title of the thesis - Department of Geology - Queen's University

2.5.1.2 Descriptions of quartz CPO patterns ...................................................................... 38
2.5.1.3 Quartz CPO deformation temperatures .................................................................. 45
2.5.2 Rigid clast vorticity analysis ......................................................................................... 47
2.5.3 Summary of microstructural analyses ........................................................................... 50
2.6 Geochronology and thermochronology ............................................................................... 52
2.6.1 U-Th-Pb monazite geochronology ................................................................................ 53
2.6.1.1 Methodology .......................................................................................................... 54
2.6.1.2 Results .................................................................................................................... 55
2.6.1.3 Summary of U-Th-Pb geochronology .................................................................... 69
2.6.2 40 Ar/ 39 Ar thermochronology .......................................................................................... 71
2.6.2.1 Methodology .......................................................................................................... 72
2.6.2.2 Results .................................................................................................................... 74
2.6.2.3 Summary of 40 Ar/ 39 Ar thermochronology .............................................................. 79
2.7 Discussion ............................................................................................................................ 81
2.7.1 South-directed extrusion of the GHS ............................................................................ 83
2.7.1.1 Initial south-directed extrusion .............................................................................. 83
2.7.1.2 Timing of south-directed extrusion ........................................................................ 84
2.7.2 Orogen-parallel extension ............................................................................................. 85
2.7.2.1 ESE-WNW deformation and exhumation .............................................................. 85
2.7.2.2 Timing of ESE-WNW deformation and cooling ................................................... 87
2.7.3 Transition from south-directed extrusion to orogen-parallel extension ........................ 88
2.7.3.1 Upper Karnali valley .............................................................................................. 88
2.7.3.2 Himalayan transition .............................................................................................. 90
2.7.4 Tectonic model explaining orogen-parallel extension .................................................. 94
2.8 Conclusions .......................................................................................................................... 97
Chapter 3 Discussion ................................................................................................................... 99
3.1 Summary .............................................................................................................................. 99
3.1.1 Middle Miocene orogen-parallel extension and east-directed lower-crustal flow ........ 99
3.2 Future research considerations ........................................................................................... 103
3.2.1 Why did south-directed mid-crustal extrusion cease, and why did east-directed lower
crustal flow initiate ............................................................................................................. 103
3.2.2 Is the Karakoram fault linked to faults of the upper Karnali valley .......................... 104
Chapter 4 Microstructural analyses: proposals for advancing and validating current
techniques ................................................................................................................................... 106
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