Structural, Kinematic and Geochronologic Evolution of The

STRUCTURAL, KINEMATIC AND GEOCHRONOLOGIC EVOLUTION OF THE

HIMALAYAN FOLD-THRUST BELT IN KUMAUN, UTTARANCHAL, NORTHWEST

INDIA

SUBHADIP MANDAL

DELORES M. ROBINSON, COMMITTEE CHAIR

ANDREW M. GOODLIFFE IBRAHIM ÇEMEN C. FRED T. ANDRUS MATTHEW J. KOHN

A DISSERTATION

Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in the Department of Geological Sciences in the Graduate School of The University of Alabama

TUSCALOOSA, ALABAMA

2014

ABSTRACT

The Lesser Himalaya is a key tectonostratigraphic zone of the Himalayan fold-thrust belt;

however, its poorly defined chronostratigraphy and erroneous stratigraphic correlations hamper

the determination of valid structural models. In Kumaun, northwest India, I reassess the

tectonostratigraphic and structural architecture using U-Pb zircon geochronology, whole rock

neodymium isotopes, and structural data to establish that rock in the Almora klippe and north of

the Main Central thrust have Neoproterozoic (~900 Ma) detrital zircon ages and similar εNd(0)

(-7.6 to -11.8) values, which suggests that these two units are the same tectonostratigraphic unit, and that the Almora klippe is the southern continuation of the Main Central thrust or another thrust in the Greater Himalayan thrust system. However, north of the Almora klippe, detrital zircon age populations establish the presence of Palaeoproterozoic Lesser Himalayan rock [ca.

1600 Ma youngest zircon, εNd(0)=-22.0] instead of the previous interpretation of Neoproterozoic

rocks. South of the klippe, the Ramgarh-Munsiari thrust carries both the less metamorphosed

Palaeoproterozoic and Neoproterozoic Lesser Himalayan rocks, in disagreement with the idea

that only Neoproterozoic-Cambrian Lesser Himalayan rocks are present south of Almora klippe.

U-Pb ages, Hf isotopes and whole rock trace element geochemical data coupled with

detail mapping establish that the rocks in the Askot klippe belong to Paleoproterozoic Lesser

Himalayan rock, and do not continue to the south as the rock in the Almora klippe. The Askot

klippe consists of 1856.6±1.0 Ma granite-granodiorite gneiss, coeval 1869±12 Ma felsic volcanic

rocks, and ca. 1820 Ma Berinag Formation quartzite. These rocks represent a small vestige of a

Paleoproterozoic continental arc that formed on the northern margin of the northern Indian

cratonic block during the Paleo-Mesoproterozoic amalgamation of the supercontinent Columbia.

εHf(0) values from ca. 1850 Ma detrital zircons from the Berinag Formation quartzite (-9.6 to

-1.1, with an average of -4.5) overlap with the εHf values of the ca. 1850 Ma granite-granodiorite

gneiss of the Askot klippe [εHf(0)=-5.5 to -1.2, with an average of -2.7] and other ca. 1850 Ma arc-related granite gneiss [εHf(0)=-4.8 to -2.2, with an average of -4.0] within the Lesser

Himalaya. Subchondritic εHf(0) values (1.1 to -4.9) of ca. 1850 Ma granite-granodiorite gneiss indicate pre-existing older crust, which underwent crustal reworking at ca. 1850 Ma.

This revised chronostratigraphy along with new structural mapping provide the basis for a new structural model for the evolution of the fold-thrust belt in Kumaun that establishes the thrust system as a forward propagating system and contains a hinterland dipping duplex composed of Lesser Himalayan rocks. A balanced cross-section reveals a total minimum shortening estimate of 541-575 km or 79-80% between Main Frontal thrust and South Tibetan

Detachment system, with the MCT accommodating 163-128 km, the RMT accommodating 112 km, the LHD accommodating 270 km, the MBT accommodating 8 km, and the Subhimalayan thrust system accommodating ~22 km. Adding the shortening from the Tethyan Himalaya from published work brings the total minimum shortening estimate for the Himalayan fold-thrust belt along this cross-section line to 674-751 km.

The Ramgarh-Munsiari thrust is the roof thrust of the Lesser Himalayan duplex, and its footwall rocks, the Ramgarh, Berinag, Chiplakot and Munsiari Formations, are part of the same, once continuous stratigraphic unit that was dissected and turned into the Ramgarh-Munsiari

thrust sheet and other thrust sheets in the Lesser Himalayan duplex.

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DEDICATION

This dissertation is dedicated to the wonderful people of Kumaun, India!

LIST OF ABBREVIATIONS AND SYMBOLS

Ar Argon

ASTER Advanced Spaceborne Thermal Emission and Reflection Radiometer

BT Berinag thrust

CHUR Chondrite uniform reservoir

CITZ Central Indian Tectonic Zone

CL cathodoluminescence

DM depleted mantle

DZ detrital zircon

ε epsilon

Eu Europium

FTB Fold thrust belt

Ga time in billions of years

GG granite-granodiorite

Gh Greater Himalaya

HCl Hydrochloric Acid

Hf Hafnium

HF Hydroflouric Acid

HFSE High Field Strength elements

IZ igneous zircon kbar pressure in kilobar(s)

LA-ICPMS Laser Ablation Inductively Coupled Mass Spectrometry

Lu Lutetium

Pb Lead

La Lanthanum

Li Lithium

LIL Large Ion Lithophile elements

LH Lesser Himalaya

LHD Lesser Himalayan Duplex

LREE Light Rare Earth Element(s)

Lu Lutetium

m meter

MBT Main Boundary thrust

MCT Main Central thrust

MFT Main Frontal thrust

MSWD mean sum of weighted deviations

µ micron

Ma time in millions of years

Nd Neodymium

NIB north Indian cratonic block

O Oxygen

Pb Lead

Rb Rubidium

REE Rare Earth Element(s)

RMT Ramgarh-Munsiari thrust

SCT South Chiplakot thrust

Sm Samarium

σ sigma

S.D. standard deviation

SH Subhimalaya

Sr Strontium

SRTM Shuttle Radar Toppgraphy Mission

STDS South Tibetan Detachment Systems

T Time

Ti Titanium

Th Thorium

TH Tethyan Himalaya

Yb Ytterbium

Y Yttrium

U Uranium

UA University of Alabama

U.C Unconformity

VE vertical exaggeration

VMS volcanogenic massive sulphide wt% weight percent (concentration)

Zr Zirconium

vii

ACKNOWLEDGMENTS

I am pleased to have this opportunity to thank many people who have helped me with this project over the past few years. First, I am most indebted to my advisor and mentor, Dr. Delores

M. Robinson, for her guidance, sharing research expertise, and providing inspiration for this project. She gave me the freedom to choose a project that would fulfill my research zeal. I would also like to thank my committee members, Dr. Andrew M. Goodliffe, Dr. C. Fred T.

Andrus, Dr. Ibrahim Çemen, and Dr. Matthew J. Kohn for their invaluable support of both the dissertation and my academic progress. Dr. Kohn was especially helpful in this project and in editorial process. The University of Alabama Department of Geological Sciences (DGS) staff members, Dr. Sid Bhattacharyya, James Donahoe, and Debbie Frank, are thanked for helping me in various ways for past few years.

This project was funded by the National Science Foundation (EAR0809405, awarded to

Dr. Robinson; EAR0809428, EAR1048124, and EAR1321897, awarded to Dr. Kohn), and by the Society of Economic Geologists Foundation’s Hugh E. McKinstry Student Research Grant.

The Department of Geological Sciences Johnson Travel Fund and University of Alabama

Graduate School supported me to present at professional meetings.

Completion of this project would not have possible without the help from scientists and students of the Wadia Institute of Himalayan Geology (WIHG), Dehradun, India. Dr. Sudip

Paul, Dr. Koushik Sen, Dr. Barun Mukherjee, Dr. Sumit Kumar Ghosh, Koushick Sen, Souvik

Das, and Reetam Choudhury from WIHG are thanked for their help in logistics and technical

viii

discussions. I would like to thank my present and former lab mates, Subodha Khanal, Lance

Wilson, Bryan Hunt, Ian Hunter, Andrea Gregg, and Will Jackson, and other University of

Alabama friends, Crystal Hout, Jeffrey Madden, and Jaydeep Ghosh for their help. Dr. Ashraf

Uddin and Dr. David King, my former professors at the Auburn University, are thanked for their

encouragement and suggestions to pursue my doctoral research at the University of Alabama.

Finally, I would like to thank my family members for their inspiration and support throughout

the good and bad times. Most of all, I thank my wife, Dr. Oindrila Das, for her professional and emotional support, encouragement, and love.

CONTENTS ABSTRACT ...... ii DEDICATION ...... iv ACKNOWLEDGMENTS ...... viii LIST OF TABLES ...... xiii LIST OF FIGURES ...... xiv CHAPTER 1: INTRODUCTION ...... 1 1.1. Dissertation Format ...... 2 1.2. References ...... 4 CHAPTER 2: REDEFINING THE TECTONOSTRATIGRAPHIC AND STRUCTURAL ARCHITECTURE OF THE ALMORA KLIPPE AND THE RAMGARH-MUNSIARI THRUST SHEET IN NORTHWEST INDIA ...... 6 2.1. Abstract ...... 6 2.2. Introduction ...... 7 2.3. Tectonostratigraphy ...... 10 2.3.1. Subhimalayan Rocks ...... 12 2.3.2. Lesser Himalaya ...... 13 2.3.3. Greater Himalaya ...... 19 2.3.4. Tethyan Himalaya ...... 21 2.4. Methods ...... 21 2.4.1. Geologic Map ...... 21 2.4.2. U-Pb Zircon Geochronology ...... 22 2.4.3. Nd Isotope Analyses ...... 24 2.5. Results ...... 25 2.5.1. U-Pb Geochronology ...... 25 2.5.1.1. Detrital Zircons from North and South of the Almora klippe ...... 25 2.5.1.2. Crystallization age of the Debguru Porphyroid ...... 27 2.5.1.3. Detrital Zircons from the Almora Klippe ...... 29 2.5.2. Nd Isotopic Analyses ...... 30 2.6. Discussion ...... 30 2.7. Conclusions ...... 42 2.8. Acknowledgements ...... 43

2.9. References ...... 44 CHAPTER 3: ZIRCON U-PB AGES AND HF ISOTOPIC DATA FROM THE PALEOPROTEROZOIC INNER LESSER HIMALAYAN SEQUENCE, KUMAUN, INDIA: IMPLICATIONS FOR TECTONICS, BASIN EVOLUTION AND ASSOCIATED METALLOGENY OF THE NORTHERN INDIAN CRATONIC MARGIN ...... 56 3.1. Abstract ...... 56 3.2. Introduction ...... 57 3.3. The Askot Klippe ...... 60 3.4. Regional Geologic Setting ...... 61 3.5. Geology of the Askot Klippe ...... 64 3.6. Analytical Methods ...... 69 3.6.1. U-Pb Zircon Geochronology ...... 69 3.6.2. Lu-Hf Isotopic Analysis ...... 70 3.6.3. Trace Element Geochemistry ...... 71 3.7. Results ...... 72 3.7.1. U-Pb Zircon Geochronology ...... 72 3.7.2. Zircon Lu-Hf Isotopes ...... 77 3.7.3. Trace Element Geochemistry ...... 78 3.8. Discussion ...... 80 3.8.1. Stratigraphic Affinity of the Askot Klippe ...... 80 3.8.2. Implications of U-Pb Geochronologic and Hf Isotopic Data on Paleoproterozoic Crustal Evolution of the Northern Margin of the NIB ...... 86 3.8.3. Askot Volcanogenic Massive Sulphide Deposit ...... 88 3.9. Conclusions ...... 92 3.10. Acknowledgements ...... 93 3.11. References ...... 93 CHAPTER 4: UPPER CRUSTAL STRUCTURE AND SHORTENING ESTIMATE FROM THE HIMALAYAN FOLD THRUST BELT IN KUMAUN, NORTHWEST INDIA ...... 101 4.1. Abstract ...... 101 4.2. Introduction ...... 102 4.3. Geological Background ...... 104 4.4. Mapping Methods ...... 106

4.5. Kumaun Tectonostratigraphy ...... 108 4.5.1. Subhimalaya ...... 108 4.5.2. Lesser Himalaya ...... 109 4.5.3. Greater Himalaya ...... 113 4.6. Geochronology and Regional Correlation ...... 114 4.6.1. Zircon U-Pb Dating and Results ...... 114 4.6.2. Whole rock Nd Isotope Analyses and Results ...... 116 4.6.3. Interpretation and Regional Correlations ...... 119 4.7. Balanced Cross Section ...... 123 4.7.1. Methods of Cross Section Construction and Assumptions and Limits ...... 123 4.7.2. Structural Geology Results ...... 124 4.7.2.1. Main Central Thrust Sheet ...... 124 4.7.2.2. Ramgarth- Munsiari Thrust Sheet ...... 125 4.7.2.3. Lesser Himalayan Duplex ...... 127 4.7.2.4. Almora Klippe ...... 128 4.7.2.5. Lesser Himalayan Imbricate Zone ...... 128 4.7.2.6. Subhimalayan Thrust System ...... 129 4.7.3. Estimation of Shortening and Comparisons ...... 131 4.8. Kinematic History and Discussion ...... 135 4.9. Conclusions ...... 139 4.10. Acknowledgements ...... 140 4.11. References ...... 140 CHAPTER 5: CONCLUSIONS ...... 150

xii

LIST OF TABLES

CHAPTER 2 Table 1. U-Pb zircon geochronology sample locations for Kumaun, NW India…………...21 Table 2. Whole rock Nd isotope sample locations, Kumaun, NW India……………………32 CHAPTER 3 Table 1. Analyzed geochemical sample locality information ………………………………74 Table 2. Whole rock REE and trace element compositions…………………………………80 CHAPTER 4 Table 1. Generalized stratigraphy of Kumaun, India with thickness of various units organized from north to south along the cross section line …………………………….....114 Table. 2. Locality information for the samples used in U-Pb zircon geochronology and whole rock Nd analyses…………………………………………………………………….117 Table 3. Whole rock Nd isotopic analysis results………………………………………….120 Table 4. Estimation of shortening along the cross section line ……………………………136 Table 5. Compilation of shortening estimates across the Himalayan fold thrust belt ……..136

xiii

LIST OF FIGURES

CHAPTER 2 Figure 1. (a) Shaded relief map of India and adjoining areas. (b) Generalized tectonostratigraphic map of Nepal and NW India with major bounding thrusts ……………..8 Figure 2. Shaded relief map showing major thrusts architecture in Kumaun and Garhwal, Uttaranchal, NW Inida ………………………………………………………………………11 Figure 3. Generalized stratigraphy of Kumaun and Garhwal, Uttaranchal, NW……………14 Figure 4. Field photographs …………………………………………………………………16 Figure 5. Detrital zircon age distributions curves of various siliciclastic strata from the footwall of the Almora thrust ………………………………………………………………28 Figure 6. Detrital zircon age distributions of metasediments from the Almora klippe ……..29 Figure 7. Modified Geologic map of Kumaun around Almora klippe with available geochronology and isotopic data ……………………………………………………………33 Figure 8. Schematic preliminary cross-section ……………………………………………..34 CHAPTER 3 Figure 1. Tectonic map of peninsular India and the adjoining Himalayan orogen …………59 Figure 2. Geological map of the Askot klippe……………………………………………....66 Figure 3. Schematic cross section (VE=1) of the Askot klippe …………………………….67 Figure 4. Field photos of the Askot Klippe rocks …………………………………………..68 Figure 5. Drill core sample and thin section photomicrograph ……………………………..69 Figure 6. Underground exposure of the massive sulphide ………………………………….69 Figure 7. CL images of igneous zircons from the Askot klipp……………………………..75 Figure 8. (a) U-Pb Concordia plot of sample SM11-028 …………………………………..76 Figure 9. (a) U-Pb Concordia plot for sample SM10-026 …………………………………77 Figure 10. Relative age probability plot and pie chart distribution of the sample SM10-021 …………………………………………………………………………………...78 Figure 11. (a) Normalized REE plot, and (b) normalized spider diagram ………………….81

xiv

Figure 12. Trace element discrimination diagrams …………………………………………83 Figure 13. Composite U-Pb detrital zircon normalized age spectra of various Paleoproterozoic inner Lesser Himalayan rocks in NW India ……………………………...86 Figure 14. (a) Plot of 176Hf/177Hf versus U-Pb ages of zircons, (b) Plot of εHf versus U-Pb ages of zircons from Askot klippe ………………………………………………………….87 Figure 15. Schematic diagrams of Paleoproterozoic tectonic evolution of the NIB’s northern margin (present day Himalaya) and formation of the VMS deposit ………………………..92 CHAPTER 4 Figure 1. (a) Digital elevation model and (b) Generalized tectonostratigraphic map of the Himalaya …………………………………………………………………………………..109 Figure 2. Tectonic models of the Himalaya ………………………………….……………110 Figure 3. Transect map of Kumaun India with the cross section line ……………………113 Figure 4. Field photographs and detrital zircon age plot …………………………………..119 Figure 5. U-Pb Concordia plots and weighted average plots of igneous samples…………120 Figure 6. Composite U-Pb detrital zircon spectra of inner Lesser Himalayan units ………………………………………………………………………………………..123 Figure 7. Composite U-P detrital zircon spectra of outer Lesser Himalayan units ………..124 Figure 8. Field structural photographs …………………………………………………….132 Figure 9. Field structural photographs ……………………………….……………………133 Figure 10. Balanced cross section (a) and restored section (b) ……………………………135

CHAPTER 1:

INTRODUCTION

Continued convergence between India and Asia, which began at ~55 Ma (Najman et al.,

2010 and reference therein), created the vast Himalayan-Tibetan orogenic system, the largest

deformed Cenozoic continental region in the world (van Hinsenberg et al., 2011). The

Himalayan fold-thrust belt (FTB) is a first-order physiographic expression of this orogenic

system at the southern edge of the Tibetan Plateau and covers an along-strike distance of ~2500

km from northern Pakistan to the Namcha Barwa syntaxis. This FTB is composed of scrapped

off folded and faulted Paleoproterozoic to Cretaceous rocks that blanketed the northern margin

of the ca. 2500 Ma Indian cratonic basement.

Although our understanding of the growth and kinematic evolution of this FTB has

increased dramatically over the past 15 years, some regions still have outstanding questions due

to the structural complexity, poor exposures, and lack of knowledge of the stratigraphic

architecture. Moreover, most of the models of the Himalaya emerge from pressure-temperature

data of the high-grade metamorphic core, i.e., from Greater Himalayan rock, which occupies

30% surface area of the Himalaya (Le Fort et al., 1986; Yin, 2006; Chambers et al., 2008;

Célérier et al., 2009b). The Lesser Himalayan rock occupies more than ~50% of the surface area

of this FTB, and is a key Himalayan tectonostratigraphic zone; however, the stratigraphic and structural architecture of this zone is poorly known due to: 1) paucity of common fossils for

biostratigraphic dating, 2) poor knowledge of depositional ages of clastic units, 3) scarcity of igneous rocks for geochronologic age dating, except Paleoproterozoic orthogneiss (Kohn et al.,

2010), and 4) ambiguous local names of same stratigraphic unit in various parts along strike.

Thus, the lack of stratigraphic knowledge led to an erroneous kinematic evolution and growth models of the Himalaya, in Kumaun, Uttaranchal, northwest India.

Recent developments in U-Th-Pb zircon geochronology enable researchers to collect high-resolution age data along with other information (e.g., Hf, O, Li isotopic signatures) in a fast and robust method, which further helps to solve first order stratigraphic issues in the

Himalaya and other fold-thrust belts with very complex geology (Richards et al., 2005;

McQuarrie et al., 2008; Célérier et al., 2009a; Long et al., 2011; Martin et al., 2011; McKenzie et al., 2011; Webb et al., 2011). The broad objective of this research project is to study the structural, kinematic and chronologic evolution of the Lesser Himalayan (LH) rocks in Kumaun.

This study, concentrates on the evolution of the FTB in Kumaun and draws upon the published data from Himachal Pradesh, Garhwal and Nepal. Kumaun is an ideal location because all tectonostratigraphic units are exposed and its location in the central part of the Himalayan arc should record the greatest amount of shortening (c.f. DeCelles et al., 2002).

1.1. Dissertation Format

This dissertation consists of three research papers with minor overlap in content. Each paper will be published in peer-reviewed journals. The first paper, Chapter 2, is entitled

“Redefining the tecotonostratigraphic and structural architecture of the Almora klippe and the

Ramgarh-Munsiari thrust sheet in northwest India”. This paper has been accepted for publication in the Journal of the Geological Society of London, Special Publications, and is co-authored with

Delores M. Robinson, Subodha Khanal, and Oindrila Das. In this study, we integrate U-Pb

zircon geochronology and εNd(0) values with field mapping to determine which

tectonostratigraphic units are represented to the north, south, and within the Almora klippe in

Kumaun, northwest India. Because of the differing interpretations regarding which rock units are

present in Kumaun, we present data from the Almora klippe and the footwall and hanging wall

of the Almora thrust to determine if the rocks are GH, Palaeoproterozoic LH, or Neoproterozoic

LH rock. We also present structural and isotopic data that determine if the Ramgarh-Munsiari

thrust sheet is continuous from its root zone in the footwall of the Main Central thrust to the hanging wall of the Main Boundary thrust. Finally, we present a preliminary idea for the structural architecture of this klippe, located towards the frontal part of the FTB in Kumaun, NW

India.

The second paper, Chapter 3, is entitled “Zircon U-Pb ages and Hf isotopic data from the

Paleoproterozoic Inner Lesser Himalayan Sequence, Kumaun, India: Implications for tectonics, basin evolution and associated metallogeny of the northern Indian cratonic margin”. This paper will be submitted to Precambrian Research, and is co-authored with Delores M. Robinson,

Matthew J. Kohn, Subodha Khanal, Oindrila Das, and Sukhanjan Bose. This paper details the structure, stratigraphy and magmato-thermal event of the Askot klippe, a klippe with dubious

stratigraphic affinity within the Lesser Himalayan zone. Further, we correlate our

geochronologic and isotopic data with published data from inner Lesser Himalayan rocks and the

western margin of the northern Indian cratonic block to understand the Paleoproterozoic crustal

evolution and metallogeny.

The third paper, Chapter 4, is entitled “Upper crustal structure and shortening estimation

of the Himalayan Fold Thrust Belt in Kumaun, NW India”. This paper will be submitted to

Geological Society of America Bulletin, and is co-authored with Delores M. Robinson, Matthew

J. Kohn, and Subodha Khanal. We reassess the structural architecture based on the data presented in the two previous papers and add new structural data, incorporating new geochronology and isotopic data, and a crustal scale geophysical data (Caldwell et al., 2013).

New and available geochronologic and isotopic data help solve first order stratigraphic issues and allow us to determine that two existing structural cross-sections (Srivastava and Mitra, 1994;

Célérier et al., 2009) are incorrect and must be reevaluated. Finally, we present a new balanced structural cross section based on field structural data, revised stratigraphic information and new ramp-flat geometry of the MHT constrained from recent geophysical data (Caldwell et al., 2013) and provide and new minimum shortening estimate for Kumaun, India.

1.2. References

Célérier, J., Harrison, T. M., Webb, A. A. G., and Yin, A., 2009, The Kumaun and Garwhal Lesser Himalaya, India: Part 1. Structure and stratigraphy: Geological Society of America Bulletin, v. 121(9-10), p. 1262-1280, doi: 10.1130/B26343.1.

Chambers, J. A., Argles, T.W., Horstwood, M.S.A., Harris, N.B.W., Parrish, R.R, and Ahmad, T., 2008, Tectonic implications of Palaeoproterozoic anatexis and Late Miocene metamorphism in the Lesser Himalayan Sequence, Sutlej Valley, NW India: Journal of the Geological Society, v. 165, p. 725-737, doi: 10.1144/0016-76492007/090.

DeCelles, P. G., Robinson, D. M., and Zandt, G., 2002, Implications of shortening in the Himalayan fold-thrust belt for uplift of the Tibetan Plateau: Tectonics, v. 21 (6), p. 1062-1087, doi: 10.1029/2001TC001322.

LeFort, P., Debon, F., Pêcher, A., Sonet, J., and Vidal, P., 1986, The 500 Ma magmatic event in Alpine southern Asia, a thermal episode at Gondwana scale: Nancy, France. Centre National de la RechercheScientifique.Sciences de la Terre Mémoire 47, 191–209.

Long, S., McQuarrie, N., Tobgay, T., Rose, C., Gehrels, G., and Grujic, D., 2011, Tectonostratigraphy of the Lesser Himalaya of Bhutan: Implications for the along-strike stratigraphic continuity of the northern Indian margin: Geological Society of America Bulletin, v. 123(7-8), p. 1406-1426, doi:10.1130/B30202.1.

Martin, A.J., Burgy, K.D., Kaufman, A.J., and Gehrels, G.E., 2011, Stratigraphic and tectonic implications of field and isotopic constraints on depositional ages of Proterozoic Lesser Himalayan rocks in central Nepal: Precambrian Research, v. 185, p. 1–17, doi: 10.1016/j.precamres.2010.11.003.

McKenzie, N.R., Hughes, N.C., Myrow, P.M., Xiao, S., and Sharma, M., 2011, Correlation of Precambrian–Cambrian sedimentary successions across northern India and the utility of isotopic signatures of Himalayan lithotectonic zones: Earth and Planetary Science Letters, v. 312(3), p. 471-483, doi: 10.1016/j.epsl.2011.10.027.

McQuarrie, N., Robinson, D., Long, S., Tobgay, T., Grujic, D., Gehrels, G., and Ducea, M., 2008, Preliminary stratigraphic and structural architecture of Bhutan: Implications for the along strike architecture of the Himalayan system: Earth and Planetary Science Letters, v. 272(1), p. 105-117, doi: 10.1016/j.epsl.2008.04.030.

