Contractional Tectonics: Investigations of Ongoing Construction of The

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2014 Contractional Tectonics: Investigations of Ongoing Construction of the Himalaya Fold-thrust Belt and the Trishear Model of Fault-propagation Folding Hongjiao Yu Louisiana State University and Agricultural and Mechanical College, [email protected]

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Recommended Citation Yu, Hongjiao, "Contractional Tectonics: Investigations of Ongoing Construction of the Himalaya Fold-thrust Belt and the Trishear Model of Fault-propagation Folding" (2014). LSU Doctoral Dissertations. 2683. https://digitalcommons.lsu.edu/gradschool_dissertations/2683

This Dissertation 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 Doctoral Dissertations by an authorized graduate school editor of LSU Digital Commons. For more information, please [email protected]. CONTRACTIONAL TECTONICS: INVESTIGATIONS OF ONGOING CONSTRUCTION OF THE HIMALAYAN FOLD-THRUST BELT AND THE TRISHEAR MODEL OF FAULT-PROPAGATION FOLDING

A Dissertation

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 Doctor of Philosophy

The Department of Geology and Geophysics

by Hongjiao Yu B.S., China University of Petroleum, 2006 M.S., Peking University, 2009 August 2014 ACKNOWLEDGMENTS

I have had a wonderful five-year adventure in the Department of Geology and

Geophysics at Louisiana State University. I owe a lot of gratitude to many people and I would not have been able to complete my PhD research without the support and help from them.

This dissertation is dedicated to my advisor, Dr. Alex Webb, who set priorities and motivation for my graduate studies. His constant encouragement, guidance, advice, enthusiasm to geology, and rigorous requirements have inspired me to make progress and helped me complete my thesis work with happiness and tears.

I also appreciate the support and inspiration I've received from my committee members and other faculty at LSU: Dr. Gary Byerly, Dr. Barb Dutrow, Dr. Darrell Henry, and Dr. Peter

Clift for their generous time and effort in guiding and reviewing my Ph.D. work.

The thermochronologic data in this dissertation was conducted in Geologie, Technische

Universitat Bergakademie Freiberg in Germany for about 9 months. I am grateful to Dr.

Raymond jonckheere for his insight and patience to advance my knowledge of Fission track technique. I benefited a lot from discussion with Dr. Lothar Ratschbacher and I also want to thank him for arranging my trip in Germany. I extend my thankfulness to Bastian Wauschkuhn,

Yang Zhao for their helpful advice on fission track sample preparation and data analysis.

I would like to thank Dr. Kyle Larson for analyzing quartz c-axis fabrics, Rick Young for making thin sections, and Kyle Barber for rock cutting.

I want to extend my appreciation to my fellow graduate students Dennis Donaldson,

Cindy Colόn, and Chase Billeaudeau in the Structural Geology group. Their helps and discussions have been always encouraging me to move forward.

Finally, I would like to express my gratefulness to my Husband Dian He and my parents in law. I owe a great debt of gratitude to my parents. Without their sacrifices and support, I would have not even started this journey abroad yet.

The Himalayan research was supported by the start-up grant from Louisiana State

University and the Louisiana Board of Regents grant to Dr. Webb, the AAPG and GSA graduate student research grants to Hongjiao Yu.

The Uncompahgre Uplift research is my intern project in Shell Oil Company. I would like to thank J.P. Brandenburg, David Wolf, Steve Naruk, David Kirschner, and Michael Gross for their guidance and discussions when I was interning at Shell.

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TABLE OF CONTENTS

ACKNOWLEDGMENTS…………………………………………………………………...……ii

ABSTRACT………………………………………………..…………………………………….vi

CHAPTER 1 INTRODUCTION…………………………………………………………………..…………….1 1.1 The Himalayan Fold-thrust Belt ………..………………………………………………….1 1.2 The Uncompahgre Uplift …..………………………………………………………………3

CHAPTER 2 EXTRUSION VERSUS DUPLEXING MODELS OF HIMALAYAN MOUNTAIN BUILDING: DISCOVERY OF THE PABBAR THRUST, NW INDIAN HIMALAYA …………...... ……5 2.1 Introduction…………………………………………………………………….…...………5 2.2 Geology of the Northwest Indian Himalaya ……………………………………………...11 2.2.1 Stratigraphic Diversity……….………………………………….……………………12 2.2.2 Tectonic framework....……………………..…………………………….…………...14 2.3 Methods……………………………………………………………………………………17 2.3.1 Field Mapping………………………………………………..……………………….17 2.3.2 Microstructural Analysis ………………...……………………….…………………..17 2.4 Results of Structural Geology Mapping ……...…………………………………………..18 2.4.1 Field Observations …………………………………………………………………...21 2.4.1.1 Tharoch Transect.………………………………..………………………………21 2.4.1.2 Lower Pabbar Transect …………………..……...... …………………………….26 2.4.1.3 Tons River Transect…..…..……………………………………………….……..28 2.4.2 Quartz Microstructures ………………………………….………………...…………30 2.5 Discussion …………………………………...……………………………………………31 2.5.1 Kinematic Evolution of the Tons Thrust, Pabbar Thrust and Berinag Thrust……...... 32 2.5.2 Along-strike Variations of Thrust Geometries and Stratigraphic Correlation…...…...33 2.6 Conclusions………………………………………………………………………………..38

CHAPTER 3 KINEMATIC EVOLUTION OF HIMALAYAN OROGEN CONSTRAINED BY NEW FISSION TRACK ANALYSIS IN NW INDIA…..…………………………….……………….41 3.1 Introduction……………………………………………………………………………...... 41 3.2 Methods: Apatite and Zircon Fission Track Analysis………….…………………………42 3.3 Results………………………………………………………………………………...... 46 3.3.1 Fission Track Analysis…………………………………………………………...... 46 3.3.2 Interpretation…….………….……………………………………………………...... 49 3.4 Balanced Palinspastic Reconstruction Across the NW Indian Himalaya…………………51 3.4.1 Restoration ca. 28 Ma……………..……………………………………………….....54 3.4.2 Restoration ca. 20 Ma……………..……………………………………………….....54 3.4.3 Restoration ca. 13 Ma……………..……………………………………………….....54 3.4.4 Restoration ca. 8.1 Ma…………….……………………………………………….....55 3.4.5 Restoration ca. 5.2 Ma…………….……………………………………………….....55

3.5 Discussion: Extrusion vs. Duplexing Models of Himalayan Mountain Building……...…56 3.6 Conclusions……...….……………………………………………………………………..58

CHAPTER 4 KINEMATIC TRISHEAR MODEL OF FAULT-PROPAGATION FOLDING TO PREDICT DEFORMATION BANDS, COLORADO NATIONAL MONUMENT, NW UNCOMPAHGRE UPLIFT, USA……………………………………………………………………………………59 4.1 Introduction………………………………………………………………………………..59 4.2 Geology Background……….…...……………………………………………………..….62 4.2.1 Tectonic History of the Uncompahgre Uplift………………………………………...62 4.2.2 Major Stratigraphy…...…………...…………………………………………………..65 4.2.3 Major Faults in CNM, Uncompahgre Uplift…….……………………………………66 4.3 Methods and Data……………………………………………………………………..67 4.3.1 Method: Kinematic Trishear Model of Fault-propagation Folding……………...…...67 4.3.2 Data: Characteristics of Deformation Bands in CNM………..………………………68 4.4 Results……………………………..……………………………………………………....69 4.4.1 Balance Reconstruction………….………………….……………………………...... 69 4.4.1.1 Cross Section Reconstruction along the East Kodels Canyon...………..………..70 4.4.1.2 Cross Section Reconstruction along the North Canyon…..…………..………..71 4.4.1.3 Cross Section Reconstruction along the East Canyon…..…………….………..71 4.4.2 Strain Calculation………...……………………………..…………………….……....75 4.5 Discussion………….…………...…………………………………………………………77 4.6 Conclusions……………………………………………………………………..…………79

CHAPTER 5 SUMMARY AND CONCLUSIONS………..…………………………………………………..81 5.1 Growth of the Himalayan Fold-thrust belt Dominated Duplexing Processes…...….……..81 5.2 Kinematic Trishear Fault-propagation Folding Model to Predict Deformation Bands…...83

REFERENCES………..………………………………………………………………………....85

APPENDIX A: APATITE FISSSION TRACK DATA.……………………………………………...…………108

APPENDIX B: ZIRCON FISSSION TRACK DATA...……………………………………………...…………114

PLATE 1: SEQUENTIAL CROSS-SECTION RESTORATION ACROSS THE NW INDIAN HIMALAYA………………………….……………………………………………...…………127

VITA……………………………………………………………………………………………128

ABSTRACT

This dissertation focuses on the kinematic evolution of contractional tectonics: the

Himalayan fold-thrust belt along the collisional orogenic belts, and growth of the basement- cored monoclines in Colorado Plateau.

Ongoing Himalayan growth is generally thought to be dominated by duplexing and/or extrusion processes. Duplexing models highlight accretion of material from the subducting plate to the over-riding orogenic wedge, whereas extrusion models focus on up-dip translation of a block bounded by out-of-sequence faults. Here, a primary outstanding question involves the uncertain relationship of the Berinag thrust and the Tons thrust, structures with displacements of >80 km and >40 km, respectively. The uncertainty allows the complete range of duplexing and extrusion processes for the integrated kinematic history since the Middle Miocene.

To address this issue, field mapping, kinematic analysis, and analysis of quartz recrystallization textures were performed. Our results reveal a new discovery: a ~ 450 m thick top-to-southwest shear zone, termed the Pabbar thrust. The Pabbar thrust placed the Outer Lesser

Himalayan Sequence (the Tons thrust hanging wall) directly on the Berinag Group (the Berinag thrust hanging wall). This discovery requires that the Pabbar thrust developed first, followed by footwall accretion of the Berinag-Tons thrust sheet, operating as a single structure. The Berinag thrust and Tons thrust are in fact the same structure. Low temperature thermochronological data, and a line-length balanced palinspastic reconstruction across the NW Indian Himalaya place robust constraint on Himalayan mountain building process: (1) Late Oligocene–Middle Miocene emplacement of the Great Himalayan Crystalline Complex (GHC) and juxtaposing of the THS atop the Lesser Himalayan Sequence (LHS). (2) Middle–Late Miocene accretion of the Berinag-

Tons thrust sheet; and (3) subsequent growth via a hinterland-dipping upper crustal duplexing and an antiformal stack of mid-crustal horses developed simultaneously.

Trishear provides an alternative model of fault-propagation. It is successfully applied to create balanced cross sections for the monoclines in Uncompahgre Uplift. Forward modeling of strains around the fault tip zone demonstrates excellent agreement with field-based strain calculated from deformation bands, and can explain distribution and orientation of deformation bands in eolian sandstone.

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CHAPTER 1 INTRODUCTION

1.1 The Himalayan Fold-thrust Belt

The Himalaya is an excellent natural laboratory for studying growth of fold-thrust belts because it is active, has rapid convergence along a ~2500 km long arc, and is impacted by the powerful climatic system of the Asian monsoon (e.g., Hodges, 2000; Avouac, 2003; 2008; Yin,

2006). This system has received intense study over the last decade, which has produced numerous hypotheses and discoveries of interactions between climatic, erosional, and tectonic processes (e.g., Beaumont et al., 2001; 2004; Hodges et al., 2001; Zeitler et al., 2001, Burbank et al., 2003; Vance et al., 2003; Bookhagen et al., 2005a; 2005b; Grujic et al., 2006; Montgomery and Stolar, 2006; Dupont-Nivet et al., 2007; Rahl et al., 2007; Clift et al., 2008; Jessup et al.,

2008; Robl et al., 2008; Royden et al., 2008; Wobus et al., 2008; Boos and Kuang, 2010;

Armstrong and Allen, 2011; Iaffaldano et al., 2011). However, first-order aspects of the kinematics of ongoing mountain-building remain uncertain, which is generally thought to be dominated by duplexing and/or extrusion processes. Duplexing models are dominated by accretion of material from the downgoing plate to the over-riding wedge, with only minor out-of- sequence deformation. Extrusion models highlight southward extrusion of a fault-bounded block, with an out-of-sequence thrusting below and a normal faulting above.

Exploration is largely focused on a ~20-50 km wide orogen-parallel band of rapid uplift and exhumation, marked by a steep topographic rise, that first appears ~70-100 km north of the range front. Extensive efforts to understand the kinematic development across this zone include structural balancing (e.g., DeCelles et al., 2001; Robinson et al., 2006; Robinson, 2008;

McQuarrie et al., 2008; Mitra et al., 2010; Yin et al., 2010; Long et al., 2011), thermochronology

(e.g., Wobus et al., 2003; Thiede et al., 2004; 2005; 2009; Huntington et al., 2006; Blythe et al.,

2007; Deeken et al., 2011), thermobarometry coupled to geochronology (e.g., Harrison et al.,

1997; Catlos et al., 2001; 2004; Robinson et al., 2003; Bollinger et al., 2004), and thermokinematic and mechanical modeling (e.g., Godard et al., 2006; Godard and Burbank, 2011;

Wobus et al., 2006; Whipp et al., 2007; Herman et al., 2010). The proposed out-of-sequence thrust faulting coincides with trace of the Munsiary thrust. The hanging wall of the proposed out- of-sequence coincides in map view with the proposed duplexing region along a mid-crust ramp in a ~20-50 km wide. Detailed thermokinematic modeling of thermochronometric data from this zone has failed to rule out either duplexing or out-of-sequence models (Wobus et al., 2006;

Whipp et al., 2007; Herman et al., 2010).

Analog (sandbox) and numerical simulations of fold-thrust belt evolution highlight the importance of strength heterogeneities and erosion (Konstantinovskaia and Malavieille, 2005;

2011; Bonnet et al., 2007; Stockmal et al., 2007). Experiments with multiple decollements, erosion and syntectonic sedimentation results in the development of an hinterland antiformal stacking underlying a zone of maximum exhumation, and hinterland dipping duplex by upper crustal foot accretion or imbricated stacks by frontal accretion towards the foreland

(Konstantinovskaia and Malavieille, 2005; Naylor et al., 2005; Bonnet et al., 2007; Stockmal et al., 2007; Malavieille, 2010).

The proposed study will investigate the kinematics of ongoing mountain building, in particular the development of the rapid exhumation zone, by integrated geological research across the NW Indian Himalaya. Our work is composed of three components: (1) structural and kinematic mapping combined with microstructural investigations to address key questions about the regional structure; (2) apatite and zircon fission track thermochronology to address the

2 important regional gap in such data, to the south of the zone of rapid uplift; (3) interpretation of data from the first two research components via balanced palinspastic reconstruction.

1.2 The Uncompahgre Uplift

The Uncompahgre uplift is one of several NW-SE trending anticlines in the Colorado plateau. This area experienced three major tectonic events: 1) Proterozoic extension generated the basement-penetrating normal faults (e.g., Marshak and Paulsen, 1996; Karlstrom and

Humphreys, 1998; Marshak et al., 2000; Timmons et al., 2001; Whitmeyer and Karlstrom,2007);

2) The Late Paleozoic Ancestral Rockies orogeny (320-245 Ma) created a series of basins and basement-core uplifts by crustal shortening on high-angle reverse and thrust faults (e.g., Kluth and Coney, 1981; Bally et al., 1989; Ye et al., 1996); and 3) The Late Cretaceous to middle

Eocene (~70-50 Ma) Laramide Orogeny generated a series of highly asymmetrical, fault-cored anticlines via reactivation of inherited Precambrian basement faults (e.g., Stearns and Jamison,

1977; Brewer et al., 1982; Allmendinger et al., 1982; Heyman, 1983; Heyman et al., 1986;

Brown, 1988, 1993; Blackstone, 1993; Huntoon, 1993; Schmidt et al., 1993; Foos, 1999;

Marshak et al., 2000; Erslev et al., 2001; Bump and Davis, 2003; Bump, 2004; Erslev and

Koenig, 2009; Brandenburg et al., 2012). This study focuses on the Laramide monoclines because classic deformation bands in eolian sandstone are associated with the growth of those fault-core monoclines (e.g., Jamison 1979; Jamison and Stearns, 1982). Those basement-cored monoclines are thought to be developed by fault-propagation folding (e.g., Erslev, 1991; Erslev and Rogers, 1993; Kellogg et al., 1995; Erslev and Selvig, 1997; Tindall and Davis, 1999;

Brandenburg et al., 2012). The traditional kink-band based fault-propagation folding features angular fold hinges, uniform dips and constant thickness of fold limbs due to homogeneous strain as a result of layer-parallel shear, and fixed fault propagation/slip ratio (P/S = 2) (e.g.,

Suppe, 1983; Suppe and Medwedeff, 1990). Those characteristics of kink-band based fault- propagation folding failed to explain inclined Precambrian basement-Mesozoic rock contact, curved fold hinges and thickening and thinning of fold limbs. Previous workers in this area propose that multiple faults spread from the main thrust can create a triangular shape of basement rocks that allow the rotation of the contact (e.g., Scott et al., 2001). However, there is no geophysical data to support the existence of this kind of main thrust.

Trishear provides an alternative model of fault-propagation folding characterized by heterogeneous strain generated by inclined shear in a triangular zone above the fault tip, which commonly exhibits curved hinges, broad crested anticlines, non-uniform dips, and changing thickness of fold limbs (e.g., Erslev, 1991; Allmendinger, 1998; Hardy and Allmendinger, 2011;

He et al., 2014 in review). Trishear model has already been applied to other monoclines in the

Colorado Plateau to successfully explain the geological features there (e.g., Erslev and Selvig,

1997; Cristallini and Allmendinger, 2001; Bump, 2003; Cristallini et al., 2004; Brandenburg et al., 2012).

In this study, the trishear model is applied to reconstruct the basement-cored monocline growth in Uncompahgre uplift along three balanced cross sections. The best-fit parameters are determined for fault movement from reconstruction, which are used later for forward trishear modeling of the target fault movement to calculate corresponding maximum shortening strain.

The modelling strain demonstrates excellent agreement with field-based strain calculated from deformation bands, and can explain distribution and orientation of deformation bands in eolian sandstone. The correlation may have significant implications with regard to better constraining on the fluid pathways around faults because of low permeability of deformation bands.

