STUDY OF THE RECENT STRUCTURAL EVOLUTION OF CONTINENTAL BASINS IN ALTAI-SAYAN (CENTRAL ASIA)

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OUTLINE

The active deformation in most of Northeast Altai ( chapter 1 ) is far from understood, mainly because of the poor tools geologists have in assessing active structures and determining active faults in basement terranes. Except from the historical earthquake related fault movements and deformation in large Cenozoic basins such as Chuya and Zaisan, the timing of Cenozoic faulting and related deformation remains unknown. The Cenozoic kinematics of the major faults in the region has only been estimated from single-image remote-sensing and large-scale modelling on lithospheric scale, and detailed remote-sensing and field-based data are lacking. The behaviour of the tectonic stress field in highly heterogenous basement terranes and its relation to the active and upper crustal movements are poorly understood. And finally, the perception of the tectonic and geodynamic meaning of the specific wrench-zone related deformation in the area, combining range uplift with extensional basin formation is poor.

The study area a is typical locality of complex active deformation that is difficult to assess by classical geological and/or geophysical tools (based on stratigraphy), due to the lack of a developed stratigraphic sequence for the Cenozoic. We focus on the determination of active and recent deformation and tectonism, using remote sensing, structural field observations and geophysical information. The use of these methods is discussed in the following three chapters (chapter 2 , chapter 3 and chapter 4 ). Chapter 5 gives a synthesis of the way the different methods can be combined to deduce information concerning the active deformation and local tectonism.

The problem of extensional basin formation in the transpressional deformation zone under study is addressed by investigating the largest extensional basin in the area, the Lake Teletskoye basin. This basin forms a key structure in the junction between different tectonic terranes. Based on the new observations, we propose a conceptual model for its development. We show how it can serve as an example displaying the architecture, kinematics and dynamics of the initial stage in the development of an extensional basin, due to its very young age. It can serve as a example of a possible analogue to the initial structures of deep rifts such as Baikal and Tanganyika. The Teletsk basin is discussed in detail in Chapter 6 .

The active tectonics of the Shapshal zone (numbers 3, 4 and 6 on fig. 1.10) and related structures in northeast Altai (numbers 3, 4 5 and 8 on fig. 1.12), and their relation with the Teletsk basin, are discussed in detail in Chapter 7 . The structural details of the active structures in West-Sayan and Tuva (numbers 7, 11-16 on fig. 1.10), that generally trend northeasterly to easterly (right part of fig. 1.10, fig. 1.11 and fig. 1.12) and their relation to basin formation are discussed in Chapter 8 .

The last part (Chapter 9 ) summarizes the conclusions and present a deformation model for the area.




TABLE OF CONTENTS          I

ACKNOWLEDGEMENT         IV

SAMENVATTING         V

INTRODUCTION           1


        PART I

CHAPTER 1 .     GEOLOGICAL AND GEODYNAMICAL SETTINGS OF ALTAI-SAYAN    4
         1.1     Location    4
         1.2     Physiography    6
         1.3     Geodynamics    9
             1.3.1     Introduction    9
             1.3.2     Basement structure    9
             1.3.3     The stress field in the Central Asia    11
             1.3.4     The deep structure    12
                Introduction    12
                The mantle    13
                The crust    14
             1.3.5     Models of deformation    16
             1.3.6     The Altai-Sayan zone    21
                Kinematics and seismicity in Altai and Sayan    21
                Seismicity    21
                Active faulting    23
                Seismotectonics    23
                Pre Cenozoic Tectonics    25
                Active tectonics    27
         1.4     Outline of the study    30


CHAPTER 2.      MORPHOLOGICAL ASPECTS: RELIEF ELEMENTS    31
         2.1    Introduction    31
        2.2     Digital Terrain Models    32
        2.3    Satellite imagery and photo-geology    40
        2.4    Remote sensing as a tool for tectonic analysis and interpretation: structural relations    45
            Introduction    45
            Morphotectonics    47
            Lineament analysis    47