Najman, Y., Appel, E., Boudagher-Fadel, M., Bown, P., Carter, A., Garzanti, E., Godin, L., Han, J., Liebke, U., Oliver, G., Parrish, R., and Vezzoli, G., 2010, Timing of India-Asia collision: Geological, biostratigraphic, and palaeomagnetic constraints: Journal of Geophysical Research, v. 115, p. B12416, doi: 10.1029/2010JB007673.

van Hinsbergen, D. J., Kapp, P., Dupont‐Nivet, G., Lippert, P. C., DeCelles, P. G., and Torsvik, T. H., 2011, Restoration of Cenozoic deformation in Asia and the size of Greater India: Tectonics, v. 30 (5), p. TC5003, doi: 10.1029/2011TC002908.

Yin, A., 2006, Cenozoic tectonic evolution of the Himalayan orogen as constrained by along- strike variation of structural geometry, exhumation history, and foreland sedimentation: Earth Science Reviews, v. 76(1), p. 1-131, doi: 10.1016/j.earscirev.2005.05.00.

CHAPTER 2:

REDEFINING THE TECTONOSTRATIGRAPHIC AND STRUCTURAL ARCHITECTURE OF THE ALMORA KLIPPE AND THE RAMGARH-MUNSIARI THRUST SHEET IN NORTHWEST INDIA 2.1. Abstract

We integrate U-Pb zircon geochronology and εNd(0) values with field mapping to

determine which tectonostratigraphic units are represented to the north, south, and within the

Almora klippe in Kumaun, northwest India. Rock in the Almora klippe and north of the Main

Central thrust have Neoproterozoic (~900 Ma) detrital zircon ages, coupled with similar εNd(0) (-

7.6 to -11.8) values, suggesting that these two units are the same tectonostratigraphic unit, and that the Almora klippe is the southern continuation of the Main Central thrust or another thrust in the GH thrust system. However, north of the Almora klippe, detrital zircon age populations establish the presence of Palaeoproterozoic rock instead of the previous interpretation of

Neoproterozoic rocks. These Palaeoproterozoic Lesser Himalayan rocks are carried by the

Ramgarh-Munsiari thrust dipping south and folded underneath the klippe. South of the klippe, the Ramgarh-Munsiari thrust carries both the less metamorphosed Palaeoproterozoic and

Neoproterozoic Lesser Himalayan rocks, in disagreement with the idea that only Neoproterozoic-

Cambrian Lesser Himalayan rocks are present south of Almora klippe. These results suggest that previous cross sections in Kumaon are incorrect and must be revaluated.

2.2. Introduction

Between the Tibetan Plateau to the north and the Indo-Gangetic plain to the south (Fig.

1), northwest India has two states in the Himalayan fold-thrust belt (FTB), Himachal Pradesh to

the west and Garhwal-Kumaun Uttaranchal to the east (Fig. 2). In this study, we concentrate on

the evolution of the FTB in Kumaun and draw upon the published data from Himachal Pradesh,

Garhwal and Nepal. Kumaun is an ideal location because it has all tectonostratigraphic units

exposed and because its location in the central part of the Himalayan arc, should record the

greatest amount of folding and faulting (cf. DeCelles et al., 2002).

The Himalayan FTB developed as a result of the India-Asia collision, which likely started

at ca. 55-50 Ma (Rowley, 1996; Hodges, 2000, Guillot et al., 2003, Dupont-Nivet et al., 2010,

Najman et al., 2010). As the collision progressed, the Greater Indian northern margin crumpled,

resulting in a southward propagating thrust system where far traveled thrust sheets are thrusted

on top of others, with a few except such as out-of-sequence deformation (see reviews by

Mukherjee et al., 2012; Mukherjee this volume) and backthrusting (Mukherjee 2013a). The

Main Central thrust (MCT), known as the Vaikrita thrust in northwest India, places Greater

Himalayan (GH) rocks on top of the Palaeoproterozoic Lesser Himalayan (LH) rocks. In other

parts of the Himalaya, the Ramgarh-Munsiari thrust (RMT) carries this Palaeoproterozoic LH

rock (Robinson and Pearson, 2013), and both the RMT and MCT (Fig. 1b) each translate rocks

more than 100 km southward towards the foreland (DeCelles et al., 2001; Robinson et al., 2003;

Kohn et al., 2004; Pearson and DeCelles, 2005; Mitra and Bhattacharyya, 2010; Khanal and

Robinson, 2013; Robinson and Pearson, 2013).

Higher grade metamorphic rocks are located on top of the Lesser Himalayan rocks and are

known as the “Lesser Himalayan Crystalline nappes/klippen”. The Almora klippe (Fig. 1b), the

largest of the klippen distributed along the Himalayan arc, crops out towards the frontal part of

the FTB in Garhwal-Kumaun (Heim and Gansser, 1939; Valdiya, 1980; Joshi and Tiwari, 2009),

and extends into western Nepal, where it is known as Dadeldhura klippe (Upreti, 1990; DeCelles

Figure 1. (a) Shaded relief map of India and adjoining areas (from the ASTER Global digital elevation dataset, data source: http://gdex.cr.usgs.gov/gdex/). White solid line indicates state boundary of Garhwal-Kumaun Uttaranchal, NW. (b) Generalized tectonostratigraphic map of Nepal and NW India with major bounding thrusts. Solid box indicates study present study area. MFT, Main Frontal thrust; MBT, Main Boundary thrust; TT, Tons thrust; JT, Jutogh thrust; RMT, Ramgarh-Munsiri thrust; LHD, Lesser Himalayan duplex; MCT, Main Central thrust; STDS, South Tibetan Detachment system; GCT, Great Counter thrust; AK, Almora klippe; DK, Dadeldhura klippe (modified from Robinson and Pearson, 2013).

et al., 2001; Robinson et al., 2006; Antolin et al., 2013). This synformal klippe is bound to the

north and south by the folded Almora thrust (Valdiya, 1980; Thakur, 1992).

Improper identification of the hanging wall and footwall rocks in the klippen throughout the Himalaya, the bounding faults and the emplacement mechanism has led to erroneous kinematic evolution models. The klippen may be erosional outliers of GH rocks (Gansser, 1964;

Stöcklin, 1980; Schelling, 1992), which suggests that the MCT continues to the south and is the

same thrust as the Almora thrust. However, Hodges (2000) argues that correlating the klippen

with GH rocks is tenuous because there is a difference in metamorphic grade and the absence of

cordierite-bearing monzogranite in GH rocks, which is common within the klippen. Another idea

is that the klippen are composed of GH rocks but are not from the same thrust sheet as the MCT

(Rai et al., 1998; Upreti, 1999; Khanal et al., 2014a). Valdiya (1980) suggests that the GH rocks

are bound by two major thrusts at the base, the MCT and the structurally lower Munsiari thrust,

and the Munsiari thrust sheet forms the Almora klippe. Srivastava and Mitra (1994) and Célérier

et al. (2009) drew their cross sections following the ideas of Valdiya (1980). One final possibility

is that the MCT continues to the south and is renamed the Almora thrust bounding the Almora

klippe and that the Munsiari thrust continues to the south and crops out to as the

Palaeoproterozoic LH rock structurally underneath the Almora thrust to the north and south of

the klippe (DeCelles et al., 2001; Robinson et al., 2003).

GH and LH rocks are difficult to distinguish near the MCT from one another because

both have sedimentary protoliths, are intruded by igneous rocks, and sometimes have similar

metamorphic grades. This has led to the so called “MCT zone” (Stephenson et al., 2000; Vannay

and Grasemann, 2001; Catlos et al., 2001, Dasgupta et al., 2004) suggesting a multi-kilometer

thick shear zone where GH and LH rocks are lumped together (reviewed in Mukherjee 2013b).

The lower (= southern) and the upper (= northern) boundaries of the MCT zone are described by

general terms such as MCT2 and MCT1 (Arita, 1983), and MCT-Lower and MCT-Upper (Godin

et al., 2006; Mukherjee and Koyi 2010 a, b). However, a combination of U-Pb zircon

geochronology, whole rock εNd(0) values, and field mapping can differentiate between GH rock,

Palaeoproterozoic LH rock and Neoproterozoic LH rock (Whittington et al., 1999, Argles et al.,

2003; Martin et al., 2005; Tobgay et al., 2010; McKenzie et al., 2011; Khanal et al., 2014b).

Because of the differing interpretations regarding which rock units are present in Kumaun, we

present data from the Almora klippe and the footwall and hanging wall of the Almora thrust to

determine if the rocks are GH, Palaeoproterozoic LH, or Neoproterozoic LH rock. We also

present structural and isotopic data that determines if the Munsiari thrust sheet is continuous

from its root zone in the footwall of the Main Central thrust to the hanging wall of the Main

Boundary thrust. Finally, we present a preliminary idea for the structural architecture of the

Himalayan FTB of NW India.

2.3. Tectonostratigraphy

The supracrustal rocks from Greater India are divided into four major lithotectonic zones.

From north to south, these are the Tethyan Himalayan (TH) strata, which include the Lower

Proterozoic to Cambrian sediments of the Haimantas Group (Frank et al., 1995) and the

Paleozoic-Eocene Tethyan sedimentary sequence, Neoproterozoic though Ordovician high-grade

metamorphic rocks of the Greater Himalaya (GH), high- to low-grade Palaeoproterozoic to

Figure 2. Shaded relief map showing major thrusts architecture in Kumaun and Garhwal, Uttaranchal, NW India (Valdiya, 1980; Célérier et al., 2009). Filled triangles are U-Pb zircon geochronology samples, small white circles are whole rock Nd samples. LK, Lansdowne klippe; AK, Almora klippe; ASK, Askot klippe; CHK, Chiplakot klippe; BK, Bajnath klippe.

Cambrian Lesser Himalayan (LH) metamorphic rocks, and Cenozoic foreland basin sediments of the Subhimalaya (SH) (Fig.1b) (Gansser, 1964; LeFort, 1975; Hodges, 2000). Major faults from north to south are: South Tibetan Detachment system (STDS), Main Central thrust (MCT or

Vaikrita thrust, VT), Ramgarh-Munsiari thrust (RMT), Lesser Himalayan (LH) duplex, Main

Boundary thrust (MBT), and Main Frontal Thrust (MFT). These thrust systems sole down into the Main Himalayan thrust (MHT), the basal décollement, at depth. Some researchers suggest that GH rocks are simply the high-grade metamorphic equivalent of the younger Lesser

Himalayan strata (Parrish and Hodges, 1996), or the Palaeozoic Tethyan strata (Myrow et al.,

2003), whereas others interpret GH as an exotic terrane, which was amalgamated to the northern

Indian margin during the Pan-African (500±50 Ma) orogenic event (DeCelles et al., 2000).

Cambro-Ordovician granitoids are evidence of this Pan-African tectono-thermal event and are omnipresent in the eastern, central and western Himalaya within the GH (LeFort et al., 1986;

Garzanti et al., 1996; Garzanti, 1999; Argles et al. 2003; Gehrels et al., 2003, 2006, McQuarrie et al., 2013) and the TH (Chambers et al., 2009, Tripathi et al., 2012).The MCT, a crustal scale ductile fault originally defined by Heim and Gansser (1939) as the fault that places GH over LH rocks, acts as the structural base for the GH. The MCT and the overlying GH rocks have been passively folded due to growth of the LH duplex since middle Miocene time (Robinson et al.,

2003).

2.3.1. Subhimalayan Rocks

The youngest part of the SH consists of mid-Miocene to Pliocene (ca. 11-1 Ma) synorogenic sediments of the Siwalik Group shed from the adjacent Himalayan FTB (Quade et al., 1995; DeCelles et al., 1998; Kumar et al., 2003; Najman et al., 2004; Ravikant et al., 2011).

The Siwalik Group is informally divided into lower, middle and upper units, and is bound by

MFT to the south and MBT to the north (Fig. 2; Tokuoka et al., 1986; Harrison et al., 1993;

Quade et al., 1995; DeCelles et al., 1998; Ojha et al., 2000). Approximately 20-13 Ma foreland basin strata (Najman, 2006; Ravikant et al., 2011), the Dumri Formation and its equivalents

(Lugar Gad Formation in eastern Kumaunn), are present in the hanging wall of the MBT along the Himalayan arc in Garhwal and Kumaun of NW India, western Nepal, and Arunachal

Pradesh, NE India. However, in the Subathu sub-basin in Himachal Pradesh, the Kasauli

Formation, <22 Ma foreland basin strata is present at the base of the SH and incorporated into the SH thrust system between the MBT and MFT (Raiverman et al., 1983; Raiverman, 2002;

Mukhopadhyay and Mishra, 2005; Acharyya, 2007; Ravikant et al., 2011), indicating that the

MHT is at different stratigraphic levels along strike in the Himalayan arc.

2.3.2. Lesser Himalaya

Along the Himalayan arc, the LH rocks are exposed north of the MBT (Fig. 2) and are composed of the Palaeoproterozoic-Cambrian LH sequence, and Paleogene foreland basin sequence in some locations. The LH sequence is ~8-13 km of clastic and carbonate sediments, low-medium grade metasediments, and Palaeoproterozoic intrusive rocks (Robinson et al.,

2006). In Nepal, Sikkim and Bhutan, the Late Palaeozoic to Mesozoic Gondwana sequence is exposed (Bashyal, 1986; Robinson et al., 2006; McQuarrie et al., 2008; Sitaula, 2009; Long et al., 2011) but these rocks are not at the surface in NW India.

In Kumaun, the LH has an inner LH sequence and outer LH sequence (Fig. 3). Although

Paleogene foreland basin sediments (Subathu/Bhainskati Formations) have been reported from

Garhwal and western Nepal in the MBT hanging wall (Srivastava and Mitra, 1994; Najman,

2006;

Figure 3. Generalized stratigraphy of Kumaun and Garhwal, Uttaranchal, NW India (modified after Valdiya, 1980; Pant and Shukla, 1999; Kohn et al., 2010).

Robinson et al., 2006), no Paleogene rocks are exposed in the MBT hanging wall in Kumaun.

The Tons thrust (Fig. 2) is a major tectonic boundary that separates the inner LH to the north from the outer LH to the south (Srivastava and Mitra, 1994; Ahmad et al., 2000; Richards et al.,

2005; Célérier et al., 2009; McKenzie et al., 2011). The inner LH is unfossiliferous with a

Paleoproterozoic age (1900-1600 Ma), whereas, the outer LH is fossiliferous with a

Neoproterozoic to Cambrian age (800-500 Ma, Richards et al., 2005). The Munsiari and Berinag

Formations (Fig. 3) are metamorphosed to amphibolite-grade (Chambers et al., 2008; Spencer et

al., 2012a). Although Ghosh et al. (2012) describe the Damatha Group as the base of the LH

rocks, based on our analyses, the Munsiari and Berinag Formations are the oldest LH rocks. The

contact between Damatha and Berinag formations is faulted, which may have led to the incorrect

interpretation. The Berinag Formation is ~700 m thick (Rupke, 1974), composed of sericitic

quartzite, garnet-mica schist with amphibolite sills and dikes and is equivalent to the Rampur

Formation of Himachal Pradesh (Richards et al., 2005; Webb et al., 2011). Miller et al. (2000) report a ca. 1800 Ma-aged metabasalt from the Rampur Formation, and similar rocks exist in the

Berinag Formation. The Munsiari Formation has the same lithological assemblage as the Berinag

Formation; however, metapelites are dominant over quartzite. The Berinag and Munsiari formations have 1.85 Ga orthogneiss intrusions, part of Paleoproterozoic arc (Mandal et al., submitted), and are mapped in the northern part of the FTB, south of the MCT.

The Damatha Group consists of the lower Chakrata and the upper Rautgara formations.

Célérier et al. (2009) map a regional unconformity separating the Berinag Formation from the younger Chakrata Formation. Ghosh et al. (2012) correlate Rautgara with the outer LH Nagthat

Formation; however, their basis for correlation is not clear. The Chakrata Formation is ~2,000 m thick (Valdiya, 1980), consists of quartz-wacke, siltstone and shale with soft-sediment deformation, and was deposited in an inter-tidal to supra-tidal environment (Ghosh et al., 2012).

Its equivalent in Himachal Pradesh is the Dhargad/Sundernagar Formation (McKenzie et al.,

2011; Bhargava et al., 2011). The Chakrata Formation is conformably overlain by the Rautgara

Formation (Fig. 4a), which is ~2,900 m thick sequence of quartz-arenite/sublitharenite and purple shale with abundant mafic sills and dikes. The Damatha Group is further conformably

Fig. 4. (a) Very thick to thin bedded Rautgara Quartzite with sharp contact, 30 cm hammer for scale. (b) Tightly folded bedded Deoban Dolomite, north of the Almora klippe, marker for scale. (c) White clean quartzite (Qt) with intercalated mafic (Mf) schist, 30 cm hammer for scale. This quartzite is, locally known as Bhowali Quartzite. (d) Muddy quartzite, nearly 0.85 northeast of the sample SM11-004, Nagthat Quartzite. (e) Interlayered thin-bedded quartzite (Qt) and phyllite (Ph) from the southern margin of the Almora klippe, 30 cm hammer for scale. (f) Mylonitic granite-augen gneiss (SM11-009) from the Debguru porphyry, pen for scale.

overlain by ~1,000 m thick Tejam/Deoban Group and contact is characterized by sharp change

from siliciclastic to carbonate facies (Tewari and Sial, 2007).

The age of the Tejam/Deoban Group is in question but is usually placed in the inner LH

sequence because it crops out north of the Tons thrust (McKenzie et al., 2011). The

Tejam/Deoban Group is divided into the lower stromatolite-bearing, shelf-facies, cherty dolomite

and dolomitic limestone known as Deoban/Gangolihat dolomite (Fig. 4b), and the upper gray

slate and carbonaceous phyllite of the Mandhali Formation (Raupke, 1974; Valdiya, 1980). The

age of Gangolihat dolomite in Kumaun and its correlation with the Deoban dolomite of the Tons

valley are controversial. Based on the presence of stromatolites, the age of the Deoban dolomite

is assigned a Mesoproterozoic (mid-late Riphean) age (Raupke, 1974; Valdiya, 1980; Bhargava

et al., 2011). Sarkar et al. (2000) assigned an age of 1550-1700 Ma for Deoban dolomite based

on the model Pb-Pb ages of galena. However, an age of 839±139 Ma was assigned to the Deoban

equivalent in Himachal Pradesh, called the Shali Formation, based on Re-Os dating of black

shale (Singh et al., 1999). Calc-silicate rocks within the Shali-Deoban Formation possess an

inner LH Nd isotopic signature (Ahmad et al., 2000). The Gangolihat dolomite may have an

Ediacaran-Cambrian age (Azmi and Paul, 2004; Tiwari and Pant, 2009 and reference therein); however, McKenzie et al. (2011) argue that the Gangolihat dolomite is Palaeoproterozoic (ca.

1600 Ma) because similar stromatolite species within the Gangolihat dolomite are found within

the ~1600 Ma old Rohtas Formation of the Semri Group of lower Vindhyan successions of

cratonic India.

The outer LH consists of lower Neoproterozoic Jaunsar Group, regarded as a facies

variant of the Simla Group of Himachal Pradesh (Bhargava, 1976), and the upper

Neoproterozoic to Cambrian Mussoorie Group. Kumar (1985) divided the Jaunsar Group into

lower Mandhali, middle Chandpur and upper Nagthat Formations (Fig. 3); however, Valdiya

(1980) mapped Mandhali Formation as upper part of Tejam Group. The overlying Mussoorie

Group consists of the Blaini-Krol-Tal formations (Auden, 1934; Valdiya, 1980). The Mandhali

Formation is ~2,500 m thick succession of carbonaceous pyritic phyllite, limestone and pebble

conglomerate exposed north of the Almora klippe. Webb et al. (2011) state the age of the

Mandhali Formation as 839±139 Ma citing the work of Singh et al. (1999), however, the latter

workers dated the Shali-Deoban Formation, not the Mandhali Formation. The Mandhali

Formation is correlated with the Basantpur Formation of the lower Simla Group (Kumar and

Brookfield, 1987; Webb et al., 2011). The Neoproterozoic Chandpur Formation is an ~2,000 m

thick sequence of meta-greywacke, meta-siltstone, slate, phyllite and locally carbonaceous gray

phyllite. The upper part contains well preserved load cast and graded bedding indicating a deeper

water facies (Kumar, 1985). The Chandpur Formation is unconformably overlain by the mid-

Neoproterozoic (850-630 Ma) Nagthat Formation (Figs. 4c and 4d), which is a ~1,400 m thick

(Pant and Shukla, 1999) succession of quartzarenite associated with penecontemporaneous mafic

lava flows (Valdiya, 1980; Ghosh, 1991; Pant and Shukla, 1999).

Hofmann et al. (2011) report minimum ages of 733±10 Ma for Nagthat sandstone from

Garhwal. The presence of siliciclastic lithofacies with interlayered mafic sills (Fig. 4c) has led

many to incorrectly correlate this unit with the Berinag Formation (Pant and Shukla, 1999;

Ghosh, 1991, Valdiya, 1980; Ghosh et al., 2012). The depositional environment of Nagthat

Formation is interpreted as fluvio-deltaic (Raupke, 1974), shallow marine (Valdiya, 1980;

Ghosh, 1991), or a progradational barrier island systems (Pant and Shukla, 1999). In eastern

Kumaun, the Nagthat Formation is divided into the lower Bhimtal Volcanics, consisting of

amygdaloidal vesicular basalt, chlorite schist and amphibolite, and the upper Bhowali quartzite,

consisting of quartzarenite, conglomerate, purple slate and siltstone (Pant and Shukla, 1999).

Nagthat quartzite is thrust over the Palaeoproterozoic Amritpur Granite (1900±100 Ma; Trivedi and Pande, 1993; Shah et al., 2012) near the MBT in Kumaun.

The Nagthat Formation is conformably overlain by the Mussorie Group, a glaciomarine arenaceous-argillaceous sequence containing pink dolomite (Blaini Formation), grayish-black shale and sandstone (Infra-Krol Formation). The ~200 m thick diamictite-quartzite

Neoproterozoic sequence of Blaini Formation has been interpreted as glacial (Auden, 1934;

Bhargava, 1976; Brookfield, 1993) and glaciomarine (Jain and Varadarai, 1978). In the type area, the Blaini Formation is composed of two diamictite units, separated by alternating sandstone and shale (Brookfield, 1987). The Infra-Krol Formation is conformably overlain by the Neoproterozoic Krol Group, a thick succession of limestone, dolomite and shale (Jiang et al.,

2003; Kaufman et al., 2006), and the Cambrian Tal Group, a siliciclastic dominated unit. The early Cambrian lower Tal Formation (Hughes et al., 2005) is an ~600 m thick sequence (Thakur,

1992) of organic-rich shale and phosphorites containing abundant nodules of pyrite, indicating an anoxic depositional environment; whereas, the upper Tal Formation is an ~450 m thick sandstone with interlayered shale and siltstone (Thakur, 1992; Mazumdar and Banerjee, 1998).

2.3.3. Greater Himalaya

GH rocks are bound at the base by MCT and at the top by STDS (Fig. 1b), and are high- grade metamorphic and intrusive rocks that form the metamorphic core of the Himalayan orogen.

Grades of metamorphism vary from upper amphibolite to granulite facies (DiPietro and Pogue,

2004; Yin, 2006 and references therein). Gehrels et al. (2011) and Parrish and Hodges (1996) suggests that all GH protoliths are younger than 800-1200 Ma, and that some may be as young as

540-750 Ma. The minimum age of GH rocks is constrained by granitic bodies from 470 to 550

Ma (Cawood et al., 2007).

Medium- to high-grade metamorphic rocks also crop out in the Almora klippe. Geologic,

structural and metamorphic histories of the klippe have been studied by various workers (Merh

and Vashi, 1965; Misra et al., 1973; Valdiya, 1980; Srivastava and Mitra, 1994; Srivatava, 2004;

Joshi and Tiwari, 2009; Rawat and Sharma, 2011). The Almora thrust bounds the klippe to the

north and south. This klippe forms an asymmetrical synform with a WNW-ENE trending axis,

and is sometimes referred to as a lower Ramgarh nappe and the overlying Almora nappe (Joshi,

1999). The Almora klippe is composed of kyanite-garnet-mica schist, graphitic schist, quartzite,

paragneiss, orthogneiss, and ~500 Ma intrusive granites. These rocks are metamorphosed to

green-schist and upper amphibolite facies with temperatures from 500-700ºC and pressures of 4-

8 kbar (Rawat and Sharma, 2011), which is little lower than the ~850ºC and ~14 kbar from the

GH in Garhwal (Spencer et al., 2012a). The Almora klippe rock is known as the Almora Group

and is divided into the lower Saryu Formation (Fig. 4e) and the upper Champawat granodiorite and Gumalikhet Formation (Valdiya, 1980). The Saryu Formation is intruded by Cambro-

Ordovician (~500 Ma) granitoids (Champawat granitoids and Almora granite; Trivedi et al.,

1984), similar to the Cambro-Ordovician Dadeldhura granite (Kaphle, 1992; DeCelles et al.,

2001; Gehrels et al., 2006) in the Dadeldhura klippe in Nepal, the eastward continuation of the

Almora klippe. The Almora thrust is regionally correlated with the Dadeldhura thrust in western

Nepal (Gehrels et al., 2006), where the klippe rock structurally overlies the Palaeoproterozoic

LH rock (DeCelles et al., 2001; Gehrels et al., 2006).