CHAPTER 2 EXTRUSION VERSUS DUPLEXING MODELS OF HIMALAYAN MOUNTAIN BUILDING: DISCOVERY OF THE PABBAR THRUST, NW INDIAN HIMALAYA

2.1 Introduction

Knowledge of ongoing orogenic growth processes along the Himalayan front of the

India-Asia collision has expanded considerably in recent years. Along- and across-strike variations in large-scale kinematics have revealed the importance of river erosion and radial expansion in focusing deformation (Montgomery and Stolar, 2006; Murphy et al., 2009), and the range continues to serve as a primary testing ground for climate-erosion-tectonic interaction models (e.g., Grujic et al., 2006; Adlakha et al., 2013; Thiede and Ehlers, 2013; Scherler et al.,

2014). It has been demonstrated that climate-driven changes in orogenic topography can produce resolvable changes in plate kinematics (Iaffaldano et al., 2011). Many of these discoveries provide a new three-dimensional understanding of the orogenic evolution. Nevertheless, ongoing

Himalayan growth is primarily controlled by essentially two-dimensional arc-perpendicular shortening. This shortening is generally thought to be dominated by duplexing and/or extrusion processes.

Duplexing models are dominated by accretion of material from the downgoing plate to the over-riding wedge, with only minor out-of-sequence deformation (e.g., Schelling and Arita,

1991; Robinson et al., 2003; Bollinger et al., 2004; Konstantinovskaia and Malavieille, 2005;

Herman et al., 2010; Grandin et al., 2012). Duplexing may occur through any or all of three processes: frontal accretion involving forward propagation of the frontal thrust (e.g., Schelling and Arita, 1991), expansion of the orogen via incremental accretion along the basal shear zone

(e.g., Searle et al., 2008), and discrete accretion of km-to-10 km-scale thrust horses along ramps

5 of the Himalayan sole thrust (Figure 2.1A, 2.1B, 2.1C) (e.g., Robinson et al., 2003; Bollinger et al., 2004; Robinson, 2008; Webb, 2013). Extrusion models also involve such accretion, but explain a zone of rapid exhumation and steep physiography across the Himalayan hinterland via southward extrusion of a fault-bound block, with major out-of-sequence thrust faulting below and normal faulting above (Figure 2.1D) (e.g., Harrison et al., 1997; Hodges et al., 2001; Wobus et al., 2005; Whipp et al., 2007; McDermott et al., 2013). The only duplexing process that can

Figure 2.1 Simplified kinematic models for ongoing growth of the Himalayan fold-thrust belt. (A) Frontal accretion through forward-propagation of a basal thrust (e.g., Schelling and Arita, 1991). (B) Out-of-sequence faulting (e.g., Harrison et al., 1997). (C) Discrete duplexing of thrust horses from the downgoing plate to the fold-thrust belt (e.g., Bollinger et al., 2004). (D) Expansion of the orogen via incremental accretion along the basal shear zone (e.g., Searle et al., 2008).

6 explain this rapid exhumation zone is enhanced accretion along ramps (Figure 2.1C), which can produce rapid uplift via antiformal stacking (Bollinger et al., 2004; Konstantinovskaia and

Malavieille, 2005, McQuarrie et al., 2014).

These models may be tested by reconstructing Himalayan fold-thrust belt growth since the Middle Miocene, because it is generally thought that the deformation modes of this period are broadly consistent with ongoing processes (Lyon-Caen and Molnar, 1985; DeCelles et al.,

2001; Hodges et al., 2001; Robinson et al., 2003; Bollinger et al., 2004; Yin, 2006). Orogenic growth over the last ~15-10 Ma has been mostly achieved by accretion and deformation of the

Lesser Himalayan Sequence (LHS), a package of rocks which dominates the southern half of the

Himalaya (Gansser, 1964). Therefore, we set out to reconstruct the deformation of the LHS in a key region, the northwest Indian Himalaya (Figure 2.2). This region provides a specific advantage: it preserves the most diverse LHS stratigraphy of the range (e.g., Valdiya, 1980;

Célérier et al., 2009a; McKenzie et al., 2011; Webb et al., 2011a), and thus offers the best opportunity to construct a high resolution understanding of regional structural geometry.

Recent investigations of the northwest Indian Himalaya have significantly advanced our knowledge of the Lesser Himalayan structural development here (Célérier et al., 2009a; 2009b;

McKenzie et al., 2011; Webb et al., 2011a; Webb, 2013). Most work has increasingly suggested a dominant role for duplexing processes (e.g, cf. Thiede et al., 2004 vs. Thiede and Ehlers, 2013), but our knowledge of basic structural geometry remains too fragmentary to resolve the issue. A primary outstanding question involves the relationship of the Berinag thrust and the Tons thrust, structures with displacements of >80 km and >40 km, respectively (Figure 2.2). These thrusts are adjacent, yet have no known intersection, and this uncertainty allows that the complete range of

Figure 2.2 (A) Regional geological map of the central northwestern Indian and west Nepal Himalaya. Main sources are Bhargava (1976), Valdiya (1980), Jain and Anand (1988), Singh and Thakur (2001), Robinson et al. (2006), Célérier et al. (2009), Webb et al. (2011a), and our observation. In west Nepal Himalaya, the Ramgarh thrust, placing the Paleoproterozoic rocks (Ranimata-Kushma Formation) of the Lesser Himalaya upon younger Lesser Himalaya rocks or foreland basin deposits, is labeled as the Berinag thrust since their hanging wall rocks have identical lithology, age (~1.8 Ga), and metamorphic grade (e.g., Miller et al., 2000; DeCelles et al., 2001; Pearson and DeCelles, 2005; Richards et al., 2005; Célérier et al., 2009a). Recent detrital zircon U-Pb dating of hanging wall rocks of the Ramgarh thrust (south of the Almora klippe) mentioned by Valdiya (1980) in northwest Indian Himalaya indicates the same age as the Outer LHS (~800Ma) (Célérier et al., 2009a), therefore we interpreted it as a minor local thrust duplicating the Outer LHS rocks in our map. Cross section A-A’ is show in Figure2.2 B; Field observation shows the Deoban-Damtha Groups were highly deformed at 100-m scale (Webb et. al., 2011a). Here the Deoban-Damtha groups developed a hinterland-dipping duplex via discrete horses at ~km scale without considering the internal deformation, so the surface dip data is not fully consistent with the cross section construction. As discussed in Webb (2013), a mushward duplex is another possibility, with similar areal and line length balance results. Positions of Figure 2.4 and figure 2.5 are outlined in black boxes in Figure 2.2 A.

9 extrusion and duplexing processes discussed above provide viable models for their integrated kinematic history (Figure 2.3) (Webb et al., 2011a).

Figure 2.3 Possible geometric and kinematic relationships of Tons and Berinag thrusts, proposed by Webb et al. 2011. (A) The Tons thrust terminates along the Berinag thrust; (B) the Berinag thrust terminates along the Tons thrust; (C) the Berinag thrust and Tons thrust are a single structure, such that the distinct hanging wall rocks are separated by a depositional contact.

Map relationships suggest that the Berinag and Tons thrusts must intersect in the region of the upper Tons River Valley (Webb et al., 2011a). We performed field mapping, kinematic analysis, and analysis of quartz recrystallization textures here to determine the relationship of these two structures. We found that the hanging walls of the two faults are divided by a third structure, which we term the Pabbar thrust. This discovery 1) requires that discrete duplexing processes dominated growth of the LHS in northwest India and 2) resolves a major stratigraphic continuity problem across the India – west Nepal border.

2.2 Geology of the Northwest Indian Himalaya

The Himalaya has a simple architecture that persists throughout the northwest Indian

Himalaya: it is dominated by three units that are largely defined by their structural positions.

From north to south, these are the Tethyan Himalayan Sequence (THS), the Greater Himalayan

Crystalline complex (GHC), and the LHS (e.g., Heim and Gansser, 1939; Gansser, 1964; Le Fort,

1975; Burg et al., 1984; Burchfiel et al., 1992). Protoliths for all three units are pre-collisional strata of the northern portions of the Indian craton (e.g., Gansser, 1964; Myrow et al., 2003; Yin

2006; McKenzie et al., 2011; Webb et al., 2013; McQuarrie et al., 2014). The units have been long recognized as a dominantly north-dipping, three-layer stack partitioned by two faults, the

South Tibet detachment (STD) above and the MCT below (e.g., Le Fort, 1996; Hodges, 2000;

Yin and Harrison, 2000; DeCelles et al., 2001). In recent years, this understanding has been modified due to detection of a branch line joining the STD with the MCT across the southern

Himalaya (Yin, 2006; Webb et al., 2007; 2011a; 2011b; Kellett and Grujic, 2012). It is thus demonstrated that the Tethyan Himalayan Sequence is juxtaposed atop the Greater Himalayan

Crystalline complex along the STD in the northern Himalaya, whereas in the southern Himalaya the Tethyan Himalayan Sequence occurs directly atop the LHS along the MCT. The Greater

Himalayan Crystalline complex is bounded by the STD above and the MCT below, and by the merger of these faults in the southern Himalaya. The LHS is restricted to the MCT footwall, and it is locally intercalated along depositional contacts and thrust faults with deformed Cenozoic foreland basin strata (e.g., West, 1939; Valdiya, 1980). These latter rocks are termed the Sub-

Himalayan Sequence, and these are separated from the undeformed foreland along the discontinuously exposed Main Frontal thrust, i.e., the leading surface expression of the

Himalayan sole thrust (e.g., Lavé and Avouac, 2000).

2.2.1 Stratigraphic Diversity

The stratigraphic diversity that distinguishes the southern portions of the northwest

Indian Himalaya consists of intercalated Sub-Himalayan strata and four fault-bound LHS stratigraphic packages: the Neoproterozoic–Cambrian Outer Lesser Himalayan Sequence (Outer

LHS), the Paleoproterozoic–Neoproterozoic Damtha and Deoban Groups, the Paleoproterozoic

Berinag Group, and the Paleoproterozoic Munsiari Group (Figure 2.2; Table 2.1) (Auden, 1934;

Valdiya, 1980; Célérier et al., 2009a; Webb et al 2011a). Most of these units have along-strike equivalents along the length of the arc, but Outer LHS exposure is limited to the northwest

Indian Himalaya (Table 2.1).

Previous work in this area correlates part of the Outer LHS with the Berinag Group (e.g.,

Valdiya, 1980; Srivastava and Mitra, 1994). However, subsequent detrital zircon geochronology and other geochemical data invalidate this inference because the sequences have distinct age differences of ~1 Gyr (e.g., Ahmad et al., 2000; Richards et al., 2005; McKenzie et al., 2011;

Webb et al., 2011a). Field observations can also commonly distinguish these two units (e.g.,

Célérier et al., 2009a). The Berinag Group is dominated by thick bedded, medium-to-coarse grained, greenschist-facies (sericitic) quartzite of white to green color. In contrast, previously- correlated quartzite in the Outer LHS (i.e., of the Shimla Group) (Table 2.1) is medium-to-thick bedded, fine-to-medium grained, with varying degrees of metamorphism ranging up to greenschist facies, and of white to grey-brown color.

The Damtha Group is a thick succession of purple, white, brown graywackes succeeded by fine-to medium grained quartzite (e.g., Rupke, 1974; Valdiya, 1980). The overlying Deoban

Group is an extensive succession of stromatolite-bearing grey, white, and pink dolomite and limestone (e.g., Rupke, 1974; Valdiya, 1980; Raha and Sastry, 1982; Srivastava and Mitra, 1994;

Srivastava and Kumar, 2003; Tewari, 2003). The Munsiari Group is dominated by two gneissic lithologies: ~1.85 Ga Wangtu augen gneiss and the Paleoproterozoic Jeori metasedimentary gneiss, which includes garnet-, kyanite-, and sillimanite-bearing metapelitic rocks (Vannay and

Grasemann, 1998; Jain et al., 2000; Miller et al., 2000; Chambers et al., 2008).

At the western and northern limits of our study area, LHS rocks are overlain by Tethyan

Himalayan Sequence and Greater Himalayan Crystalline complex rocks along the MCT. Tethyan

Himalayan Sequence rocks here are psammitic and pelitic Neoproterozoic metasedimentary rocks, intruded by early Paleozoic granitoids, metamorphosed at upper greenschist- to amphibolite-facies conditions (e.g., Epard et al., 1995; Vannay and Grasemann, 1998; Wiesmayr and Grasemann, 2002; Leger et al., 2013). The GHC is dominated by similar protoliths that have been metamorphosed at amphibolite-facies conditions (e.g., Frank et al., 1977; Vannay and

Grasemann, 1998; Manikavasagam et al., 1999). Discontinuous slivers of ~1.85 Ga mylonitic augen gneiss up to ~1.5 km thick occur within the MCT shear zone itself and are termed the

Baragaon gneiss (Trivedi et al., 1984; Miller et al., 2000; Webb et al., 2011a). These rocks are correlative to the Wangtu gneiss and fit within the broader designation of “Ulleri” augen gneiss, as described by Kohn et al. (2010).

2.2.2 Tectonic Framework

The major faults of the MCT footwall in northwestern India include, from northeast to southwest, (1) the Munsiari thrust, (2) the Berinag thrust, and (3) the Krol-Tons thrust system

(e.g., Auden, 1934; Valdiya, 1980; Célérier et al., 2009a). These thrusts accommodated top-SW motion and can be generally characterized by dominant hanging wall stratigraphy: the Munsiari thrust underlies the Munsiari Group, the Berinag thrust underlies the Berinag Group, and the

Krol-Tons thrust system underlies the Outer LHS. Across the region these structures are folded into numerous ~10 km-scale windows and klippen.

The Munsiari thrust can be traced along most of the central Himalaya (e.g., Sharma, 1977;

Valdiya, 1980; Jain and Anand, 1988; Upreti, 1999; Yin, 2006; Célérier et al., 2009a, 2009b), and is referred to MCT-I in central Nepal (Bordet et al., 1972; Arita, 1983). Thermochronologic data sets along the length of this thrust suggest it was active in the Late Miocene or later (e.g.,

Harrison et al., 1998; Catlos et al., 2004; Vannay et al., 2004). Two local kinematic models are proposed for development of this thrust: 1) it is an out-of-sequence thrust that accounts for ≥10 km of exhumation of the LHS (e.g., Harrison et al., 1997; Thiede et al., 2004); 2) it underlies an underplated thrust sheet within the LHS duplexing (e.g., Robinson et al., 2003; Bollinger et al.,

2004; 2006; Yin, 2006) and any out-of-sequence heave is late and minor (≤3 km) (Webb, 2013).

The Berinag thrust is cut by the Munsiari thrust. The southern exposure of the thrust - in the Munsiari thrust footwall - places the Berinag Group over the Deoban and Damtha Groups, whereas the northern thrust exposure - in the Munsiari thrust hanging wall - places the Berinag

Group over the Wangtu gneiss (Valdiya, 1980; Srivastava and Mitra, 1994; Vannay and

Grasemann, 1998; Vannay et al., 2004; Célérier et al., 2009a; Webb et al., 2011a). Minimum displacement along the Berinag thrust is 80 km, as estimated from across-strike thrust exposures placing older atop younger rocks (Figure 2.2).

The Krol thrust underlies the Outer LHS along the southern flank of these rocks, whereas the Tons thrust is the name used to describe the underlying thrust farther north (e.g., Srikantia and Sharma, 1976; Valdiya, 1980; Célérier et al., 2009a). These may be generally considered the same structure, with the proviso that a variety of subsequent, cross-cutting structures may juxtapose Outer LHS rocks against Sub-Himalayan Sequence rocks to the south and yet be

15 termed the “Krol thrust” (or “Main Boundary thrust”) in literature (e.g., Meigs et al., 1995). Such later structures would not correlate with the Tons thrust. The footwall of the Tons thrust is dominated by Deoban and Damtha Group rocks which are locally depositionally overlain by rocks of the Singtali and/or Subathu Formations (Pilgrim and West, 1928; Jain, 1972; Bhargava,

1976; Valdiya, 1980). Because the Singtali and Subathu Formations locally form the immediate

Tons thrust footwall and these units are Cretaceous and Paleogene, respectively, the Tons thrust must be a Cenozoic structure. Minimum displacement along the Tons thrust is 40 km, as determined from across-strike exposure (Figure 2.2). Célérier et al (2009a) proposed that the

Tons thrust accommodated south-directed motion during the Eocene–Oligocene, earlier than

MCT movement, such that the later MCT would represent a massive out-of-sequence structure cutting across the earlier Tons thrust. Alternatively, it may represent a thrust horse accreted to the over-riding plate during the mid- to late- Miocene (Webb et al., 2011a; Webb, 2013).

Preliminary thermochronologic work (Yu et al., in prep.) favors the second hypothesis.

Both the Berinag and Tons thrust faults have discontinuous lenses of Ulleri

Paleoproterzoic granitic gneisses (~1.85 Ga) exposed along them, ranging in scale up to km thicknesses (Figure 2.2) (Valdiya, 1980; Célérier et al., 2009a). These exposures are generally analogous to the correlative Baragaon gneiss exposures along the MCT zone (Trivedi et al., 1984;

Miller et al.2000; Webb et al., 2011a). These relationships require either that both Berinag and

Tons thrust hanging wall rocks were deposited on Ulleri gneiss or both thrust systems accreted slivers of this rock during translation.

The interaction of the Berinag thrust and the Tons thrust is uncertain in terms of both geometry and kinematics. Three proposed geometries of these two thrusts are: (A) the Tons thrust terminates along the Berinag thrust; (B) the Berinag thrust terminates along the Tons thrust;

The first two geometries can be accomplished by either out-of-sequence faulting or duplexing. In the third case, the different rocks of the Berinag and Tons thrust hanging walls are separated along a depositional contact. In the following, we show that the Berinag thrust terminates along the Tons thrust, and their hanging walls are separated by a third structure, which we term the

Pabbar thrust.

