36.34 3.48 15.96 0.052 17.27 0.0167 13.15 0 0.2114 0.0198 8.39 0.0192 5.09 99.9991 7 35.52 3.58 16.52 0 18.29 0.0155 12.82 0.027 0.2006 0 8.55 0.0202 4.46 100.0033 8 35.23 2.7785 16.72 0.0666 17.08 0.0622 13.38 0.0343 0.2221 0 7.8 0.0274 6.6 100.0011 95092B Bt 2 1 35.78 3.57 16.07 0.0029 16.9 0.0836 13.58 0.0418 0.2065 0.0777 8.32 0.0273 5.35 100.0098 95152B Bt 1 1 35.42 3.16 19.44 0.03 18.92 0.09 9.54 0.09 0 0.21 9.49 0.04 3.58 100.01 2 35.02 3.14 19.57 0.05 18.63 0.14 9.59 0.07 0 0.3 9.63 0.02 3.85 100.01 3 35.52 3 19.67 0.04 19.53 0.13 9.24 0.21 0 0.32 8.5 0 3.85 100.01

APPENDIX III: BIOTITE EMPA DATA, CONTINUED wt% SiO2 TiO2 Al2O3 Cr2O3 FeO MnO MgO CaO BaO Na2O K2O Cl H2O Total 95152B Bt 2 1 35.74 2.93 19.13 0.05 18.5 0.07 10.12 0.04 0 0.29 10.21 0.02 2.91 100.01 2 33.88 2.7 19.43 0.07 20.75 0.2 9.12 0.03 0 0.17 9.35 0.02 4.28 100 3 34.24 2.88 19.18 0.08 19.34 0.15 10.06 0.03 0 0.04 9.27 0.02 4.7 99.99 95152B Bt 3 1 35.38 2.66 19.2 0.01 18.22 0.13 9.43 0.12 0 0.24 10.06 0.02 4.54 100.01 2 34.23 2.29 20.03 0.04 19.31 0.14 9.93 0.17 0 0.23 9.19 0.02 4.42 100

APPENDIX IV: PLAGIOCLASE EMPA DATA wt% SiO2 Al2O3 CaO BaO Na2O K2O FeO MgO Total 95072A Pl1 1 56.42 27.52 9.42 0 6.25 0.1438 0.2219 0.0101 99.9858 2 56.96 27.21 9.29 0.0158 6.57 0.1332 0.1098 0 100.2888 3 57.13 27.08 8.94 0.007 6.49 0.1094 0.0772 0.019 99.8526 4 57.53 27.01 8.67 0 6.25 0.1045 0.1001 0.0651 99.7297 5 55.87 27.32 9.21 0.0316 6.33 0.1396 0.1604 0.0535 99.1151 6 56.4 27.6 9.71 0 5.84 0.1285 0.0688 0 99.7473 7 55.97 27.89 9.55 0.0263 6.21 0.0997 0.0675 0.0405 99.854 8 57.65 27.38 8.97 0 6.62 0.0987 0.0615 0.0408 100.821 9 54.91 28.71 10.49 0.0333 5.48 0.1236 0.0953 0.024 99.8662 10 56.58 27.86 9.71 0.0263 5.83 0.0886 0.047 0.0229 100.1648 11 54.35 28.7 10.81 0 5.53 0.1267 0.076 0.0123 99.605 12 54.6 29.15 11.21 0.0088 5.22 0.116 0.1411 0.0126 100.4585 13 56.1 28.01 9.75 0 6.16 0.1146 0.1061 0 100.2407 14 54.93 29.11 11.31 0 5.4 0.1384 0.158 0 101.0464 15 54.52 28.61 10.54 0.0351 5.38 0.1425 0.1134 0.0972 99.4382 16 54.62 29.52 11.53 0 5.23 0.1366 0.1424 0 101.179 17 54.72 28.75 10.75 0.0176 5.69 0.1481 0.1797 0 100.2554 18 55.33 29.04 10.81 0.0281 5.55 0.1417 0.1436 0.0432 101.0866 19 58.92 26.06 7.3 0.028 7.32 0.1986 0.1835 0.0323 100.0424 20 59.99 21.95 3.98 0 6.69 0.933 1.391 0.8967 95.8307 95131A Pl1 1 55.59 28.2 9.95 0 5.87 0.1075 0.327 0 100.0445 2 55.82 27.97 10.28 0.0509 5.82 0.1113 0.3185 0.021 100.3917 3 57.61 26.65 8.34 0 6.62 0.1496 0.3017 0.0222 99.6935 4 58.53 26.38 8.26 0 7.02 0.1622 0.3283 0 100.6805 5 58.3 26.33 7.9 0 6.91 0.1366 0.2498 0 99.8264