2.3.4. Tethyan Himalaya

TH rocks overlie GH rocks (Fig. 1b), and are composed of Neoproterozoic to Cambrian pre-rift sediments of the Haimantas Group (Frank et al., 1995) and the Paleozoic-Eocene passive margin Tethyan sedimentary sequence (Gansser, 1964; Brookfield, 1993; Gaetani and Garzanti,

1991; Garzanti, 1999; Steck, 2003; DiPietro and Pogue, 2004; Yin 2006; Thiede et al., 2006)

Chambers et al., 2009). Based on isotopic data and faunal evidence, Myrow et al. (2003) argue that the LH, GH and TH rocks are part of a continuous passive margin off the northern margin of

India preceding Himalayan orogenesis. Alternatively, TH rocks could be less metamorphosed

GH rocks (Gehrels et al., 2006; Webb et al. 2011) or could have been deposited unconformably on top of GH and inner LH rocks. TH rocks were deposited on the southern margin of Tethyan ocean basins, as a composite of two superimposed rift to passive margin sequences (Brookfield,

1993; Yin, 2006). Isolated bodies of TH sediments are present in the Dadeldhura klippe unconformably overlying GH rock in western Nepal (Kaphle, 1992; Robinson et al., 2006,

Gehrels et al., 2006). However, Antolin et al. (2013) suggest that the TH rock in the klippe is bound at the base by the STDS, not an unconformable contact. No TH rocks exist in the Almora klippe.

2.4. Methods

2.4.1. Geologic Map

We produced a high resolution map of Kumaun by integrating our field mapping with the published map of Valdiya (1980) georeferenced using ArcMap 10.0TM, an ESRI mapping

software package. Twenty controlling points, like the confluence of major rivers, were

georeferenced. A hill-shade map was created using Advanced Spaceborne Thermal Emission and

Reflection Radiometer (ASTER) Global Digital Elevation Model Version 2 (GDEM V2) dataset

(Data source: http://asterweb.jpl.nasa.gov/gdem.asp). The georeferenced map was draped over the hillshade map to cross check the georeferencing. Further, we updated the lithology and structural data by conducting field work at a scale of 1:50,000.

2.4.2. U-Pb Zircon Geochronology

Nine igneous and detrital samples (Fig. 2, Table 1) were collected from the LH and

Almora klippe. U-Pb geochronologic analyses of in-situ zircon grains were conducted using

laser-ablation multicollector inductively coupled plasma mass spectrometry (LA-MC-ICPMS) at

the University of Arizona following methods described in Gehrels et al. (2006, 2008). The

analyses involve ablation of zircon with a 193nm ArF excimer laser (Photon Machines Analyte

G2) using a spot size of 30 μm. For detrital zircons, approximately 100 grains were analyzed per

sample. Analyses that were > 10% discordant were rejected. The resulting ages were plotted

using Isoplot 3.0 (Ludwig, 2003) to generate U-Pb probability density distributions and

Concordia diagrams. The age-probability diagrams were constructed by assigning a normal

(Gaussian) distribution to each analysis based on the reported age and the uncertainty, and also

by summing the probability distribution of every acceptable analysis into a single curve. Each

session consist of analysis of five unknowns, bracketed by Sri Lanka zircon standard, with a

known age of 563±3.2 Ma (2σ error). At the middle and end of each session, R33 was used as

secondary standard, with known age of 419.3±0.4 Ma (Black et al., 2004), to ensure accuracy

and to evaluate reproducibility. Data reduction procedures were followed as stated in Gehrels et

Table 1. U-Pb zircon geochronology sample locations for Kumaun, NW India.

Sample No Coordinates Formation Lithology

0N (dd.ddddd) 0E (dd.ddddd)

SM11-004 29.188350 80.091833 Nagthat (Bhowali Clean quartzite associated (DZ), quartzite) with mafic sills

SM11-006 (DZ) 29.194550 80.096417 Nagthat Muddy quartzite, and siltstone

SM11-009 (IZ) 29.214933 80.054467 Debguru porphyry Granite-gneiss

SM11-019 (DZ) 29.297617 80.100317 lower Almora Thin bedded qurtatite Group within phyllite

SM11-021 (DZ) 29.437717 80.096217 upper Almora Thick bedded quartzite Group

SM11-022 (DZ) 29.513767 80.128917 Rautgara Quartzite interlayered with slate and phyllite

SM11-051 (DZ) 29.703450 79.898383 Rautgara Quartzite interlayered with slate and phyllite

SM11-057 (DZ) 29.469233 79.602367 Nathuakhan Bedded quartzite within (Ramgarh Gp) the green phyllite

SM10-036 (DZ) 29.391250 79.533933 Nagthat Thin bedded quzrtzite

al. (2008), and analyses were rejected with (1) high 204Pb, (2) low 206/204Pb ratio, (3) greater than

5% error on 206Pb/207Pb age, (4) greater than 10% error on the 206Pb/238U date, (5) greater than

25% normal discordance, (6) high U concentration, or high U/Th ratio. The best ages of detrital zircons were selected following methods given in Gehrels et al., (2011). 206Pb/207Pb ages were used as best ages if the grain was older than 1400 Ma, whereas 206Pb/238U ages were used for grains younger than ca. 1400 Ma.

2.4.3. Nd Isotope Analyses

Sm-Nd isotopic systematics are unaffected by crustal events, and model ages provide the age of the source material since its extraction from the mantle (McCulloch and Wasserburg,

1978). The εNd(0) value assesses the geochemical affinity of the original source material of the

sedimentary rock. If the εNd(0) value is more negative, the sedimentary protolith is more evolved

from primitive mantle, and if the value is less negative; the sedimentary protolith is less evolved

from primitive mantle. Contrasting εNd(0) values from two different sedimentary sequences

indicate distinct source regions. GH rocks have an average εNd(0) value of -16 while LH rocks

have an average value of -23, suggesting the sedimentary source for the GH is not the same as

LH (Ahmad et al., 2000, Robinson et al., 2001; Martin et al., 2005; Richards et al., 2005;

Imayama and Arita, 2008). This difference in the εNd(0) values has been successfully applied to determine the location of GH versus LH units, and thus, locating the MCT (Martin et al., 2005;

Richards et al., 2005; Imayama and Arita, 2008).

Five argillaceous rocks were sampled for whole rock Nd analyses from the LH and klippe rocks. Rock samples were powdered in a ring and puck style mill. About 300 mg of rock were digested for one week in ~10:1 HF: HNO3 mixtures in steel jacketed Polytetrafluoroethylene

(PTFE) bombs in a standard convection oven at 160°C. The samples produced a clear solution following bomb dissolution and conversion from fluorides to chlorides. Samples were spiked with mixed 149Sm-150Nd tracer, and Sm and Nd were isolated using established ion-

chromatographic techniques (Patchett and Ruiz, 1987; Vervoort and Patchett, 1996). The isotopic analyses were performed at Washington State University using a ThermoFinnigan

Neptune multi-collector–inductively coupled plasma mass spectrometer (MC-ICPMS).

Elemental concentrations of Sm-Nd as well as parent/daughter ratios (147Sm/144Nd) were

determined by isotope dilution using the same solution as the isotope composition measurement,

following the approach of Boelrijk (1968). Total uncertainty is estimated to be better than

0.003% for 143Nd/144Nd and 0.5% for 147Sm/144Nd (Vervoort et al., 2004). The five samples show no evidence for partial melting so we assume that the Nd isotopic characteristics are representative of the sedimentary protolith.

2.5. Results

2.5.1. U-Pb Geochronology

The detrital zircon age spectra describes the ages of the rocks exposed in the source region at the time of sediment transport and deposition. U-Pb zircon isotopic age data are shown

as relative age probability plots (Figs. 5 and 6). The probability density function plot has an

advantage over the histogram as it plots values show the associated uncertainty.

2.5.1.1. Detrital Zircons from North and South of the Almora klippe

Sample SM11-004 (Fig. 5), mapped by Valdiya (1980) as Nagthat quartzite and locally known as Bhowali quartzite, is a clean, white quartzite associated with mafic sills (Fig. 4c) in the hanging wall of the MBT (Fig. 2). Our field observations show that these mafic sills follow bedding, and are interpreted as penecontemporaneous/interbedded mafic flows. The age spectra shows age clusters at ca. 1850 Ma, between 2300-2800 Ma, and a pronounced peak at ca. 1865

Ma. This sample yields no ages younger than ca. 1830 Ma. The weighted mean of three young

zircon grains is 1849±9.5 Ma. We add the uncertainty and round up to the nearest 10 Ma

following the technique of Martin et al. (2011). Thus, we interpret ca. 1860 Ma as the maximum

depositional age. These data are the first report of Palaeoproterozoic metasedimentary rocks

south of the Almora thrust.

Sample SM11-006 (Figs. 4d and 5) was sampled 0.85 km northeast from SM11-004 (Fig.

2), and is a fine- to medium-grained, muddy quartzite. Maximum age peaks cluster between ca.

500-600, 1600-2000 Ma with strong peaks at ca. 1850 Ma and around 2500 Ma. The weighted

mean of the three youngest ages is 537±19 Ma. We assign a maximum depositional age as 560

Ma for this unit.

Two quartzite samples, nearly 30 km apart, from north of the Almora thrust (Fig. 2) were

analyzed to confirm the presence of reported Palaeoproterozoic rock. Sample SM11-022 (Fig. 5)

is from the type locality of the Rautgara Formation, immediate north of the Almora klippe and

provides 87 usable ages. The dominant age peaks are ca. 1850 Ma and ca. 2500 Ma, with a few

small peaks. Four young grains yield ages of 1545.8±4.9 Ma, 1562±2.6 Ma, 1579.5±9.7 Ma, and

1595±6.0 Ma. The weighted mean of these ages is 1564±25 Ma; thus, we assign 1590 Ma as the maximum possible depositional age for this sample. Sample SM11-051 (Fig. 5) is from a muddy quartzite in the Rautgara Formation, immediate north of the Almora klippe (Fig. 2), and provides

97 usable ages. Age peaks are clustered between ca. 1800-2100 and ca. 2300-2600, with two

pronounced peaks at ca. 1870 and ca. 2530. This sample yields no grains younger than 1707±6.7

Ma. Five young grains provide ages of 1707.4±6.7 Ma, 1720.3±5.9 Ma, 1747.8±8.9 Ma,

1757.1±3.7 Ma, and 1758.4±2.6 Ma. The weighted mean of these ages, including systematic

error is 1750±23 Ma. We assign a maximum depositional age of 1780 Ma.

Sample 11-057 (Fig. 5) is from a thin bedded quartzite within green phyllite, collected

from south of the Almora thrust (Fig. 2), and from which detrital age spectrum of 85 concordant

grains are reported. Age peaks cluster between ca. 800-1000 Ma, 1700-1900, and 2300-2600 Ma,

with a number of minor peaks. Three grains yield ages of 844.8±8.0, 852.6±17.7, and

889.7±35.9. The weighted mean of these ages is 848±27 Ma, so we assign a maximum depositional age of 880 Ma.

Sample SM10-036 is a very fine-grained silty quartzite (Fig. 2) mapped by Valdiya

(1980) as Nagthat quartzite. This sample only provided 4 usable grains (see supplementary data).

These ages range between ca. 2600-1800 Ma. We did not plot these grains because such a low frequency does not portray the true age distribution of source areas.

2.5.1.2. Crystallization age of the Debguru Porphyroid

Sample SM11-009 (n=17, core and rims) from the Debguru porphyry (Figs. 4f and 5) yielded U-Pb crystallization ages (<10% discordance) from 1852.3±7.4 Ma to 1879.4±5.2. These grains were mostly devoid of inherited cores, yielding similar ages in rims and cores except one core with an age of 2193.1±58.5 Ma. The weighted of 15 mean ages (<10% discordance) is

1866±1.7 Ma (n=15, MSWD= 1.6) suggesting a crystallization age. One inherited core has an age of 2193±58.5 Ma (93.6% concordance).

Figure 5. Detrital zircon age distributions curves of various siliciclastic strata from the footwall of the Almora thrust, south of the Almora klippe, and age Concordia (lower right) plot of Debguru porphyry.

Fig. 6. Detrital zircon age distributions of metasediments from the Almora klippe.

2.5.1.3. Detrital Zircons from the Almora Klippe

Sample SM11-019 (Figs. 6 and 7) is from a thin bedded quartzite layer within greenish

phyllite (Fig. 4e) from the lower stratigraphic horizon of the Almora Group, and provides 91 usable grains. U-Pb crystallization age populations cluster at ca. 700-1100 Ma, 1800-1900, and

2300-2550 Ma. 16 grains yield ages between ca. 765.9±18.7 and 826.9±12.3 with a weighted mean of 806.0±6 (2 S.D., MSWD=3.6). We assign a maximum depositional age of 810 Ma.

Sample SM11-021 is a thick bedded rusty quartzite from the center part of the klippe

(Figs. 6 and 7), and provides 84 usable grains with U-Pb crystallization ages from 538.2±2.3 Ma

to 3873.7±7.2 Ma. Major peaks are ca. 538-632 Ma, 909-1026 Ma, 2348-2820 Ma, with a number of smaller peaks. Five younger grains yield ages of 538±2.3, 584.3±16.2, 598.3±10.5,

625.1±9.3, and 632.3±12.7, with a weighted mean of 549±37. We assign a maximum depositional age of 580 Ma.

2.5.2. Nd Isotopic Analyses

We analyzed five samples (Table 2) from the north, south and inside the Almora klippe.

Two samples, SM11-022 and SM11-053, from north of the klippe (Fig. 2), yield εNd(0) values of

-24.6 and -23.0, respectively. Sample SM11-007, south of the Almora klippe in the hanging wall of the MBT (Fig. 2) yields an εNd(0) value of -13.8. Sample SM11-018 (Table 2, Fig. 2) from the central part of the klippe yields an εNd(0) value of -11.8 Sample SM11-056, from the southern part of the klippe, (Fig. 2) yields an εNd(0) value of -11.3.

2.6. Discussion

Detrital U-Pb zircon geochronology is used for characterizing tectonostratigraphy along the Himalayan arc, provenance analysis, timing of orogenic uplift using provenance tracing, and to determine reasonable predeformational palaeogeographic reconstructions (DeCelles et al.,

2000; Myrow et al., 2003; Martin et al., 2005; McQuarrie et al., 2008; Célérier et al., 2009;

Gehrels et al., 2011; Long et al., 2011; McKenzie et al., 2011; Webb et al., 2011; Spencer et al.,

2012b). The pronounced difference in depositional ages can discriminate Palaeoproterozoic inner

LH rocks from Neoproterozoic to Cambrian GH/outer LH rocks (Ahmad et al., 2000; DeCelles et al., 2000; Richards et al., 2005; Tobgay et al., 2008; McKenzie et al., 2011; Long et al., 2011).

Field observations of the metamorphic grade discriminate outer LH from GH rocks. Outer LH rocks are low-grade to non-metamorphosed, and GH rocks are upper amphibolite to granulite- grade. Ahmad et al. (2000) report εNd(0) values of LH and GH rocks from Garhwal and found

that (1 ) the Munsiari Formation ranges from -22.9 to -27.7, (2) the Berinag Formation ranges from -20.8 to -25.3, (3) the Ramgarh Group ranges from -24.3 to -24.5, and (4) the GH (Vaikrita) rocks have values ranging from -11.2 to -18.8. Two samples from Ahmad et al. (2000), KR50

(sandstone) and KR44 (shale), are stated as part of the Chandpur Formation; however, the map of Valdiya (1980) show these samples in the Nagthat Formation. Assuming these two samples are from the Nagthat Formation, the εNd(0) value of the outer LH ranges from -17.8 to -18.1;

however, this is a tenuous interpretation. McKenzie et al. 2011) reported εNd(0) values from the

uppermost part of the Rautgara Formation (inner LH) of -22.0, immediate north of Almora

klippe, and from the Blaini Formation (outer LH) of -16.0, from MBT hanging wall, south of the

Almora Klippe. In western Nepal, Robinson et al. (2001) reported εNd(0) values of the

Palaeoproterozoic LH Ranimata Formation of -21.9 to -25.5, and eastern continuation of the

Almora klippe, the Dadeldhura klippe of -7.6 to -11.8.

Table 2. Whole rock Nd isotope sample locations, Kumaun, NW India.

Sample No Coordinates Rock type Formation Sm Nd 147Sm/ 143Nd/1 Abs std err eNd(0) ± 0N (dd.ddddd) 0E (dd.ddddd) (ppm) (ppm) 144Nd 44Nd

SM11-007 29.195183 80.089717 Green Chandpur 4.65 20.6 0.1365 0.511921 0.000009 -13.8 0.18 phyllite

SM11-018 29.348933 80.096883 Chl-musco- Almora Klippe 7.63 41.0 0.1126 0.512024 0.000009 -11.8 0.18 grt schist

SM11-023 29.499433 80.126700 Mylonitic Almora Klippe 6.40 34.3 0.1128 0.511367 0.000008 -24.6 0.16 granite

SM11-053 29.692800 79.857883 Greenish Almora Klippe 7.25 38.1 0.1150 0.511447 0.000007 -23.0 0.14 phyllite

SM11-056 29.490283 79.626117 Green Almora/Ramgar 3.97 20.0 0.1198 0.512047 0.000009 -11.3 0.18 phyllite h

GNG 29.576833 80.087967 Black shale Upper part of 6.58 36.5 0.1089 0.511510 0.000006 -22.0 NA (McKenzie et Rautgara al., 2011)

Figure 7. Modified Geologic map of Kumaun around Almora klippe with available geochronology and isotopic data. All lithological units were draped over a shaded relief map of this area. A-A’ is the cross-section line (Fig. 8).

Figure 8. Schematic preliminary cross-section along line A-A’, showing stratigraphic and structural configuration to the north and south of the Almora klippe.

In the field, GH and inner LH rocks are difficult to distinguish from one another because

of similar lithologies, metamorphism and ductile deformation. This ambiguity has led to the

interpretation that rocks in the Almora klippe are part of the inner LH Munsiari Formation

(Valdiya, 1980; Srivastava and Mitra, 1994; Ahmad et al., 2000; Rawat and Sharma, 2011).

Sample SM11-018 (Table 2, Fig. 7) from the central part of the klippe yields an εNd(0) value of

-11.8, and sample SM11-056 from the southern part of the klippe (Fig. 7) yields an εNd(0) value of -11.3. The Dadeldhura klippe in far-western Nepal has similar values of ~-11. Hence, we conclude that the Almora klippe rocks are GH rocks and not part of inner LH Munsiari

Formation because the inner Paleoproterozoic LH units have average values of -23 (Ahmad et al., 2000; Robinson et al., 2001; Martin et al., 2005). GH detrital zircon populations are between ca. 860 Ma and ca. 540 Ma (Parrish and Hodges, 1996; DeCelles et al., 2000; Cawood et al.,

2007; McQuarrie et al., 2008; Gehrels et al., 2011; Spencer et al., 2012b) and εNd(0) values are

an average of -16 (n=11, Ahmad et al., 2000). The outer LH detrital zircon populations are

between ca. 900-500 Ma (Richards et al., 2005), and εNd(0) values are an average of -17.5 (n=8,

Ahmad et al., 2000; McKenzie et al., 2011). The εNd(0) values in the klippe could be construed

to look similar to the outer Neoproterozoic LH rocks; however, the klippe/GH rocks have a less

negative εNd(0) value than outer Neoproterozoic LH rocks, and a higher metamorphic grade than

the weakly metamorphosed outer Neoproterozoic LH rocks. When reconstructing the Greater

Indian margin, the klippe/GH rocks may have been once continuous with the outer LH rocks or

deposited in a different basin but have the same source terrane.

The Palaeoproterozoic Rautgara Formation is mapped by Valdiya (1980) to the

immediate north of the Almora thrust; however, Célérier et al. (2009) map these rocks as the ca.

800 Ma Chandpur Formation based on detrital zircon ages. Our detrital zircon sample SM11-022

(Figs. 5 and 7) shows that the Rautgara Formation has a late Palaeoproterozoic ca. 1600 Ma

depositional age, similar to the Palaeoproterozoic age from the Rautgara Formation reported by

McKenzie et al. (2011). Sample SM11-051 (Figs. 5 and 7) from north of klippe ~30 km

northwest of SM11-022 in the Rautgara Formation yields an older depositional age of 1780 Ma.

We interpret that SM11-022 is from the upper part of the Rautgara Formation and SM11-051 is

from the lower part of the formation, or alternatively, it may be that SM11-022 was located in

part of the Rautgara basin that did not receive younger zircons. However, our data conflicts with

the results of Célérier et al. (2009), which suggest the rocks to the north of the Almora thrust are

800 Ma (their sample GW18-06). Using the coordinates in Célérier et al. (2009), we found that

GW18-06 belongs to the Neoproterozoic Mandhali Formation in the lower Jaunsar Group.

Presence of the late Palaeoproterozoic Rautgara Formation is also supported by an εNd(0) value of -22 (McKenzie et al., 2011; sample GNG, Fig. 7) from a shale sample collected from below the phosphorite horizon of ~1600 Ma Gangolihat dolomite. Thus, we interpret that the

Palaeoproterozoic Rautgara Formation is present along the northern part of the Almora klippe.

The Rautgara Formation has symmetrical ripple marks, a shallow water depositional feature, calling into question the previous interpretation as a turbidite deposit (Célérier et al., 2009). Our

field mapping indicates turbidite beds in the ca. 1600 Ma part of the Rautgara Formation (Fig.

4a) with occasional interbedded mafic sills or dikes. Furthermore, we did not locate the southerly

dipping Tons thrust that is supposed to separate ca. 800 Ma Chandpur in the hanging wall from ca. 1600 Ma Gangolihat dolomite north of the Almora thrust (Célérier et al., 2009). Instead, we found a gradational contact between Rautgara Formation and overlying Deoban Formation, similar to what Validiya (1980) suggests.

The εNd(0) values of the two fine-grained metasediments from the northern part of the

klippe are -24.6 (SM11-023) and -23.0 (SM11-053). These values are consistent with the average

εNd(0) value of -23 for the inner Palaeoproterozoic LH rocks, e.g., Ramgarh, Berinag or Munsiari

Formation (Ahmad et al., 2000; Robinson et al., 2001; Martin et al., 2005). Furthermore, these

metasediments are spatially associated with Palaeoproterozoic (ca. 1.85 Ga) granitoids and are

present in the Berinag thrust sheet as well as within the Munsiari thrust sheet (Spencer et al.,

2012b). Thus, we interpret these rocks as part of the LH Ramgarh/Berinag Group of rocks,

carried by the Ramgarh/Berinag thrust, and not part of the GH Almora Group. Also, we interpret

that the Almora thrust, that separates LH rock from Almora klippe/GH rock, is located further

south than where it is mapped by previous workers (Valdiya, 1980; Srivastava and Mitra, 1994;

Célérier et al., 2009) to accommodate the presence of these Palaeoproterozoic rocks (Fig. 7).

Thus, the Almora thrust separates GH/klippe rock from lower LH Palaeoproterozoic rock carried

by the Ramgarh/Berinag thrust (Fig. 8). The Almora thrust is either the same thrust as the MCT

or another thrust in the GH thrust system. The Palaeoproterozoic LH rocks with associated

Palaeoproterozoic granites in the footwall of the MCT, the Munsiari Formation, are the same

rocks as those carried by the Ramgarh/Berinag thrust sheet, and these rocks are present in a

southward dipping thrust north of the Almora thrust sheet. Thus, we suggest that there is one

continuous thrust sheet called the Ramgarh-Munsiari thrust (RMT) sheet that is the roof thrust

for the LH duplex composed of the north dipping Munsiari thrust in the footwall of the MCT, the

south dipping Ramgarh thrust north of the northern Almora thrust. The Berinag thrust is one of

the multiple thrusts in the LH duplex.

South of the Almora klippe, sample SM11-009 (Fig. 7) is from the ca. 1.85 Ga

Palaeoproterozoic mylonitic granitoid gneiss known as the Debguru porphyry from the hanging

wall of the Ramgarh thrust sheet as mapped by Valdiya (1980). A similar crystallization age,

1856±9.6 Ma, is reported by Célérier et al. (2009) from the Debguru porphyry at the base of the

Ramgarh thrust sheet; however, they interpret these rocks as a part of the Indian cratonic

basement. In contrast, we argue that the Debguru porphyry is part of the same group of LH

Palaeoproterozoic rocks that contains 1.85 Ga granitoids, including the Munsiari, Berinag and

Ramgarh Formations. Richards et al. (2005) describe the rock carried by the Ramgarh thrust as having 2.6-1.8 Ga Palaeoproterozoic zircons with bulk rock model Nd ages of 2.7-2.3 Ga and ca.

1.85 Ga orthogneiss. Therefore, we interpret that the RMT sheet is folded underneath the Almora

klippe and crops out south of the Almora thrust, mapped by Valdiya (1980) as Ramgarh thrust

sheet (Fig. 8). However, the Ramgarh thrust sheet, to the south of klippe, is unconformably

overlain by Neoproterozoic (ca. 880 Ma) low-grade metasediments (sample SM11-057),

consistent with reported Neoproterozoic ages (ca. 800 Ma, sample GW21-06) based on detrital

zircon analysis by Célérier et al. (2009). Thus, we interpret that the RMT carried inner LH rocks

distal to cratonic India, and carried inner as well as outer LH rocks more proximal to cratonic

India (Fig. 8). The outer LH (SM11-057), immediate south of the Almora klippe (Figs. 6 and 7),

we call the Nathuakhan Formation as named by Valdiya (1980), instead of the Chandpur

Formation after Célérier et al. (2009). The Nathuakhan Formation, made up of sericitic quartzite

and phyllite, has been correlated with Chail metasediments of the Himachal Pradesh (Valdiya,

1980). However, it is worthwhile to note that the affinity of the Chail Group is ambiguous. Webb

et al. (2011) mapped Chail as part of the Tethyan Sequence rock. However, others map is as part

of outer Lesser Himalaya (Richards et al., 2005). An alternative interpretation is that sample

SM11-057 is from low grade GH rock and the Almora thrust would be located between the

Neoproterozoic rock and the Paleoproterozoic LH rock. We did not see a fault between these two

units and such low grade GH rock has not been reported; however, it is still a viable possibility.

If this alternative interpretation is correct, this would mean that the RMT would only carry the lower Paleoproterozoic LH rock, as it does along the Himalayan arc.

Further, we disagree with the interpretation from Célérier et al. (2009) that the 1.85 Ga rocks (Fig. 7) are Indian cratonic basement and that the deformation style is basement involved.