2.3 Methods

2.3.1 Field Mapping

We conducted mapping and sampling in the Tons valley along three local rivers, listed from west to east: the Tharoch river, the lower Pabbar river, and the upper Tons river (Figure

2.4 and Figure 2.5). Lithology and deformation features of major structures were documented in the field.

2.3.2 Microstructural Analysis

Microstructures resulting from dynamic deformation of quartz were used to semi- quantitatively to constrain regional deformation temperature. Three quartz grain-boundary recrystallization regimes have been defined in both experimental and natural quartz samples to generally correlate with deformation temperature, although other factors such as strain rate and inclusion populations can also modulate these effects (e.g., Hirth and Tullis, 1992; Stipp et al.,

2002): bulging recrystallization (BLG, 280-380 °C); subgrain rotation recrystallization (SGR,

380-500 °C), and grain boundary migration (GBM, >500 °C). The SGR regime can be further sub-divided into SGR-I (380-450 °C) and SGR-II (450-500 °C) (Figure 2.6).

Figure 2.4 Local geological map and equal area stereoplots along the lower Pabbar River area in the Tons valley and its cross section A-A’. The thick dashed line indicates the leading edge of the Berinag Group. The map pattern shows the Tons hanging wall directly overlaying the Berinag hanging wall along a thrust contact, the Pabbar thrust. Thrust symbols are same in as in the figure 2.2 Locations of field photographs and microphotographs are annotated.

2.4 Results of Structural Geology Mapping

Map relationships indicate that the Berinag and Tons thrusts must intersect in the region of the upper Tons River Valley (Webb et al., 2011a). We conducted mapping and sampling in the Tons valley along three local rivers, listed from west to east: the Tharoch river, the lower

Pabbar river, and the upper Tons river (Figure 2.4 and Figure 2.5). Previous work in the Tons

Figure 2.5 Geological map and cross section C-C’ along the upper Tons River area based on the map from Jain and Anand (1988) and our own observations. The map pattern and cross section show that the Berinag thrust was truncated by the out-of-sequence Munsiari thrusting. Black color structural data are from this study; white color structural data are taken from Jain and Anand (1988), and were used for cross section construction. Locations of field photographs and microphotographs are annotated.

19 valley established the position of MCT shear zone and the Munsiari thrust zone (e.g. Bhargava,

1976; Srikantia and Bhargava 1988; Jain and Anand, 1988).

Figure 2.6 Characteristic microstructures of three dynamic recrystallization mechanisms of quartz in the study area. (a) Bulging recrystallization (BLG) (280-380°C). Inhomogeneously, slightly flattened detrital grains exhibit irregular and patchy undulatory extinction. The grain boundaries appear diffuse. Very fine recrystallized grains occur locally along the grain boundaries. Proportion of recrystallized grains (%) is <15%. (b) Subgrain rotation recrystallization (SGR-I) (380-450°C). Homogeneously elongated porphyroclasts exhibit irregular and patchy undulatory extinction. Subgrains are very obvious. Grain boundaries are relative straight. Recrystallized grains and remnant detrital grains commonly develop "core and mantle” structures. The proportion of recrystallized grains is 15-60%. (c) SGR-II, the proportion of recrystallized grains is 60-90%. In the center of the photo, the relict detrital grain is still visible. (d) Grain boundary migration recrystallization (GBM) (>500°C). Almost no relict porphyroclasts can be found. The grain boundaries are lobate and grain contacts are interfingering. Irregular grain sizes, shapes and boundaries due to the increased grain boundary migration.

2.4.1 Field Observations

2.4.1.1 Tharoch Transect

The transect extends across Deoban Group, Outer LHS, THS/Haimanta rocks which dip

10~30° to the north-northeast, crossing the Tons thrust and MCT from south to north (Figure

2.4). The Tons thrust here is marked by the up section lithological change from the Deoban

Group carbonate to the Outer LHS rocks near the south end of this transect. The thrust contact itself is not exposed, although it can be determined within ~50 m in the field. Deoban Group here includes massive bluish grey limestone and pink to greenish grey dolomite. Bedding thicknesses range from ~30 to ~200 cm. The Tons thrust hanging wall section is ~2 km thick.

From south to north, lithological changes of the Outer LHS are: carbonaceous shale/slate to medium-size quartzite (30-50 cm) of brown color interbedded with carbonaceous shale/slate

(~400 m), to chlorite phyllite with boudinage quartzite (~1200 m), to quartzite-rich chlorite phyllite (~400 m). Structural style is distinct across the buried Tons thrust: Folds with wavelength and amplitude of tens of meters and brittle faults are common in the footwall, whereas south-southwest-verging, tight to open folds with wavelengths ranging from a few millimeters to a few meters were commonly observed in the hanging wall Outer LHS rocks

(Figure 2.7A, 2.7B). At north end of this transect, the MCT is a ~800 m thick shear zone (also see Bhargava, 1976). Quartzite-rich garnet mica schists of Haimanta Group in the upper~600 m of the shear zone are dominated by top-SW S-C fabrics and sigma-type porphyroclasts (Figure

2.8A). In the lower ~200 m of the shear zone, mylonitized biotite-quartz-schists of the Outer

LHS are characterized by strong foliations and southwest-northeast directed lineations defined by biotite.

Figure 2.7 Field photographs of the Tons, Berinag, and Pabbar thrusts and their hanging wall. (A) SW verging asymmetric fold of the Outer Lesser Himalayan rock in the Tons hanging wall, indicating top-to-SW shearing. (B) SWt verging asymmetric folds of the Outer Lesser Himalayan rock near the Tons thrust, indicating top-to-SW shearing. (C) S-C fabric in the Berinag quartzite. (D) Deformed quartz veins developed in Berinag quartzite of the Pabbar thrust footwall, indicating top-to-SW shearing. (E) Sheath fold of the OLH rock, within the Pabbar thrust zone, with its hinge line parallel with local stretching lineation indicating strong NE-SW directed shearing. (F) Sheath folds by strongly deformed OLH rock within the Pabbar thrust zone, with hinges dipping to NE. (G) NE-SW directed stretching lineation of quartz within the Pabbar thrust zone. (H) The Tons thrust exposed near the structural window along the Pabbar transect. (I) The Overturned Berinag thrust (the overturned limb of the anticline in cross section B-B’ exposed near the structural window along the Pabbar transect. (J) Asymmetric folds of the Berinag group near the Berinag thrust, indicating top-to-SW shearing. (K) The Munsiari thrust exposed in the upper Tons River. (L) slickenfibers on the foliation surface indicating SW directed brittle thrust within the Munsiari thrust zone (M) Schuppen zone of quartzite within the Munsiari thrust zone.

Figure 2.7 continued

2.4.1.2 Lower Pabbar Transect

A ductile shear zone was mapped along this transect, separating Outer LHS hanging wall above from Berinag Group footwall below. We term this structure the Pabbar thrust. From south to north, this transect extends across the Berinag thrust, the Pabbar thrust, and a structural window formed by folding of the Pabbar thrust, the Berinag thrust and the Tons thrust at the northern end of this transect.

Figure 2.8 Photomicrographs of deformation fabrics associated with the Tons, Berinag and Pabbar thrusts. All thin sections are cut perpendicular to foliation and parallel to lineation. (A) Sample HY112311-1: σ-type garnet porphyroclast within the MCT zone along the Tharoch River, indicating top-to-SW shearing. (B) Sample Yu91118-06 in the footwall of Pabbar thrust: Berinag quartzite with σ-quartz porphyroclast indicating top-to-SW shearing. (C) Sample HY112811-02 within the Pabbar thrust zone: mylonitized Berinag quartzite bearing feldspar fish with strain shadow indicating top-to-SWvshearing. (D) Sample HY112611-07 within the Pabbar thrust zone: mylonite of OLH sequence with S-C fabrics, indicating top-to-SW shearing. (E) Sample HY112611-05 in the hanging wall of the Pabbar thrust: OLH quartzite with S-C structure shown by two groups of mica foliations, indicating top-to-SW shearing. (F) Sample HY110312-01 within the Pabbar thrust zone: S-C structure defined by mica foliation-C and deformed quartz-S, indicating top-to-W shearing.

Near the junction of the Tons River and the Pabbar River at southern end of the transect, the Berinag thrust separates Berinag Group quartzite above from the Deoban Group carbonate below. The thrust contact itself is buried within a ~600 m gap in exposure. Deoban Group carbonate is dark-gray limestone with bedding thickness of ~30-50 cm; no foliation is observed.

Berinag quartzite is fine-medium grain, white, and sericitic quartzite with original bedding thickness of 0.2-2 m. Foliation is defined by chlorite, muscovite, and biotite. Weak northeast- trending stretching lineations defined by mica were observed in the Berinag quartzite near the buried contact (Figure 2.4). The Berinag thrust hanging wall section is ~ 2 km thick. S-C fabrics

(Figure 2.7C), deformed quartz veins (Figure 2.7D) and σ-quartz (Figure 2.8B) are pervasive in the upper ~600 m.

At the northern limit of this Berinag section, the ~450 m ductile shear zone of the Pabbar thrust separates Outer LHS above from Berinag Group below. In the lower ~300 m of the shear zone, white and light-green Berinag quartzite with 2-3mm large grains (pinkish/ colorless) surrounded by ~0.02-0.05 mm fine grains is strongly mylonitized, dominated by Sigma-type porphyroclasts and S-C fabrics. All observed shear fabrics indicate strong top-to-southwest sense of motion. The large grains are remnant detrital grains which escaped incomplete dynamic recrystallization of quartz and feldspar (3-5% of mode) (Figure 2.8C). In the upper ~150 m of the shear zone, Outer LHS rocks are fine-grain, grey quartzite with original bedding thickness of

~20-30 cm interbedded with dark-grey phyllite. Those rocks are dominated by mylonitic fabrics

(Figure 2.8D) including sheath folds of cm to m scale (Figure 2.7E, 2.7F). Northeast trending stretching lineations deﬁned by strongly deformed quartz are parallel to the long axes of sheath folds (Figure 2.4, Figure 2.7G).

The Outer LHS rocks immediately overlying the Pabbar shear zone are medium-to-coarse grained, grey quartzite with foliations defined by biotite and chlorite. S-C fabrics expressed by two orientations of the mica are common throughout the Pabbar thrust hanging wall section

(Figure 2.8E). The Pabbar thrust hanging wall section is ~3.5 km thick.

Near the northern end of this transect, the Tons thrust, the Pabbar thrust and the Berinag thrust occur folded in an overturned km-scale anticline, creating a structural window that exposes

Deoban Group carbonate (Figure 2.4). The shear zone of the Pabbar thrust is exposed here again

(Figure 2.8F), intersecting with the Berinag thrust and the Tons thrust near the west termination of the window. The Tons thrust is exposed in the northern limb of the anticline (Figure 2.7H).

The Outer LHS in the hanging wall is fine-to-medium grained, white /brown quartzite with foliations and southwest trending stretching lineations defined by mica. Deoban Group in the footwall includes dark-grey limestone with bedding thickness of 10-30 cm, and no foliation development. The Berinag thrust is exposed in the southern overturned limb of the anticline

(Figure 2.7I). Berinag Group quartzite near the contact is of brown and dark-green color, with 2-

4 mm large grains (light blue) surrounded by ~0.02-0.05 mm fine grains, and is strongly mylonitized. Foliation is defined by chlorite and biotite. Northeast trending lineations defined by mica are common. Deoban Group carbonate in the Berinag thrust footwall here shares the same lithological and structural features with the Tons thrust footwall. At the east side of the window, the Pabbar thrust intersects with the MCT.

2.4.1.3 Tons River Transect

This ~35 km long transect extends across Deoban Group, Berinag Group, and Munsiari

Group rocks from southwest to northeast (Figure 2.4, Figure 2.5). These rocks dominantly dip moderately to the northeast. The structural geometry involves three main elements. First,

28 although the immediate hanging wall of the Berinag thrust consistently comprises the Berinag

Group, the footwall varies from Deoban Group rocks in the southwest to Munsiari Group rocks in the northeast. Second, the Berinag thrust occurs in both the footwall and hanging wall of the

Munsiari thrust. Third, all structures are warped via open folds.

At the southwest end of this transect, the Berinag thrust places the Berinag group quartzite atop the Deoban Group carbonate. The thrust contact itself is buried in a ~500 m covered span. Metamorphic grade and deformation styles exhibited by the Deoban and the

Berinag Group rocks here match observations from the southern end of the Pabbar transect.

Asymmetric folds in the Berinag Group indicate top-to-southwest shear (Figure 2.7J). The

Berinag thrust hanging wall section is about 2 km thick, and is exposed along ~14 km of the transect. Several km-scale open folds are developed along this transect, resulting in local exposures of Deoban carbonate.

Farther to the northeast, the Berinag Group rocks are underthrust along the Munsiari thrust below a package of the Berinag and the Munsiari Group rocks divided by the Berinag thrust. The southern limits of the Berinag and Munsiari Group rocks in the Munsiari thrust hanging wall form a fault-cutoff (Figure 2.5). The Berinag Group rocks in the hanging wall consist of fine-grained, white & light-green quartzite with 1-2 mm large remnant detrital grains, whereas the Munsiari Group rocks consist of augen gneiss and granitic schist with ~20 cm long feldspar. The Munsiari Group is exposed as footwall of Berinag thrust and hanging wall of

Munsiari thrust along ~ 20 km of the transect; this Munsiari Group section is ~4 km thick.

The Munsiari thrust is folded in a km-scale syncline-anticline pair, and its footwall

Berinag Group rocks are exposed in the anticline core (Figure 2.5; Figure 2.7K). The Munsiari thrust is exposed here as a 1–2-km-thick top-to-the-south / top-to-the-south-southwest shear zone.

It features S-C mylonitic fabrics in the Munsiari Group rocks which are overprinted by a >50-m- thick schuppen zone along the Munsiari Group - Berinag Group lithologic contact. The schuppen zone features south-southwest–directed Riedel shears, cataclasite, and slickenﬁbers and is comprised of 2 to15 m thick horses of quartzite and granitic gneiss (Figure 2.7L, 2.7M). Jain and

Anand (1988) report the northernmost exposure of the Berinag thrust just beneath the MCT as a ductile shear zone which emplaced the Berinag Group atop the Munsiari Group. The thickness of the Berinag Group there is 300-500 m.

The observed structural repetition of the Berinag thrust along the Munsiari thrust requires a specific kinematic evolution along the Tons transect. The Berinag thrust developed first, juxtaposing Berinag Group atop Deoban Group in the southwest and Munsiari Group in the northeast. Next, out-of-sequence thrusting along the Munsiari thrust repeats the Berinag thrust.

The out-of-sequence thrusting heave is 4-5 km (Figure 2.5). The late warping of all other structures by open folding is likely due to continued duplexing and/or motion over bends in the

Himalayan sole thrust.

2.4.2 Quartz Microstructures

BLG quartz microstructure dominates in the Tons hanging wall rocks along Tharoch transect, except for the sample immediately below the MCT, which displays SGR fabrics (Figure

2.9). Other quartzite samples display inhomogeneously flattened detrital grains (0.3-0.8mm) with very fine recrystallized grains (≤ 0.05mm) locally along grain boundaries. The above observation indicates that deformation across the Tons thrust hanging wall occurred below ~380°C.

SGR-II quartz microstructure dominates the Berinag, Pabbar, and Tons thrust hanging walls along the lower Pabbar and Tons river transects (Figure 2.9). GBM recrystallization occurs only along and immediately above the Pabbar shear zone: here 80-90% of detrital grains were

30 recrystallized. Grain boundaries are lobate and interfingering. These observations indicate that deformation along the Pabbar thrust hanging wall occurred at >500 °C.

Figure 2.9 Results of quartz recrystallization mechanisms study annotated in the simpliﬁed Local geological map in the Tons valley. Thrust symbols are same in as in the figure 2.2.

2.5 Discussion

Our mapping in the northwestern Indian Himalaya documents a new discovery: a ~ 450 m thick top-to-southwest shear zone, termed the Pabbar thrust, in the NW Indian Himalaya. The

Pabbar thrust placed the Outer Lesser Himalayan Sequence (the Tons thrust hanging wall) directly on the Berinag Group (the Berinag thrust hanging wall). The shear zone is characterized by sheath folds, S-C fabrics and mylonitic fabrics, all with top-to-the-southwest shear sense.

Quartz microstructures in the study area indicate that deformation along the Pabbar thrust and its immediate hanging wall occurred above ~500°C, deformation across most of the Berinag Group occurred between 400-450 ° C and deformation across most of the Outer LHS occurred below

~380°C. Additional mapping indicates that the Munsiari thrust duplicates the Berinag thrust and its hanging wall and footwall rocks by out-of-sequence faulting, but the heave of out-of-sequence

31 faulting is limited to ~5km. Below we discuss the kinematic evolution of the Tons thrust, the

Pabbar thrust and the Berinag thrust; along-strike variations in thrust geometries and deformed stratigraphy; and implications for kinematic evolution of the Himalayan fold-thrust belt.

2.5.1 Kinematic Evolution of the Tons Thrust, Pabbar Thrust and Berinag Thrust

The Pabbar thrust separates the Outer LHS above from the Berinag Group below (Figure

2.4). This map geometry can be accomplished via two kinematic processes: out-of-sequence faulting of the Pabbar thrust across the Berinag thrust, or accretion of the Berinag thrust sheet to the Pabber thrust hanging wall (Figure 2.3B). In the first case, the Berinag thrust should slip first.

In this model, the Pabbar thrust and the Tons thrust are a single structure. In the second case, the

Pabbar thrust developed first, followed by accretion of the Berinag sheet. Continued motion along the new sole thrust toward the foreland becomes the Berinag and Tons thrusts, operating as a single structure.

Our field mapping documented that mylonitic structural fabrics developed in both hanging wall and footwall of the Pabbar thrust, whereas foliations developed in hanging wall of the Berinag thrust and the Tons thrust but not in footwalls of these structures. This distinction indicates that the Pabbar thrust developed as a ductile shear zone whereas brittle deformation along the Berinag and Tons thrusts overprints ductile deformation of their hanging wall rocks.

