Himalayan Thick-Skin Basement Deformation of the Ladakh Batholith, Leh-Ladakh Region, NW India

This book presents the first report and interpretation of the deformation, structural style, and geo-tectonic evolution of a 600km2 area of the Ladakh batholith, NW India, centred on the city of Leh, Ladakh. The Ladakh (and westerly Kohistan ) batholith comprises a large component of the Jurassic-Oligocene Kohistan-Ladakh Arc-Terrane (KLA), with magmatism spanning island arc, continental margin, and post-Himalayan collision tectonic environments. The KLA is bounded to the north by the Shyok-Northern Suture and to the south by the Indus Suture. The batholith illustrates basement thick-skin tectonic deformation and is divided/partitioned into a series of crustal blocks separated by lateral accommodation structures which allow independent movement in horizontal and vertical space. Thin skinned deformation within the adjacent sedimentary molasse Indus Suture Rocks produced large thrust stacks that predominantly moved towards the N-NE. Whilst deformation within cover sequences influences the basement structures, and helps break up the basement into crustal blocks, there is a clear distinction in deformation between the basement and cover sequences. Basement batholith deformation is more complex and heterogeneous, reflecting the variable transmission of tectonic stress within crystalline crust and the presence of a wide range of precursory inherited weaknesses and anisotropies. Models of time-space deformation are presented using data derived from field and extensive photograph / photo-mosaic image interpretation. The batholith was deformed during at least Palaeocene-Pliocene times at crustal depths that correspond to the ductile-brittle transition zone and shallower. Preface 7 Acknowledgements 9 Introduction 10 Contents 12 About the Author 14 List of Figures 15 List of Tables 43 1 Geo-tectonic and, Topographic, and Geographical Setting of the Leh–Ladakh Region: Study Scope and Methodology 44 1.1 Broad Geo-tectonic and Geographical Contexts of This Study 44 1.2 Research Objectives and Methodology of This Study 50 References 53 2 Overview of the Geology, Structure, and Tectonics of the Ladakh Batholith and Indus Suture Rocks 54 2.1 Overview of the Kohistan–Ladakh Batholith 55 2.2 Overview of the Indus Suture Rocks 60 2.3 Broad Palaeo-environments and Unroofing Evidence Recorded by the Indus Suture Rocks 66 2.4 Structure, Deformation, and Uplift of Ladakh, with References to Kohistan 69 References 75 3 Geology and Lithological Variations of the Ladakh Batholith Within the Leh–Ladakh Region 81 3.1 Batholith Overview in the Leh–Ladakh Region 81 3.2 Meta-sedimentary Rocks 83 3.3 Gabbro–Diorites 89 3.4 Granodiorites–Granites (Granitoids) 91 3.5 Minor Intrusions and Assorted Minerals Veins 92 3.6 Larger Scale Examples from the Batholith 95 3.7 Summary of the Key Aspects of the Leh–Ladakh Batholith and Intrusive-Deformation Model 98 Reference 106 4 Structural Geology of the High Strain Zone: Ladakh Batholith, Leh Region, NW India 107 4.1 The Structuctural High Strain Zone (HSZ) 108 4.2 Taroo High Strain Zone Structural Geology 111 4.3 Phyang High Strain Zone Structural Geology 114 4.4 Leh Valley High Strain Zone 117 4.5 Saboo–Shey–Thiksey–Stakna High Strain Zone 127 4.6 Whole-High Strain Zone Structural Synthesis 134 4.6.1 Primary and Secondary Fracture/Thrust/Shear Structural Data Analysis 134 4.6.2 High Strain Zone (HSZ) Structural Data Synthesis 139 Reference 142 5 Structural Geology of the Northern and North-Eastern Zone (N–NE Zone), Leh–Ladakh Region 143 5.1 Introduction, Zonal Structural Styles, and Variations 143 5.2 Structural Data, Geological Cross Sections, and Structural Analysis of the N–NE Zone 153 6 Structure and Lithology of the Indus Suture Rocks (Indus Formation) in the Leh–Ladakh Region 160 6.1 Scope of This Chapter 160 6.2 Lithological Characteristics of the Indus Suture Rocks in the Leh–Ladakh Region 161 6.3 Structural Interpretation of the Indus Suture Rocks (ISR) in the Leh–Ladakh Region 165 7 Deformation Model for the Ladakh Batholith in the Leh–Ladakh Region 172 7.1 Geotectonics Structure and Deformation 172 7.2 Crustal Deformation Model: Fractured Basement 179 References 188