The Indian cratonic basement is 2.5 Ga with a similar composition to rocks exposed in the

Bundekhand craton, south of the Indo-Gangetic plain (Saha and Mazumdar, 2012). Similar

Palaeoproterozoic (ca. 1.85 Ga) metasediments and granitoids exist within the Aravalli Group, which overlies the 2.5 Ga Archean basement (Kaur et al., 2012). The geometry explained by

Célérier et al. (2009) is not structurally admissible as the basal thrust cuts down section into the basement rock. Alternatively, Kohn et al. (2010) suggest a subduction system existed on the northern part of the Greater India ca. 1.85 Ga and these granitoids were formed as a part of a continental arc on the northern side of the northern Indian cratonic block and intruded into the volcaniclastic metasediments of the inner Palaeoproterozoic LH rocks.

Our field and zircon geochronology data indicate SM11-004 from the immediate hanging wall of the MBT has a maximum depositional age of ca. 1860 Ma, and is associated with mafic sills. This unit is unconformably overlain by muddy quartzite and siltstone with a maximum

depositional age of ca. 560 Ma (SM11-006). Valdiya (1980) maps both these Palaeo- and

Neoproterozoic rocks as the Nagthat quartzite. However, our data show otherwise. Based on

detrital zircon analyses from Garhwal, Hofmann et al. (2011) report the age of the Nagthat

Formation as Neoproterozoic, with minimum age of 733±10 Ma. We interpret that the lower unit, the Bhowali quartzite with interlayered mafic sills (Trivedi and Pande, 1993), as a facies variant of ca. 1800 Ma Berinag quartzite. Also, the Bhowali quartzite is spatially associated with

1888±46 Ma Amritpur granite (Trivedi and Pande, 1993), similar to the ca. 1.85 Ga granite found in association with Berinag quartzite. However, we interpret the upper muddy quartzite unit with younger depositional ages to be the equivalent of the outer Neoproterozoic Nagthat quartzite. Thus, there is either a fault or a large unconformity between the two units.

Based on the data we present, Neoproterozoic rock crops out north of the Almora klippe and Palaeoproterozoic rock crops out south of the Almora klippe. In the past, the Tons thrust was defined as separating inner Palaeoproterozoic LH to the north from the outer Neoproterozoic LH to the south (Srivastava and Mitra, 1994; Ahmad et al. 2000; Richards et al., 2005; Célérier et al.,

2009; McKenzie et al., 2011). Thus, the Tons thrust is not an orogenic scale boundary that separates outer from inner LH rock. Instead, inner Palaeoproterozoic LH rock south of the

Almora klippe is carried by the RMT and Neoproterozoic rock north of the Almora klippe is brought to the surface by the thrust sheets in the LH duplex.

Two detrital samples from klippe/GH rocks, SM11-019 and SM11-021, from the margin and internal part of the klippe, show Neoproterozoic and Cambrian ages. Sample SM11-019 is from the lower part of the stratigraphy with an 810 Ma maximum depositional age, and SM11-

021 is from the upper part of the stratigraphy with a 580 Ma maximum depositional age. The

Almora klippe/GH rock is intruded by Cambro-Ordovician granites, the Almora granite and

Champwat granite (Trivedi et al., 1984). Cambro-Ordovician granites are present in the adjacent

Dadeldhura klippe (Kaphle, 1992; Gehrels et al., 2006; Robinson et al., 2006; Antolin et al.,

2013). We found an εNd (0) value of -11.82 (SM11-018) from the Almora klippe, which

corresponds to the Dadeldhura klippe with values of -7.6 to -11.8 (Robinson et al., 2001),

suggesting that the klippe is an southern erosional outlier of the GH rocks. However, as discussed previously, this rock could be the Neoproterozoic LH rock metamorphosed to a higher

degree than found elsewhere. In the Dadeldhura klippe, TH rock is present (Robinson et al.,

2006); thus, one could argue that this rock is TH rock, but there are no reports of TH rock in the

Almora klippe. In fact, TH, GH, and Neoproterozoic outer LH rock are difficult to distinguish

from one another because they were probably laterally continuous on the Greater Indian margin,

just more or less metamorphosed. However, the rock in the Almora klippe is clearly not the

Palaeoproterozoic LH Munsiari Formation as has been thought in the past (Valdiya, 1980;

Srivastava and Mitra, 1994; Célérier et al., 2009). Metamorphic pressure-temperature data

indicate that GH/klippe rock is slightly lower-grade (Beyssac et al., 2004; Naeraa et al., 2007;

Antolin et al., 2013) than the MCT GH hanging wall rocks (Spencer et al., 2012a) to the north.

However, this can be explained by the MCT cutting up section to the south and carrying rock

from higher in the GH stratigraphy that have not been buried as deeply as GH rocks to the north.

Rock in the Almora klippe and north of the MCT have Neoproterozoic (~900 Ma) detrital zircon

ages, coupled with similar εNd(0) ( -7.6 to -11.8) values, suggesting that these two units are the same tectonostratigraphic unit. Because the metamorphic grade is similar to GH rock as well as matching the detrital zircon and εNd(0) values, we suggest that the Almora klippe is the southern

continuation of the MCT or another thrust in the GH thrust system.

This idea is different that presented by Valdiya (1980) and used by Srivastiva and Mitra

(1994) and Célérier et al. (2009). Valdiya (1980) suggests that the GH rocks are bound by the

MCT at its base and in its footwall is the Munsiari thrust that carries the Almora Group rock to the south and forms the Almora klippe. Srivastava and Mitra (1994) illustrate this in their cross sections. However, we suggest that rock in the hanging wall of the Munsiari thrust, which we term, the Ramgarh-Munsiari thrust sheet, is Paleoproterozoic LH rock and that the rock is carried to the south under the Almora klippe and crops out to the north and south Almora klippe. This implies that the Ramgarh-Munsiari thrust sheet is rooted in the footwall of the MCT and continues south nearly all the way to the MBT. Clearly, the Ramgarh-Munsiari thrust sheet is a very long thrust sheet (e.g. Robinson and Pearson, 2013). In addition, we show that rock in the

Almora klippe is GH rock that has been moved southward on the MCT or a similar thrust in the

GH thrust system. These two changes in the balanced cross section will increase the shortening estimate in Kumaun and Garhwal. The cross section of Célérier et al. (2009) is difficult to evaluate because it is not balanced or viable. However, given the data presented in this paper, the cross section would have to be redrawn to account for the far-traveled Ramgarh-Munsiari thrust sheet and dismisses their ideas that the thrust system has incorporated slivers of Indian basement.

Instead, these are the Paleoproterozoic granitic intrusions found within the Paleoproterozoic LH rocks.

Detrital zircons older than 3.0 Ga occur in sample SM11-004 (see supplementary data), which is interpreted as Palaeoproterozoic LH rock south of the Almora klippe, and similar ages of zircons also have been reported from the Palaeoproterozoic LH rocks north of the klippe

(McKenzie et al., 2011). However, Long et al. (2011) report from correlative Palaeoproterozoic

LH units along strike in Bhutan and Nepal the absence of >3.0 Ga zircons, and suggest that

Indian cratonic basement was covered by supracrustal sediments or Palaeoproterozoic LH and

not receiving sediments from the Indian craton. Sample SM11-004 refutes that statement because

of the presence of >3.0 Ga zircons, which are prolific within the various gneiss and Archean

greenstone vestiges of the Aravalli-Bundelkhand craton (Mondal et al., 2002), and an evidence

of differing cratonic sources along the strike of the Himalayan arc (Ravikant et al., 2011).

2.7. Conclusions

We present new mapping, U-Pb detrital zircon and igneous zircon data, and εNd(0) values from Kumaun, northwest India and find that:

1) Neoproterozoic (~900 Ma) detrital zircon ages, coupled with similar εNd(0) ( -7.6 to -11.8)

values, of rocks in the Almora klippe and in the MCT hanging wall suggest that these are the

same tectonostratigraphic unit.

2) The rock north of the Almora klippe is not the Neoproterozoic Chandpur Formation; instead,

these are Palaeoproterozoic siliciclastic shallow to deep marine rocks of the Rautgara Formation,

and are exposed along the north of the northern Almora thrust.

3) These Palaeoproterozoic rocks on the north side of the Almora klippe also include the inner

Lesser Himalayan Ramgarh Group/Munsiari Formation rocks. The root zone of this thrust sheet

is in the footwall of the MCT and is continuous to the south as the Ramgarh-Munsiari thrust

sheet and is folded underneath the Almora klippe.

4) The Ramgarh-Munsiari thrust sheet emerges south of klippe, containing the Palaeoproterozoic ca. 1.85 Debguru porphyry in its hanging wall. The Palaeoproterozoic granites are present throughout the lower Lesser Himalayan Palaeoproterozoic rock and are not part of the 2.5 Ga

Indian craton.

5) South of the Almora klippe, Palaeoproterozoic and Neoproterozoic Lesser Himalayan rocks crop out. We interpret that the Ramgarh-Munsiari thrust is folded underneath the Almora klippe and emerges south of the klippe carrying both Neoproterozoic and Palaeoproterozoic rock.

These structures indicate a thin-skinned style of thrust with no Indian cratonic basement involved structures.

6) In Kumaun, we see no evidence that the Tons thrust separates Palaeoproterozoic Lesser

Himalayan rocks from Neoproterozoic Lesser Himalayan rocks. Palaeoproterozoic Lesser

Himalayan rocks are present south of the Almora klippe on the Ramgarh-Munsiari thrust sheet and Neoproterozoic Lesser Himalayan rocks are present north of the Ramgarh-Munsiari thrust sheet in the Lesser Himalayan duplex.

2.8. Acknowledgements

D. Robinson acknowledges support from the National Science Foundation, NSF EAR

0809405, and Mandal’s research was supported by this NSF grant. Mandal would also like to thank the Graduate School and the Department of Geological Sciences, University of Alabama for travel support to carry out the field work and U-Pb zircon geochronologic analyses. We thank

Mark Pecha, Nicky Giesler and Mauricio Ibanez for their help in U-Pb zircon geochronology at the Arizona Laserchron Center (ALC), University of Arizona, USA and support for the ALC from NSF EAR-1032156. We also like to thank Dr. Jeff Vervoort, Washington State University,

USA, for performing the whole rock Nd analyses. Constructive reviews from Rasmus Thiede,

Barun Mukherjee, editor Soumyajit Mukherjee and an anonymous reviewer significantly improved the original manuscript. We thank Barun Mukherjee for editorial handling of this manuscript.

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CHAPTER 3:

ZIRCON U-PB AGES AND HF ISOTOPIC DATA FROM THE PALEOPROTEROZOIC INNER LESSER HIMALAYAN SEQUENCE, KUMAUN, INDIA: IMPLICATIONS FOR TECTONICS, BASIN EVOLUTION AND ASSOCIATED METALLOGENY OF THE NORTHERN INDIAN CRATONIC MARGIN 3.1. Abstract

Integrated U-Pb ages, Hf isotopic and whole rock trace element geochemical data coupled with detail mapping of the Askot klippe rocks establish that they belong to the

Paleoproterozoic inner Lesser Himalayan rocks, and do not continue to the south as the Greater

Himalayan Almora klippe rocks. The Askot klippe consists of 1856.6±1.0 Ma granite- granodiorite gneiss, coeval 1869±12 Ma felsic volcanic rocks, and ca. 1800 Ma Berinag

Formation quartzite. These rocks represent a small vestige of a Paleoproterozoic continental arc that formed on the northern margin of the northern Indian cratonic block during Paleo-

Mesoproterozoic amalgamation of the supercontinent Columbia. εHf values from ca. 1850 Ma detrital zircons of Berinag Formation quartzite (-9.6 to -1.1, with an average of -4.5) overlap with the εHf value of ca. 1850 Ma granite-granodiorite gneiss of the Askot klippe (εHf:-5.5 to -

1.2, with an average of -2.7) and other ca. 1850 Ma arc-related granite gneiss (εHf: -4.8 to -2.2, with an average of –4.0) within the Lesser Himalayan zone. These overlapping data suggest a proximal arc source of the metasediments. Subchondritic εHf values (1.1 to -4.9) of ca. 1850 Ma granite-granodiorite gneiss indicate pre-existing older crust, which underwent crustal reworking at ca. 1850 Ma. Similar crustal reworking occurred at that time in the Arvalli-Delhi orogenic

belt, suggesting an analogous Paleoproterozoic crustal evolutionary history to the northern and western margin of the north Indian cratonic block. A wide range of εHf values of ca.1850 detrital zircons (-15.0 to -1.1) suggests a heterogeneous crustal source supplied detritus to the northern margin. An extension-related volcanogenic massive sulphide deposit within the Askot klippe and a 1658±19 Ma hydrothermal event indicate the formation of a late Paleoproterozoic back arc basin. Extension related to ca. 1600 Ma magmatism is recorded in inner Lesser Himalayan rocks as the addition of the juvenile crust suggested by superchondritic εHf values (1.9 to 7.6).

3.2. Introduction

The Precambrian Indian shield consists of four major Archean cratonic nuclei: the

Aravalli-Bundelkhand craton to the north, also known as north Indian cratonic block (NIB), and the Singbhum, Bastar, and Dharwar cratons to the south, collectively known as south Indian cratonic block (SIB) (Fig. 1). The NIB and SIB are separated by the Central Indian Tectonic zone (CITZ, Fig.1), a Proterozoic orogenic belt formed by continent-continent collision at ca.

1.06 to 0.94 Ga during assembly of the Neoproterozoic supercontinent, Rodinia (Roy and Prasad,

2003; Bhowmik et al., 2012). In the western margin of the NIB, the Delhi-Aravalli orogenic belt exposes large tracts of Paleoproteroandzoic rocks, which are extensively studied (Kaur et al.,

2011 and reference therein) because the Paleoproterozoic era marks a major change in Earth’s thermal and tectonic regime from the Archean (Condie, 1997; Brown, 2006). Pre-Rodinian

Paleoproterozoic supracrustal rocks of NIB affinity are also exposed within the Himalayan fold- thrust belt (FTB) in various thrust sheets known as inner Lesser Himalayan (LH) rocks. These exposures in the FTB provide an unparalleled opportunity to study the stratigraphic development of the Paleoproterozoic NIB's northern margin, which retains important information about

Earth's ancient Paleo-Mesoproterozoic supercontinent, Columbia (Rogers and Santosh, 2002).

Figure 1 Inset is a tectonic map of peninsular India and the adjoining Himalayan orogen. Cratonic India is composed of two major Archean cratonic blocks, the NIB (northern Indian cratonic block) and the SIB (southern Indian cratonic block), separated by a CITZ (central Indian tectonic zone). Boundaries of NIB and SIB are adopted from Roy and Prasad (2003) and Bhowmik et al. (2012). The white solid line shows the location of Kumaun-Garhwal, India. Abbreviations: DAB: Delhi-Aravalli Belt. The larger map is a detailed tectonic and thrust architecture map of Kumaun-Garhwal, Uttaranchal, India. Black solid rectangle shows study area. Abbreviations: MFT: Main Frontal thrust; MBT: Main Boundary thrust; BT: Berinag thrust; RMT: Ramgarh-Munsiari thrust; MCT; Main Central thrust; STDS: South Tibetan Detachment system; AK: Almora klippe; LK: Lansdowne klippe; BK: Bajnath klippe; ASK: Askot klippe; CHK: Chiplakot klippe.

However, our knowledge about this Paleoproterozoic margin remains incomplete due to: (1) lack of studies focusing on Paleoproterozoic NIB’s northern margin rocks, (2) poor understanding of the stratigraphy of the NIB’s northern margin rocks, presently exposed within the Himalayan

FTB, and (3) insufficient age data on these Paleoproterozoic rocks. This study improves our understanding of the pre-Himalayan Paleoproterozoic stratigraphic architecture of this margin.

The pre-Himalayan northern margin of the NIB has been interpreted conventionally as a passive margin (Brookfield, 1993; Upreti, 1999; Myrow et al., 2003; Gehrels et al., 2006).

Alternatively, a rift or plume related tectonic environment has been proposed based on analyses of the clastic strata and penecontemporaneous mafic flows in inner LH rocks (Bhat et al., 1998;

Ahmad et al., 1999; Ghosh et al., 2012; Sakai et al., 2013). Recently, a continental arc margin was proposed based on petrologic and geochronologic studies of the LH granitoids and associated rocks (Kohn et al., 2010; Rao and Sharma, 2011). Our study focuses on analyses that potentially discriminate among these three possibilities. Most importantly, the Askot klippe contains these inner Lesser Himalayan Paleoproterozoic rocks and also hosts a volcanogenic sulphide (VMS) deposit.

In this study, we characterize the structure, stratigraphy and magmato-thermal event(s) of the Askot klippe through field mapping, combining zircon U-Pb and Hf analysis, and whole rock trace element geochemical analysis of various klippe units. Further, we correlate our geochronologic and isotopic data with published data from inner LH rocks and the western margin of the NIB to: (1) determine the origin and stratigraphic development history of the LH

Paleoproterozoic rocks, (2) understand Paleoproterozoic magmatism and associated ore deposit style to the northern margin of the NIB, (3) establish the stratigraphic affinity of the dubious

Askot klippe rocks, and (4) compare the Paleoproterozoic evolution of the NIB’s northern

margin with the western margin, the Delhi-Aravalli orogenic belt.

3.3. The Askot Klippe

The Askot klippe, also known as Askot crystalline, is located in northern India near the

western border of Nepal (Fig. 1), and is one of the many crystalline klippen within the LH

tectonostratigraphic zone (Valdiya, 1980). Valdiya (1980) interprets the klippe as an

allocthonous sheet that originated from the high grade Greater Himalaya (GH) metamorphic rock

found to the north and that correlates with the Almora klippe to the south (see also Célérier et al.,

2009; Rao and Sharma, 2011). However, he includes the Munsiari Formation as part of the GH rocks, whereas recent work (Webb et al., 2011) interprets classically mapped “Munsiari” rocks as consisting of both GH and LH rocks. The klippe is made up of granitic gneiss alternating with garnet-mica schist and interbanded amphibolite bands (Valdiya, 1980), with a whole-rock Rb-Sr isochron age of 1983±80 Ma for the granitic gneiss (Bhanot et al., 1980). Recently, Mandal et al.

(2014) established the Almora klippe as the southward continuity of the GH rocks and not the same rock as the LH components of the Munsiari Formation. However, they did not address the tectostratigraphic affinity of the Askot klippe.

The Askot polymetallic (Cu-Zn-Pb±Ag±Au) sulphide deposit is located in the easternmost edge of the Askot klippe near the India-Nepal border (Fig. 1). This Zn-rich deposit is the largest known sulphide deposit in the NW Himalaya with a reserve of 1.86 million tons of copper, zinc, lead, silver and gold (Boswell, 2006). Sulphide mineralization is hosted within the chlorite-biotite-muscovite schist, tuffaceous (sericitic) schist, and biotite-augen gneiss. The

Askot VMS deposit serves as a proxy to the tectonic setting of the Paleoproterozoic northern margin of the NIB as it is established that VMS deposits form in extensional tectonic settings,

including both oceanic seafloor spreading and arc environments (Galley et al., 2007, Huston et al., 2010).

3.4. Regional Geologic Setting

Following early workers (Heim and Gansser, 1939; Gansser, 1964), the Himalayan FTB

is divided into four major tectonostratigraphic zones; from north to south, these are the

Neoproterozoic through Eocene strata of the Tethyan Himalaya (TH), Neoproterozoic through

Ordovician high-grade rocks of the Greater Himalaya (GH), Paleoproterozoic to Cambrian strata of the Lesser Himalaya (LH), and Cenozoic foreland basin strata of the Subhimalaya (SH). The

South Tibetan Detachment system (STDS) separates the TH to the north from GH to the south.

The Main Central thrust (MCT or Vaikrita thrust, VT) separates GH from LH. The Ramgarh-

Munsiari thrust (RMT) and the LH duplex (LHD) are intra-LH thrusts. The Main Boundary

thrust (MBT) separates the LH from the SH to the south. The Main Frontal thrust (MFT)

separates the SH from the Indo-Gangetic plain (Fig. 1). All faults sole into the Main Himalayan

thrust (MHT), the basal décollement, at depth. The MCT, a crustal scale ductile fault, originally

defined by Heim and Gansser (1939) as the fault that places high-grade GH over low-grade LH

rocks, acts as the structural base for the GH. Some researchers suggest that GH rocks are simply

the high-grade metamorphic equivalent of the younger LH strata (Parrish and Hodges, 1996), or

the Paleozoic TH strata (Myrow et al., 2003); in contrast, others interpret the GH as an exotic

terrane that was amalgamated to the northern side of the Greater India during the Pan-African

(500±50 Ma) orogeny (DeCelles et al., 2000). The preponderance of Cambro-Ordovician granitoids within the GH (LeFort et al., 1986; Garzanti et al., 1996; Garzanti, 1999; Argles et al.,

2003; Gehrels et al., 2003, 2006, McQuarrie et al., 2012) serves as evidence of this Pan-African tectono-thermal event. The LH is an 8-13 km thick succession of clastic and carbonate

sediments, low-medium grade metasediments, and Paleoproterozoic igneous rocks, and is

divided into two parts in NW India, the inner and outer LH (Srivastava and Mitra, 1994). The

inner LH units are ca. 1900-1600 Ma; whereas, the outer LH units are ca. 950-500 Ma (Hughes

et al., 2005; Richards et al., 2005; McKenzie et al., 2011), separated by a ca. 500 Ma long

unconformity. The Tons thrust is mapped as separating the inner LH to the north from the outer

LH to the south (Srivastiva and Mitra, 1994; Ahmad et al., 2000; Célérier et al., 2009a; Richards

et al., 2005; McKenzie et al., 2011). However, Mandal et al. (2014) found Paleoproterozoic

strata within outer LH exposures to the south of the Tons thrust, and question whether the Tons

thrust separates inner and outer LH rock.

Unfortunately, along- and across-strike differences in lithologies and metamorphic grade

have led to a profusion of names. Here we emphasize the most common naming conventions, but

refer to other correlative units on an as-needed basis. The inner LH consists of the Munsiari,

Berinag, Jutogh, and Ramgarh Formations, and the overlying Damtha and Tejam/Deoban

Groups. Although Ghosh et al. (2012) describe the Damtha Group as the base of the LH rocks,

the base of the Damtha Group is not exposed, and the Berinag and Munisari Formations, which

are mapped in the northern part of the FTB immediately below the MCT, are thought to be older.

The Munsiari, Jutogh and Berinag Formations are amphibolite-grade metasediments (Chambers

et al., 2008; Spencer et al., 2012), whereas, the Ramgarh Group is greenschist-grade

metasediments. The Berinag Formation is the lateral equivalent to the Rampur Formation of

Himachal Pradesh and contains abundant sericitic quartzite and associated garnet-mica schist

with interlayered amphibolite sills and dikes. Miller et al. (2000) report an 1800±13 Ma

metabasalt from Rampur Formation. The Munsiari Formation bears lithological similarities to

the Berinag Formation, but metapelites are dominant over quartzite. The Berinag and Munsiari

Formations are spatially associated with 1.85 Ga orthogneiss found in the basal part of the LH

rocks (Kohn et al., 2010). These Paleoproterozoic granite-gneisses include both I- and S-type

granitoids and are interpreted to represent either a continental arc (Kohn et al., 2010; Sen et al.,

2013) or a continental collision belt (Sen et al., 2013).

The Damtha Group unconformably overlies the Berinag Formation (Celerier et al., 2009)

and consists of the lower Chakrata and the upper Rautgara Formations. Ghosh et al. (2012)

correlate the (inner LH) Rautgara Formation with the (outer LH) Nagthat Formation, but the

basis for correlation is not clear. The Chakrata Formation consists of a sequence of quartz- wacke, siltstone and shale, shows soft-sediment deformation, and was deposited in an inter-tidal to supra-tidal environment (Ghosh et al., 2012). Its equivalent in Himachal Pradesh is the

Dhargad/Sundernagar Formation (McKenzie et al., 2011; Bhargava et al., 2011). The Rautgara

Formation overlies the Chakrata Formation and is a ~2900 m thick sequence of quartzarenite/sublitharenite, and purple shale with abundant mafic sills and dikes (Ghosh et al., 2012).

The Tejam/Deoban Group conformably overlies the Damtha Group and is divided into a

lower stromatolite-bearing shelf-facies cherty dolomite and dolomitic limestone (Raupke, 1974)

of the Deoban/Gangolihat Dolomites, and an upper gray slate and carbonaceous phyllite of the

Mandhali Formation. The age of the Gangolihat Dolomite is variously assigned to the

Mesoproterozoic (mid-late Riphean; Raupke, 1974; Valdiya, 1969, 1980; Bhargava et al., 2011)

or Ediacaran-Cambrian (Azmi and Paul, 2004; Tiwari and Pant, 2009 and reference therein) and

its correlation to the Deoban is not well established (McKenzie et al., 2011). The Mandhali

Formation is younger than 950 Ma (McKenzie et al., 2011).

3.5. Geology of the Askot Klippe

The Askot klippe occupies an asymmetrical synform in the northern part of the FTB (Fig.

1). We combine existing maps (Valdiya, 1980) with new field data and construct a schematic

cross section (Figs. 2 and 3) to reassess stratigraphic and structural configurations. Rocks include

quartzite, hornblende-biotite schist, chlorite-muscovite-biotite schist, tuffaceous (sercitic) schist, and biotite-augen gneiss. The core of the klippe exposes the Askot granite (Valdiya, 1980), an alkali granite-granodiorite gneiss (GG, Fig. 4a) with an L-S tectonite fabric. Major oxide geochemical data (Rao and Sharma, 2009) indicate a metaluminous composition. Himalayan deformation altered the primary contact between the central GG gneiss and the underlying supracrustal rock. Consequently, Valdiya (1980) interpreted the base of the GG gneiss as a ductile shear zone – the Askot thrust – and correlated it with the Almora thrust to the south

(which carries GHS rock in its hanging wall; Mandal et al., 2014). According to Valdiya (1980),

the Askot thrust was emplaced on Berinag Formation quartzite, a Paleoproterozoic LH unit.