Given the spatial proximity of these structures - e.g., mapping presented in Figure 2.4 documents their intersection - the brittle overprinting relationship indicates that motion along the Berinag and Tons thrusts postdates motion along the Pabbar thrust. Quartz microstructure study shows that deformation across the Pabbar thrust occurred at the higher temperature (> 500°C) than that across hanging wall of the Berinag (400-500°C) and Tons thrust (< 380°C). Therefore the field observations and quartz microstructures indicate the Pabbar thrust developed earlier and hotter

(i.e., deeper) than the Berinag and Tons thrusts. These findings are inconsistent with an out-of- sequence evolution, but consistent with duplexing processes. Because the Berinag thrust and the

Tons thrust appear contiguous (Figure 2.4) and move as a single structure in the duplexing model, we henceforth refer to them as the Berinag-Tons thrust.

The duplexing evolution of the Pabbar thrust and the Berinag-Tons thrust here confirms the overall dominance of duplexing during the ongoing growth of the Himalayan fold-thrust belt since the Middle Miocene. Our new interpretation of the kinematic evolution of the Munsiari thrust also indicates the extent of out-of-sequence faulting along the structure: less than 10 km of throw, and less than 5 km of heave. Expansion of the orogen by incremental accretion is also precluded here because the prediction of pervasive shear features through the LHS is not consistent with field observations. Instead, shear is concentrated within 100-meter-scale fault zones.

2.5.2 Along-strike Variations of Thrust Geometries and Stratigraphic Correlation

Here we explore the implications of the duplexing evolution along the Pabbar thrust and

Berinag-Tons thrusts for structural variations along the strike of the orogen. We find that along- strike extension of these kinematics and corresponding geometries is consistent with the observed orogenic framework and resolves a stratigraphic continuity problem across the India – west Nepal border, where structures appear continuous but stratigraphy does not match.

Before analyzing specific map patterns, it is useful to consider how minor variations in the duplexing process could result in changes to structural geometries. In particular, after motion along the Pabbar thrust, minor differences in Berinag-Tons thrust development could produce a range of geometries (Figure 2.10). Our mapping indicates that the Berinag-Tons thrust accretes a new sheet of Berinag Group material to the overriding wedge. If the southern limit of the newly

Figure 2.10 Sketched kinematic evolutions of the Pabbar thrust and the Berinag-Tons thrust. (A) Duplexing of the Pabbar thrust. (B) Duplexing of the Berinag-Tons thrust. Dash lines represent possible positions of the Berinag Group hanging wall ramp of the Berinag-Tons thrust. (C) Case ①: position of the Berinag Group hanging wall ramp of the Berinag-Tons thrust is south to the Pabbar thrust and MCT branch line, which explains structural geometries along cross sections a- a’, d-d’, and e-e’ in Figure 2.11 and Figure 2.12. Case ②: position of the Berinag Group hanging wall ramp of the Berinag-Tons thrust is very close to the Pabbar thrust and MCT branch line, which explains structural geometry along cross section b-b’ in Figure 2.11 and Figure 2.12. Case ③: position of the Berinag Group hanging wall ramp of the Berinag-Tons thrust is north to the Pabbar thrust and MCT branch line, which explains structural geometry along cross section c-c’ in Figure 2.11 and Figure 2.12.

accreted Berinag Group material is south of the Pabbar thrust - MCT branch line (Figure 2.10 C-

1), then the juxtaposition of the Outer Lesser Himalaya and the Berinag Group along the ductile shear zone of the Pabbar thrust will be preserved, as observed in the study area (Figure 2.4).

However, if the southern limit of the newly accreted Berinag Group material is north of the

Pabbar thrust - MCT branch line (Figure 2.10 C-3), then the juxtaposition of the Outer Lesser

Himalaya and the Berinag Group along the ductile shear zone of the Pabbar thrust will not occur.

We note a series of different structural geometries across the western Himalaya that are consistent with minor variations in the kinematic evolution of the Pabbar thrust and the Berinag-

Tons thrust, as described above. These structural geometries are described via five sketch NE-

SW cross sections located on a simplified tectonic map (Figure 2.11) and displayed in Figure

2.12. Cross sections a-a’, b-b', c-c', and d-d' occur from west to east across the northwestern

Indian Himalaya, and cross section e-e' is in far-western Nepal. Cross section a-a’: the position of the Berinag Group hanging wall ramp of the Berinag-Tons thrust is south of the Pabbar thrust

- MCT branch line (Figure 2.10 C-1). A large segment of the Pabbar thrust was preserved via the accretion of the Berinag-Tons thrust sheet. All the structures are wrapped by continue duplexing process, therefore only small portion of the Pabbar thrust was buried and the rest was eroded away. In map view, the Outer LHS outcrops are separated from the Berinag Group outcrops by the footwall rocks (Deoban Group) for ~20 km. Cross section b-b’: the position of the Berinag

Group hanging wall ramp of the Berinag-Tons thrust is very close to the Pabbar thrust - MCT branch line. Only a small segment of the Pabbar thrust was preserved via the accretion of the

Berinag-Tons thrust sheet (Figure 2.10 C-2). Cross section c-c’: the position of the leading edge of the Berinag Group is north of the Pabbar thrust - MCT branch line (Figure 2.10 C-3). In this case, the relationship of the Outer LHS rocks over the Berinag Group which characterizes the

Pabbar thrust does not occur. Locally, MCT hanging wall rocks directly overlie Deoban Group rocks.

Similar along-strike variations of thrust geometries can also explain an abrupt stratigraphic change across the India-west Nepal border. In the vicinity of the Almora-

Figure 2.11 Sketched regional geological map of the central northwestern Indian and west Nepal Himalaya from figure 2A annotated with published detrital zircon dating, showing the along strike lithological variations of the Outer LHS and the Berinag group: exposure of the Outer LHS is limited to northwest Indian Himalaya, whereas just across the India-West Nepal border, the Paleoproterozoic Ranimata-Kushma Formation (equivalent of Berinag Group, Table 2.1) is exposed.

Dadeldhura klippe of the MCT, Neoproterozoic Outer LHS rocks (~ 800 Ga) dominate the hanging wall of the Berinag-Tons thrust on the Indian side, whereas Paleoproterozoic rocks

(~1.8 Ga) occur in the same structural position in far-western Nepal (Celerier et al., 2009). Cross sections d-d’ and e-e’ (Figure 2.11 and Figure 2.12) illustrate how the Pabbar thrust geometry can resolve this problem. Cross section d-d’: The Berinag Group hanging wall ramp of the

Berinag-Tons thrust is south to the Pabbar thrust - MCT branch line (Figure 2.10 C-1). The

Pabbar thrust remains buried so that only the Outer LHS outcrops in the hanging wall get exposed south of the Almora-Dadeldhura klippe in map view (Figure 2.11 and Figure 2.12). Just across the border, the Pabbar thrust hanging wall rocks (the Outer LHS) are eroded away (cross section e-e’), therefore only the Berinag Group is exposed (Figure 2.11 and Figure 2.12).

2.6 Conclusions

Our work in the northwestern Indian Himalaya advances knowledge about ongoing

Himalayan growth, which is generally thought to be dominated by duplexing and/or extrusion processes. Duplexing models highlight accretion of material from the subducting plate to the over-riding orogenic wedge, whereas extrusion models generally focus on southwards translation of a fault-bounded block towards the surface.

We examined the viability of these models for a region of the Himalaya with rich stratigraphy across the younger portions of the mountain chain, because rich stratigraphy affords a high resolution view of deformation. The study region in northwestern India held a key structural mystery (Webb et al., 2011): three possible geometries could relate two dominant structures, the Berinag thrust and the Tons thrust. In turn, this set of possible geometries allows a range of ongoing growth kinematics, such that either duplexing or extrusion could represent the dominant mountain-building mechanism here since the middle Miocene.

Figure 2.12 Serial cross sections showing along strike variations of structural geometries can be explained by minor variations of kinematic of the Pabbar thrust and the Berinag-Tons thrust. Positions of those cross sections are marked in Figure 2.11.

Our field-based analytical work shows that the Berinag thrust and the Tons thrust are in fact the same structure. It has long been understood that these faults share the same footwall rocks (e.g., Valdiya, 1980). A previously unrecognized shear zone, which we term the Pabbar thrust, separates the distinct hanging wall rocks. The resultant structural framework is consistent with duplexing processes and limits extrusion to a minor role in mountain-building. These findings are consistent with results from thermo-kinematic modeling of rich thermochronological data across the central Nepal Himalaya (Herman et al., 2010). Therefore northwestern India offers a study region wherein the stratigraphic diversity and structural resolution is sufficiently rich to allow investigation of the discrete structures which accomplish the accretion process modeled in a continuum fashion across Nepal. This advantage suggests that this region will continue to offer key insights as we advance exploration of climate-erosion-tectonic interactions during collision.

CHAPTER 3 KINEMATIC EVOLUTION OF HIMALAYAN OROGEN CONSTRAINED BY NEW FISSION TRACK ANALYSIS IN NW INDIA

3.1 Introduction

We test kinematic models of Himalayan growth by determining the geometry and kinematics of key regional structures which deformed the Lesser Himalayan Sequence in northwest India. In this chapter, we will provide a new set of robust low temperature thermochronological data across the strike of major thrusts and a line-length balanced palinspastic reconstruction across the NW Indian Himalaya to further constrain the Himalaya mountain building process. Our previous work reveals 1) a previously unrecognized shear zone, which we term the Pabbar thrust, 2) the Berinag thrust and the Tons thrust are in fact the same structure, which we term the Bering-Tons thrust. The Pabbar thrust placed the Outer Lesser

Himalayan Sequence directly on the Berinag Group, followed by the accretion of Berinag-Tons thrust sheet. The resulting revised structural framework is consistent with duplexing, and demonstrates that extrusion accomplishes only minor shortening since the middle Miocene. In this chapter, we will provide a new set of robust low temperature thermochronological data across the strike of major thrusts and a line-length balanced palinspastic reconstruction across the

NW Indian Himalaya to further constrain the Himalaya mountain building process.

Previous thermochronological studies in this area and adjacent region mainly focus on the north portion of the wedge. U-Th monazite-inclusion dating, 40Ar/39Ar muscovite cooling ages, and zircon fission track ages from the GHC along the Sutlej River imply Early to Late Miocene activity of the MCT in the north (e.g., Schlup, 2003; Vannay et al., 2004; Thiede et al., 2005;

Caddick et al., 2007; Chambers et al., 2008). The 40Ar/39Ar muscovite analysis of the Berinag

Group yielded cooling ages between 13.5 to 4.3 Ma and younger ages are proximal to the

Munsiari thrust, which is interpreted to be related to the thermal relaxation following emplacement of the MCT hanging wall: samples near the leading edge of the MCT sheet cooled earlier than those near the root as a result of the retreat of the white mica closure isotherm toward thermal equilibrium (Célérier et al., 2009b). Alternatively, these 40Ar/39Ar ages indicate initiation of the Berinag-Tons thrust during Late Miocene and the broad younging age pattern towards the

Munsiari thrust is due to the flat-ramp geometry of the Main Himalayan Thrust. Abundance of apatite fission track (AFT) ages in the GHC and the Munsiari Group in this area and regions to the east show < 4 Ma cooling ages indicating a rapid exhumation period (e.g., Bojar et al., 2005;

Patel and Carter, 2009; Patel et al., 2011; Singh et al., 2012).

The incomplete thermal history limits time constraint on the balanced palinspastic reconstruction. Peak metamorphic temperature of the Outer LHS is indicated under ~330°C recorded by Raman spectroscopy of carbonaceous material (RSCM) study (Célérier et al.,

2009b), which makes the AFT and zircon fission track (ZFT) dating suitable for the southern part of the Himalaya. In this chapter, a new set of AFT and ZFT data covering the southern portion of the Himalaya along the Alaknanda River transect is presented. The yielding results are consistent with our duplexing concept of the Pabbar thrust and the Berniag-Tons thrust, restrict the Late

Miocene movement of the Berinag-Tons thrust, and place a well constraint on tectonic depth of

Damtha /Deoban Group and the Outer LHS. With the above findings, our balanced palinspastic reconstruction along the Alaknanda River transect provide vigorous control of kinematic evolution of the Himalayan wedge.

3.2 Methods: Apatite and Zircon Fission Track Analysis

In order to constrain the deformation history of northwestern Himalaya, 15 samples were collected along the Alaknanda River transect for apatite and zircon fission track analysis using

42 the external detector method (Naeser, 1979; Wagner and Van den Haute, 1992; Dumitru, 2000).

Samples are evenly distributed along the transect, and across the major thrusts in order to constrain timing of those thrusts.

Fission track analysis is a useful technique to document low temperature thermal history during orogeny. Fission track cooling ages represent the elapsed time since rocks cool below an effective closure temperature of specific mineral (e.g., Price and Walker 1963; Fleischer et al.,

1975; Zeitler et al. 1982; Corrigan 1991; Gallagher 1995; Ketcham et al., 2000; Hodges 2003;

Jonckheere et al., 2003; Donelick et al., 2005; Tagami 2005; Tagami and O’Sullivan 2005;

Reiners and Brandon, 2006; Bernet, 2009). Closure temperature of mineral may change with regional cooling rates (e.g. Hodges 2003). An effective closure temperature of 135 ± 10°C for apatite and 240 ± 30 °C for zircon is used in this study (e.g. Bernet et al., 2006; Thiede et al.,

2009).

Apatite and zircon concentrates were prepared by standard crushing, heavy liquid separation using Bromoform (CHBr3), Methylene Iodide (CH2I2) and magnetic separation.

Fission track analysis was conducted in Geologie, Technische Universitat Bergakademie

Freiberg, Germany.

Apatite grains were mounted in epoxy, ground, and polished. Apatite samples for age dating were etched for 15s in 23% HNO3 at 25 °C and the muscovite external detectors in 40%

HF for 30 min at room temperature. Pooled ages were determined using the zeta approach, employing the IRMM-540R uranium glass; Zeta values were calibrated by counting Durango and Fish-Canyon tuff apatite age standards (Table 3.1). Tracks were counted on prismatic apatite surfaces with a Zeiss Axioplan microscope in transmitted light. The muscovite external detectors

43 were repositioned, trackside down, on the apatite mounts in the same position during irradiation; where possible, we counted at least 20 grains of each sample.

Apatite samples for confined track-length measurements were etched for 20s at 21 °C in

5.5N HNO3 (Donelick et al., 1999). All samples were irradiated with heavy ions at GSI

Darmstadt to increase the number of etchable confined tracks (Jonckheere et al., 2007).

Hand-picking zircon grains were mounted in Teflon, ground, and polished. Tracks in zircon grains were etched in a eutectic mixture of KOH and NaOH at 228 °C for 2–30 hours. We prepared three mounts (etched for different time) for each sample to guarantee enough grains for counting. Etched samples were covered with 50 μm thick, uranium-free muscovite external detectors, and packed between three mounts of uranium glass (IRMM-541). Samples were irradiated in the hydraulic channel of the FRM-II reactor, Munich, Germany. The muscovite external detectors were etched in 40% HF for 30 min at room temperature. Pooled fission track ages are calculated using zeta calibration method (Hurford and Green, 1982, 1983). Zeta values were calibrated by counting Fish-Canyon tuff zircon age standards irradiated together with samples (Table 3.1). Tracks were counted on prismatic zircons with a Zeiss Axioplan microscope in transmitted light; and the corresponding muscovite external detectors were counted using an Autoscan (Autoscan Systems Pty. Ltd, Australia) system.

3.3 Results

3.3.1 Fission Track Analysis

Apatite fission track age data were obtained from six samples (the other nine samples didn’t yield enough apatite grains). Apatite track length data were not obtained since all those samples only contains zero to several confined tracks. Zircon fission track age results were obtained from thirteen samples, and pooled ages are reported with 1σ error. Further details on the age calculation are provided in Appendix A and Appendix B.

Six AFT samples yield cooling ages between 8.4±0.4 and 1.1±0.1 Ma. Analytical results are shown in Table 3.1 and Figure 3.1. AFT ages show younger trend towards north: the southernmost sample YU 91129-6 of Early Paleozoic granite gneiss was collected from the MCT hanging wall in the Lansdowne Klippe, which yields the oldest AFT age of 8.4±0.4 Ma. Sample

YU 91130-6 of sandstone from Berinag-Tons thrust footwall (Damtha/Deoban Group) yields

AFT age of 6.7 ±0.6 Ma. Two samples (YU 91130-9 and YU 91201-9) from Berinag-Tons thrust hanging wall (Outer LHS) yield AFT ages of 6.2±0.3 Ma and 3.7±0.3 Ma, respectively. Sample

YU 91208-4 of Baragoan augen gneiss within the MCT zone in Baijnath Nappe yields AFT age of 4.0±0.3 Ma. Sample YU 91206-1 of granite gneiss from Munsiari Group in the hanging wall of Munsiari thrust yields the youngest age of 1.1±0.1 Ma.

ZFT ages were obtained from 13 samples (Table 3.1). The southernmost sample YU

91129-1 of Outer LHS immediately in the Krol thrust hanging wall yields multiple age groups ranging between 34.0±7.5 to 554.5±126 Ma (Figure 3.2A). Three samples of Damtha/Deoban

Group in the footwall of Berinag-Tons thrust also yield multiple ZFT age groups: Sample YU

91130-2 yields age ranging between 76.9±11.0 to 315.1±45.9 Ma (Figure 3.2B), sample YU

Figure 3.1 (A) Zircon fission track and Apatite fission track data annotated in regional geological map of the central northwestern Indian and west Nepal Himalaya. Number of red color represents zircon fission track age. Number of dark blue color represents apatite fission track age. In this map the Berinag thrust and the Tons thrust is marked by the same fault symbol because our work shows that they are in fact a same structure. The Damtha Group and Deoban Group are treated as one unit for our restoration purpose (see discussion in the text). See other notes as in Figure 2 in Chapter 2. (B) Fission track ages are plotted against distance to the Krol thrust. Solid symbols are from this study, whereas empty symbols are from Pater and Carter (2009). Pink color symbols represent zircon fission track data. Blue color symbols represent apatite fission track data. (C) Cross section A-A’: dash lines with arrows point to positions of samples in cross section. Pink color stars on dash lines represent samples with non-reset zircon fission track ages. Abbreviations: MCT-Main Central Thrust, STD-South Tibet Detachment.

