ASPECTS OF EXHUMATION OF ROCKS IN EXTENSIONAL AND COMPRESSIONAL MOUNTAIN BELTS. A COMPARATIVE STUDY A thesis submitted to the Faculty of Natural Sciences, Karl-Franzens-Universität Graz (University of Graz), Austria, in partial fulfillment of the requirements for the degree of Doctor of Science By SYED ALI TURAB Institute of Earth Sciences Karl-Franzens-Universität Graz (University of Graz) Austria (November 2016) Acknowledgements I would like to thank Kurt Stüwe for supervising this work and providing continuous support and freedom during these four years. Fin Stuart (SUERC, Glasgow) is also thanked for his help and guidance during lab analysis. David Chew and Nathan Cogné (TC, Dublin) are acknowledged for AFT and apatite U-Pb analysis and providing help in understanding and running thermal history modelling software, the QTQt. Luigia Di Nicola, Mahmoud Hassan, Gustav Hanke, Tamer Abu-Alam, Jamil Hassan, Gisela Domej, Angela Oswald, Sylvia Umschaden, Daniel Döpke, Katarzyna Luszczak, Christoph Pucher and Elena Sizova are also thanked for providing help at various stages. All thanks to the friends in the Saudi Geological Survey (SGS) Geologic Mapping Unit, headed by Khalid A. Kadi and the field group Saad M. Al Garni, Mubarak M. Al Nahdi and Abdullah Al Shammari are thanked for providing help in the field. This work was financially supported by Higher Education Commission (HEC) of Pakistan and Austrian Agency for International Cooperation in Education and Research (OeAD- GmbH) at different levels. Partial support for the field work was provided by Heinrich-Jörg Stiftung funding scheme of University of Graz, Austria, National Centre of Excellence in Geology (NCEG), University of Peshawar, Pakistan, and Saudi Geological Survey (SGS). At last but not the least, I thank my family and friends whose constant support helped me to achieve this goal. i Turab, S.A., 2016 Table of Contents Acknowledgements .................................................................................................................... i Table of Contents ..................................................................................................................... ii Preamble and Outline of the thesis ........................................................................................ iv Abstract .................................................................................................................................... vi Zusammenfassung ................................................................................................................. viii Chapter 1. New constraints on exhumation of the western Himalayan syntaxis. A low temperature thermochronometry of the Neelum River region, Pakistan ........................... 1 ABSTRACT ........................................................................................................................................ 2 INTRODUCTION ............................................................................................................................... 3 GEOLOGICAL BACKGROUND ...................................................................................................... 5 LOW TEMPERATURE THERMOCHRONOLOGY: SAMPLES AND TECHNIQUES ................ 8 THERMOCHRONOLOGICAL RESULTS ..................................................................................... 10 MORPHOLOGICAL ANALYSIS .................................................................................................... 16 DISCUSSION ................................................................................................................................... 20 Tectonic Interpretation .................................................................................................................. 22 Cause of Exhumation .................................................................................................................... 25 CONCLUSIONS ............................................................................................................................... 27 Chapter 2. Escarpment evolution at the Red Sea continental margin of southwestern Saudi Arabia ........................................................................................................................... 29 ABSTRACT ...................................................................................................................................... 30 INTRODUCTION ............................................................................................................................. 31 GEOLOGICAL BACKGROUND .................................................................................................... 35 LOW TEMPERATURE THERMOCHRONOLOGY: SAMPLES AND TECHNIQUES .............. 37 THERMOCHRONOLOGICAL RESULTS ..................................................................................... 38 Line 1 ............................................................................................................................................. 40 Line 2 ............................................................................................................................................. 40 Line 3 ............................................................................................................................................. 47 Line 4 ............................................................................................................................................. 48 MORPHOLOGICAL ANALYSIS .................................................................................................... 48 DISCUSSION ................................................................................................................................... 50 Total Amount and Timing of Uplift .............................................................................................. 50 Escarpment Evolution ................................................................................................................... 55 Concept of Rifting/Active Vs Passive Rifting ............................................................................... 57 ii Turab, S.A., 2016 CONCLUSIONS ............................................................................................................................... 60 Chapter 3. Overall Conclusions ............................................................................................ 61 Appendix A ............................................................................................................................. 64 Appendix B .............................................................................................................................. 69 References ............................................................................................................................... 76 iii Turab, S.A., 2016 Preamble and Outline of the thesis Exhumation of rocks in orogenic belts may occur due to the three end member processes of (a) extension, (b) erosion and (c) selective exhumation in compressional tectonics due to ductile flow (Ring, et al., 1999). In extensional environments, normal faulting can directly be responsible for the exhumation of rocks. The classic example of this type of exhumation is the formation of metamorphic core complexes (Lister and Davis, 1989), where normal faults are the direct agent responsible for the exhumation of high grade metamorphic rocks from mid crustal levels to the surface. In the field, this process is evidenced by the presence of normal faults bounding the exhumed rocks. Conversely, erosion can also be directly responsible for the exhumation. Clearly, this process is only possible if there is topography, so that exhumation by erosion is usually directly correlated with mountain building. In compressional mountain belts, erosion is the typical exhuming process (e.g. England, 1981). Finally, selective exhumation by ductile flow is a process that allows spatially confined bodies of rocks to be squeezed to the surface, often in compressional environments. The exhumation of individual eclogite bodies in subduction zones is an example for this process (Chemenda, 1995). Much debate has been given to the relative importance of these three processes in orogenic belts. One of the principal discriminating pieces of evidence is the distribution of exhumation of rocks in space and time and its relationship to active deformation features. In order to contribute to this debate, two of the globally most spectacular examples of mountain building in contrasting tectonic environments were chosen and the exhumation processes studied. In particular, I have chosen: (a) the western syntaxis region of the Himalayan orogeny around Nanga Parbat as a text-book example to study the exhumation processes in a mountain belt formed by collision of two plates and (b) the 3000 m high mountains of the western Saudi Arabian escarpment as an exemplary mountain belt formed due to a divergent plate margin, namely that between Africa and the Arabian sub-continent. In my study, I have focused on the exhumation of rocks in the uppermost crust, a process that can be studied with the aid of low- temperature thermochronology. Accordingly, the thesis is structured in the form of three chapters and two appendices. In Chapter 1, a multi-method approach is used to study the exhumation of rocks in northwest Himalayan syntaxis region. So the geomorphic analysis of the region are combined with results of multiple thermochronometric methods