However, our mapping and cross-section (Figs. 2 and 3) reveal that the klippe is bounded to the

south and north by a structurally lower, folded thrust that places older Berinag Formation

quartzite at the base of the Askot klippe atop younger carbonaceous phyllite of the Mandhali

Formation (Fig. 4b; locally known as Tejam phyllite, Valdiya, 1980). The folded basal thrust is

the Berinag thrust, and it controls the geometry of the klippe. Our field mapping shows that the

southern contact between the GG augen gneiss and the underlying mica schist is sheared (Fig.

4c). The southern limb of the klippe dips north at an average angle of 35°, whereas the northern

limb is overturned to steeply south-dipping.

Lithologically, the lower part of the klippe consists of clean cross-bedded quartzite (Fig.

4d) with subordinate schist whereas the upper part is dominated by light colored, sericitic schist

Figure 2. Geological map of the Askot klippe. Geology draped over terrain model. A-A/ is the cross-section line for Figure 3. Abbreviations: BT-Berinag thrust; SCT: South Chiplakot thrust. Roads are shown with white lines.

Figure 3. Schematic cross-section (VE=1) of the Askot klippe along A-A’ in Figure 2.

Fig. 4e), i.e. the overall sequence fines upward. Both the quartzite and schist are intruded by mafic sills (Fig. 4f), which are strongly foliated in places to form chlorite-biotite schist. Mafic

(amphibolite) sills are more concentrated upwards (Fig. 2). In the upper part of the sequence

(Fig. 2), a biotite augen gneiss contains abundant “quartz eyes” (Fig. 5) in both hand specimen and thin section, and also exhibits some compositional layering (Fig. 5). This augen gneiss is intercalated with meta-pelites (mica-schist) and minor quartzite/sericitic quartzite. Valdiya

(1980) mapped the supracrustal rock of the klippe as the Saryu Formation and correlated the rocks with those in the Almora klippe based on lithologic and metamorphic similarities.

The Askot klippe hosts a VMS (Fig. 6) base metal deposit (Boswell, 2006) within the tuffaceous schist, chlorite-sericite-biotite schist and biotite-augen gneiss. These rocks are characterized by intensive wall rock alteration with pink-orange weathering surfaces (Fig. 6).

Chalcopyrite, galena and sphalerite are major ore mineral assemblages, with minor amounts of pyrhotite, and arsenopyrite (Bosewell, 2006). Mineralization forms massive, lenticular sulphide lenses with an average thickness of 2.5 m and runs for a strike length of 645 m (Bosewell, 2006).

Figure 4. Field photos of the Askot Klippe rocks. (a) alkali granite-granodiorite (GG) gneiss from the central part of the klippe with ductily deformed k-spar porphyroclast, 2 cm coin for scale. (b) Exposure of Berinag thrust that placed Berinag Formation quartzite on top of the Mandhali Formation phyllite to the south of the klippe, person for scale. (c) Sheared contact of foliated granite augen (GG) gneiss and muscovite-biotite (MS) schist, 32 cm long hammer for scale, aligned parallel to the foliation plate. (d) Cross bedded very coarse-grained clean quartzite, 15 cm ruler for scale from the southern part of the klippe. (e) Chlorite-biotite schist, the host rocks for mineralization, from the underground mine, 15 cm ruler for scale. (f) Interlayered thin- bedded quartzite (Qtz) and amphibolite (amp) sill from the northern part of the klippe. 32 cm hammer for scale.

Figure 5. (a) and (b) Drill core sample of the augen gneiss. (c) Thin section photomicrograph showing “quartz-eyes” of probable sedimentary or felsic volcanic rock precursor. Quartz and feldspar grains are up to 5-7 mm long. Quartz grains are strained and alkali feldspar altered into sericite. Both quartz and alkali feldspar phenocrysts are set in a quartzose rich matrix with subordinate muscovite.

Figure 6. Underground exposure of the massive sulphide with pink-orange oxidation stains, in the Askot underground mine. 30x2.5 cm2 hammer head for scale.

3.6. Analytical Methods

Two igneous (IZ: SM11-028, SM10-026) and one detrital (DZ: SM11-021) samples were

collected from granite-granodiorite (GG) gneiss, biotite-augen gneiss and quartzite unit of the

klippe (Fig. 2, Table 1). We collected four 1-2 kg rock samples and separated zircons following

standard methods by using a jaw crusher, disk mill, water table, magnetic separator, and heavy

liquids. A split of the zircon grains was mounted in epoxy together with Sri Lanka and R33 zircon standards. These mounts were sanded down approximately halfway through individual

zircon grains and then imaged using backscattered electrons and cathodoluminescence (CL) at

the University of Arizona.

3.6.1. U-Pb Zircon Geochronology

U-Pb ages of in-situ zircon grains were collected using the Nu HR ICPMS at the

University of Arizona Laserchron Facility following methods described in Gehrels et al. (2006,

2008; Supplementary Table 1). The analyses involve ablation of zircon with a 193nm ArF

excimer laser (Photon Machines Analyte G2) using a spot size of 30 μm. For detrital zircon

sample SM10-021 approximately 100 grains were analyzed. Analyses with > 10% discordance

were rejected. The resulting ages were plotted using Isoplot 4.15 (Ludwig, 2003) to generate U-

Pb probability density distributions and Concordia diagrams, and to estimate weighted mean

ages. The age-probability diagrams were constructed by assigning a normal (Gaussian)

distribution to each analysis based on the reported age and the uncertainty, and also by summing

the probability distribution of every acceptable analysis into a single curve. Each set of 5

analyses of unknowns was bracketed by analyses Sri Lanka zircon standard, with a known age of

563±3.2 Ma (2σ error). At the middle and end of each sample, two R33 zircon standards with

known age of 419.3±0.4 Ma (Black et al., 2004) were also analyzed. Data reduction procedures

follow Gehrels et al. (2008), and analyses were rejected with (1) high 204Pb, (2) low 206/204Pb ratio, (3) greater than 5% error on 206Pb/207Pb age, (4) greater than 10% error on the 206Pb/238U

date, (5) greater than 25% normal discordance, (6) high U concentration, or (7) anomalously

high U/Th ratio. The best ages of detrital zircons were selected following Gehrels et al. (2011).

206Pb/207Pb ages were used as best ages if the grain was older than 1400 Ma, whereas 206Pb/238U ages were used for grains younger than ca. 1400 Ma. We report uncertainties only for analytical precision. Age accuracy, as reflected in the reproducibility of standards, is not better than ~±1% for 207Pb/206Pb, or ±15-20 Ma for our samples and ~±2% for 206Pb/238U.

3.6.2. Lu-Hf Isotopic Analysis

U-Pb dating of zircons can provide valuable insights into the provenance of rocks,

paleogeographic reconstructions, and magmatic events in the source area; however, this

technique can neither distinguish grains with similar ages derived from different sources, nor

provide any information on whether the crust is juvenile or reworked. Combining U-Pb dating

and Hf analysis provides valuable information about the petrogenetic character and ages of each

zircon's parental magma to make such distinctions (Amelin et al., 1999, 2000; Harrison et al.,

2005; Belousova et al., 2006) in geologically complex regions and to discriminate similar-aged

zircon populations derived from different source areas (e.g., Howard et al., 2009; Davis et al.,

2010). Whole rock Sm-Nd systematics provide analogous information (Vervoort and Blichert-

Toft, 1999), but less variable176/177Hf values than 143/144Nd ratios in the mantle permit less

ambiguous interpretations (Clements et al., 2012). High Hf content, low Lu/Hf ratio and physical

resilience to sedimentary recycling and high-grade metamorphism make zircons amenable for Hf

isotopic analysis (Kemp et al., 2009a). Therefore, combined zircon U-Pb and Hf-isotope studies

of zircons results in detailed crustal-evolution models and sedimentary provenance

interpretations (Belousova et al., 2006; Hawkesworth et al., 2009; Kaur et al., 2011, Zhou et al.,

2011; Ravikant et al., 2011; Clements et al., 2012 and references therein). In general, zircons

derived from juvenile crust vs. reworked continental crust will yield positive vs. negative εHf

values, and zircons derived from a mixed melt of depleted mantle and continental crust

(contaminated magma) will have intermediate εHf values (Faure and Mensing, 2005).

In this study, we collected Lu-Hf analyses (Supplementary Table 2) with the same Nu

HR ICPMS using a 40 μm spot size with the ablation pits located on top of the U-Pb analysis

pits. CL images were taken to ensure that the ablation pits do not overlap multiple age domains

or inclusions. After every 10 to 15 unknowns one standard was analyzed; these standards are

Mud Tank, 91500, Temora, R33, FC52, Plesovice, and Sri Lanka. Uncertainty in 176Hf/177Hf was c. 0.00007 (2) or ~±2.5 epsilon units. Using a 176Lu decay constant of 1.867x10-11 a-1 (Scherer et al., 2001; Söderlund et al., 2004), the 176Hf/177Hf at time of crystallization was calculated from

measurement of present-day 176Hf/177Hf and 176Lu/177Hf and the age of the corresponding spot.

These data represent one of the few combined U-Pb geochronological and Hf isotopic studies of

zircons in the Himalaya (Richards et al., 2005; Ravikant et al., 2011; Spencer et al., 2012a).

3.6.3. Trace Element Geochemistry

Four representative whole rock granitoid and metasediment samples of ~30 grams (Table

1) were analyzed to obtain REE and trace element concentrations. Fresh rock samples, without any signs of weathering, were cut, rinsed in acetone and 2 M HCl before jaw crushing, and then, powdered using a ring-and-puck mill. Sample powders were mixed with doubly distilled HF acid in PFA vials for total dissolution following the procedure in Stowell et al. (2010). Finally, the resulting solutions were diluted in doubly distilled nitric acid for analysis on the Perkin Elmer

Elan 6000 ICP-MS at the University of Alabama.

Solution concentrations obtained from ICPMS analyses were converted to dry weight

concentrations based on the weight of sample used during dissolution and normalized to

chondrite (McDonough and Sun, 1995). Accuracy was monitored based on standard solutions

from CPI International (SM4400-080324BD01) and High Purity (SM-1013-004). The precision

of REE and trace element data is better than 5%, except La (>9%), and Hf (>9%).

3.7. Results

3.7.1. U-Pb Zircon Geochronology

Sample SM11-028 is an alkali GG augen gneiss from the central part of the klippe (Fig.

2), which was dated by Bhanot et al. (1980) with a whole rock Rb-Sr age of 1983±80 Ma. A

higher precision age for this GG gneiss is necessary to assign tectonostratigraphic affinity of the

Askot klippe and interpret the associated ore deposits. Zircons from this augen gneiss are prismatic (Fig. 7) with oscillatory zoning and contain low to high U concentration (~400-1600 ppm, one grain 2744 ppm). U/Th ratios of zircons from this igneous sample range from 3.7 to

23.4 with an average of 9.9. We obtained coherent analyses tightly clustering on or around

Concordia with an upper intercept of 1855.9±2.1 Ma and a lower intercept of 40±5.3 Ma (Fig.

8a). Weighted mean of 20 ages (>90% concordance) is 1856.6±1.0 Ma (n=20, MSWD=3.8,

Fig.8b) suggesting a crystallization age with no inherited cores.

Sample SM10-026 is a biotite augen gneiss (Fig. 9a) and is the host rock for

mineralization from the upper part of the supracrustal/metasedimentary sequence. A precise age

helps determine its relationship with the GG augen gneiss (sample SM11-028) and

mineralization. Zircons from this sample are prismatic with oscillatory zoning (Fig. 7),

confirming an igneous origin, and contain low to moderate U concentrations (~176-712 ppm,

one grain 1094 ppm). U/Th ratios of zircons from this igneous sample range from 1.4 to 13.4, with an average of 3.3. We obtained two age populations with high concordance (>90%), one with a weighted average age of 1869±12 Ma (n=12, MSWD=0.004, Fig. 9b) and the other with a weighted average of 1658±19 Ma (n=6, MSWD=052, Fig. 9c). One inherited core (SM110026-

3C, Supplementary Table 1) yielded an age of 2257.2±10.3 Ma (98% concordance).

Table 1: Analyzed geochemical sample locality information

Sample No Coordinates Lithology Analysis

0N (dd.dddd) 0E (dd.dddd) SM10-021 29.7627 80.3474 Bedded quartzite U-Pb-Hf (DZ) SM10-026 29.7581 80.3314 Biotite-augen gneiss U-Pb-Hf (IZ), and trace elements SM11-027 29.7560 80.3350 Chlorite-biotite- Trace elements muscovite schist SM11-028 29.7607 80.3187 Granite-granodiorite U-Pb-Hf (IZ) and (GG) gneiss trace elements SM11-009* 29.2149 80.0544 Granite-granodiorite U-Pb-Hf (IZ) and (GG) gneiss from trace elements Ragarh Thrust sheet SM11-022* 29.5137 80.1289 Beeded muddy U-Pb-Hf (DZ) quartzite

SM11-004* 29.1883 80.0918 Bedded clean U-Pb-Hf (DZ) quartzite with penecontemporaneous mafic sills

DZ= detrital zircon, IZ= igneous zircon, *= U-Pb ages published in Mandal et al. (2014).

Figure 7. CL images of igneous zircons from the Askot klippe. Solid circles represent position of U-Pb laser spot with 207Pb/206Pb ages and 1σ error, and dashed circles represent position of Lu-Hf laser spot (sample Sm11-028) with initial 176Hf/177Hf calculated using Pb-Pb age obtained from the same spot.

Sample SM10-021 (Fig. 2) is from a thick bedded Berinag Formation quartzite towards the base of the Askot klippe. Uranium content of these zircons ranges from 110-3435 ppm with an average of 794 ppm, and U/Th ratios of zircons range from 0.7 to 18.0, with an average of

3.7. The age spectra have a strong peak around ca. 1860 Ma, with a small peak around 2500 Ma.

The age distributions (Fig. 10) show that 77% of the zircons range between 1750-1900 Ma. This sample contains no grains younger than 1771±2.2 (86% concordance). Analyses of zircons from this sample yielded 91 usable dates. The weighted mean of three younger zircons is 1772±17

(MSWD=15). We add the uncertainty and round up to the nearest 10 Ma following the technique

of Martin et al. (2011). Thus, we interpret ca. 1800 Ma as the maximum depositional age of the

Berinag Formation quartzite from the klippe.

Figure 8. (a) U-Pb Concordia plot of sample SM11-028 Alkali granite-granodiorite (GG) gneiss from the central part of the klippe. (b) Weighted average age of the same sample suggesting a crystallization age for this GG gneiss.

Figure 9. (a) U-Pb Concordia plot for sample SM11-026 biotite-augen gneiss, the host rock for mineralization. (b) and (c) Weighted average age plots for the ca. 1600 Ma and ca. 1800 zircon populations. The crystallization age, 1869±12 Ma, correspond to age of existing continental arc to the northern margin of NIB, whereas, the age of 1658±19 Ma correspond the age of hydrothermal ore deposit formation of the Askot klippe.

Figure 10. Relative age probability plot and pie chart distribution of the sample SM10-021, a quartzite unit from the klippe, showing distribution of various age populations.

3.7.2. Zircon Lu-Hf Isotopes

We analyzed 5 samples, SM11-004 (DZ), SM10-021 (DZ), SM11-022 (DZ), SM11-028

(IZ) and SM11-009 (IZ) for Lu-Hf. U-Pb zircon data of samples SM11-004 (max. depositional

age ca. 1860 Ma), SM11-022 (max depositional age ca. 1780 Ma) and SM11-009 (crystallization

age 1866±1.7 Ma) were published in Mandal et al. (2014). 176Hf/177Hf (T) of the GG gneiss ,

SM11-028, ranges from 0.281457 to 0.281563, with an average of 0.281525, and εHf (T) value

ranges from -5.5 to -1.2 (T=1850 Ma, no inherited core), with an average (n=12) of -2.7. Sample

SM11-009 (Fig. 1) is from ca. 1850 Ma Debguru porphyry (a Paleoproterozoic augen gneiss),

from south of the Almora klippe on the Ramgarh-Munsiari thrust hanging wall. 176Hf/177Hf (T) of sample SM11-009 ranges from 0.280865 to 0.281538, with an average of 0.281403, and εHf

(T) values of ca. 1850 zircon ranges from -4.8 to -2.2, with an average (n=7) of -4.0. One inherited core with a crystallization age of 2193±58 (93% concordance) yielded an εHf value of -

18.3.176Hf/177Hf (T) of sample SM10-021 ranges from 0.280969 to 0.281562, with an average of

0.281360. εHf values of ca. 1850 zircon ranges from -9.6 to -1.1, with an average of -4.5. ε(T)

values of ca. 2500 Ma zircons ranges from -7.3 to 4.9, with an average of -3.8.176Hf/177Hf (T)

values of sample SM10-022 from the Rautgara Formation quartzite ranges from 0.280838 to

0.28942, with an average of 0.281462. εHf (T) values of ca. 1850 zircon ranges from -15.1 to

7.6, with an average of -2.9, whereas εHf of ca. 2500 zircon ranges from -12.1 to 6.1. Two zircon

grains of this sample (SM11-022) have εHf (T) values of -9.7 (T=2205 Ma) and -1.2 (T=1546).

3.7.3. Trace Element Geochemistry

Four samples, SM11-009, SM10-026, SM11-027 and SM11-028, were analyzed for trace

element geochemistry to determine the petrogenesis of the granitoids and to trace the provenance

of the metapelites (SM11-027). All trace element data are in Table 2. Chondrite-normalized rare

earth element (REE) data show relative enrichment in LREE with (La/Yb)N values of 11.3-19.0

(Fig. 11a). The strong enrichment of lighter trace elements and LREE indicates a continental crustal source. All samples exhibit negative Eu anomalies [(Eu/Eu*)N= 0.18-0.82], suggesting either residual plagioclase during fractional melting or plagioclase fractionation during crystallization.

A primitive mantle-normalized trace element plot (Fig. 11b) shows pronounced negative

Ti, Nb, Sr and Zr anomalies and high LIL/HFSE ratios. This suggests that granitoids and source

rocks of the metasediments were formed in a continental arc, possibly through remelting of pre- existing continental crust.

Table 2. Whole rock REE and trace element compositions

Analyte SM11-009 SM10-026 SM11-027 SM11-028 Rb 121.42 141.89 211.48 520.25 Y 32.99 27.10 37.90 19.16 Zr 13.28 5.97 2.29 0.80 Nb 18.60 11.40 13.86 12.44 La 70.09 46.66 70.09 17.11 Ce 121.46 81.21 94.57 33.56 Pr 13.75 9.16 13.12 3.76 Ce 121.98 83.11 94.69 33.62 Nd 49.39 33.24 48.10 13.18 Eu 1.12 0.94 1.67 0.18 Sm 9.07 6.07 8.72 3.40 Eu 1.14 0.96 1.70 0.19 Gd 3.64 2.90 4.36 2.47 Tb 0.94 0.72 0.97 0.62 Dy 6.36 4.97 6.84 3.91 Ho 1.20 0.97 1.36 0.63 Er 2.99 2.54 3.68 1.45 Tm 0.44 0.38 0.55 0.19 Yb 2.50 2.24 3.33 1.02 Lu 0.33 0.30 0.44 0.11 Th 31.63 22.05 16.69 19.56 U 9.40 4.65 3.48 7.69 Hf 0.57 0.27 0.09 0.05 Nb 17.80 13.54 13.64 11.46 (Eu/Eu*)N 0.59 0.68 0.82 0.18 (La/Yb)N 19.03 14.16 14.31 11.39

Figure 11 (a) Normalized REE plot of granitoids and metasediments showing LREE enrichment, Eu anomaly and flat HREE pattern. (b) normalized spider diagram showing pronounced negative Ti, Nb, Sr and Zr anomalies and high LIL/HFSE ratios.

3.8. Discussion

3.8.1. Stratigraphic Affinity of the Askot Klippe

U-Pb zircon geochronology is applied to characterize Himalayan tectonostratigraphy,

trace sediment provenance and pathways, date volcano-magmatic events, and determine

reasonable pre-deformational paleogeographic reconstructions through matching zircon ages of

source terranes (DeCelles et al., 2000; Myrow et al., 2003; Martin et al., 2005, 2011; Gehrels et al., 2006, 2011; Cawood et al., 2007; McQuarrie et al., 2008; Célérier et al., 2009; Kohn et al.,

2010; Long et al., 2011; McKenzie et al., 2011; Webb et al., 2011; Spencer et al., 2012).

Pronounced differences in depositional ages and spatial association of ca. 1850 Ma granitoids can discriminate Paleoproterozoic inner LH rocks from Neoproterozoic to Cambrian GH/outer

LH rocks (Ahmad et al., 2000; DeCelles et al., 2000; Richards et al., 2005; Tobgay et al., 2008;

McKenzie et al., 2011; Long et al., 2011).

The GG gneiss, sample SM11-028, from the central part of the Askot klippe (Fig. 2) yields a crystallization age of 1856.6±1.0 Ma (Fig. 8), similar to the previously reported ca. 1850

Ma granite-granodiorite plutons (Kohn et al., 2010 and references therein) associated with the inner LH rocks along the Himalayan arc. This sample plots within the volcanic arc or syn- collisional field in the trace element tectonic discrimination diagram (Fig. 12), similar to other

Askot gneisses (Rao and Sharma; 2009). εHf(T=1850Ma) values of this GG gneiss, range from -1.2 to – 5.4 (See Supplementary Table 1). This rock is strikingly similar to the Debguru porphyry

(SM11-009), a granodiorite gneiss in the Ramgarh-Munsiari thrust hanging wall (Fig. 1), south of the Almora klippe, with crystallization age of 1852.3±7 Ma (Mandal et al., 2014). SM11-009 has εHf (T=1850Ma) values of -2.3 to -4.9, and also plots within the volcanic arc or syn-collisional field in the tectonic discrimination diagram (Fig. 12). Therefore, we interpret that these ca. 1850 granitoids plutons are intruded into older sections of the Berinag, Munsiari and Ramgarh

Formations and that these rocks units are all equivalent just currently residing on different thrust sheets, the Ramgarh-Munsiari thrust, and the Berinag thrust. These Paleoproterozoic granitoids were once part of the NIB’s northern margin continental arc; however, this arc is now dissected because of Cenozoic Himalayan thrusting.

Figure 12. Trace element discrimination diagrams, showing syncollisional/arc-related source of these samples.

Sample SM10-026 (Figs. 5and9) is from the upper part of the supracrustal sequence mapped as biotite augen gneiss (Fig. 2). Presence of abundant “quartz eyes” and prismatic zircons with distinct oscillatory zoning within this sample suggest that it may be a metamorphosed felsic volcanic rock, which yielded a crystallization age as 1869±12 Ma. Similar

(1840±16 Ma) ages are reported by Miller et al. (2000) from a rhyodacite within the Rampur

Formation, a stratigraphic equivalent of Berinag Formation quartzite. Thus, we this felsic volcanic rock is at least coeval and likely comagmatic with the ca. 1850 Ma plutons that occur

within the inner LH rocks.

The Berinag Formation quartzite, sample SM10-021 (Fig. 2), from the lower part of the

Askot Klippe, yields Paleoproterozoic ages with no grains younger than 1771 Ma and ~77% of

zircons are between 1771-1900 Ma (Fig. 10). The pronounced age peak at ca. 1865 Ma (Fig. 10)

matches the age of the felsic volcanic rock (SM10-026), though older zircons (ca. 2500 Ma)

represent 14% of the zircons. We assigned a maximum depositional age of ca. 1800 Ma. A

similar ca. 1800 Ma quartzite is reported from inner LH rocks along the Himalayan arc

(DeCelles et al., 2000; Richards et al., 2005; Célérier et al., 2009; McKenzie et al., 2011; Long et

al., 2011; Spencer et al., 2012). εHf values of ca. 1850 Ma zircons (-9.6 to -1.1, with an average

of -4.5) overlap with the εHf value of continental arc origin GG augen gneiss of the Askot klippe

(SM11-028, εHf:-5.5 to -1.2, with an average of -2.7) and of the Debguru porphyry (SM11-009,

εHf: -4.8 to -2.2, with an average of -4.0), suggest a proximal arc source. Presence of a

tuffaceous (sericitic) schist within this unit further suggests a volcanogenic source. “Munsiari”

rocks have also been ascribed to a volcanic source (Kohn et al., 2010). Similar REE trends

among the GG gneiss, augen gneiss, and metapelites, which is interbedded with the quartzite,

provide further support a proximal arc source of the Berinag Formation quartzite, the basal unit

of the inner LH rocks (Fig. 11).

Older zircons (ca. 2500 Ma) with εHf values ranging from -7.3 to -2.1 (Fig. 14b) indicate

derivation from reworked Archean NIB, which experienced major crustal reworking and copious

granite magmatism at ca. 2500 Ma (Mondal et al., 2002). Similar εHf values for the1856.6±1.0

Ma Askot GG gneiss (SM11-028), ca. 1850 Ma zircon grains of quartzite sample SM10-021(-5.5

to -1.2), Wangtu orthogneiss (-0.9 to -2.8), and Rampur Formation metasediments (-1.5 to -3.7,

Richards et al., 2005) from the Sutlej Valley confirm a strong stratigraphic affinity of the Askot

klippe with other inner LH rocks. Pre-1900 Ma zircons grains from the Berinag Formation

quartzite of the Askot klippe, however, contrast with the Munsiari Formation northwest of the present study area, which lacks pre-1900 Ma grains (Spencer et al., 2012a).

Miller et al. (2000) report an 1800±13 Ma zircon evaporation age of a metabasalt sill from the Rampur Formation quartzite (equivalent of Berinag Formation quartzite). Similar mafic sills and dikes are mapped within the Berinag Formation quartzite in the Askot klippe. These

mafic sills may signal the onset of continental extension, implying some portions of the Berinag

Formation must have been deposited before ca. 1800 Ma.