91130-6 yields similar age groups ranging between 23.2±2.8 to 440±144.4 Ma (Figure 3.2C), and Sample YU 91204-9 yields age groups ranging from 14.0±2.4 to 423.2±60.1 Ma (Figure

3.2D). ZFT samples with a single age group also show a generally younger pattern towards north

(Table 3.1 and Figure 3.1). ZFT ages range between 26.8±1.9 and 28.8±1.8 Ma for two samples in the hanging wall of MCT in the Lansdowne Klippe. Four Outer LHS samples in the hanging wall of Berinag-Tons thrust yield ages between 12.5±0.4 to 4.7±0.3 Ma from south to north.

Sample YU 91209-1 of Berinag quartzite in the Berinag-Tons thrust hanging wall yields age of

6.7±0.6 Ma. Sample YU 91208-4 of Baragoan augen gneiss within the MCT zone in the Baijnath

Nappe yields ZFT age of 6.0±0.5 Ma. Sample YU 91206-1 of granite gneiss from Munsiari

Group in the hanging wall of Munsiari thrust yields the youngest ZFT age of 1.5±0.1 Ma.

3.3.2 Interpretation

The southernmost sample YU 91129-1 was collected just above the Krol thrust from the

Outer LHS. The majority of ZFT age groups of this sample are older than the collision age (~50

Ma), and younger than its sedimentation age (Neoproterozoic–Cambrian), which are interpreted to reflect pre-collision tectonic history (Figure 3.2A). This non-reset ZFT age indicates the maximum tectonic burial depth of the leading edge of Outer LHS in the south does not exceed

ZFT closure temperature isotherm (240±30°C, ~8km assuming a geothermal gradient of

~30 °C/km) before the collision. All samples of the Outer LHS towards north yield reset ZFT ages, which indicate the tectonic burial depth of Outer LHS in the north is deeper and hotter than the ZFT closure temperature isotherm (240±30°C, ~8km). The whole Damtha/Deoban Group

(two samples in the south, one sample in the north) yield non-reset ZFT ages, but reset AFT

(sample YU 91130-6) providing robust control on the tectonic burial depth of Damtha/Deoban

Group between AFT closure temperature isotherm (135±10°C, ~4km) and ZFT closure temperature isotherm (240±30°C, ~8km).

Figure 3.1B shows Fission track ages plotted against distance to the Krol thrust. The southernmost five AFT ages show nearly linear trend with distance without apparent offsets across the MCT and the Berning-Tons thrust, which indicate 1) the MCT hanging wall rocks and the Berinag-Tons thrust hanging wall rocks behaved as a single tectonic unit during Late

Miocene cooling. 2) The Berinag-Tons thrust in the Lansdowne Klippe ceased motion in Late

Miocene by ~7 Ma. Youngest AFT age of 1.1±0.1 Ma (Sample YU 91206-1) in the hanging wall of Munsiari thrust to the north is constant with published young AFT data in the same area (Patel and Carter, 2009) and along the arc (e.g., Jain et al., 2000; Thiede et al., 2004, 2005, 2009; Patel et al., 2007; Patel and Carter, 2009), which represent a rapid uplift zone.

Figure 3.2 Radial plot of non-reset zircon fission track data.

The Bering-Tons thrust must be active during Late Miocene (~13 Ma) since the whole

Berinag-Tons thrust hanging wall rocks in the north of Lansdowne Klippe yield Late Miocence

ZFT ages (12.5±0.4 to 4.7±0.3 Ma) atop the Damtha Group with non-reset ZFT ages. Therefore the Berinag-Tons thrust hanging wall sheet must have cooled to the north of the Damtha Group in Late Miocene and concurrently/subsequently been emplaced. The abrupt change of ZFT ages

(28.8±1.8 to 26.8±1.8 Ma) from the MCT hanging wall in Lansdowne Klippe to ZFT age of

12.5±0.4 Ma from the Outer LHS is probably due to accretion of the Berinag-Tons thrust sheet.

The old ZFT ages in the MCT hanging wall in Lansdowne Klippe are probably link to initiation of the MCT and emplacement of THS/GHC in Late Oligocene/ Early Miocene.

Both AFT ages and ZFT ages show younger trend towards north, and comparing age differences between ZFT and AFT of each sample indicates relatively slower cooling rate across the southern Berinag-Tons thrust sheet. The above pattern is consistent with the Flat-ramp geometry of the Main Himalayan Thrust derived from geophysics data (e.g., Hetenyi, et al., 2006;

Rai et al., 2006; Nabelek et al., 2009; Acton et al., 2010; Chamoli et al., 2011; Caldwell et al.,

2013), geodetic data (e.g., Pandey et al., 1995; Avouac, 2003, 2007; Berger et al., 2004), and structural reconstruction (e.g., Schelling and Arita,1991; DeCelles et al., 2001; Pearson and

DeCelles, 2005; Robinson et al., 2006; McQuarrie et al.,2008; Célérier et al., 2009a; Webb et al.,

2011a; Webb 2013).

3.4 Balanced Palinspastic Reconstruction Across the NW Indian Himalaya

Our field-based analytical work along the Tons Valley in Chapter 2 indicates the overall dominance of duplexing process during ongoing growth of the Himalayan fold-thrust belt since the Middle Miocene, and provides strong control on kinematic evolution of major thrusts and along strike changes of structural geometry and stratigraphy. Our new AFT and ZFT data here

51 offer robust constraint on the pre-collision stratigraphic framework and timing of major thrusts activity of Northern India.

To assess the Cenozoic kinematic history, a balanced palinspastic reconstruction of the studied segment of the Himalayan arc was made, which extends from the Sub-Himalayan

Sequence, across the LHS, and into the THS fold-thrust belt (Plate 1). Restored time steps were constructed by progressively “undeforming” the deformed section using a combination of 2D

Move software (Midland Valley) and Adobe Illustrator. Layer parallel simple shear was applied to unfold fold limbs. Geometry of the Main Himalayan Thrust is approximately consistent with the latest seismic receiver-function results: flat-ramp-flat (Caldwell et al., 2013). The upper flat is ~4 km below sea level connecting to a mid-crustal ramp dipping at ~16°. The lower flat is ~15 km below sea level. Deformation across the Sub-Himalayan Sequence and THS was simplified

(Powers et al., 1998). Approximate periods of five restored time steps are 28 Ma, 20 Ma, 13 Ma,

8.1 Ma and 5.2 Ma. All time estimates were determined by measuring shortening distance and using the geodetic shortening rate of 13.6 mm/yr (Styron et al., 2011) to calculate an age. Ages assigned to time-steps A (28 Ma), C (13 Ma), D (8.1 Ma), and E (5.2 Ma) are also consistent with our AFT and ZFT data sets discussed above.

A “pinch-out” model for the pre-collision stratigraphic framework is adopted in this study

(Webb et al., 2011a; Webb 2013): 1) Damtha and Deoban Group, the Outer LHS, the THS were stacked and tilted to northeast, and all of them were exposed to surface before the collision since these units are overlain by Late Cretaceous and early Cenozoic rocks locally (e.g., Valdiya, 1980;

Célérier et al., 2009a); 2) the Paleoproterozoic–Neoproterozoic Damtha and Deoban Group represent the southernmost shallow units pinching out towards northeast, whereas, the

Neoproterozoic–Cambrian Outer LHS represent deeper unit pinching out to the southwest; 3)

52 the Haimanta Group of THS, Greater Himalayan Crystalline complex, and Shimla Group of

Outer LHS represent deformed parts of a formerly continuous unit; 4) the Baragaon granitic gneiss and Munsiari Group are the oldest deformed units, representing the base of the pre- collision stratigraphic framework. In our restoration, the Damtha and Deoban Group are treated as one unit instead of simply overlaying the Deoban Group on the Damtha Group. The internal deformation of Damtha and Deoban Group is complex (e.g., Webb et al., 2011a; Webb 2013), and simple overlay relationship can’t explain the map pattern, e.g., immediately north of the

Lansdowne Klippe, only Damtha Group crops out without exposure of Deoban ; alternatively, the Damtha Group exposed there might be the Mandhali Formation of the Deoban Group. The pinch-out model is consistent with our new AFT and ZFT data. Non-reset ZFT ages and reset

AFT ages imply the maximum depth of Damtha/Deoban Group does not exceed ~8 km (ZFT closure temperature isotherm). Non-reset ZFT age from the leading edge of the Outer LHS and reset ZFT ages in the northern part indicates depth of southernmost Outer LHS is less than ~8 km, but the Outer LHS to the north is deeper than ~8 km. The reset ZFT ages of THS in

Lansdowne Klippe means the burial depth of THS before the collision is deeper than ~8 km.

Therefore, the Outer LHS and THS represent a far-traveled thrust sheet relative to the Deoban and Damtha Groups along the Berinag-Tons thrust and MCT, respectively. The discovery of the

Pabbar thrust indicates the Outer LHS is further north than the Berinag Group. Our AFT and

ZFT data validate the concept that younger rocks originated at equal and greater depth in the northeast compared with older rocks in the southwest (Webb et al., 2011a; Webb 2013). This reconstruction of relative pre-collision structural positions explains thrusting of younger rocks atop older rocks in the Himachal Himalaya, e.g., the southern portions of the Berinag-Tons thrust and the MCT place Neoproterozoic rocks atop Mesoproterozoic and/or Paleoproterozoic rocks.

3.4.1 Restoration ca. 28 Ma

The reconstruction progresses from the period before the initiation of the MCT around

Late Oligocene (Plate 1A). Imbricate stacking in the THS fold-thrust belt before 28 Ma is not drawn here (e.g., Wiesmayr and Grasemann, 2002). Most of the units were still deeply buried at this time, such as the GHC, the LHS. Dashed red lines shown across the restored geometry highlight fault traces that were active in next step.

3.4.2 Restoration ca. 20 Ma

Deformation during 28-20 Ma time interval is dominated by the emplacement of the

Main Central thrust sheet (Plate 1B). Tectonic wedging of the GHC occurred between the STD as backthrusting and the MCT. The THS are thrust over the Outer LHS. Two discontinuous thin slivers of the Baragaon gneiss are interpreted to slide together with the THS along the MCT since discontinuous slivers of the Baragaon gneiss occur within the Main Central thrust shear zone in outcrops (Figure 3.1). The emplacement of the Main Central thrust sheet and tectonic wedging of the GHC require ~108 km of shortening. Thermochronological data across the southern portion of the line of section is used to infer the position of the ground surface at this time. ZFT ages range between 26.8±1.9 and 28.8±1.8 Ma for the southern portion of the THS indicate the THS was above the ZFT closure temperature isotherm at this time. Units that remain deeply buried at this time include the leading edge of the GHC, the Baragaon gneiss, the central portion of THS, and The LHS. Solid red lines shown represent reactivation along previous fault traces in next step. Thick solid black lines represent non-active faults.

3.4.3 Restoration ca. 13 Ma

The ongoing growth during 20-13 Ma period is continued by accretion of the Pabbar thrust sheet, which emplaced the Outer LHS rocks over the Berinag Group and the

Deoban/Damtha Group (Plate 1C). Part of the Deoban and Damtha rocks and small portion of the Berinag Group is inferred to be transported together with the Outer LHS along the Pabbar thrust towards the foreland. The GHC, the THS and the Baragaon gneiss were also translated to the southwest and thrust over the Berinag Group due to initiation of the Pabbar thrust. The estimate total shortening accomplished during this period is ~95 km. Note that the pre- deformation traces of the Berinag-Tons thrust slice through the Baragaon gneiss. Therefore, a discontinuous sliver of the Baragaon gneiss is interpreted to slide along the Berinag-Tons thrust since discontinuous thin fragments of the Baragaon gneiss occur along the Berinag-Tons thrust in map (Figure 3.1).

3.4.4 Restoration ca. 8.1 Ma

The Berinag-Tons thrust hanging wall was accreted to the Pabbar thrust sheet during 13-

8.4 Ma time interval, and the Berinag, Outer LHS rocks, and a thin fragment of the Baragaon gneiss were translated farther south atop of the Deoban and Damtha Groups (Plate 1D). The hangingwall cutoff of Deoban/Damtha rocks, the Beriang Group and the Sub-Himalaya rocks are interpreted to be completely eroded away by ca. 8.1Ma. Only a small portion of the Pabbar thrust was preserved after movement of the Berinag-Tons thrust. The GHC was still deeply buried at this time. The Late Miocene ZFT ages of the Berinag-Tons thrust Hanging wall rocks are used to infer the ground surface. The estimate total shortening accomplished along the Berinag-Tons thrust is ~67 km.

3.4.5 Restoration ca. 5.2 Ma

Continued mountain building is accomplished by the accretion of horses of the Deoban

/Damtha Group and of Munsiari Group (Plate 1E, 1F). Growth since the late Miocene continues via duplexing of the Deoban and Damtha Groups, antiformal stacking of the Munsiari Group,

55 out-of-sequence faulting along the Munsiari thrust, and frontal accretion of the sub-Himalaya.

Frontal accretion of sub-Himalayan rocks is presumably ongoing throughout the whole construction of the Himalaya, but only the most recently deformed portions of this unit are preserved. The hanging wall rocks of the Berinag-Tons thrust, the Pabbar thrust, and MCT have been passively warped and transferred towards the foreland by late accretion. Duplexing of three horses of the Deoban/Damtha Group were developed first during 8.1-5.2 Ma. Followed by the antiformal stacking of four thrust horses of Munsiari Group and continue duplexing of six horses of the Deoban/Damtha Group. The Munisar Group and GHC were exposed after ~5.2 Ma. This is good match with thermochronological results that abundance of AFT ages in the Munsiari

Group and the GHC show < 4 Ma cooling ages. Out-of-sequence thrusting of the Munsiari thrust occurred late and only accommodated ~3 km heave and ~10 km throw.

3.5 Discussion: Extrusion vs. Duplexing Models of Himalayan Mountain Building

The deformation history of Himalayan mountain building involves the emplacement of

THS/GHS, and followed by the ongoing growth dominated by the deformation of LHS.

Currently models for both stages can be divided in two categories: extrusion vs. duplexing.

Extrusion models for the emplacement of THS/GHS emplacement include: 1) the wedge extrusion models (e.g. Burchfiel and Royden, 1985), and 2) channel flow model (e.g., Nelson et al., 1996; Beaumont et al., 2001). Extrusion models describe emplacement of GHC as southward extrusion of a fault-bound block, with the MCT below and the STD above as a normal fault.

Extrusion models predict 1) the MCT and STD are largely subparallel or merge downdip to the north; 2) exposure of the GHC and THS in the north is required to happen during the main motion along the MCT and STD in the Early and Middle Miocene. Duplexing models include the tectonic wedging model which describe emplacement of GHC as accretion of the MCT sheet

56 with STD acting as a sub-horizontal backthrust off of the MCT synchronously (e.g., Yin 2006;

Webb et al., 2007). Duplexing model predicts 1) the MCT and STD merge updip to the south; 2) exposure of the GHC and THS in the north is post the STD activity during Middle to Late

Miocence to Pliocene. The MCT-STD branch line concept is introduced by the duplexing model.

North of the MCT-STD branch line, the hanging wall rocks of the MCT is the GHC; whereas, south of the MCT-STD branch line, the hanging wall rocks of the MCT is the THS (Haimanta

Group, which share similar protoliths, ages, metamorphic grade with the GHC) (Webb et al.,

2011a, 2011b). Recent structural geology investigation in northwest Indian Himalaya and Nepal

Himalaya describe the existence of the MCT-STD branch line (Webb et al., 2011a, 2011b; He et al., 2014 in review).

Extrusion models for the ongoing growth of the Himalayan orogeny generally focus on southwards translation of a fault-bound block towards the surface, with an out-of-sequence thrust below (Munsiari thrust), and normal fault above (STD). Duplexing models highlight accretion of material from the subducting plate to the over-riding orogenic wedge with only minor out-of- sequence deformation (e.g., Schelling and Arita, 1991; Robinson et al., 2003, Bollinger et al.,

2004; Konstantinovskaia and Malavieille, 2005; Herman et al., 2010, Grandin et al., 2012).

Duplexing may occur through any or all of three processes: frontal accretion involving forward propagation of the frontal thrust (e.g., Schelling and Arita, 1991), expansion of the orogen via incremental accretion along the basal shear zone (e.g., Searle et al., 2008), and discrete accretion of km-to-10 km-scale thrust horses along ramps of the Himalayan sole thrust (e.g., Robinson et al., 2003; Bollinger et al., 2004; Robinson, 2008; Webb, 2013). Our field-based and analytical work in Chapter two resolves the kinematic evolution of Pabbar thrust and Berinag-Tons thrust.

The resultant structural framework is consistent with duplexing processes and limits extrusion to

57 a minor role in mountain-building. Our low temperature thermochronology data places well constraint on the Late Miocene activation of the Berinag-Tons thrust. These findings are consistent with results from thermo-kinematic modeling of rich thermochronological data across the central Nepal Himalaya (Herman et al., 2010). Balanced palinspastic reconstruction across the NW Indian Himalaya also confirms the overall dominance of duplexing process.

3.6 Conclusions

The new set of thermochronological data place robust time constraint on Himalayan mountain building process: 12.5±0.4 to 6.5±0.5 Ma zircon fission track ages of the Berinag-Tons thrust hanging wall rocks; 26.8±1.8 to 28.8 ±1.8 Ma zircon fission track ages of the southernmost exposure of the THS in the hanging wall of the MCT. A balanced palinspastic reconstruction across the northwestern Indian Himalaya reveals ~380km (66%) shortening along the MCT, the STD and deformation of the LHS. The Mountain building process includes 1) Late

Oligocene–Middle Miocene emplacement of the GHC, and juxtaposing of the THS atop LHS. 2)

Middle–Late Miocene accretion of the Pabbar thrust sheet and the Berinag-Tons thrust sheet and

3) subsequent growth via a hinterland-dipping upper crustal duplexing and an antiformal stack of mid-crustal horses developed simultaneously. The kinematic relationship of the Pabbar thrust and the Berinag-Tons thrust, and our palinspastic reconstruction demonstrate that discrete duplexing processes dominated ongoing growth of the northwest Indian Himalaya and limited extent of out-of-sequence faulting (<3% of shortening).