CHAPTER 3.       SUB-SURFACE ASPECTS: SEISMICS AND RADON    49
        3.1     Introduction    49
        3.2     A high resolution seismic reflection study    50
        3.3     A gas-geochemical study    53


CHAPTER 4.     MICRO-STRUCTURAL ANALYSIS OF FAULT MOVEMENTS: FAULT KINEMATICS AND PALEOSTRESS         57
        4.1     Problem statement: stress and strain    58
        4.2     Paleostress reconstructions    60
        4.3     Fault rocks, rheology and depth of faulting    62
                4.3.1    Rheology: Model of a shear zone    62
                4.3.2    Fault rock and slickenlines    66
                Gauge and fault breccia    67
                Cataclasite    67
                Pseudotachylyte    68
                Slickensides    68
        4.4     Fabrics in fault zones    70
        4.5     Application: use and limits    71


CHAPTER 5.     SYNTHESIS: STRUCTURAL-TECTONIC MODELS AND TIMING RECONSTRUCTION        73
        5.1    Introduction    73
        5.2    The interpretation of structural elements    73
            5.2.1    Extensional tectonics    74
            5.2.2    Contractional tectonics    77
            5.2.3    Transcurrent tectonics    79
            5.2.4    Oblique-slip tectonics    81
        5.3    Timing reconstructions    83
        5.4    Concluding remarks    84

   
    PART II

CHAPTER 6.      THE TELETSK BASIN    85
        6.1    General background    86
        6.2     Main basement shear zones    87
        6.3     Structural features of on-shore geology    90
            6.3.1     Satellite images and photo-geology: lineament analysis    90
            6.3.2 Morphotectonics: integrating remote sensing and field observations    91
                Morphology of the lake border faults    91
                Structural field-investigations    92
                 The West-Sayan fault zone    95
                 The Altyntauss massif    102
                 The Kyga region    105
            6.3.3    Paleostress Reconstructions    107
                Methodology    107
                Results    108
                Discussion    109
            6.3.4    Conclusions    112
        6.4    Structural deformation within the sediment column    113
            6.4.1    Structural characteristics of the basin fill    113
            6.4.2    Seismic sections    117
                Seismic refraction profile    117
                Seismic reflection profiles    118
                 The deeper sequence    118
                 The shallow sequence    124
                Summarized structural outline of the basin    127
                Timing criteria    129
        6.5    Gas geochemistry: radon emanation and exhalation    130
            6.5.1    Results    130
                Radon emanation and exhalation    130
                Mercury    138
            6.5.2    Discussion    139
                Radon emanation and exhalation    139
                Radon in water    141
                Mercury    142
            6.5.3    Conclusions    143
        6.6    Kinematic evolution of the Teletsk basin: a synthesis    144


CHAPTER 7.      NORTHEAST ALTAI    149
        7.1    Introduction    149
        7.2     Basement structure    150
        7.3     Cenozoic evolution    151
            7.3.1    Dzhulukul basin    152
            7.3.2     South Chulyshman-Yazula region    157
            7.3.3     The Chulyshman valley    160
            7.3.4     Shapshal-Kyga    163
        7.4    Synthesis    165


CHAPTER 8.      TUVA AND WEST-SAYAN     169
        8.1    Introduction    169
        8.2    Tannu-Ola and the Ubsu-Nuur basin    171
        8.3    The Khemchuk depression    175
        8.4    The West-Sayan fault    176
        8.5    Conclusions    177


    PART III

CHAPTER 9.      SYNTHESIS    179
        9.1     The study of active deformation in mountainous basement terrains    179
        9.2     Kinematics and dynamics of the studied regions    181
            9.2.1     Wrench deformation    181
            9.2.2     Contractional deformation    182
            9.2.3     Extensional basin formation    183
            9.2.4     Differences between Altai and Sayan-Tuva    183
            9.2.6     Concluding remarks    184

APPENDIX A. Technical aspects of bathymetric mapping    187

APPENDIX B. Basic concepts used in dynamic fault analysis    189

APPENDIX C. Methodology for statistical determination of the reduced paleostress tensor    197

APPENDIX D. Compilation of the interpreted high resolution seismic sections    198


REFERENCES     200