Presence of ca. 1850 Ma GG gneiss and Paleoproterozoic inner LH rocks within the

Askot klippe suggest that it is the southern continuation of the Munsiari Formation (Valdiya,

1980). However, we argue that the both GG gneiss and underlying supracrustal rocks together constitute the klippe and are not separate tectonostratigraphic units, although some have mapped the Askot thrust between them (Valdiya, 1980; Célérier et al., 2009). In addition, the Askot klippe should not be correlated with the Almora klippe to the south. The latter is associated with

Cambro-Ordovician granite, is composed of Neoproterozoic metasedimentary rocks, and has

distinct Nd isotopic and U-Pb zircon signatures (Mandal et al., 2014), so must be GH not LH

rocks.

The 1856.6±1.0 Ma Askot GG gneiss and coeval ca. 1850 Ma GG gneiss are probably

shallow plutons at the base of the NIB’s northern margin Paleoproterozoic cover sequence. The

profuse ca. 1850 Ma felsic magmatic event links to the amalgamation of the Paleo-

Mesoproterozoic supercontinent “Columbia” (Rogers and Santosh, 2002; 2009; Zhao et al.,

2004; Hou et al.,2008; Kohn et al., 2010) to the northern margin of the NIB. However, we argue

that the GG gneiss is not a part of the NIB’s basement (Célérier et al., 2009a) sensu stricto,

which instead is tonalitic-trondjhemitic (TTG) in composition with an age of 2.49 Ga (Mondal et al., 2002).

Figure 13. Composite U-Pb detrital zircon normalized age spectra of Paleoproterozoic inner Lesser Himalayan rocks in NW India. All other data are compiled from McKenzie et al. (2011); Spencer et al. (2012), Mandal et al. (2014). The number (n) indicates the total number of zircon grains analyzed. Note the strong peak at ca. 1850 Ma, corresponds to continental arc related magmatism to northern margin of NIB.

Figure 14.(a) Plot of 176Hf/177Hf versus U-Pb ages of zircons for the inner LH metasediments and granitoids, and metasediments from Aravalli Supergroup. (b) Plot of εHf versus U-Pb ages of zircons from Askot klippe, other inner LH and Aravalli Group metasediments (Kaur et al., 2013).

3.8.2. Implications of U-Pb Geochronologic and Hf Isotopic Data on Paleoproterozoic Crustal

Evolution of the Northern Margin of the NIB

Combining U-Pb zircon ages with Lu-Hf data helps establish the Paleoproterozoic evolution of the NIB’s northern margin (inner LH; Richards et al., 2005; Spencer et al., 2012; this study) and its western margin (the Delhi-Aravalli orogenic belt; Kaur et al., 2013). Kaur et al. (2013) correlate the Paleoproterozoic crustal evolution of the Delhi-Aravalli orogen with inner LH rock based on one sample of the Munsiari Formation that has no pre-1900 Ma grains

(Spencer et al., 2012a). A composite normalized-probability detrital zircon age plot of inner LH

rock (Fig. 13) yields a strong peak at ca. 1850, suggesting that the Berinag Formation (SM10-

021, this study; CV1 and NDIC from McKenzie et al., 2011), Munsiari Formation (GH 74,

Spencer et al., 2012) and a Paleoproterozoic quartzite (SM11-004, Mandal et al., 2014; locally

known as Bhowali quartzite but mapped by Valdiya, 1980, as Neoproterozoic Nagthat quartzite)

were receiving detritus from proximal ca.1850 volcanic or plutonic sources. Only the Munsiari

Formation in Garhwal is devoid of any pre-1900 Ma grains, suggesting that using the Munsiari

Formation alone for crustal evolution correlation studies misrepresents age and isotopic age

signals. A wide range of negative εHf values of ca.1850 zircons (SM11-022, -15.0 to -1.6,

SM10-021, -9.1 to -1.1) suggests a heterogeneous crustal source. This more comprehensive Hf

isotopic dataset for ca. 1850 Ma inner LH rocks (Berinag/Munsiari Formation) and pre-Delhi

(Aravalli) quartzite (Fig. 14b), corroborate previous inferences of similar crustal sources (Kaur et

al., 2013). Negative εHf values for zircons from the Munsiari Formation and ca. 1850 Ma

granitoids (SM11-028 and SM11-009, Fig. 14) suggest that pre-existing crust underwent crustal

reworking at ca. 1850 Ma.

Positive and negative εHf values of ca. 2500 Ma zircons from inner LH and Aravalli

rocks are consistent with shared, heterogeneous sources, including contributions of juvenile and reworked material (Fig. 14). Younger (ca. 1600 Ma) zircons from the Paleoproterozoic Rautgara

Formation quartzite (SM11-022: -17.2 to 7.5) also show positive to negative εHf (Fig. 14), again

suggesting juvenile and reworked components. Overall, ca. 1850 Ma zircons are consistent with

reworking of pre-existing crust along both the northern and western margins of the NIB, whereas

older and younger zircons suggest additional juvenile mantle contributions, possibly under a

different tectonic regime.

3.8.3. Askot Volcanogenic Massive Sulphide Deposit

Mineral deposits help to determine the tectonic setting, evolving environmental conditions, and changes in Earth’s thermal history. Supercontinent cycles can be correlated using the distribution of the ore deposits because tectonic settings of ore deposits are tied to plate margin processes (Cawood and Hawkeswoth, 2014). The Askot klippe hosts a VMS deposit and thus, serves as a proxy for the tectonic environment, as VMS deposits forms in extensional tectonic settings including back arc basins and the margins of volcanic arcs and mid-ocean ridges

(Galley et al., 2007; Huston et al., 2010). The Askot VMS deposit is located on the northern limb of the Askot syncline (Fig. 2) and is hosted within the upper part of the supracrustal sequence, i.e., chlorite-biotite-muscovite schist, tuffaceous (sericitic) schist, and biotite-augen gneiss. This deposit is spatially associated with the 1856.6±1 Ma Askot GG gneiss that occupies the core of the klippe (Fig. 2). The trace element composition of the gneiss suggests it formed in a volcanic arc or syn-collisional tectonic setting (Fig. 12). Similar REE trends and trace element ratios in granitoids, augen gneiss (felsic volcanic rocks) and metapelites (Figs. 11 and 12) suggest proximal sources for Paleoproterozoic metasediments of the basal unit of the inner LH rocks.

Given these lithologies and geochemical characteristics, we rule out a mid-ocean ridge as a tectonic environment for the formation of this deposit and consider other tectonic scenarios.

The biotite-augen gneiss (sample SM10-026), one of the mineralized host rocks, yields a crystallization age of 1869±12 Ma, suggesting that it is coeval/comagmatic with the Askot GG gneiss (1856.6±1 Ma). This biotite augen gneiss probably has an altered volcanic precursor, as evident from: (1) presence of abundant “quartz eyes” (Fig. 5), (2) well developed prismatic zircons with oscillatory zoning (Fig. 7), and (3) igneous U/Th ratios (0.16 to 0.49, with one grain

0.07). Extensive sericitic alteration of feldspars indicates later hydrothermal alteration. We

assign the younger weighted age of 1658±19 Ma for 6 zircon analyses (Supplementary Table 2)

as the age of formation of the Askot VMS deposit in a locally extensional setting.

Our preferred tectonic model (Fig. 15) begins with a well-established, ca. 1850 Ma arc on

2.5 Ga rocks along the northern margin of the NIB (Fig. 15a; Kohn et al., 2010), followed by ca.

1800 and 1650 Ma extension. Extension may have developed in response to a switch in tectonic styles (termination of subduction) or slab roll back at ~1800 Ma (Fig. 15b), as indicated

by1800±13 Ma mafic sills (Miller et al., 2000), which are abundant within the Berinag

Formation and equivalent siliciclastics along the arc. Note that although Kohn et al. (2010)

argued for arc activity until 1780 Ma, age uncertainties allow termination of felsic arc

magmatism as early as 1800 Ma. Either back arc extension prevailed until 1658±19 Ma or a new

extensional event occurred at that time, forming the Askot VMS deposit. This age matches ca.

1650 Ma muscovite40Ar/39Ar ages (Sakai et al., 2013) from the inner LH Kuncha Formation in

Nepal, and granulite-facies zircon ages in the Delhi-Aravalli orogen (Roy et al., 2005). Shallow-

level ca. 1650 granite-granodiorite plutons probably drove magmatic hydrothermal systems (Fig.

15b).

The fining-up sequence of the Askot supracrustal metasediments indicates the basin

deepened progressively, culminating in the deposition of the ca. 1600 Ma Rautgara turbidite

(McKenzie et al., 2011; Mandal et al., 2014) towards the southern fringe of the back arc basin

(Fig. 15b). Extension is further supported by positive εHf (1.9 to 7.6) values from the 1600 zircons of Rautgara Formation quartzite (Fig. 14), which is indicative of the addition of juvenile crust. Kemp et al. (2009b) suggest that juvenile magmatic input can be enhanced during extensional, back arc rifting episodes that immediately follow crustal thickening, suggesting a relationship between slab rollback and continental growth.

In the Himalaya, apart from the Askot deposit, Paleoproterozoic VMS deposits occur at

Gorubathan (Darjeeling, West Bengal, India) and Rangpo (east Sikkim; Sarkar et al., 2000) that

are hosted within the siliciclastic-mafic dominated Paleoproterozoic basal unit of the inner LH

rock. The Rangpo VMS deposit is hosted within the Gorubathan sub-group of Paleoproterozoic

Daling Formation, the lower unit of the Daling-Shumar Group (McQuarrie et al., 2008). Host

rocks of Rangpo mineralization include chlorite-quartz schist, phyllite, quartz-sericite schist,

sericitic quartz schist and quartzite (Sarkar et al., 2000), similar to the arc derived sediments of

the Askot klippe. In addition, Rangpo and Gorubathan VMS deposits are spatially associated

with Lingtse gneiss, dated at ca. 1850 Ma (Mottram et al., 2014). The Rangpo VMS deposit is

interpreted to be of sedimentary diagenetic origin; however, its strong resemblance in lithology

and spatial association of ca. 1850 Ma arc related granitoids as is found in the Askot klippe leads us to reinterpret the Askot, Rangpo and Gorubathan as similar kinds of volcanogenic/volcanic- hosted sulphide deposits that formed at ca. 1650 Ma, hosted within the inner LH rock.

Figure 15. Schematic diagrams showing different stages of Paleoproterozoic tectonic evolution of the NIB’s northern margin (present day Himalaya) and formation of the VMS deposit. (a) margin at ca. 1850 Ma (b) margin at ca. 1600 Ma.

3.9. Conclusions

Integrated U-Pb geochronologic data, Hf isotopic data and whole rock trace element

geochemical studies coupled with detail mapping of the Askot klippe rocks leads to following

conclusions:

1) The Askot klippe consists of a 1856.6±1.0 Ma granite-granodiorite gneiss, coeval 1869±12

Ma felsic volcanic rock, and ca. 1800 Ma quartzite, and is a small vestige of a Paleoproterozoic

continental arc that formed on the northern margin of the northern Indian cratonic block as a part of the Paleo-Mesoproterozoic supercontinent, Columbia. Overlapping 1850 Ma ages and

εHf(T=1850) values suggest Askot klippe rocks correlate with Munsiari Formation rocks to the

north. These same rocks are exposed further south underneath the Almora klippe as the

Ramgarh-Munsiari thrust sheet.

2) The Paleoproterozoic crustal evolution of the north Indian cratonic block’s northern margin in

Paleoproterozoic and Archean time is strikingly similar to that reported from Delhi-Aravalli

orogen along the western margin of the north Indian cratonic block’s, evident from a

preponderance of ca. 1850 Ma ages and similar ranges of εHf values. These data whic suggest a

much older crust (ca. 2.5 Ga) was reworked at ca. 1850 Ma.

3) An extensional event initiating as early as 1800 Ma is recorded in abundant mafic sills and

dikes intruding upper Berinag Formation quartzites. This event could reflect a tectonic switch

from subduction to extension, or continued subduction with regional back-arc extension.

4) Around 1650 Ma, widespread extension occurred, evident from : (a) addition of juvenile crust

at ca. 1650 Ma, and (b) mafic sills in the ca. 1650 Ma Rautgara Formation, and (c) extension

related volcanogenic massive sulphide deposits along the Himalayan arc.

5) The Neoarchean and Paleoproterozoic northern Indian margin had very heterogeneous crustal

assemblages as is evident from the large range of εHf values (7.5 to -18.1).

3.10. Acknowledgements

This project was funded by the National Science Foundation (EAR0809405, DMR;

EAR0809428, EAR1048124, and EAR1321897, MJK), and by the Society of Economic

Geologists Foundation’s Hugh E. McKinstry Student Research Grant (SM). Mandal thanks the

Graduate School and the Department of Geological Sciences, University of Alabama for travel

support to carry out the field work and U-Pb zircon geochronologic analyses. Mark Pecha, Nicky

Giesler, and Mauricio Ibanez are thanked for their help during U-Pb and Hf analysis of zircons at

the Arizona Laserchron Facility (NSF EAR 1032156). We thank Sidhartha Bhattacharyya and

Harold Stowell for helping in whole rock geochemical analysis at the University of Alabama.

Finally, we thank Andrew Nevin, Gyan Singhai and Barun Kumar of Pebble Creek Limited of

Canada and owner of the Askot Deposit for their kind help and giving permission to conduct this

study.

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CHAPTER 4:

UPPER CRUSTAL STRUCTURE AND SHORTENING ESTIMATE FROM THE HIMALAYAN FOLD THRUST BELT IN KUMAUN, NORTHWEST INDIA

4.1. Abstract

In the Himalayan fold-thrust belt of northwest India, a revised chronostratigraphy, new mapping and structural interpretations reveals that the thrust system is a forward propagating system and contains a hinterland dipping duplex composed of Lesser Himalayan rocks. A balanced cross section reveals that a total of 541-575 km or 79-80% of shortening was accommodated between Main Frontal thrust and South Tibetan Detachment system with each system accommodating the following minimum amount of shortening: the Main Central thrust-

163-128 km, Ramgarh-Munsiari thrust - 112 km, Lesser Himalayan duplex - 270 km, Main

Boundary thrust -8 km, Subhimalayan thrust system -~22 km. By adding in shortening from the

Tethyan Himalaya, we estimate a total minimum shortening of 674-751 km. The roof thrust, the

Ramgarh-Munsiari thrust, and the Lesser Himalayan duplex is breached by erosion separating the Paleoproterozoic Lesser Himalayan rocks of the Ramgarh-Munsiari thrust into isolated klippen. This thrust carries Lesser Himalayan rocks 120 km southward from the footwall of the

Main Central thrust, folded underneath the Almora klippe, to the hanging wall of the Main

Boundary thrust. The Ramgarh, Berinag, Chiplakot and Munsiari Formations are part of the same, once continuous stratigraphic unit, which was dissected and turned into the Ramgarh-

Munsiari thrust sheet and other thrust sheets in the Lesser Himalayan duplex because they are all

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Paleoproterozoic Lesser Himalayan rocks, they contain ca. 1850 Ma granite of continental arc affinity, and they have similar whole rock εNd values (-20 to -25).

The new geological observations, continuous and folded Ramgarh-Munsiari thrust structurally underlying the Main Central thrust acting as the coupled roof thrust, and the reconstruction demonstrate that the southward propagation was a key mechanism for the growth of the Himalaya, subsequent to the Early-Middle Miocene emplacement of mid-crustal Greater

Himalayan rocks in the form of channel.

4.2. Introduction

Continental lithospheric collision between India and Asia has occurred since ca. 55 Ma

(Najman et al., 2010 and reference therein) creating the Himalayan-Tibetan orogenic system.

The Himalayan fold-thrust belt (FTB) stretches for ~2,500 km along the southern edge of the

Tibetan Plateau from northern Pakistan to the Namcha Barwa syntaxis (Fig. 1a). This FTB consists of Paleoproterozoic to Cretaceous Greater Indian affinity upper crustal rocks, scraped off to form south vergent thrust sheets (e.g., Heim and Gansser, 1939; Gansser, 1964; LeFort,

1975; Mattauer, 1986; Hauck et al., 1998; Hodges, 2000). Although our understanding of the growth and kinematic evolution of this FTB has increased dramatically over the past 15 years, some regions still have outstanding questions due to the structural complexity, poor exposure, and lack of knowledge of the stratigraphic architecture. Moreover, most of the models for the evolution of the Himalaya emerge from pressure-temperature data of the high-grade metamorphic core, the Greater Himalayan rock, which occupies only 30% of the surface area of the Himalayan FTB (e.g., Yin, 2006; Célérier et al., 2009). A wide range of growth models and mechanisms exist to explain the tectonic development of the FTB (see review in Webb, 2013).

The channel flow model suggests southward flow of low viscosity mid-crustal material in the

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form of a ductile-channel in Greater Himalayan rocks, developed due to attainment of critical

crustal thickness in mid Miocene time as a result of focused denudation in the frontal part of the mountain belt (e.g., Nelson et al., 1996; Beaumont et al., 2001, 2004; Harris, 2007 and references therein). The critical taper model suggests that Greater Himalayan rocks may have flowed in the mid-crustal prior to be exhumed; however, since Early Miocene time, the FTB developed and propagated through frontal accretion, out of sequence faulting, and/or underplating (e.g.,

Schelling and Arita, 1991; Harrison et al., 1997; Avouac, 2003, 2007; Robinson et al., 2003,

2006; Bollinger et al., 2004; Konstantinovskaia and Malavieille, 2005; Wobus et al., 2005;

Robinson and Pearson, 2006; Kohn , 2008; Herman et al., 2010; Long et al., 2012). The tectonic wedge model assumes the South Tibetan Detachment system (STDS) is a backthrust of the Main

Central thrust (MCT), and continues to the north as Greater Counter thrust (GCT), recently proposed from studies in NW India and central Nepal (e.g., Yin, 2006; Webb et al., 2007; Kellett and Grujic, 2012; Webb, 2013).

Upper crustal shortening variations along the Himalayan arc provide data for testing predictions of how convergence is accommodated throughout the Himalaya, and the estimate of material available to construct the Tibetan Plateau (DeCelles et al., 2002). Amount of upper crustal shortening is equivalent to the length of subducted lower crust and mantle lithosphere of

Indian Plate (Robinson et al., 2006), and the shortening magnitude may control the width of the

Tibetan Plateau (DeCelles et al., 2002). This study reassesses the structural architecture and shortening estimates of the Himalayan FTB in Kumaun, northwest India with new structural data, new and available geochronology (Célérier et al., 2009; McKenzie et al., 2011; Mandal et al., 2014a and b) and existing geophysical data (Caldwell et al., 2013). Kumaun is a critical area to study the kinematic evolution and estimate maximum shortening because it is located in the

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central part of the Himalayan arc and may have accommodated the maximum amount of

shortening recorded in the Himalaya. The geochronologic and isotopic data determine the

stratigraphic architecture, solve first order stratigraphic issues, and evaluate existing cross-

sections in northwest India (Srivastava and Mitra, 1994; Célérier et al., 2009). A line-length

balanced cross section and palinpastic reconstruction provides a viable model for the structural

geometry, minimum slip along faults and a new estimation of minimum shortening in Kumaun

and correlation with other parts of the Himalaya. With the aid of revised chronostratigraphy, the

new structural interpretation of Kumaun, NW India, provides a foundation to test which growth

models better fits in this part of the Himalaya.

4.3. Geological Background

The Himalaya FTB (Fig. 1a) is composed of scrapped off Greater Indian pre-Cenozoic

northern margin rocks, which were deposited over the ca. 2500 Ma Indian basement. The Greater

Indian rocks were incorporated into the FTB as the locus of deformation gradually shifted toward

the south (DeCelles et al., 2001; Avouac, 2003; Robinson et al., 2003; 2006; Bollinger et al.,

2006; Kohn, 2008; Herman et al., 2010; Robert et al., 2011; Robinson and Martin., in review).

The Himalaya is divided into four tectonostratigraphic zones, which are from south to north, the

Subhimalaya (SH), Lesser Himalaya (LH), Greater Himalaya (GH) (synonymous with High

Himalayan Crystalline Series), and Tethyan Himalaya (TH) (Fig. 1b; Gansser, 1964; Lefort,

1975; Hodges, 2000; Yin, 2006). Each of these zones is characterized by a distinctive

stratigraphic and metamorphic grade, and separated from adjacent zones by major crustal scale

faults. The South Tibetan Detachment system (STDS) separates the TH from the GH. The Main

Central thrust/Vaikrita thrust (MCT/VT) separates the GH from the LH. The

Ramgarh/Munsiari/Berinag thrusts (RT/MT/BT) and Lesser Himalayan duplex (LHD) are

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intraformational faults within the LH rocks. The Main Boundary thrust (MBT) separates the LH

from the SH. The Main Frontal thrust (MFT) separates the SH from the Indo-Gangetic plain.

These faults sole down into Main Himalayan thrust (MHT), the basal décollement, at depth.The

SH zone is composed of the mid-Miocene to Pliocene Siwalik Group of synorogenic sediments

that were eroded from the adjacent Himalaya (Quade et al., 1995; DeCelles et al., 1998; Kumar

et al., 2003; Najman et al., 2004; 2008). The Siwalik Group is informally divided into lower,

middle and upper members (Tokuka et al., 1986; Harrison et al., 1993, Quade et al., 1995;

DeCelles et al., 1998a; 2001; 2004; Robinson et al., 2006). These synorogenic sediments

determine the uplift and exhumation history of the Himalayan mountain belt as well the

development of the peripheral foreland basins (DeCelles et al., 1998b; Najman et al., 2005; Bera

et al., 2008 and references therein). Pre-Siwalik Group foreland basin units (e.g.,

Subathu/Bhainskati, Dagshai-Kasauli/Dumri Formations) crop out intermittently in the hanging

wall of MBT in Nepal and Kumaun-Garhwal of NW India (Robinson et al., 2006; Srivastava and

Mitra, 1994). The LH zone is composed of the Paleoproterozoic-Cambrian unmetamorphosed to

greenschist facies sedimentary rocks and intrusives. The GH zone is composed of high-grade

(upper amphibolite to granulite facies) Neoproterozoic-Ordovician metasedimentary and meta-

igneous rocks (Parrish and Hodges, 1996; DeCelles et al., 2000; Yin, 2006; Cawood et al., 2007;

Gehrels et al., 2011) of mid-crustal affinity. GH rocks are intruded by Miocene leucogranite (see

Godin and Harris, 2014). The GH rocks may be simply the high-grade metamorphic equivalent

of the LH strata (Parrish and Hodges, 1996), may be equivalent to the Paleozoic TH (Myrow et

al., 2003) or may be an exotic terrane, not affiliated with the Indian craton, which amalgamated

onto the northern Indian margin during a Pan-African (500±50 Ma) orogenic event (DeCelles et

al., 2000).

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4.4. Mapping Methods

This study presents a high resolution geological map of Kumaun (Fig. 3) by integrating our field data with the published map of Valdiya (1980), which was georeferenced using

ArcMap 10.0TM, an ESRI mapping software package. A hill-shade map was created using

Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) Global Digital

Elevation Model Version 2 (GDEM V2) dataset (Data source: http://asterweb.jpl.nasa.gov/gdem.asp). The georeferenced map was draped over the hillshade map to cross check the georeferencing. Structural and lithologic mapping occurred at scales of

1:50,000 and 1: 100,000 along a north- to-south traverse ~150 km long between the STDS and the MFT. We incorporated the detailed maps of the Chilpakot klippe (Patel et al., 2007, 2011), the Askot klippe (Mandal et al. in review) and of the STDS (Patel et al., 2011) in our geological map (Fig. 3).

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Figure 1. (a) Digital elevation model (using ASTER Global digital elevation dataset) of India and adjoining areas. The Himalayan FTB is south of the Tibetan Plateau stretches along the arc for ~2,500 km. The red dash line delineates the present day northern limit of exposed the Indian craton, and pale pink areas represent basement ridges underneath the Indo-Gangetic plain (Godin and Harris, 2014). DH: Delhi-Haridwar Ridge; FB: Faridabad Ridge; MS: Munger Saharsa Ridge. (b) Generalized tectonostratigraphic map of the Himalaya (modified from Robinson and Pearson, 2013). Study area is shown in black polygon.

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Figure 2. Tectonic models of the Himalaya (modified from Webb et al., 2011) showing emplacement of the GH rock.1. Channel flow model (focused denudation) (Nelson et al., 1996; Beaumont et al., 2001); 2. Critically tapered wedge model (DeCelles et al., 2001; Gehrels et al., 2003); 3. Tectonic wedging model (Yin, 2006; Webb et al., 2007). Abbreviations: MBT - Main Boundary thrust; MCT - Main Central thrust; STDS - South Tibetan Detachment system; ITS - Indus-Tsangpo suture; SH - Subhimalaya; LH - Lesser Himalaya; GH - Greater Himalaya; TH - Tethyan Himalaya.

4.5. Kumaun Tectonostratigraphy

4.5.1. Subhimalaya

In Kumaun, the SH (Fig. 3) is composed of a ~5.5 km thick, coarsening upward, Neogene synorogenic sedimentary sequence (Najman, 2006; Jain et al., 2009; Ravikant et al., 2011). The lower Siwalik unit was deposited between 13 and 11 Ma (White et al., 2002; Ravikant et al.,

2011) and is an ~1800 m thick (Fig. 4) succession of alternating sandstone and mudstone deposited by southerly flowing meandering river systems (Prakash et al., 1980). The middle

Siwalik unit is an >2,300 m thick multistory sandstone complex deposited between 11 and 4.5

Ma by avulsing braided rivers (Kumar et al., 2004). The transition from lower to middle Siwalik units is diachronous along-strike within the foreland basin as it occurred at 11 Ma in the Potawar

Plateau, 10 Ma in northwest India, 10.8-9.7 Ma in Nepal (Johnson et al., 1985; DeCelles et al.,

1998; Robinson and McQuarrie, 2012). The upper Siwalik unit is an ~2,300 m thick succession

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of bedded conglomerate with lenticular bodies of sandstone and rare mudstone deposited in

alluvial mega fan system near to the orogenic front between 4.5 and 1 Ma (Sangode et al., 1996;

Kumar et al., 2003).