CHAPTER 4 KINEMATIC TRISHEAR MODEL OF FAULT-PROPAGATION FOLDING TO PREDICT DEFORMATION BANDS, COLORADO NATIONAL MONUMENT, NW UNCOMPAHGRE UPLIFT, USA

4.1 Introduction

The objective of this study is to explore a quantitative method to describe and predict distribution and orientation of deformation bands related to reverse faulting. The correlation may have significant implications with regard to better constrain the fluid pathways around faults because of the potential effect on fluid flow of deformation bands (e.g. Pitman, 1981; Jamison and Stearns, 1982; Gabrielsen and Koestler, 1987; Antonellini and Aydin, 1994, 1995; Beach et al., 1997; Crawford, 1998 ; Gibson, 1998; Antonellini et al., 1999; Heynekamp et al., 1999;

Hesthammer and Fossen, 2000; Taylor and Pollard, 2000; Lothe et al., 2002; Ngwenya et al.,

2003; Shipton et al., 2002, 2005; Sternlof et al., 2004; 2005; Flodin et al., 2005; Fossen and Bale,

2007; Wibberley et al., 2007; Torabi and Fossen, 2009; Ballas et al., 2012, 2013). The

Uncompahgre uplift in Colorado plateau is an ideal locality because this region has key advantages. First, classic deformation bands developed in Late Triassic to Early Jurassic eolian

Wingate Sandstone associated with basement-cored monocline growth. Second, characterization of those deformation bands including types, density, orientation, thickness and petrophysical properties are fully documented in published data (e.g. Jamison, 1979; Jamison and Stearns,

1982; Jamison, 1989 ). Third, sufficient surface structural data allow us to better constrain geometries of the target faults (Scott et al., 2001).

The Uncompahgre uplift was formed due to the Late Cretaceous to Middle Eocene (~70-

50 Ma) Laramide Orogeny by reactivation of inherited high-angle Precambrian basement faults at depth (e.g., Kelly, 1955; Cashion, 1973; Stone, 1977; Davis, 1978; Davis, 1999; Tindall and

Davis, 1999; Bump and Davis, 2003; Bump, 2004; Timmons et al., 2007). The traditional kink- band based fault-propagation folding featured by angular fold hinges, uniform dips and constant thickness of fold limbs failed to explain inclined Precambrian basement-Mesozoic rock contact, curved fold hinges and thickening and thinning of fold limbs (e.g., Suppe, 1983; Suppe and

Medwedeff, 1990). Trishear provides an alternative model of fault-propagation folding characterized by heterogeneous strain generated by inclined shear in a triangular zone above the fault tip, which commonly exhibits curved hinges, broad crested anticlines, non-uniform dips, and changing thickness of fold limbs.

Deformation bands are brittle microfaults with tiny shear offset on the scale of millimeter to centimeter without clearly defined slip surface, a few millimeters thick and a few meters to tens of meters long (Aydin, 1978; Aydin and Johnson, 1978, 1983; Antonellini et al., 1994;

Mollema and Antonellini, 1996; Fossen and Hesthammer, 1997; Fossen et al., 2007). They are usually developed in deformed porous sandstones and sediments (e.g., Jamison and Stearns,

1982; Fisher and Knipe, 2001; Antonellini et al., 1994; Cashman & Cashman, 2000; Hooke and

Iverson, 1995; Hesthammer and Fossen, 1999; Wennberg et al., 2013). Deformation bands are formed due to strain localization, which may involve granular flow (grain boundary sliding, rotation, translation), cataclasis (grain crushing, frictional sliding), phyllosilicate smearing, dissolution and cementation (e.g., Aydin, 1978, Fossen et al., 2007). They may occur naturally as single bands, deformation band clusters, and slip surfaces at the edge of deformation band clusters. Deformation bands can be classified into two categories: shear bands with dominant shear component, compaction bands with pure compaction (volume decrease) or dilation

(volume increase) with no evidence of shear (e.g. Issen and Rudnicki, 2000; Bésuelle, 2001;

Aydin et al. 2006; Chemenda et al., 2011).

Deformation bands have drawn attention to geologist and petrologist since 1980s because of their relatively low permeability compared to the host rocks and their potential role as barriers to fluid flow. They are found in a large range of geological settings: the Late Triassic to Early

Jurassic eolian sandstones of southwestern USA related to both normal and reverse faulting events (e.g., Jamison and Stearns, 1982; Jamison, 1989; Mollema and Antonellini, 1996; Davis,

1999; Davis et al., 1999; Shipton and Cowie, 2001; Eichhubl et al., 2004; Katz et al., 2004;

Schultz, 2009; Schultz et al., 2010; Solum et al., 2010; Brandenburg et al., 2012); the pre-rift sandstones related to normal faulting during rifting in Suez Rift (e.g., Beach et al., 1999; Bernard et al., 2002; Rotevatn et al., 2008); the continental shelf sandstones related to extension and inversion structures (e.g., Fisher and Knipe, 2001; Hesthammer et al., 2002; Lothe et al. 2002 ); the unconsolidated, glaciolacustrine delta sands (e.g., Brandes and Tanner, 2012) and Marine terrace sediment (e.g., Cashman and Cashman, 2000). A lot of research focuses on the laboratory experimental investigation and numerical modelling on deformation mechanism and corresponding petrophysical properties of deformation bands (e.g., Wong et al., 1997; Bésuelle,

2001; Borja and Aydin, 2004; Chemenda, 2007, 2009; Wang et al., 2008; Charalampidou et al.,

2011, 2012; Klimczak et al., 2011; Cilona et al., 2012; Chemenda et al., 2012). The above research indicates: 1) most observed deformation bands show one to six orders of magnitude reduction in permeability compared to their host rocks. Their practical influence on flow path may related to deformation mechanism , thickness, connectivity, and three dimension extension of deformation bands (e.g., Knott, 1993; Main et al., 2000; Jourde et al., 2002; Lothe et al., 2002;

Fossen, 2007; Fossen and Bale, 2007; Olierook et al., 2014; Saillet and Wibberley, 2013). 2)

Density and distribution of deformation bands have direct relationship with fault displacement and corresponding strain accumulation (e.g., Solum et al., 2010; Brandenburg et al., 2012;

Schueller et al., 2013; Soliva et al., 2013; Ballas et al., 2014), however, a clearly quantitative relationship between distribution of deformation bands and kinematic evolution of fault development is still uncertain and needs further investigation.

The kinematic trishear model of fault-propagation folding has been used to simulate monocline growth associated with high-angle reverse faults in the Colorado Plateau (e.g., Erslev and Selvig, 1997; Cristallini and Allmendinger, 2001; Bump, 2003; Cristallini et al., 2004;

Brandenburg et al., 2012). In this study, trishear model is used to reconstruct the basement-cored monocline growth in Uncompahgre uplift along three balanced cross sections. The best-fit parameters are determined for fault movement from reconstruction, which are used later for forward modeling strain in fault tip zone. The modelling strain result demonstrates excellent agreement with the strain calculated from deformation bands, and the distribution and orientation of deformation bands in the field.

4.2 Geology Background

The Uncompahgre uplift, one of several NW-SE trending anticlines in the Colorado plateau, extends from western Colorado into easternmost Utah. The Colorado National

Monument (CNM) is located on the northeast edge of the Uncompahgre uplift, which is defined by the basement-cored monocline (Figure 4.1).

4.2.1 Tectonic History of the Uncompahgre Uplift

This area experienced complex tectonic history. First, Proterozoic extension events generated the basement-penetrating normal faults (e.g., Marshak and Paulsen, 1996; Karlstrom and Humphreys, 1998; Marshak et al., 2000; Timmons et al., 2001; Whitmeyer and Karlstrom,

2007). The plateau was then exposed to erosion until Cambrian. Throughout the plateau, extensive erosion stripped away kilometers of metamorphic rocks and exposed high grade

Figure 4.1 Geological map of the Uncompahgre Uplift, NW of Colorado National Monument. This map is simplified from the Geological map of public resource of U.S. Geological Survey (Geological Investigations Series I-2740).

metamorphic cores, and the hiatus is known as the Great Uncomformity (e.g., Foos et al., 1999;

Scott et al., 2001). The second tectonic event that affected the Colorado plateau is the Late

Paleozoic Ancestral Rockies event (320-245 Ma), related to collisional orogeny along North

America’s eastern and southern margins (e.g., Kluth and Coney, 1981; Bird,1988; Ye et al.,

1996). The Ancestral Rockies event created a series of basins and basement-core uplifts (e.g.,

Kluth and Coney, 1981; Bally et al., 1989; Ye et al., 1996). Those basement-core uplifts are indicated to be exhumed by reactivation along high-angle normal faults inherited in Proterozoic basement (e.g., Marshak et al., 2000). The Ancestral Uncompahgre Highlands is one of those

63 northwest-southeast trending basement-cored uplifts, bounded on the southwest by the Paradox basin and on the northeast by the Central Colorado trough (e.g., White and Jacobson, 1983;

Kluth and DuChene, 2009). Following exhumation, the Precambrian crystalline rocks and the

Lower Paleozoic marine units were exposed to erosion on uplifts and were transported to adjacent basins. Those uplifts were eventually worn down to a level plain to receive Mesozoic sediments on Precambrian crystalline basement throughout late Triassic to Late Cretaceous.

During the Late Cretaceous to middle Eocene (~70-50 Ma), the plateau was subject to another mountain building event-Laramide Orogeny, which is the response to the stress generated by plate convergence along the west coast of North America (e.g., Stone, 1977;

Brewer et al., 1982; Engebretson et al., 1985; Cross, 1986; Dickinson et al., 1988; Hamilton,

1988; Livaccari, 1991; Burchfiel et al., 1992; Cowan and Bruhn, 1992; Miller et al., 1992;

Monger and Nokleberg, 1996; Davis, 1999; Bump and Davis, 2003; Conner and Harrison, 2003;

English et al., 2003; Bump, 2004; DeCelles, 2004; Erslev, 2005; Erslev and Larson, 2006).

Laramide Orogeny created a series of highly asymmetrical, fault-cored anticlines like the Kaibab,

Monument, Uncompahgre uplifts etc. (e.g., Cashion, 1973; Powell, 1973; Stone, 1977; Davis,

1978; Dutton, 1982; Davis, 1999; Tindall and Davis, 1999; Bump and Davis, 2003; Bump, 2004;

Timmons et al., 2007). They were formed by reactivation of inherited Precambrian basement faults (e.g., Stearns and Jamison, 1977; Brewer et al., 1982; Allmendinger et al., 1982; Heyman,

1983; Heyman et al., 1986; Brown, 1988, 1993; Blackstone, 1993; Huntoon, 1993; Schmidt et al.,

1993; Foos, 1999; Marshak et al., 2000; Erslev et al., 2001; Bump and Davis, 2003; Bump, 2004;

Erslev and Koenig, 2009; Brandenburg et al., 2012). Both the northeast and southwest flank of the Uncompahgre lift are featured by the basement-cored monoclines (e.g., Stearns and Jamison,

1977; Stone, 1977; Jamison, 1979; Jamison and Stearns, 1982; Heyman, 1983; White and

Jacobson, 1983; Heyman et al., 1986; foos, 1999; Scott et al., 2001). Those basement-cored monoclines are thought to be developed by fault-propagation folding (e.g., Erslev, 1991; Erslev and Rogers, 1993; Kellogg et al., 1995; Erslev and Selvig, 1997; Tindall and Davis, 1999;

Brandenburg et al., 2012). Modern topography in the Colorado Plateau is the interaction result between Post-Laramide regional uplift and river erosion, which is still active in present day (e.g.,

Steven et al., 1997; McMillan et al., 2006)

4.2.2 Major Stratigraphy

The exposed lithology packages in the CNM include Precambrian crystalline rocks,

Mesozoic sedimentary rocks, and Quaternary non-marine deposits (Figure 4.1). The Precambrian basement rocks are composed of Early Proterozoic dark schist and light migmatitic pegmatite, granite gneiss, and Middle Proterozoic dikes (see Scott et al., 2001 for detail lithology description).

The Precambrian basement is overlain directly by the Late Triassic Chinle Formation dominated by distinctive red colored mudstone deposited in flood plain environment (e.g., Foos,

1999; Scott et al., 2001). The Chinle Formation is of ~30m thickness, which is overlain by Late

Triassic and Early Jurassic sandstone: the porous, cliff-forming Wingate Sandstone with thickness of ~100 m and thin layer of resistant, silica-cemented Kayenta Formation with thickness of ~15 m (e.g., Foos, 1999; Scott et al., 2001). The well-sorted, fine-grained Wingate sandstone is of high porosity (Ø= ~23%) and high permeability (e.g., Jamison, 1979). Eolian sandstones from the Colorado Plateau attract much attention because of their classic deformation bands development (e.g., Jamison and Stearns, 1982; Jamison, 1989; Mollema and Antonellini,

1996; Davis, 1999; Davis et al., 1999; Shipton and Cowie, 2001; Eichhubl et al., 2004; Katz et al., 2004; Schultz, 2009; Schultz et al., 2010; Solum et al., 2010; Brandenburg et al., 2012). The

65 most spectacular primary sedimentary feature of the reddish eolian Wingate Sandstone is the enormous cross-bedding, which can be used as markers for measuring offsets of deformation bands. The upper part of Kayenta Formation is eroded away in this area (e.g. Foos, 1999), which is overlain by lower Middle Jurassic sandstone (~50 m), and mudstone rocks of upper Middle

Jurassic (~15 m), Upper Jurassic (~220 m) and Cretaceous (~1300 m) (e.g., Dunham, 1962;

Pipiringos and O’Sullivan, 1978; Kocurek and Dott, 1983; Peterson, 1988; Aubrey, 1998;

Peterson and Turner, 1998). Due to the Laramide Orogeny, this area became structurally high again and only received the Quaternary non-marine deposits on regional unconformity above the

Late Cretaceous rocks (e.g., Chapin and Cather, 1983; Cole and Moore, 1994; Scott et al., 2001).

4.2.3 Major Faults in CNM, Uncompahgre Uplift

The Uncompahgre Uplift is bounded by high-angle reverse faults along both northeast and southwest flanks. This study only deals with the fault system along the northeast boundary in

CNM, i.e., the Redlands Fault system. The northwest striking Redlands Fault dips southwest to south between 62° and 83° in CNM, which is parallel to the trend of the Late Paleozoic

Ancestral Rockies fault systems (e.g., Jamison, 1979; Scott, et al., 2001). The Redlands reverse fault extends across the whole length of the CNM, but only gets exposed in a few locations

(Figure 4.1). Part of this basement fault cuts though the Chinle Formation and dies out into lower part of the Wingate Sandstone (East Kode Canyon), whereas part of the fault only cuts lower part of the Chinle Formation (East Canyon). The dips of Mesozoic strata increased from horizontal to almost 60-70° in the fault zone (Figure 4.1). The Wingate Sandstone is significantly attenuated around the fault tip zones (Jamison, 1979; Jamison and Stearns, 1982; Heyman, et al., 1986;

Davis, 1999). The offsets along the Redlands Fault vary between 400-500 m (Jamison, 1979 and this study). In the northwest portion of the CNM (northwest from East Canyon), there is another

66 fault system, the Fruita Canyon Fault, mapped by Jamison (1979), with tens of meters offsets.

Several other sealed basement faults are inferred in this area indicated by several changes of dip domains of Mesozoic strata towards northeast, which suggests the existence of underlying faults

(Figure 4.1).

4.3 Method and Data

Three balanced cross sections were made and reconstructed along East Canyon, North

Canyon and Kodels Canyon using trishear model of fault-propagation folding in Move software

(the Midland Valley software). The best-fit parameters that constrain the kinematic evolution of the Redlands Faults are determined from the reconstruction. Those parameters are used for trishear forward modeling of strain in the Redlands Fault tip zone in SVS software (in-house software developed by Shell International Exploration & Production Company). The Geological map and structural data, topographic data are derived from public resource of U.S. Geological

Survey (Geologic Investigations Series I-2740): Geologic Map of Colorado National Monument and Adjacent Areas, Mesa County, Colorado. Field data of deformation bands are all from published data by Jamison (1979) and are summarized below.

4.3.1 Method: Kinematic Trishear Model of Fault-propagation Folding

The traditional kink-band based fault-propagation folding features angular fold hinges, uniform dips and constant thickness of fold limbs due to homogeneous strain as a result of layer- parallel shear, and fixed fault propagation/slip ratio (P/S = 2) (e.g., Suppe, 1983; Suppe and

Medwedeff, 1990). Those characteristics of kink-band based fault-propagation folding failed to explain the following geological features of Uncompahgre Uplift. First, monoclines in

Uncompahgre Uplift are basement involved, thick-skin structure. Second, Precambrian basement-Mesozoic rock contact dips steeply to the northeast. Previous workers in this area propose the model that multiple faults spread from the main thrust can create a triangular shape

67 of basement rocks that allow the rotation of the contact (e.g., Scott et al., 2001). However, there is no geophysical data support the existence of this kind of main thrust. Third, the monoclines in

Uncompahgre Uplift show curved fold hinges and thickening and thinning of fold limbs, for example, the Wingate Sandstone changes thickness around the fault tips.

Trishear provides an alternative model of fault-propagation folding. Trishear models were initially developed due to the inapplicability of kink-band models for basement-involved, thick-skin structures in some geological settings (Erslev, 1991; Allmendinger, 1998). Trishear defined the distributed, heterogeneous strain generated by inclined shear in a triangular zone above the fault tip, which commonly exhibits curved hinges, broad crested anticlines, non- uniform dips, and changing thickness of fold limbs (e.g., Erslev, 1991; Allmendinger, 1998;

Hardy and Allmendinger, 2011; Dian, 2013). There are six controlling parameters determining the shape of a fault-propagation fold in trishear model: the fault slip, P/S (ratio between fault propagation rate and slip rate), trishear angle (the angle between the two boundaries of the trishear zone), fault dip angle, and x and y positions of the fault tip (e.g., Hardy and Fort, 1997;

Allmendinger, 1998; Zehnder and Allmendinger, 2000; Brandenburg et al., 2012; Dian, 2013).