APPENDIX IV: PLAGIOCLASE EMPA DATA, CONTINUED wt% SiO2 Al2O3 CaO BaO Na2O K2O FeO MgO Total 6 57.44 27.36 9.14 0.0018 6.7 0.1241 0.2812 0.0259 101.073 7 55.67 27.62 9.72 0 5.77 0.1004 0.3064 0.0465 99.2333 8 55.82 27.99 10.32 0.0018 5.92 0.1251 0.3751 0.0149 100.5669 9 55.5 27.99 9.79 0 6.03 0.0979 0.3149 0 99.7228 10 55.89 28.03 10.41 0.0825 5.97 0.097 0.2955 0 100.775 95092B Pl1 11 58.51 24.93 6.63 0.0193 7.5 0.1089 0.584 0.0009 98.2831 12 57.58 25.27 7.27 0.0473 7.22 0.0926 0.5538 0.0704 98.1041 13 57.09 25.39 7.32 0.0298 7.33 0.1051 0.6127 0.0064 97.884 95152B Pl1 13 60.93 24.65 5.74 0.05 8.33 0.27 0.02 0 99.99 14 60.9 24.81 5.6 0.06 8.04 0.3 0 0 99.71 15 61.93 24.58 5.48 0.02 8.41 0.31 0 0 100.73 16 61.75 24.13 5.59 0 8.12 0.36 0.04 0 99.99 17 60.76 24.49 5.96 0.05 7.74 0.4 0.04 0.03 99.47 18 60.23 24.77 5.95 0.01 8.37 0.24 0.06 0.02 99.65 19 60.98 24.95 6.11 0.07 7.86 0.23 0.06 0 100.26

APPENDIX V: MINERAL STANDARDS

Element Amphibole Standard Garnet Standard Biotite Standard Plagioclase Standard Si Kakanui Hornblende Toronto Almandine Kakanui Hornblende Tornoto Albite Ti Kakanui Hornblende Kakanui Hornblende Kakanui Hornblende * Al Kakanui Hornblende Toronto Almandine Kakanui Hornblende Lake Country Plagioclase Cr Chromite Tiebaghi Mine Chromite Tiebaghi Mine Chromite Tiebaghi Mine * Fe Kakanui Hornblende Toronto Almandine Kakanui Hornblende Kakanui Hornblende Mn Ilmenite, Ilmen. Mtns. Toronto Rhodonite Toronto Rhodonite * Mg Kakanui Hornblende Kakanui Pyrope Kakanui Hornblende Kakanui Hornblende Ca Kakanui Hornblende Garnet, Roberts Victor Mine Kakanui Hornblende Lake Country Plagioclase Ba Kakanui Hornblende * Toronto Sanidine Toronto Sanidine Na Kakanui Hornblende * Kakanui Hornblende Toronto Albite KK * * Toronto Biotite Toronto Sanidine FK * * Fluorapatite, Durango * Cl * * * *

VITA

Chase Billeaudeau is a native of Erwinville, Louisiana. He enrolled in Louisiana State

University and earned a Bachelor of Science degree in Geology in December of 2011.

Afterwards, he accepted full-time employment with Conestoga-Rovers & Associates as a geologist. With a goal set to join the oil and gas industry, Chase went on to pursue his Master of

Science degree in Geology beginning in August 2012. He interned with Marathon Oil in summer of 2014. His interests lie in the challenging field of exploration geology.