In eastern Kumaun, the lower Siwalik unit, as well as the Neogene pre-Siwalik foreland

basin strata known as Lugad Gad Formation (Rupke, 1974), crops out between the MFT and

MBT. The Subhimalayan thrust system consists of two thrust sheets, the MFT sheet and the

MDT (Main Dun thrust) sheet. The MFT sheet is ~2,900 m (across strike and contains a

mudstone-sandstone sequence with paleosols, which are characteristic of the lower Siwalik unit,

and the thickly bedded multistory grey sandstone of the middle Siwalik unit. The basal part of

the overlying MDT sheet contains ~2,200 m of pale greenish-biotite rich sandstone of Lugad

Gad Formation (Rupke, 1974; Karunakaran and Rao, 1979), which is equivalent to Early

Miocene Dumri Formation of western Nepal and Kasauli/upper Dharamshala Formation of

Himachal Pradesh (Najman, 2006). The Lugad Gad Formation is conformably overlain by mudstone-dominated lower Siwalik Group in the MDT sheet (Fig. 3).

4.5.2. Lesser Himalaya

In Kumaun, the LH contains clastic rock, carbonate, schist and gneiss between the MCT and the MBT (Fig. 3). Details of the LH stratigraphy are beyond the scope of this study and are presented elsewhere (Valdiya, 1980; Srivastava and Mitra, 1994; Célérier et al., 2009; Patel et al., 2007, 2011; Mandal et al., 2014a). However, a generalized stratigraphy is presented in Table

1. The LH sequence is divided into the 1900-1600 Ma inner LH and 1000-500 Ma outer LH

(Ahmad et al., 2000; Richards et al., 2005; Célérier et al., 2009). In Kumaun, Berinag, Rautgara,

Deoban and Mandhali Formations consist of inner LH Sequence, whereas, Chandpur, Nagthat,

Blaini, and Krol Formations consist of outer LH Sequence. Paleoproterozoic inner Lesser

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Himalaya has large negative εNd values (~-24.0, Ahmad et al., 2000; Robinson et al., 2001;

Martin et., 2005; Richards et al., 2005; Mandal et al., 2014a). Similar Neoproterozoic depositional ages and less negative εNd values (-11 to -16, Ahmad et al., 2000; Robinson et al.,

2001; Richards et al., 2005) of the outer LH, GH and TH rocks (McKenzie et al., 2011 and references therein) make these tectonostratigraphic units difficult to distinguish from one another. They may have been part of a single Neoproterozoic continental margin. An estimated

LH minimum thickness is 8.7-10.9 km in far western Nepal (Robinson et al., 2006). In Kumaun, we use a thickness of ~11 km as determined by previous studies (Srivastava and Mitra, 1994;

Célérier et al., 2009) and from our mapping.

An intra-LH thrust, known as Tons thrust (Srivastava and Mitra, 1994; Richards et al.,

2005; Célérier et al., 2009) is mapped as a structure that separates Paleoproterozoic inner LH rocks to the north from the Neoproterozoic outer LH rocks to the south. However, Mandal et al.

(2014a) refutes this idea based on presence of Paleoproterozoic inner LH rocks exposed south of the Almora klippe on the Ramgarh-Munsiari thrust sheet and the MBT hanging wall, and

Neoproterozoic LH rocks north of the Ramgarh-Munsiari thrust sheet in the LHD (Fig. 3).

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Figure 3. Geologic map of Kumaun, India, with the cross-section line A-A’ as a white dashed line (Fig. 10) and sample locations. AK: Almora klippe; ASK: Askot klippe; CHK: Chiplakot klippe; IZ: Igneous zircon sample; DZ: Detrital zircon sample.

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Table 1. Generalized stratigraphy of Kumaun, India with thickness of various units organized from north to south along the cross section line.

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Medium-grade (greenschist to lower amphibolite) schist and gneiss crop out as synformal

klippen within the LH rock, known as the “Lesser Himalayan Crystalline nappes/klippen”, e.g.,

the Askot klippe, Chiplakot klippe, and Bajnath klippe. Previous maps show that these klippen are carried by the Berinag-Ramgarh thrusts (Valdiya, 1980; Célérier et al., 2009). Based on field mapping and isotopic data, Mandal et al. (2014b) trace the Ramgarh-Munsiari Thrust sheet rocks to the north of the Almora klippe and show that these klippe are Lesser Himalayan rocks and are part of the Ramgarh-Munsairi thrust.

4.5.3. Greater Himalaya

GH rocks crop out north of the MCT and within the Almora klippe. The MCT carries upper amphibolite to granulite facies metasedimentary and meta-igneous rocks (Virdi, 1986),

known as Vaikrita Group, and is divided into lower Joshimath, middle Pandukeswar, and upper

Badrinath Formations (Fig. 4; Spencer et al., 2012a). These three units likely correspond to GH

units I, II and III in central Nepal (LeFort, 1974, 1994; Colchen et al., 1986).

Medium- to high-grade metamorphic rocks of GH affinity also crop out within the

Almora klippe (Mandal et al., 2014a), carried by Almora thrust. Valdiya (1980) describes these

klippen as an allocthonous unit originating from the upper amphibolite to granulite facies GH

metamorphic rock found to the north and correlated with the Almora klippe to the south.

However, he includes the Munsiari Formation as part of the GH rocks. This idea was further

adopted by others (Célérier et al., 2009; Rao and Sharma, 2011). Ambiguity in distinguishing

inner LH Munsiari Formation from GH rock led Valdiya (1980) and others to correlate the

Almoar klippe as southern continuation of the Munsiari thrust sheet. However, Mandal et al.

(2014a) establish as the Almora klippe is the southward continuity of GH rocks and are not the

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LH Munsiari Formation. The Almora klippe is composed of kyanite-garnet-mica schist, graphitic

schist, quartzite, paragneiss, orthogneiss, and ~500 Ma intrusive granites. These rocks are

metamorphosed to green-schist and upper amphibolite facies with temperatures from 500-700ºC

and pressures of 4-8 kbar (Rawat and Sharma, 2011), which is little lower than the ~850ºC and

~14 kbar from the GH in Garhwal, India to the west (Spencer et al., 2012a).

4.6. Geochronology and Regional Correlation

Integrated U-Pb zircon geochronology and εNd values are useful in delineating first-order stratigraphic issues, like separating Paleoproterozoic inner LH rocks from Neoproterozoic to

Cambrian outer LH/GH/TH rocks across the Himalaya (Ahmad et al., 2000; DeCelles et al.,

2000; Robinson et al., 2001; Richards et al., 2005; Martin et al., 2005, 2011; Célérier et al., 2009;

Tobgay et al., 2008; McKenzie et al., 2011; Long et al., 2011). Lack of systematic age constraints and stratigraphic ambiguity impose difficulties for regional correlations of the LH rocks because proper identification of tectonostratigraphic units and their proper stratigraphic positions are key controls in interpreting the structural and kinematic evolution of an orogenic belt.

4.6.1. Zircon U-Pb Dating and Results

Five samples were collected for U-Pb isotopic analysis of igneous and detrital zircons. U-

Pb geochronologic analyses of in-situ zircon grains were conducted using laser-ablation multicollector inductively coupled plasma mass spectrometry (LA-MC-ICPMS) at the University of Arizona following methods described in Gehrels et al. (2006, 2008). Detailed analytical procedures are in Mandal et al. (2014a, 2014b).

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Sample SM11-032 is from a pebbly quartzite bed (Fig. 4a) within the carbonaceous slate/phyllite Mandhali Formation with the distribution of ages in Figure 4b. The age spectra show large clusters around ca. 1800 Ma and ca. 2500 Ma. To determine the depositional age, we add the uncertainty and round up to the nearest 10 Ma following the technique of Martin et al.

(2011). Thus, we interpret the maximum depositional age of this unit as ca. 500 Ma.

Table. 2. Locality information for the samples used in U-Pb zircon geochronology and whole rock Nd analyses. Abbreviations: DZ: detrital zircon; IZ: igneous zircon; Nd: Neodymium.

Sample Coordinates Unit Lithology

0N (dd.ddddd) 0E (dd.ddddd)

SM11-032 (DZ) 29.798761 80.415655 Mandhali Fm. Pebbly quartzite SM11-045 (IZ) 30.029030 80.578234 Chiplakot Klippe Augen gneiss SM111-48 (IZ) 30.130862 80.245917 Munsiari Fm. Granite-granodiorite augen gneiss SM11-58 (DZ) 29.458224 79.583645 Nathuakhan Fm. Gray quartzite with mud partings SM11-59 (IZ) 29.436516 79.562599 Debguru Fm. Granite-granodiorite augen gneiss SM11-035 (Nd) 30.068653 80.606967 Vaikrita Gp. (GH) Pelitic schist SM11-039 (Nd) 30.062817 80.587733 Munsiari Fm. Pelitic schist SM11-046 (Nd) 30.166358 80.250152 Vaikrita Gp. (GH) Pelitic schist/schistose gneiss SM11-049 (Nd) 30.107226 80.243676 Munsiari Fm. Schistose gneiss

Sample SM11-058 is a gray quartzite with mud partings (Fig. 4c) from Nathuakhan

Formation, an outer LH unit mapped by Célérier et al. (2009) as the ca. 800 Ma Chandpur

Formation, south of the Almora klippe. The age spectra (Fig. 4d) shows age clusters around ca.

1000 Ma, 1800 Ma, and 2500 Ma. Four younger zircons yield ages between 751-765 Ma with more than 90% concordance at 1σ. Thus, we assign a maximum depositional age of this unit at

750 Ma.

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Sample SM11-045 is a granite-granodiorite augen gneiss of the Chiplakot klippe (Fig. 3).

Sample SM11-045 yields a mean crystallization age (n=17, both core and rims) of 1857±2 Ma

(MSWD=0.26, probability=0.99, Fig. 5a). No inherited cores older than ca. 1850 Ma are present.

Sample SM11-048 is granite-augen gneiss (Fig. 3) from the hanging wall of what Valdiya

(1980) maps as the Munsiari thrust (Fig. 3). This sample yields a mean crystallization age of

1860±3.0 Ma (n=17, both core and rims; Fig. 5b), with no inherited core older than ca. 1850 Ma.

Sample SM11-059, is from the Debguru porphyry of the Ramgarh Group, 50 km west of our cross-section line (Fig. 3). This sample yields a mean crystallization age of 1867±8 Ma (n=

15, core and rims), and no inherited core older than ca. 1850 are present (Fig. 5c).

4.6.2. Whole rock Nd Isotope Analyses and Results

Four whole-rock metasediment samples were collected from the MCT and Munsiari thrust hanging walls with results in Table 3. Samples (SM11-039, SM11-049) from the Munsiari

Formation yield large negative values (-22. 9 and -25.6), whereas samples (SM11-035, SM11-

046) from lower part of the GH (Joshimath Formation) yields less negative (-16.1 and -15.14)

εNd values.

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Figure 4. (a) Photographs of SM11-032, a pebbly quartzite unit in the inset, and a photograph of the outcrop with a 30 cm hammer laying on the road for scale, 5 cm long pen for scale in the inset; (b) SM11-032 detrital zircon age spectra with pie chart (inset), showing distribution of age populations; (c) Photographs of SM11-058, a muddy quartzite unit with rock hammer for scale, and (d) SM11-058 detrital zircon age spectra with the pie chart (inset).

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Figure 5. U-Pb Concordia plots and respective weighted average (insets) of igneous rock samples: (a) SM11-045, from the Chiplakot klippe, (b) SM11-048, from the Munsiari Formation, (c) SM11-059, from the Debguru porphyry, and (d) representative cathodoluminescence images of sample SM11-045, SM11-048, and SM11-059.

Table 3. Whole rock Nd isotopic analysis results

147 144 143 144 (ppm) Sample Sm Nd Sm/ Nd Nd/ Nd ± (abs stderr) Nd(0) ± (ppm) SM11-035 5.96 31.9 0.1129 0.511805 0.000005 -16.0 0.10 SM11-039 6.48 32.8 0.1193 0.511454 0.000007 -22.9 0.14 SM11-046 5.09 25.4 0.1213 0.511854 0.000006 -15.1 0.12 SM11-049 8.29 50.5 0.0992 0.511320 0.000006 -25.5 0.12

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4.6.3. Interpretation and Regional Correlations

The ca. 500 Ma depositional age for SM11-032 (Fig. 4b) is the first report of any

Paleozoic age from the Mandhali Formation. SM11-058, from the Nathuakhan Formation, yields

a ca. 750 Ma, which is a little younger compared with reported ca. 800 Ma depositional age from

same unit (Célérier et al., 2009). Sample SM11-045 (Fig. 3) is a granite granodiorite gneiss from the Chiplakot klippe with a crystallization age of 1857±1.8 Ma, which has a much smaller error than a reported age of 1906±220 Ma using the Rb-Sr isochron method (Singh et al., 1985).

Therefore, our new age data suggests that Chipkot klippe is part of the Paleoproterozoic inner

LH rocks, and should not be correlated with GH rock as proposed by others (Patel et al., 2007,

2011; Célérier et al., 2009; Rao and Sharma, 2011). Sample SM11-048 (Fig. 3), from the

Munsiari thrust hanging wall, yielded a crystallization age of 1860±3 Ma. A similar age is

reported by Célérier et al. (2009) from the Paleoproterozoic inner LH Ramgarh Group (their

sample 0602006). Sample SM11-059, a granite-granodiorite gneiss from the Ramgarh thrust

sheet, south of the Almora klippe, has a crystallization age of 1867±8 Ma, similar ages are

present from granite gneiss in this thrust sheet along strike (Célérier et al., 2009; Mandal et al.,

2014a). Therefore, it is evident that the Munsiari, Chiplakot, Berinag, and Ramgarh thrust sheet

rocks all contain ca. 1850 granitoids and are part of the same depositional unit into which the

granitoids intruded. Kohn et al. (2010) and Mandal et al. (2014b) suggest that this unit formed in

a continental arc set up.

U-Pb detrital zircon geochronologic data show that the Paleoproterozoic (inner, Fig. 6)

LH and Neoproterozoic (outer, Fig. 7) LH rocks are exposed on the either side of the Almora

klippe. Therefore, it is inappropriate to state that only Neoproterozoic rocks are exposed to the

south of the Almora klippe as stated by Célérier et al. (2009). The inner LH composite zircon

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spectra (Fig. 6) show that the Paleoproterozoic Rautgara Formation contains some younger (ca.

1600 Ma) zircons compared to the Berinag-Munsiari Formations and Ramgarh Group, which has no zircons younger than ca. 1800 Ma (McKenzie et al., 2011; Spencer et al., 2012b; Mandal et al., 2014). Similar detrital zircon ages from the Ramgarh Group, Berinag and Munsiari formations, associated ca. 1.85 Ga granites (Mandal et al., 2014 a and b), and similar more negative εNd values (-20 to -25, Ahmad et al., 2000; McKenzie et al., 2011; Mandal et al.,

2014a) suggest that these rocks are the same unit and that the granites intruded the units. The outer LH composite zircon spectra (Fig. 7) show major source age peaks at ca. 1000 Ma, 1800

Ma and 2500 Ma. Similar age spectra in the Nagthat Formation and overlying Blaini Formation

(minimum ages: 784±14 Ma and 789± 12 Ma; Hofmann et al., 2011) suggest a major recycling of sediments. The composite age spectra shows that Nagthat Formation in Kumaun (SM11-006, minimum age 537±19 Ma; Mandal et al., 2014a) has younger zircons than that of Garhwal (Fig.

5b, minimum age is 784±14 Ma; Hofmann et al., 2011).

Whole rock Nd isotopic data coupled with field mapping allow GH rocks to be differentiated from inner LH rocks and therefore, be used as a technique to determine the location of the MCT. Two samples (SM11-035 and SM11-046) from the lower part of the

Vaikrita Group show εNd values of -15, similar to that reported elsewhere from GH rocks

(Ahmad et al., 2000; Robinson et al., 2001). In contrast, the Munsiari Formation (SM11-039 and

SM11-049) exhibits large negative εNd values (-22.9 to -25.5), consistent with reported values from inner LH rock (Ahmad et al., 2000) to the west of Kumaun. εNd values of the GH rocks are similar to the values in the Almora Group (εNd= -11.0, Mandal et al., 2014a); thus, the Almora klippe rocks correlate with the GH Vaikrita Group, not with the LH Munsiari Formation.

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Figure 6. Composite U-Pb detrital zircon spectra of inner LH units from Kumaun and Garhwal, NW India

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Figure 7. Composite U-P detrital zircon spectra of outer Lesser Himalayan units from Kumaun and Garhwal, NW India

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4.7. Balanced Cross-Section

4.7.1. Methods of Cross-Section Construction and Assumptions and Limits

A balanced cross-section is a powerful tool in interpreting complex structures, especially

in a foldthrust belt with sparse data. A balanced cross-section is one that is geometrically viable

and will restore to its initial undeformed state through kinematically reasonable steps (Mitra,

1992). Restoration is essential to ensure a balanced cross-section and for estimating the

minimum shortening or extension. Line length balanced cross sections assume that line lengths

are conserved during deformation (Dahlstrom, 1969a; Suppe, 1983, 1985). Using modern rules of thrust tectonics, line length balancing has been successfully applied to the Himalayan FTB

(Johnson, 1986; Coward and Butler, 1985; Schelling and Arita, 1991; Srivastava and Mitra,

1994; DeCelles et al., 2001, Robinson et al., 2006; McQuarrie et al., 2008; Long et al., 2011;

Khanal and Robinson, 2013 Khanal et al., 2014; Robinson and Martin, 2014) to understand the

structural and kinematic evolution and to estimate upper crustal shortening.

Seismic data in the Himalayan FTB is sparse, except for a few acquired by the Oil and

Natural Gas Corporation (ONGC) of India in 1960s, which are of poor quality. We compose a

balanced cross-section (Fig. 10a), with data projected from a foreland well (Shastri et al., 1971) and crustal scale receiver function geophysical data from Garhwal, northwest India (Caldwell et al., 2013), 125 km to the west. The cross section is oriented N15E, parallel to the direction of

Himalayan shortening, as indicated by average strike of the structures in Kumaun. The balanced cross-section is restored and line-lengths of thrust sheets measured on deformed sections were matched on restored sections (Fig.10b; Dahlstrom, 1969). Apparent dips were calculated from

the surface measurement and projected along strike on the cross section. Axial planes of folds

were determined by bisecting the inter-limb angle at the hinges, and most axial plane were drawn

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using kink method (Suppe, 1983). The cross-section excludes micro- and meso-scale

deformation; thus, shortening estimates are only minimum estimate and are likely higher. When

constructing the cross section, the unknowns are the positions of hanging wall cutoffs of the

thrust sheets because they have all been eroded. The thrust sheets may be much longer than the

cross-section and reconstruction portray. Justification for individual decisions are given in the

cross section (Fig. 10a).

4.7.2. Structural Geology Results

Four major crustal-scale Himalayan faults, the STDS, MCT, MBT and MFT bound major

tectonostratigraphic zones, and are recognized as key structural elements of this orogen.

However, this general subdivision does not include some major intra-formational thrusts like the

Ramgarh-Munsiari thrust (RMT, an intra-LH thrust), the Lesser Himalayan duplex (LHD) and

intra-GH thrusts (Kohn et al., 2004; Carosi et al., 2010; Imayama et al., 2012; Montomoli et al.,

2013). The RMT plays a crucial role in translating LH rocks towards the foreland for a distance

of over 100 km (Robinson and Pearson, 2013). We discuss below each structural system from

north to south. The STDS is too far north to be reached easily; thus, we incorporated the structural fabrics and location of the STDS from Patel et al. (2009, 2011).

4.7.2.1. Main Central Thrust Sheet

The Main Central thrust, a crustal-scale ductile fault originally defined by Heim and

Gansser (1939), transported GH rocks over LH rocks from the hinterland towards its foreland at

16-22 Ma in central Nepal (Khanal et al., 2014). 40Ar/39Ar muscovite cooling ages from western

Nepal (DeCelles et al., 2001; Robinson et al., 2006) suggests that the MCT was active at ca. 25-

21 Ma. One idea of how to define the MCT (Searle et al., 2008; Larson et al., 2010; Law et al.,

2013) argues that the MCT should be mapped on the basis of strain criteria and ductile

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deformation parameters. Another idea is that the MCT juxtaposes two tectonostratigraphic zones,

GH and inner LH, characterized by distinct isotopic signatures and depositional ages; therefore,

the GH and LH originate from two different source areas (Ahmad et al., 2000; Robinson et al.,

2001; Martin et al., 2005). The MCT, in Kumaun-Garhwal and Himachal Pradesh of NW India,

is known as Vaikrita thrust, which is the same thrust as the Almora thrust further south (Mandal

et al., 2014a; Fig. 10a). GH rock has a penetrative ductile fabric (Fig. 8a) throughout. Foliations

planes (S1) are generally parallel to the axial planes of the small scale mesoscopic folds and dips at 65-75°. Along the cross-section (A-A’, Fig. 3), the cross strike surface exposure of the MCT

sheet ranges between 13-18 km. In Garhwal, west of the present study area, the peak

metamorphic temperature ranges between 800-850°C, which remain constant through the GH

rocks, whereas pressure increases from 12 to 14 kbar 3 km above the MCT, then decreases to 9

kbar near the STDS (Spencer et al., 2012a).

4.7.2.2. Ramgarth- Munsiari Thrust Sheet

The RMT, a crustal scale fault, is in the proximal footwall of the MCT and plays a crucial

role in the development of the Himalayan FTB (Robinson and Pearson, 2013). This long, far

traveled thrust became active mid- to late Miocene time (Robinson and McQuarrie, 2012). In

Garhwal-Kumaun, this thrust has been mapped as two different thrusts, the Munsiari thrust to the

north and Ramgarh thrust to the south (Valdiya, 1980; Srivastava and Mitra, 1994; Ahmad et al.,

2000). Another thrust, called the Berinag thrust in the literature (e.g. Valdiya, 1980), carries

Paleoproterozoic metasediments and ca. 1850 Ma granite-granodiorite gneiss (McKenzie et al.,

2011; Mandal et al., 2014a), and is instead a klippe of the RMT. Though the metamorphic grade

varies, similarities in the whole rock εNd values (-20 to -24), ca. 1800 Ma aged metasediments

and ca. 1850 Ma granite-granodiorite gneiss within the Munsiari, Berinag and Ramgarh thrust

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sheets (Ahmad et al., 2000; McKenzie et al., 2011; Spencer et al., 2012b; Mandal et al., 2014a

and b) support our conclusion these are part of a same continuous thrust sheet, the RMT sheet

(Fig. 10).

The RMT carries Paleoproterozoic rocks and has been mapped using field and

geochemical data in western Nepal, north of the Dadeldhura thrust sheet (Robinson et al., 2001,

2006); however, in Kumaun, the RMT was not mapped to the north of Almora klippe. Mandal et

al. (2014a) establish that Paleoproterozoic inner LH of the RMT sheet are present to the north of

the Almora klippe, are folded underneath the Almora klippe and crop out south of the Almora

thrust, mapped by Valdiya (1980) as Ramgarh thrust sheet. The RMT sheet rock also contains

penetrative foliation mostly parallel to bedding, and shows evidence of ductile deformation (Fig.

8b). Foliation dips are mostly parallel to bedding and controlled by the geometry of the RMT.

The RMT is breached by some younger out-of-sequence normal and reverse faults (faults in the

middle of the horse G, see Fig.10a), and is present north of the Almora klippe (Fig. 10a). The

RMT is thicker (~7 km) to the north in the footwall of the MCT (Fig. 10a), but thins (1.8-1 km)

towards south near the MBT. The restoration (Fig. 10b) shows that the RMT cut up-section to

the south accounting for the decrease in thickness.

An increase in metamorphic grade to the north suggests that the rocks were buried deeper than those in the south during the Himalayan metamorphism. In the northern part, where the rocks carries by the RMT are known as the Munsiari Formation, these Paleoproterozoic rocks are

metamorphosed to amphibolite and granulite facies with temperatures of ~850ºC and pressures of

~14 kbar (Spencer et al., 2012a). However, Paleoproterozoic rock to the south carried by the

RMT is known as Ramgarh Group, and is metamorphosed to greenschist and lower amphibolite

facies with temperatures from 500-700ºC and pressures of 4-8 kbar (Rawat and Sharma, 2011).

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To the south near the MBT, the RMT also carries the Neoproterozoic Nathuakhan Formation, an

outer Lesser Himalayan unit (Mandal et al., 2014a), that unconformably overlies the

Paleoproterozoic rocks.

4.7.2.3. Lesser Himalayan Duplex

The LHD developed in the internal portion of this FTB south of the high peaks (e.g.

Srivastava and Mitra, 1994; DeCelles et al., 2001; Robinson et al., 2006; McQuarrie et al., 2008;

Bhattacharyya and Mitra, 2009; Long et al., 2011). The LHD is a thrust system with the MHT as

floor thrust and the RMT and MCT as the coupled roof thrusts. This system provides an effective

mechanism in transferring slip upward from the basal décollement into the FTB wedge.

Therefore, understanding the development of LHD is pivotal in deciphering the kinematics and growth of the FTB (Bhattacharyya and Mitra, 2009).

Seven thrust sheets, labeled as “A-G” (Fig. 10a) with average thickness of ~4700 m, form a hinterland dipping duplex, suggesting that displacement in each thrust sheet is less than length of each thrust sheet (Mitra, 1986). On Figures 10a and 10b, the thrust sheets are labeled A though G. Except for G, all thrust sheets contain three units, the Berinag (Fig.