Trishear models have been applied to other monoclines in the Colorado Plateau to successfully explain the geological features there (e.g., Erslev and Selvig, 1997; Cristallini and Allmendinger,

2001; Bump, 2003; Cristallini et al., 2004; Brandenburg et al., 2012).

4.3.2 Data: Characteristics of Deformation Bands in CNM

Characteristics of deformation bands are all from published field data by Jamison (1979) and are summarized below. Deformation bands localized near the Redlands Fault zone and the

Fruita Canyon Fault zone in Wingate Sandstone, rather than pervasively distributed. They occurred as single deformation bands, anastomosing bands (zones of deformation bands), and

Riedel Shear zones. The single deformation band usually forms 0.3 mm wide gouge zone, and show minimum measurable offset of ~2 mm. When the offset increases into ~5 mm, numerous deformation bands will develop in a narrow zone to form anastomosing bands. The anastomosing band shows numerous wavy and intersecting gouge zones (usually no more than 5 mm, occasionally extend to at most several centimeter wide). The Riedel Shear zone is composed of two groups of deformation bands arranged in a specific geometry, i.e., "Riedel (R) shears" and

"conjugate Riedel (R’) shears" with opposing senses of offset. The R and R’ shears (several centimeters in width) are conjugated Coulomb shears developed in response to a maximum compressive principal stress (e.g., Mandl et al., 1977; Harris and Cobbold, 1985). Both porosity and gain size are reduced in the gouge zone.

Orientation and intensity of deformation bands have been determined by Jamison (1979) in the East Kodels Canyon and North Canyon in the Redlands Fault zone. The Riedel Shear zones in outcrops are used to calculate shortening strain. This purpose of this study is to compare strain distribution modeled by trishear fault-propagation folding with field data (strain, orientation and intensity of deformation bands) along the Redlands Fault.

4.4 Results

4.4.1 Balance Reconstruction

Each of the three cross sections is perpendicular to the local strike of Redlands Fault. The

East Kodels Canyon cross section A-A’ and the North Canyon cross section B-B’ are along the exact lines where Jamison (1979) quantitatively measured deformation bands. Horizontal layers are used for pre-deformed strata, which is most likely true because outcrops of non-deformed strata in the Uncompahgre Uplift are almost horizontal. Thickness and depth of each unit is calculated from surface structural data and map pattern. Restored steps were constructed by

69 progressively “undeforming” the deformed section in 2D Move software. Trishear was applied to unfold fold limbs. Planar fault and dip slip are assumed (Davis, 1999; Bump and Davis, 2003;

Timmons et al., 2007). Whenever there is sharp change of dip domains of Mesozoic strata, an underlying basement fault was put and named North Redlands Fault-I, North Redlands Fault-II towards northeast. Structural data of Mesozoic sedimentary rocks are used for reconstruction.

Table 4.1 Trishear Solution Parameters for the Redlands Fault Fault Fault plane Trishear angle Propagation/Slip displacement (m) angle East Kodels Canyon A-A’ 45° 200 3.5 82°

North Canyon B-B’ 45° 230 3.5 79°

East Canyon C-C’ 60° 400 3.5 75°

4.4.1.1 Cross Section Reconstruction along the East Kodels Canyon

Step A represents pre-deformed stage with horizontal layers (Figure 4.2-A). Only the top of basement is shown in the cross section, and the bottom of basement is not indicated. The

Redlands Fault was the first fault initiated from the basement, penetrated the Chinle Formation, extended into top part of the Wingate Sandstone, and deformed the overlying Mesozoic strata into an “S” shape (Figure 4.2-B). The high angle Redlands Fault dipping 82° to southwest has

400 m displacement, P/S value of 3.5, and trishear angle of 45° (Table 4.1). The basement was elevated by ~200m due to the movement of Redlands Fault. In order to accommodate the inclined basement-Mesozoic rocks contact, another more shallowly dipping blind fault is indicated at ~400m northeast from the Redlands Fault, named North Redlands Fault-I (Figure

4.2-C). This fault initiated from the basement and only cut part of the Chinle Formation, with the displacement of 130 m. At about 1300 m northeast from the Redlands Fault, another fault (North

Redlands Fault-II) is inferred by the change of dip domains in the surface (Figure 4.2-D). The

North Redlands Fault-II dipping 72° to southwest has 260 m displacement, P/S value of 3.5, and trishear value of 60°. This fault originated from the basement and did not cut through the overlying sedimentary rocks. In the southwest of the Redlands Fault, the Fruita Canyon Fault system acts as minor out-of-sequence faulting (Figure 4.2-D). Strata above all these faults display attenuation and thickening.

4.4.1.2 Cross Section Reconstruction along the North Canyon

The Redlands Fault along the North Canyon is dipping 79° to southwest. The displacement is of

230m, which is larger than that in the East Kodels Canyon (Table 4.1). The Fault only cut the very bottom of the Wingate Sandstone (Figure 4.3-B). The North RedLands Fault-I lies about

350 m northeast from the Red lands Fault with 140 m displacement, which initiated and died within the basement rocks without cutting through the overlying sedimentary rocks (Figure 4.3-

C). The North Redlands Fault-II is dipping 68° to southwest, with all other parameters as same as those along the East Kodels Canyon (Figure 4.3-D). The North Redlands Fault-II also only cut through the basement rocks. In the southwest of the Redlands Fault, the Fruita Canyon Fault system acts as minor out-of-sequence faulting in basement rocks with only 60 m displacement

(Figure 4.3 -D).

4.4.1.3 Cross Section Reconstruction along the East Canyon

The Redlands Fault along the East Canyon is dipping 75° to southwest. The displacement is of 400 m, which is the largest among the three cross sections (Table 4.1). The Fault only cut the basement, and did not penetrate into the overlying sedimentary rocks (Figure 4.4-B). The

North RedLands Fault-I is close to the Redlands Fault, which has only 80 m displacement. This fault also initiated and died within the basement rocks (Figure 4.4-C). The North Redlands

Fault-II in this cross section shows the largest displacement (400 m) compared to the other two

Figure 4.2 Cross section reconstruction along the EastKodels Canyon. Abbreviations: RF – Redlands Fault, NRF-I – North Redlands Fault-I, NRF-II – North Redlands Fault-II, FF – Fruita Canyon Fault System.

Figure 4.3 Cross section reconstruction along the North Canyon. See abbreviations as in Figure 4.2.

Figure 4.4 Cross section reconstruction along the East Canyon. See abbreviations as in Figure 4.2.

(Figure 4.4-D). The Fruita Canyon Fault system is not reflected along this cross section; instead, another tiny reverse fault is indicated by the surface data to the northeast of the North Redlands

Fault-II (Figure 4.4-D).

4.4.2 Strain Calculation

The initial stage of strata in Step A, geometry of the Redlands Fault in step B, and the trishear parameters that defined the Redlands Fault are input into the SVS software to make a forward modelling of the Redlands Fault development in the East Kodels Canyon and North

Canyon. The purpose of forward model is to calculate the corresponding strain of the Redlands

Fault. The forward trishear model was run with initially circular strain maker (diameter of L0), which were deformed into ellipses. Principal shortening directions (L3, short axes of ellipse) and extension directions (long axis of ellipse) were computed. L3 corresponds to the maximum compressive stress (σ1), which is coincide with acute bisector of conjugate set of deformation bands with opposing offsets according to Mohr-Coulomb criterion. The magnitude (as a percentage) of shortening strain can then be estimated from the equation 100(1-(L3/L0)).

The modeling results for the Redlands Fault in East Kodels Canyon show the maximum shortening strain in Wingate Sandstone occurs near the fault with magnitude of ~40%, and this value decreases to ~5% at about 200 m away from the fault both in the upthrown block and downthrown block (Figure 4.5). Orientation of L3 is northeast-southwest. Plunges of L3 increase away from the fault in the upthown block (trend to be vertical), and decrease away from the fault in the downthrown block (trend to be horizontal) (Figure 4.5). According to the orientations of

L3, dip angles of deformation bands should increase away from the fault in the upthrown block and dip angles of deformation bands should decrease away from the fault in the downthrown block.

NE SW

1400 3 % Strain (1-(L3/Lo)) a b

5% 15%

20% 42%

1200 Wingate

d c

Redlands fault 1000 A

4750 4500 m e f

c b a d f e

g 13% 5% 39% 16% g

B C

Figure 4.5 Results from forward trishear model for the kinematic evolution of Redlands Fault

along section AA’. (A) Magnitude of shortening strain with finite strain ellipses: L3 = calculated principal shortening axis; (B) Densities of deformation bands localized around the Redlands Faults measured in the field by Jamison and Sterns (1982). Red colored number=permeability. Arrows point to the position where maximum shortening strain was measured from deformation bands in the field. (C) Poles of deformation bands plotted in stereo nets: red color dot represents sinstral offset; blue color dot represents dextral. Data of Both (B) and (C) is from Jamison and Sterns (1982).

The Redlands Fault in North Canyon did not cut the Wingate Sandstone. The modelling results show the maximum shortening strain (~40%) in Wingate Sandstone occurred in the triangular zone above the fault tip and decrease to ~5% at ~200 m away from the fault tip both in the forelimb and backlimb portion (Figure 4.6). Orientation of L3 exhibits the similar trend as that in East Kodels Canyon.

4.5 Discussion

Strain measured from deformation bands in outcrops are in good agreement with predictions of trishear modelling. Shortening strain are calculated using field data of deformation bands at four stations in the upthrown portion by Jamison (1979) along the East Kodels Canyon

(Figure 4.5): 39%, 16%, 13% and 5%. In the same locations, the magnitude of shortening strains predicted by modelling are about 40%, 20%, 15% and 5%, respectively. Field data show high density of deformation bands developed in the lower portion of Wingate Sandstone. Density of deformation bands increase as the magnitude of strain increases toward the fault in general.

Permeability is significantly reduced near the fault when the magnitude of shortening strain exceeds 15%. It is very hard to correlate strain with density of deformation bands in the downthrown block because the lower portion of Windgate Sandstone is not exposed (Jamison and Sterns, 1982).

Orientations of deformation bands in outcrops along the East Kodels Canyon are also consistent with predictions by trishear modelling (Figure 4.5). Field data display that deformation bands are dipping more shallowly towards the fault in upthrown block, whereas deformation bands are dipping more steeply in downthrown block towards the fault. For example, deformation bands in stations A, B, D are steeper (nearly vertical) than those in stations C and E

Figure 4.6 Results from forward trishear model for the kinematic evolution of Redlands Fault along setion BB’. (A) Magnitude of shortening strain with finite strain ellipses: L3 – calculated principal shortening axis; (B) Densities of deformation bands localized around the Redlands Faults measured in the field by Jamison and Sterns (1982). Red colored number – permeability. Arrows points to the position where maximum shortening strain was measured from deformation bands in the field. (C) Poles of deformation bands plotted in stereonets: red dots represent sinstral offset; blue dots represent dextral. Data of both (B) and (C) are from Jamison and Sterns (1982).

78 in upthrown block. Deformation bands in station F are steeper than those in station G in general in downthrown block (Figure 4.5).

Surprisingly moderate density of deformation bands occurred in cross section along

North Canyon although the Wingate Sandstone here show ~40% attenuation (Jamison, 1979;

Jamison and Stern, 1982) (Figure 4.6). The density measurement is suspected because there are several high density intervals are covered and cannot get access to (Jamison, 1979; Jamison and

Sterns, 1982). The orientations of deformation bands in this transect are in good agreement with predictions by modelling (Figure 4.6): at station J', the deformation band surfaces are nearly vertical and become nearly horizontal in the lower forelimb (station C’ and station I’).

The good agreement between modelling results and field data indicates that trishear model of fault-propagation folding can account for distribution and orientation of deformation bands in East Kodels Canyon and North Canyon. The combination of modelling results and field data suggest that density of deformation bands increases as strain increases in homogeneous lithology. Permeability will decrease significantly when shortening strain is over ~15% (this number should change in differently lithology). However strain-density relationship should be used by caution in view of the fact that under the same strain, the less porous, calcite-cemented layers in Wingate Sandstone contain less deformation bands than the porous layers nearby

(Jamison, 1979; Jamison and Stern, 1982).

4.6 Conclusions

79 that trishear model of fault-propagation folding is viable kinematics for Laramide monocline development than traditional kink-band style fault-propagation folding.

The good agreement between field data and modelling strain corresponding to the

Redlands Fault movement demonstrates that trishear model of fault-propagation folding can be used to predict distribution and orientation of deformation bands in subsurface reservoir, which might have potential influence on fluid flow path.

CHAPTER 5 SUMMARY AND CONCLUSIONS

This dissertation includes two parts: kinematic evolution of the Himalayan fold-thrust belt along the collisional orogenic belts on hundreds of kilometer scale, and trishear model of fault-propagation folding to predict deformation bands associated with growth of the basement- cored monoclines in Colorado Plateau on hundreds of meter to millimeter scale. The common goal of these two parts is to better understand contractional tectonics at different scale. Research on the Himalayan fold-thrust belt is to examine the viability of the Himalayan growth models through three components: 1) structural and kinematic mapping combined with microstructural investigations to address key questions about the regional structure (Chapter 2); 2) apatite and zircon fission track thermochronology to constrain the thermal history (Chapter 3); 3) interpretation of data from the first two research components via balanced palinspastic reconstruction (Chapter 3). Research on the Uncompahgre Uplift is to explore trishear model of fault-propagation folding to predict popularity of deformation bands associated with reverse faulting. The main conclusions of each project are summarized below.

5.1 Growth of the Himalayan Fold-thrust belt Dominated Duplexing Processes

Our work in the northwestern Indian Himalaya advances knowledge about ongoing

Himalayan growth, which is generally thought to be dominated by duplexing and/or extrusion processes. Duplexing models highlight accretion of material from the subducting plate to the over-riding orogenic wedge that may occur through any or all of three processes: frontal accretion involving forward propagation of the frontal thrust, expansion of the orogen via incremental accretion along the basal shear zone, and discrete accretion of km-to-10 km-scale thrust horses along ramps of the Himalayan sole thrust. Extrusion models generally focus on

81 southwards translation of a fault-bounded block towards the surface, with major out-of-sequence thrust faulting below and normal faulting above.

Our field-based analytical work in the northwestern Indian Himalaya resolves the uncertain relationship between two major regional structures: the Berinag thrust and the Tons thrust, which share the same footwall rocks, are in fact the same structure. Our mapping documents a new discovery: a ~ 450 m thick top-to-southwest shear zone, termed the Pabbar thrust, in the NW Indian Himalaya. The Pabbar thrust placed the Outer Lesser Himalayan

Sequence (the Tons thrust hanging wall) directly on the Berinag Group (the Berinag thrust hanging wall). The shear zone is characterized by sheath folds, S-C fabrics and mylonitic fabrics, all with top-to-the-southwest shear sense. Both the field observations and quartz microstructures indicate the Pabbar thrust developed earlier and hotter (i.e., deeper), followed by accretion of the

Berinag-Tons thrust sheet. Along-strike extension of these kinematics and corresponding geometries is consistent with the observed orogenic framework and resolves a stratigraphic continuity problem across the India – west Nepal border, where prior work suggests that structures are continuous but stratigraphy does not match. The resultant structural framework is consistent with duplexing processes and limits extrusion to a minor role in mountain-building.

Our new set of thermochronological data place robust time constraint on Himalayan mountain building process: 12.5±0.4 to 6.5±0.5 Ma ZFT ages indicate Late Miocene activity of the Berinag-Tons thrust; 26.8±1.8 to 28.8 ±1.8 Ma ZFT ages of the southernmost exposure of the

THS in the hanging wall of the MCT suggest initiation of the MCT in Late Oligocene. The thermochronological data is also used to confine the pre-deformational framework

A balanced palinspastic reconstruction across the northwestern Indian Himalaya reveals

~380km (66%) shortening along the MCT, the STD and deformation of the LHS. The Mountain

82 building process includes 1) Late Oligocene–Middle Miocene emplacement of the GHC, and juxtaposing of the THS atop LHS. 2) Middle–Late Miocene accretion of the Pabbar thrust and the Berinag-Tons thrust sheet and 3) subsequent growth via a hinterland-dipping upper crustal duplexing and an antiformal stack of mid-crustal horses developed simultaneously, and frontal accretion of sub-Himalayan rocks. The kinematic relationship of the Pabbar thrust and the

Berinag-Tons thrust, and our palinspastic reconstruction demonstrate that discrete duplexing processes dominated ongoing growth of the northwest Indian Himalaya and limited extent of out-of-sequence faulting (<3% of shortening).

5.2 Kinematic Trishear Fault-propagation Folding Model to Predict Deformation Bands

The Uncompahgre uplift was formed due to the Late Cretaceous to middle Eocene (~70-

50 Ma) Laramide Orogeny by reactivation of inherited high-angle Precambrian basement faults at depth. The traditional kink-band based fault-propagation folding featured by angular fold hinges, uniform dips and constant thickness of fold limbs failed to explain inclined Precambrian basement-Mesozoic rock contact, curved fold hinges and thickening and thinning of fold limbs.

We conducted balance cross section reconstruction along three traverses in northwest portion of CNM in Uncompahgre Uplift. Trishear modeling with planar, dip-slip fault is successfully used to reproduce geometry of the monocline. The good agreement between deformation bands data in field and modelling strain demonstrates that trishear model of fault- propagation folding is viable kinematics to predict distribution and orientation of deformation

83 bands. The correlation may have significant implications with regard to better constrain the fluid pathways around faults because of low permeability of deformation bands.

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107

APPENDIX A: APATITE FISSSION TRACK DATA

Pooled Yu91129-6 age±1σ (Ma) 8.4± 0.4 ρD ± 1σ Longitude ζ (Ma) Latitude(E) Elevation(m) Rock type [106 cm-2] (N) granite 268±4.7 0.375±0.006 29°48. 522' 78°39 829' 1209 gneiss Spontaneous Induced Spontaneous Induced n n track (Ns) track (Ni) track (Ns) track (Ni) 1 9 83 33 19 146 2 5 33 34 8 32 3 22 180 35 17 115 4 10 75 36 12 56 5 5 64 37 14 61 6 30 235 38 20 146 7 3 32 39 20 79 8 4 37 40 27 168 9 3 12 41 18 248 10 9 45 42 9 74 11 9 63 43 17 101 12 4 74 44 13 137 13 22 83 45 8 74 14 23 131 46 15 98 15 6 27 47 27 133 16 4 17 48 10 51 17 18 108 49 11 71 18 46 116 50 16 86 19 4 26 51 24 131 20 17 37 52 28 168 21 7 53 53 28 166 22 16 76 54 43 260 23 25 111 55 42 150 24 31 173 56 10 62 25 8 104 26 23 131 27 13 54 28 25 133 29 12 108 30 17 47 31 20 101

108

32 19 146 Pooled Yu91130-6 age±1σ (Ma) 6.7± 0.6 ρD ± 1σ Longitude ζ (Ma) Latitude(E) Elevation(m) Rock type [106 cm-2] (N) 268±4.7 0.383±0.006 29°56.057' 78°44.425' 628 sandstone Spontaneous Induced

n track (Ns) track (Ni) 1 6 64 2 2 25 3 3 40 4 2 25 5 7 54 6 17 180 7 6 91 8 43 299 9 8 48 10 16 109 11 4 39 12 32 141

109

Pooled Yu91130-9 age±1σ (Ma) 6.2± 0.3 ρD ± 1σ Longitude ζ (Ma) Latitude(E) Elevation(m) Rock type [106 cm-2] (N) 268±4.7 0.385±0.006 30°01.930' 78°48.148' 985 quartzite Spontaneous Induced Spontaneous Induced n n track (Ns) track (Ni) track (Ns) track (Ni) 1 2 28 26 7 66

2 20 93 27 10 46 3 10 55 28 7 55

4 1 18 29 5 19

5 8 50 30 5 55

6 3 14 31 11 92

7 13 79 32 2 28

8 5 21 33 7 86

9 8 67 34 7 33

10 8 32

11 3 17

12 5 59

13 8 55

14 3 33

15 9 51

16 5 56

17 5 50

18 4 21

19 7 93

20 12 63

21 5 42

22 6 79

23 14 79

24 9 111

25 10 51

110

Pooled Yu91201-9 age±1σ (Ma) 3.7± 0.3 ρD ± 1σ Longitude ζ (Ma) Latitude(E) Elevation(m) Rock type [106 cm-2] (N) 268±4.7 0.387±0.006 30°12.097' 78°50.920' 1367 quartzite Spontaneous Induced Spontaneous Induced n n track (Ns) track (Ni) track (Ns) track (Ni) 1 3 126 2 5 65 3 9 202 4 8 68 5 7 75 6 6 52 7 5 137 8 5 61 9 11 116 10 10 80 11 10 81 12 3 31 13 4 74 14 4 73 15 5 122 16 9 67 17 7 87 18 15 134 19 9 119 20 5 69 21 2 102 22 8 136 23 3 51

111

Pooled Yu91208-4 age±1σ (Ma) 4.0±0.3 ρD ± 1σ Longitude ζ (Ma) Latitude(E) Elevation(m) Rock type [106 cm-2] (N) Augen 268±4.7 0.393±0.006 30°21.526' 79°19.047' 960 gneiss Spontaneous Induced Spontaneous Induced n n track (Ns) track (Ni) track (Ns) track (Ni) 1 8 175 35 3 56 2 2 23 36 1 23 3 1 34 37 14 104 4 5 36 38 3 40 5 8 82 39 5 42 6 5 52 40 11 112 7 4 115 41 3 52 8 9 68 42 8 188 9 9 56 43 8 95 10 15 185 44 13 168 11 10 56 45 3 42 12 1 49 46 8 54 13 8 79 47 1 29 14 7 126 48 9 125 15 17 331 49 4 64 16 2 55 50 10 73 17 8 94 51 3 48 18 9 168 52 2 52 19 3 36 53 5 100 20 5 56 54 1 29 21 26 145 55 2 39 22 4 37 56 9 139 23 5 30 57 5 72 24 4 22 58 3 61 25 4 86 59 4 80 26 3 20 60 2 36 27 19 220 61 6 78 28 12 97 62 14 261 29 9 78 63 7 75 30 2 40 64 6 70 31 1 15 65 4 80 32 17 129 33 4 32 34 9 75

112

Pooled Yu91206-1 age±1σ (Ma) 1.1±0.04 ρD ± 1σ Longitude ζ (Ma) Latitude(E) Elevation(m) Rock type [106 cm-2] (N) granite 268±4.7 0.391±0.006 30°33.008' 79°19.047' 1786 gneiss Spontaneous Induced Spontaneous Induced n n track (Ns) track (Ni) track (Ns) track (Ni) 1 14 630 2 33 1600 3 39 1550 4 55 2320 5 20 868 6 37 2519 7 34 1967 8 46 1919 9 84 2593 10 50 2909 11 42 1772 12 50 2345 13 41 1956 14 39 2092 15 38 1326 16 85 4050 17 43 2692 18 38 1820 19 81 4520 20 66 3276 21 51 1767 22 62 2969 23 104 5741 24 47 2542 25 28 1996

113

APPENDIX B: ZIRCON FISSSION TRACK DATA

Pooled Yu91129-1 age±1σ (Ma) 119± 13 ρD ± 1σ Longitude ζ (Ma) Latitude(E) Elevation(m) Rock type [106 cm-2] (N) 97.1±2.4 0.280±0.013 29°48. 522' 78°36 861' 763 sandstone Spontaneous Induced Spontaneous Induced n n track (Ns) track (Ni) track (Ns) track (Ni) 1 630 36 34 219 13 2 117 34 35 179 11 3 114 10 36 232 45 4 66 5 37 535 20 5 94 27 38 153 26 6 77 30 39 275 18 7 135 9 40 120 45 8 155 13 41 380 13 9 242 23 42 181 55 10 150 25 43 431 25 11 141 20 44 1416 40 12 367 30 45 798 38 13 39 8 46 905 21 14 233 17 47 201 57 15 42 13 48 309 39 16 129 10 49 440 68 17 66 21 50 442 17 18 448 21 19 500 37 20 96 20 21 160 11 22 716 18 23 96 10 24 344 13 25 299 26 26 82 7 27 172 33 28 569 20 29 249 10 30 419 37 31 103 10

114

32 319 44 33 333 51 Pooled Yu91129-6 age±1σ (Ma) 28.8± 1.8 ρD ± 1σ Longitude ζ (Ma) Latitude(E) Elevation(m) Rock type [106 cm-2] (N) granite 97.1±2.4 0.261±0.012 29°48. 522' 78°39 829' 1209 gneiss Spontaneous Induced Spontaneous Induced n n track (Ns) track (Ni) track (Ns) track (Ni) 1 173 72 2 385 250 3 243 130 4 90 62 5 65 67 6 49 18 7 82 37 8 81 40 9 93 48 10 115 20 11 155 74 12 117 32 13 97 20 14 106 86 15 115 31 16 67 14 17 208 40 18 56 12 19 241 69 20 82 30 21 76 34

115

Pooled Yu91129-12 age±1σ (Ma) 26.8± 1.9 ρD ± 1σ Longitude ζ (Ma) Latitude(E) Elevation(m) Rock type [106 cm-2] (N) 97.1±2.4 0.286±0.016 29°53. 280' 78°40 432' 1496 quartzite Spontaneous Induced Spontaneous Induced n n track (Ns) track (Ni) track (Ns) track (Ni) 1 57 43 26 157 61

2 76 37 27 128 54 3 43 18 28 157 90

4 153 92 29 137 68

5 56 35 30 104 62

6 58 24 31 98 74

7 128 73 32 76 30

8 75 37 33 157 104

9 32 21 34 166 83

10 78 48 35 164 83

11 111 63 36 119 69

12 42 33

13 241 95

14 106 52

15 45 21

16 152 49

17 122 75

18 176 70

19 67 27

20 138 79

21 125 67

22 101 42

23 114 45

24 89 65

25 125 62

116

Pooled Yu91130-2 age±1σ (Ma) 183± 14 ρD ± 1σ Longitude ζ (Ma) Latitude(E) Elevation(m) Rock type [106 cm-2] (N) 97.1±2.4 0.211±0.004 29°54.592' 78°42.767' 768 quartzite Spontaneous Induced

n track (Ns) track (Ni) 1 346 35 2 816 47 3 806 59 4 530 51 5 441 58 6 1865 156 7 696 28 8 704 36 9 525 27 10 1115 45 11 490 24 12 1145 46 13 1619 51 14 1663 73 15 671 67 16 1704 62 17 633 24 18 519 32 19 2508 126 20 1265 70 21 663 29 22 1545 76 23 651 21 24 956 37 25 1329 60 26 504 18 27 814 41

117

Pooled Yu91130-6 age±1σ (Ma) 177± 18 ρD ± 1σ Longitude ζ (Ma) Latitude(E) Elevation(m) Rock type [106 cm-2] (N) 97.1±2.4 0.283±0.013 29°56.057' 78°44.425' 628 sandstone Spontaneous Induced Spontaneous Induced n track (Ns) track (Ni) n track (Ns) track (Ni) 1 41 3 37 499 18 2 127 4 38 277 18 3 516 20 39 198 8 4 48 4 40 669 24 5 247 140 41 320 10 6 391 20 42 216 8 7 303 14 43 413 25 8 230 11 44 168 9 9 201 15 45 171 14 10 121 9 46 184 12 11 184 15 47 324 24 12 220 17 48 287 20 13 361 18 49 306 12 14 200 16 50 920 30 15 45 7 51 122 6 16 157 26 52 244 13 17 124 16 53 730 28 18 92 16 54 535 21 19 349 21 55 579 25 20 117 18 56 676 35 21 316 17 57 239 15 22 33 4 58 249 17 23 447 42 59 428 28 24 114 14 60 160 7 25 89 8 27 358 25 28 50 3 29 114 13 30 156 10 31 323 13 32 87 9 33 218 14 34 410 22 35 82 5 36 251 17

118

Yu91130- 9 Pooled age±1σ (Ma) 12.5± 0.4 ζ (Ma) ρD ± 1σ [106 cm-2] Longitude (N) Latitude(E) Elevation(m) Rock type 97.1±2.4 0.273±0.015 30°01.930' 78°48.148' 985 quartzite Spontaneous track Induced Spontaneous track Induced n n (Ns) track (Ni) (Ns) track (Ni) 1 32 22 39 97 109 2 22 28 40 24 27 3 13 19 41 41 31 4 41 27 42 20 30 5 65 80 43 39 47 6 33 35 44 35 33 7 46 34 45 80 54 8 30 27 46 44 51 9 19 28 47 23 37 10 17 23 48 33 37 11 20 25 49 41 54 12 22 28 50 48 40 13 23 20 14 65 44 15 34 39 16 13 26 17 65 78 18 40 50 19 19 25 20 33 24 21 35 32 22 144 126 23 48 51 24 49 43 25 95 81 26 63 79 27 87 76 28 20 20 29 70 80 30 54 83 31 47 108 32 50 49 33 43 36 34 44 81 35 103 100 36 49 66 37 107 76 38 113 116

119

Pooled Yu91201-4 age±1σ (Ma) 12.3± 0.8 ρD ± 1σ Longitude ζ (Ma) Latitude(E) Elevation(m) Rock type [106 cm-2] (N) 97.1±2.4 0.286±0.017 30°07.453' 78°49.458' 1885 quartzite Spontaneous Induced

n track (Ns) track (Ni) 1 107 136 2 93 147 3 187 139 4 213 227 5 117 129 6 271 181 7 111 120 8 349 400 9 231 185 10 151 156 11 135 155 12 383 308 13 332 371 14 151 184 15 70 77 16 70 61 17 434 534 18 130 155 19 181 204 20 277 335 21 128 155 22 167 215 23 130 136 24 121 131 25 334 279 26 137 217 27 100 115 28 126 159 29 204 306 30 90 110

120

Pooled Yu91201-9 age±1σ (Ma) 9.5± 0.6 ρD ± 1σ Longitude ζ (Ma) Latitude(E) Elevation(m) Rock type [106 cm-2] (N) 97.1±2.4 0.250±0.017 30°12.097' 78°50.920' 1367 quartzite Spontaneous Induced Spontaneous Induced n n track (Ns) track (Ni) track (Ns) track (Ni) 1 84 124 36 148 204 2 99 103 37 39 62 3 167 201 38 39 53 4 72 136 39 46 53 5 24 47 40 99 126 6 106 125 41 55 68 7 67 68 42 120 147 8 94 128 9 115 150 10 141 177 11 89 138 12 117 149 13 99 151 14 50 113 15 104 175 16 94 121 17 147 159 18 59 88 19 114 161 20 65 111 21 114 186 25 334 279 26 137 217 27 100 115 28 126 159 29 204 306 30 90 110 31 97 132 32 88 108 33 89 115 34 51 81 35 128 158

121

Pooled Yu91204-1 age±1σ (Ma) 4.7± 0.3 ρD ± 1σ Longitude ζ (Ma) Latitude(E) Elevation(m) Rock type [106 cm-2] (N) 97.1±2.4 0.218±0.004 30°14.417' 78°49.647' 616 quartzite Spontaneous Induced Spontaneous Induced n n track (Ns) track (Ni) track (Ns) track (Ni) 1 26 92 2 26 140 3 28 56 4 39 120 5 25 49 6 35 87 7 46 99 8 51 89 9 22 66 10 53 92 11 36 65 12 40 64 13 29 36 14 30 29

122

Pooled Yu91204-9 age±1σ (Ma) 132± 22 ρD ± 1σ Longitude ζ (Ma) Latitude(E) Elevation(m) Rock type [106 cm-2] (N) 97.1±2.4 0.268±0.014 30°18.330' 79°02.113' 723 quartzite Spontaneous Induced Spontaneous Induced n n track (Ns) track (Ni) track (Ns) track (Ni) 1 352 45 31 2050 61 2 576 92 32 815 47 3 430 85 33 483 36 4 760 83 34 615 115 5 2280 125 35 2015 74 6 500 56 36 875 51 7 1400 63 37 672 48 8 600 62 9 1260 86 10 82 61 11 1454 66 12 2900 121 13 1200 43 14 900 93 15 2000 112 16 2050 61 17 815 47 18 483 36 19 615 115 20 2015 74 21 875 51 22 672 48 23 600 62 24 1260 86 25 82 61 26 1454 66 27 2900 121 28 1200 43 29 900 93 30 2000 112

123

Pooled Yu91209-1 age±1σ (Ma) 6.0± 0.5 ρD ± 1σ Longitude ζ (Ma) Latitude(E) Elevation(m) Rock type [106 cm-2] (N) 97.1±2.4 0.276±0.014 30°16.593' 79°14.156' 895 quartzite Spontaneous Induced Spontaneous Induced n n track (Ns) track (Ni) track (Ns) track (Ni) 1 56 107 31 31 55 2 46 96 32 19 46 3 81 175 33 58 143 4 59 103 34 24 79 5 50 154 35 42 180 6 14 36 36 30 56 7 58 149 37 67 178 8 65 128 38 59 122 9 30 60 39 20 55 10 18 34 11 12 60 12 70 158 13 23 52 14 79 233 15 30 64 16 39 103 17 43 125 18 41 116 19 57 106 20 47 59 21 65 121 22 25 75 23 67 133 24 73 89 25 93 253 26 52 133 27 41 74 28 31 75 29 40 67 30 32 71

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Pooled Yu91208-4 age±1σ (Ma) 5.7± 0.4 ρD ± 1σ Longitude ζ (Ma) Latitude(E) Elevation(m) Rock type [106 cm-2] (N) Augen 97.1±2.4 0.246±0.015 30°21.526' 79°19.047' 960 gneiss Spontaneous Induced Spontaneous Induced n n track (Ns) track (Ni) track (Ns) track (Ni) 1 32 51 2 39 66 3 42 81 4 64 152 5 40 94 6 42 119 7 62 92 8 89 161 9 21 36 10 46 118 11 29 63 12 33 66 13 19 40 14 39 50 15 15 34 16 48 184 17 42 86 18 32 76 19 38 56 20 57 132 21 26 52

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Pooled Yu91206-1 age±1σ (Ma) 1.5±0.1 ρD ± 1σ Longitude ζ (Ma) Latitude(E) Elevation(m) Rock type [106 cm-2] (N) Augen 97.1±2.4 0.204±0.005 30°33.008' 79°32.692' 1786 gneiss Spontaneous Induced Spontaneous Induced n n track (Ns) track (Ni) track (Ns) track (Ni) 1 82 510 21 48 250 2 40 299 22 41 252 3 34 276 23 78 435 4 26 221 24 73 549 5 32 264 25 35 350 6 47 283 26 66 397 7 52 322 27 31 245 8 30 275 28 21 191 9 65 327 29 80 459 10 45 320 30 31 204 11 52 340 31 58 442 12 43 356 32 151 648 13 42 311 33 64 527 14 62 334 15 64 344 16 53 284 17 95 547 18 31 284 19 67 558 20 55 365 21 48 250 22 41 252 23 78 435 24 73 549 25 35 350 26 66 397 27 31 245 28 21 191 29 80 459 30 31 204

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PLATE 1: SEQUENTIAL CROSS-SECTION RESTORATION ACROSS THE NW INDIAN HIMALAYA

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VITA

Hongjiao Yu was born in 1983, in Liaoning Province, China. She spent four years at

China University of Petroleum, where she earned a Bachelor of Resources Prospecting

Engineering in 2006. After that, she was offered an opportunity to pursue her study in Peking

University and earned a Master’s degree in geology in 2009. Immediately after the Master’s study, she was admitted to the Ph.D. program in the structural geology and tectonics group at

Louisiana State University in August, 2009. She has been a research assistant and teaching assistant for Structural Geology Lab for three years. During her Ph.D. study, she had two summer internships with Shell Oil Company in 2011 and 2012.

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