8c)/Ramgarh/Munsiari, Damtha, and Deoban+Mandhali (Figs. 8d and 8e) Formations. Thrust sheet G contains the younger units, the Chandpur, Nagthat and overlying younger units, and emplaced as a fault bend fold and repeated the stratigraphy beneath the Almora klippe.

Subsequently, this fault bend fold was modified by three out-of-sequence faults with both normal and thrust motion, that breach the overlying RMT and Almora thrust (Fig. 10a) and juxtapose the

Paleoproterozoic Rautgara Formation against the Paleoproterozoic Ramgarh Group, immediate north of the Almora klippe.

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4.7.2.4. Almora Klippe

The Almora klippe lies south of the LHD, and carries GH affinity rocks (Mandal et al.,

2014a). This klippe is an asymmetrically folded synform with the southern limb dipping 30° to

the north and the northern limb dipping 70° south. Ductile shearing produced asymmetrical

mesoscopic folds (Fig. 8f) with axial planes parallel to the regional foliation (S1). Three younger brittle faults are present (Figs. 9a and 10a), which suggest that these ductily deformed rock are modified by late stage brittle faulting at shallower crustal depths. Antolin et al. (2013) report from the Dadeldhura klippe, the eastern continuation of the Almora klippe, progressively younger muscovite cooling ages to the north, where the cooling age to the south of the

MCT/Dadeldhura thrust is 22.7 Ma, and to the north is 19.8 Ma, and further north in the MCT immediate hanging wall, it is 12.4 Ma. They interpreted this as the early cooling in the frontal part of the MCT, while the MCT hanging wall rocks were still buried, hot and undergoing metamorphism.

The MCT, Almora thrust and the overlying GH rocks have been passively folded due to growth of the LHD (Fig. 10a). The MCT has been tilted toward the north (Robinson et al., 2001) and the northern side of the Almora thrust, the southern extension of the MCT, toward the south.

The southern side of the Almora thrust was tilted northward at the MBT and Subhimalayan thrust system was emplaced. Subsequent erosion created the isolated synformal GH klippe at the surface.

4.7.2.5. Lesser Himalayan Imbricate Zone

South of the Almora klippe, the LH imbricate zone is bounded by MBT to the south and

RMT to the north. A damage zone exists in the frontal part of this zone (Fig. 3) that exposes

Paleoproterozoic Damtha Group rock, characterized by intense brittle deformation (Fig. 9b) in

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thrust bounded rocks. A similar damage zone is reported 55 km northwest from this study area,

in the immediate hanging wall of the MBT (Shah et al., 2012). The northern thrust of the LH

imbricate zone juxtaposes the Neoproterozoic Nagthat Formation against the Paleoproterozoic

rock (Fig. 10a). Bedding orientation defines a broad synform in this zone, which exposes the

outer LH Blaini and Krol Formations west of the cross-section line (Figs. 3 and 10a).

4.7.2.6. Subhimalayan Thrust System

The Siwalik Group crops out north of Tanakpur (Fig. 3) and across strike thickness vary

between 8-11 km. The southernmost exposure of the Siwalik Group is the slope break of the

Siwalik Hills with the Indo-Gangetic plains to the south (Fig. 3). The Subhimalayan thrust

system consists of three imbricate thrust sheets (Fig. 10a), mapped based on structural repetition.

The southernmost thrust sheet is carried by the MFT, and exposes lower and middle Siwalik

rocks with thickness of ~4500 m. Because of the gentle northern limb, we construct it as a fault

bend anticline on the cross section (Figs. 9c and 10a). Lack of southward dipping beds suggest

that the MFT hanging wall cut off has crossed through the present day erosional surface on this

section. To the north of the MFT thrust sheet, one unnamed thrust sheet carries only the Lugad

Gad Formation (western Nepal Dumri Formation equivalent). The overlying Siwalik Group rocks were pushed through the erosional surface when the overlying Main Dun thrust sheet was emplaced. The Main Dun thrust is present in western Nepal (Raiverman, 2002; Robinson et al.

2006) and carries the Lugad Gad Formation and the lower Siwalik unit. In general, the

Subhimalayan thrust system exhibits dips between 25°-55° northward.

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Figure 8. (a) Mylonitic granite gneiss from MCT hanging wall. Small scale asymmetric fold within the thicker (pink) layer shows the shear sense. 15 cm pen for scale. (b) Isoclinal fold parallel to the schistosity from the Munsiari Formation, near sample location SM11-039. 2.5 cm coin for scale (c) Regional dipping panel of bedded Berinag Formation quartzite, 5 m wide road for scale. (d) Folded bedded Deoban Formation dolomite showing kink style geometry that is used to model the structural geometry (Fig. 10a). (e) Brittle fractured Mandhali Formation phyllite with S surfaces, 15 cm pen for scale (f) Asymmetrical fold, from the southern margin of the Almora klippe, with south vergent folds indicates top-to-the-south shear sense. Looking down into a river bed.

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Figure 9. (a) Fault cataclasite from the north of the Almora klippe (Saryu River), which places Ramgarh Gp. of rocks against Rautgara Formation, 30 cm hammer for scale. (b) Intensely brittle fractured quartzite from the emplacement of the MBT, 30 cm hammer for scale. (c) South vergent asymmetrical fold (outline fold with black line and put directions on figure from the MFT hanging wall, 30 cm hammer for scale.

4.7.3. Estimation of Shortening and Comparisons

Restoration of the balanced cross-section into an undeformed geometry yields a minimum estimate of original lengths (Lo) from the MFT to the STDS of 674-751 km on this

cross-section (Table 4), taking into account of TH shortening from published work (Murphy and

Yin, 2003). The estimated shortening is a minimum estimate if the Almora klippe is southern

continuation of the GH, and a maximum estimate when the Almora klippe and GH are separate

thrust sheets and overlying GH extends to the northern edge of the klippe (Khanal et al., 2014).

The deformed length (Lf) of the cross-section is 141 km (Fig. 10a and 10b). Hence, the total

amount of minimum shortening (Lo-Lf) ranges between 541 km (79%) to 575 km (80%). Slip on

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each thrust is given in Table 4. After restoring the cross section (Fig. 10a), the MCT extends 162 km from the root zone of the MCT to the southernmost outcrop south of the Almora klippe. This is a minimum amount of slip because the southern cutoff has been eroded. Minimum shortening is estimated assuming that the Almora klippe is southern continuation of the GH, and maximum shortening is estimated assuming the Almora klippe and the GH are two different GH thrust sheet (Khanal et al, 2014). The MCT has a minimum of 128 km and maximum of 163 km of shortening. The RMT has minimum of 112 km of shortening, and the LHD accommodates a minimum of 270 km of shortening. The Subhimalayan thrust system accommodates a minimum of 22 (=7+1+14) km of shortening.

Srivastava and Mitra (1994) construct a balanced cross-section ~70 km west of our cross- section and report a minimum shortening estimate of 687-754 km or 76-79% (Table 4).

However, their cross-section is of limited utility because they correlate the Paleoproterozoic

Berinag Formation, north of Almora klippe (McKenzie et al., 2011; Mandal et al., 2014a) with the Neoproterozoic Nagthat Formation, south of the Almora klippe (Mandal et al., 2014a), and interpret the Berinag thrust of Valdiya (1980) as having normal motion.

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Figure 10.Balanced cross-section (a) along line A-A’ on Figure 3. Letters A-G indicate thrust sheets within the LHD in the cross section and restored section (b). Abbreviations: STDS, South Tibetan Detachment System; MCT, Main Central thrust; RMT, Ramgarh-Munsiari thrust; LHD, Lesser Himalayan Duplex; MBT, Main Boundary thrust; MFT, Main Frontal thrust. * denotes zircon and whole rock neodymium sample locations of Mandal et al. (2014a).

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Table 4. Estimation of shortening along the cross section line

Structures Lf L0 Shortening(km) Shortening (%) Main Frontal thrust 8.3 15.8 7.5 47.2 Main Dun thrust 4.8 19.7 14.9 75.8 Main Boundary thrust 1.5 9.0 7.6 83.3 Ramgarh-Munsiari thrust 51.7 163.9 112.2 68.5 Lesser Himalayan Duplex 59.7 329.8 270.1 81.9 **Main Central thrust 15.2 178.4 163.2 91.5 maximum *Main Central thrust minimum 15.9 143.5 128.4 89.4 Total Minimum Shortening 141.2 681.7 540.6 79.3 Total Maximum Shortening 141.2 716.6 575.4 80.3 Shortening in the TH - - 133-176 - Total shortening - - 674-751 - **Maximum if Almora klippe and GH are separate thrust sheets and overlying GH extends to northern edge of the klippe (Khanal et al., submitted), *Minimum if Almora klippe is southern continuation of GH; Shortening= (Lf-Lo) and Shortening %= [(Lf-Lo)/Lo]*100

Table 5: Compilation of shortening estimates across the Himalayan fold thrust belt

Location SH+LH in km (in SH+LH+GH in km References %) (in %) Kumaun-Garhwal, 161 (65%) 354-421 (76-79%) Srivastava and Mitra (1994) India Western Nepal 393 (77%) 691-780 (79-84%) Robinson et al. (2006) Sikkim 253 (76%) 249 (82%) Mitra et al. (2010) Bhutan 164-267 (52-66%) 138-209 (70-75%) Long et al. (2011) Central Nepal 284 (53%) 400 (75%) Khanal et al. (2013) Himachal Pradesh, - 518 (72%) Webb (2013) India Pakistan - 470 (64%) Coward and Butler (1985) Kumaun, India 412 (76%) 540-575 (79-80%) This Study

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4.8. Kinematic History and Discussion

Based on our geochronologic and isotopic data, we revised the stratigraphy of Kumaun,

thus, necessitating the construction of a new balanced cross-section (Fig. 10a). The crosssection

and reconstruction show that the system is generally a forward propagating thrust system, with some reactivation in the frontal part of the LHD (Fig. 10a), similar to western and central Nepal

(DeCelles et al., 2001; Robinson et al., 2006; Khanal et al., 2013) and in Bhutan (McQuarrie et

al., 2008; Long et al., 2011). The cross-section illustrates that in Kumaun, the evolution of the

FTB can be explained using a critically-tapered wedge (Fig. 2), at least since Miocene time when

GH rock was emplaced over the Paleoproterozoic inner LH rock along the MCT. The medium-

to high-grade metamorphic rocks of the inner LH rocks were transported to the south by the

RMT. The MCT emplaced a flat of GH rock over a flat of inner LH rock, and the RMT

emplaced a flat of inner LH rock over a flat of other LH rocks (Fig. 10b). The southernmost part

of the RMT also carries some Neoproterozoic outer LH rocks (Nathuakhan Formation, SM 11-

058), which unconformably overlies Paleoproterozoic rock (Fig. 10a), and is exposed south of

the Almora klippe. Significant thickness variations (7-1 km) from hinterland to foreland of the

RMT sheet led us to interpret that the RMT cut the Paleoproterozoic sequence at a low angle (4-

70, Fig. 10b). However, this rock is not part of the Indian cratonic basement and the RMT does

not merge with the Almora thrust as suggested by Célérier et al. (2009). The RMT and MCT are

two major crustal scale structures (Fig. 10), similar to Nepal (Robinson et al., 2006; Khanal et

al., 2013). Based on isotopic data, Mandal et al. (2014a, 2014b) establish the presence of RMT

inner LH rock to the north of the Almora klippe, which continues further to the north as Berinag

thrust sheet rock. However, the Berinag thrust is actually a klippe of the RMT and the Munsiari thrust is actually the root zone of the RMT based on 3 line of evidence: 1) inner LH

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Paleoproterozoic metasediments, 2) ca. 1850 Ma granite of continental arc affinity (Mandal et

al., in review), and 3) similar whole rock εNd values (-20 to -25). In fact, the Ramgarh, Berinag,

Chiplakot, and Munsiari thrust sheet rocks are a single continuous thrust sheet, the RMT, which

has been folded by growth of the underlying LHD and subsequently eroded. Ca. 810 Ma aged

metasediments and less negative the εNd(0) (-11, Mandal et al., 2014a) values of the Almora

klippe rocks further led us to model Almora klippe as an erosional outlier of the GH rocks, and

these klippe rocks are not the Munsiari thrust sheet rock as suggested by many workers

(Srivastava and Mitra, 1994; Célérier et al., 2009; Rawat and Sharma, 2011). The metamorphic

grade of the RMT sheet rocks varies from granulite-amphibolite facies in the MCT footwall to

greenschist facies in the Almora thrust footwall, The rock to the north was buried deeper and

exhibits higher grade, and the rock to the south was buried shallower exhibits a lower grade.

Validya (1980) and Srivastava and Mitra (1994) state that the footwall of the Almora thrust exposes the Rautgara Formation, north of the Almora klippe and Nagthat Formation south of the Almora klippe. However, our revised chronostratigraphy and structural cross-section establish that the Almora thrust was emplaced over the inner LH Paleoproterozoic rocks of the

RMT thrust sheet to the north and south of the Almora klippe. Célérier et al. (2009) found an out-of-sequence thrust north of the Almora klippe based on the presence of the Neoproterozoic

Chandpur Formation; however, their sample was located incorrectly. Instead, just north of the

Almora klippe, we found Paleoproterozoic inner LH rocks (with no zircon grains younger than ca. 1800 Ma) in the RMT and, thus, no need for an out-of-sequence fault. This is similar to the geometry in western Nepal (DeCelles et al., 2001; Robinson et al., 2006).

South of the Almora klippe, the Neoproterozoic Nathuakhan Formation crops out on the

RMT hanging wall (Fig. 3). Célérier et al. (2009) interpret Paleoproterozoic (ca. 1850 Ma) inner

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LH rocks as Indian basement and interpret the FTB as containing basement involved thrusts.

Alternatively, we interpret these are Paleoproterozoic supracrustal rocks deposited on top of the northern edge of ca. 2500 Ma northern Indian cratonic block, based on pronounced ca. 2500 Ma age peak on detrital zircon spectra (Fig. 6, Mandal et al., 2014a) and similar εHf(T=0) values (-

5.8 to -2.2) in ca. 2500 Ma zircons from basement and these supracrustal rocks (Kaur et al.,

2013; Mandal et al., in review). The RMT cuts up stratigraphic section through these rocks in thin-skinned style deformation style carrying both the metasediments and meta-igneous rocks.

Moreover, a basement involved style cannot explain the presence of Almora klippe rock, in the proximal hanging wall of the RMT, which is an erosional outlier of the GH rock and translated to the south, and is not Indian basement. The schematic structural cross-section in Célérier et al.

(2009) is not a viable cross section and cannot be balanced. Thus, our cross-section fills in this gap and incorporates new age data and recognition of the RMT and LHD to provide new shortening estimates.

Caldwell et al. (2013) present geophysical reflection data to image the shallow crustal structure in Garhwal, 125 km west of our cross-section. We projected their subsurface data eastward based on the location of major structures like the Almora klippe. Their LH ramp is located 20 km north of the ramp location drawn by Srivastava and Mitra (1994), and we use their

LH ramp location for a more accurate portrayal of the subsurface geometry. Caldwell et al.

(2013) define the geometry of the ramp as a positive impedance contrast due to juxtaposition of

Ramgarh-Berinag Munsiari Group of rocks against the carbonate rock of the Deoban and

Mandhali Formations underneath the MHT. However, Caldwell et al. (2013) follows the structural cross-section of Srivastava and Mitra (1994) and makes the dip of the ramp as 16° because the Munsiari thrust at the surface is between 12-32°. However, the Munnsiari thrust (the

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RMT) at the surface does not control the dip of the ramp in the subsurface. The geophysical data allow a dip of 25°, which is what we use because it conforms to the dips of ramps in thrust belts, andis parallel to the southern limb of the Askot klippe (Fig. 10a). Without these data, the ramp could only be located by determining the length of the Siwalik Group rock and placing the LH ramp of northern terminus of the Siwalik Group rocks in the reconstruction (e.g., DeCelles et al.,

2001; Robinson et al., 2006), less accurate way of location the ramp.

Our shortening estimates do not contrastingly different than that of the other part of the

Himalayan FTB (Table 5). However, each shortening estimates contains different assumptions, for example, Srivastava and Mitra (1994) reinterpreted the Berinag thrust (Valdiya, 1980) as

having normal slip. Our new chronostratigraphy reveals that the Berinag Formation is older than

the Damtha Formation, as the former contains older zircons (youngest zircon ca. 1800 Ma,

McKenzie et al., 2011; Mandal et al., 2014a) compared to the later (youngest zircon ca. 1600

Ma, Mandal et al., 2014a). Adding the 541-575 km shortening estimation from Murphy and Yin

(2003) in TH, there is a total shortening between 674-751 km. which is half of the estimated

shortening (~2000 km) at central part of the Himalaya, determined by van Hinsenberg et al.

(2011). Our shortening estimation is not significantly different than the estimated shortening

(687-754 km or 69-72%) of Srivastava and Mitra (1994), which was based on stratigraphic

assumptions that we have shown require revision; thus, stratigraphic assumptions may not be as important as previous thought when constructing a cross-section.

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4.9. Conclusions

We present a new mapping and a structural interpretation based on our revised chronostratigraphy in Kumaun, northwest India and finds that:

1) The Ramgarh, Berinag, Chiplakot and Munsiari Formations, including the augen gneiss, are part of a once continuous Paleoproterozoic rock unit and translated toward the south on the

Ramgarh-Munsiari thrust. Growth of the underlying Lesser Himalayan duplex deformed the thrust sheet and erosion isolated the unit into thrust sheets and synformal klippen.

2) The Almora thrust sheet is composed of Greater Himalayan rock and the Ramgarh Munsiari thrust sheet is composed of Paleoproterozoic inner Lesser Himalayan rocks. Greater Himalayan rocks have U-Pb ages of ca. 800 Ma and epsilon Neodymium values of ~-11, while the

Paleoproterozoic inner Lesser Himalayan rocks have U-Pb ages of ca. 1800 Ma and epsilon

Neodymium values of ~-24.

3) The Almora thrust sheet exhibits a flat-on-flat relationship with the underlying Ramgarh-

Munsiari thrust sheet, and the Ramgarh-Munsiari thrust sheet exhibits a flat-on-flat relationship with underlying Lesser Himalayan rocks that subsequently form the Lesser Himalayan duplex.

Growth of the Lesser Himalayan duplex folded the overlying unit to form the Almora klippe and conformably folded the Ramgarh-Munsiari thrust sheet that crops out to the north and south of

Almora klippe.

4) The FTB in Kumaun is a forward propagating thrust system, typical of thin-skinned style tectonics, and there no evidence of basement involved tectonic styles.

5) The Lesser Himalayan duplex has 270 km of minimum shortening. We estimate a total minimum shortening from the Main Frontal thrust to the South Tibetan Detachment system of

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541-575 km, and by adding shortening in the Tethyan Himalaya emerge with a total minimum

shortening between 674-751 km in Kumaun.

4.10. Acknowledgements

This project was funded by the National Science Foundation (EAR0809405, DMR;

EAR0809428, EAR1048124, and EAR1321897, MJK), and by the Society of Economic

Geologists Foundation’s Hugh E. McKinstry Student Research Grant (SM). Mandal thanks the

Graduate School and the Department of Geological Sciences at the University of Alabama for travel support to carry out the field work and U-Pb zircon geochronologic analyses. Mark Pecha,

Nicky Giesler, and Mauricio Ibanez are thanked for their help during U-Pb analysis of zircons at the Arizona Laserchron Facility (NSF EAR 1032156). We also thank Dr. Jeff Vervoort,

Washington State University, USA, for performing the whole rock Nd analyses.

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CHAPTER 5:

CONCLUSIONS

In Kumaun, northwestern India, field mapping, combined U-Pb-Hf isotopic analyses, whole rock Nd isotope analyses, whole rock trace element geochemistry, and structural analysis are combined to present an integrated view of the evolution of the Himalayan fold-thrust belt.

Chapter 2 concludes that the Almora klippe rocks are the southward continuation of the

Main Central thrust sheet rocks, and should not be correlated with the Paleoproterozoic Lesser

Himalayan Munsiari thrust sheet rocks. Almora klippe rocks yield Neoproterozoic (~900 Ma) detrital zircon ages and less negative εNd(0) ( -7.6 to -11.8) values, characteristic of Main Central

thrust sheet, i.e., Greater Himalaya. On the north side of the Almora klippe, rocks previously

mapped as part of the Almora klippe have more negative [εNd(0)= -23.0 to -24.6)] values, in contrast with the Greater Himalayan affinity Almora klippe [εNd(0) = -7.6 to -11.8)] and thus,

must be Paleoproterozoic inner Lesser Himalayan Ramgarh-Munsiari thrust sheet rock. The root zone of the Ramgarh-Munsiari thrust sheet is in the footwall of the MCT and is continuous to the south and folded under the Almora klippe as the Ramgarh-Munsiari thrust sheet. The rock north of the Almora klippe is not the Neoproterozoic Chandpur Formation; instead, these are

Palaeoproterozoic siliciclastic shallow to deep marine rocks of the Rautgara Formation. The

Ramgarh-Munsiari thrust sheet emerges south of klippe, containing the Palaeoproterozoic ca.

1.85 Debguru porphyry in its hanging wall. These Palaeoproterozoic granites (ca. 1850 Ma) are present throughout the Paleoproterozoic Lesser Himalayan rocks and are not part of the 2.5 Ga

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Indian craton. South of the Almora klippe, Palaeoproterozoic and Neoproterozoic Lesser

Himalayan rocks crop out, carried to that location by the Ramgarh-Munsiari thrust. In Kumaun, there is no evidence for the Tons thrust that is supposed to separate Palaeoproterozoic Lesser

Himalayan rocks from Neoproterozoic Lesser Himalayan rocks; instead, we found that

Palaeoproterozoic Lesser Himalayan rocks are present south of the Almora klippe on the

Ramgarh-Munsiari thrust hanging wall and its footwall, and Neoproterozoic Lesser Himalayan rocks are present north of the Ramgarh-Munsiari thrust sheet within the Lesser Himalayan duplex. Hence, the Tons thrust cannot be the boundary between the inner Lesser Himalaya

(1900-1600 Ma) and outer Lesser Himalaya (800-500 Ma). Further, we recommend abolishing the term “inner” and “outer” in the Lesser Himalayan tectonostratigraphy in northwestern India.

Chapter 3 integrates U-Pb geochronologic data, Hf isotopic data, whole rock trace element geochemical studies and detail mapping to characterize the structure, stratigraphy, and magmato-thermal event of the Askot klippe. The conclusions are that the Askot klippe consists of a 1856.6±1.0 Ma granite-granodiorite gneiss, coeval 1869±12 Ma felsic volcanic rock, and ca.

1820 Ma quartzite, and is a small vestige of Paleoproterozoic continental arc assemblage, which formed on the northern margin of the northern Indian cratonic block as a part of the Paleo-

Mesoproterozoic supercontinent, the Columbia. These rocks are the southern continuation of the

Munsiari Formation rocks, which is suggested by presence of ca. 1850 Ma granite-granodiorite gneiss and overlapping εHf(T=1850) values (Munsiari rocks = +0.6 to -7.9, Askot klippe=-1.1 to -

9.6). In addition, the same rocks that form the Askot klippe continue to the south as rocks that

are underneath the Almora klippe that compose the Ramgarh-Munsiari thrust sheet. The

Paleoproterozoic crustal evolution of the northern Indian block’s (NIB) northern margin in

Paleoproterozoic and Archean time is strikingly similar to that reported from Delhi-Aravalli

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orogen, western margin of the northern Indian block, evident from preponderance of ca. 1850

Ma and similar range of εHf isotopic values that suggest an much older crust reworked at ca.

1850 Ma. The Paleoproterozoic rocks, ca 1850 Ma, were probably deposited in the supra- subduction zone; however, near 1600 Ma, a back arc basin developed, as evidenced by (a) the addition of juvenile crust at ca. 1600 Ma, and (b) the occurrence of the extension related volcanogenic massive sulphide deposits along the Himalayan arc. These volcanogenic massive sulphide deposits are spatially associated with the ca. 1850 granite-granodiorite rocks, which served as the heat source of the hydrothermal system. The Neoarchean and Paleoproterozoic northern Indian margin had very heterogeneous crustal assemblages as is evident from the large range of εHf values (7.5 to -18.1).

Chapter 4 concludes that Ramgarh, Berinag Chiplakot and Munsiari Formations are part of the once continuous thrust sheet, the Ramgarh-Munsiari thrust sheet, which was modified by subsequent deformation and erosion, and preserve at the present erosional level in the form of isolated synformal klippe. The Almora thrust sheet and the Ramgarh-Munsiari thrust sheet are two geochemically different thrust sheets, the former has the Greater Himalayan affinity, whereas the latter is composed of Paleoproterozoic Lesser Himalayan rock. The Almora thrust sheet exhibits a flat-on-flat relationship with the underlying Ramgarh-Munsiari thrust sheet, and both have been folded by growth of the underlying Lesser Himalayan duplex. Growth of the

Lesser Himalayan duplex folded the overlying unit to form the Almora klippe and conformably folded the Ramgarh-Munsiari thrust sheet that crops out to the north and south of Almora klippe.

The fold-thrust belt is a forward propagating thrust system, typical of thin-skinned thrust tectonics, and there no evidence of basement involved tectonics as propose by others. A total of

541-575 km or 79-80% of shortening was accommodated between Main Frontal thrust and South

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Tibetan Detachment System; out of these this (541-575 km) shortening, the MCT has accommodated 163-128 km, the RMT has accommodated minimum of 112 km, the LHD has accommodated 270 km, the MBT has accommodated 8 km, and the Subhimalayan thrust system has accommodated a cumulative of ~22 km (14.9+7.5=22.4) of shortening. The Lesser

Himalayan duplex has taken up a substantial amount of shortening (270 km or 46-50% out of

541-575 km) and it is composed of an array seven stacked thrust sheets. By adding shortening in the Tethyan Himalyan, we estimate a total minimum shortening between 674-751 km in

Kumaun, NW India.

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