FACULTY OF SCIENCES Master of Science in geology Coupling basement and detrital thermochronology to constrain Meso-Cenozoic intramontane basin evolution in the northern Tien Shan (Central Asia) Simon Nachtergaele Academic year 2015–2016 Master’s dissertation submitted in partial fulfillment of the requirements for the degree of Master in Science in Geology Promotor: Prof. Dr. Johan De Grave Tutor: Elien De Pelsmaeker Jury: Prof. Dr. Marc De Batist, Dr. Damien Delvaux “Not everything that counts can be counted, and not everything that can be counted counts.“ (Albert Einstein) Acknowledgements First of all I want to thank my thesis promoter Prof. Dr. Johan De Grave for the creation of this thesis subject and giving me the possibility to join the team on the Kyrgyz field. He also corrected my strange grammar constructions and last but not least for the time that he invested in me, while he was very busy with teaching and research. Research on geochronology is time-consuming and the interpretation of geochronological data is often complex. I experienced geochronology in Central-Asia as a challenging and therefore attractive research subject. The next person that I want to thank is research assistant Elien De Pelsmaeker. Despite the heavy teaching load, she always was available for answering my questions. She also calmed me down when a lot of samples appeared to be worthless in november/december 2015. Also during the ‘zircon U/Pb disappointment’, we stayed calm and decided to focuse more on apatite fission track analysis. Our team work in the Tien Shan mountains during the summer of 2015 was an unforgettable experience. I am very grateful to Ann-Eline Debeer because she helped me out when ±10 AFT samples appeared to be not useful. Thank you for doing the separations of the ‘KB’ basement samples of the 2015 field campaign. Jan Jurceka is also thanked for making the thin-sections. The next person I want to thank is Dr. Fedor Zhimulev. He was of great help during the field work and is a great field geologist in my opinion. His translations of Russian literature about the Kyrgyz Tien Shan were of great value. The discussions about AFT, sedimentology and the activity of the Talas Fergana Fault were interesting. Prof. Dr. Marc Jolivet also was also an important member of the field work team. I am very grateful for the sedimentary logs that I received from him. It is also because of him that we could have a workshop on thermochronological modelling with QTQt. This workshop was given by Dr. Kerry Gallagher and he succeeded to bring an attractive and interesting workshop about Bayesian statistics. During the field work, Vlad and Elena Batalev perfectly assisted us in the remote mountains of Kyrgyzstan. Driver Vladimir is also a thanked for the stories about the hidden treasures on the bottom of the Issyk Kul Lake and especially for his great driving skills. Prof. Dr. Stijn Glorie did apatite fission track analysis on a few samples in Kyrgyzstan and I am grateful that I can publish his results in this thesis. Gerben Van Ranst is also thanked for answering my questions on Adobe Illustrator. The discussions on geochronology and sample preparation were fruitful. I The other professors and assistants deserve a lot of respect, because I really enjoyed the lessons and practicals. The nice atmosphere among students and staff members keeps the students motivated. The field trips to the Alps, the Boulonnais region and many other regions were the most instructive days in which we learned a lot. My girlfriend Ama always supported me – in easy and difficult days – during these five year. Even though she was volunteering in Nicaragua for a half of a year, I had the feeling that she was close to me. Last but not least, my family (especially my mom) deserves to be thanked for supporting me and paying my studies. Not every boy of 18 years gets the opportunity to study for five years. Спасибо за кумыса Simon Nachtergaele 30/05/2016 II TABLE OF CONTENT ACKNOWLEDGEMENTS I INTRODUCTION 1 CHAPTER 1: THE APATITE FISSION TRACK METHOD 3 1.1 Fission tracks: definition and formation 3 1.2 Fission track revelation and identification 4 1.3 Principles of the apatite fission track method 4 1.3.1 Thermal neutron fluence 5 1.3.2 The fundamental age equation 6 1.4 Calibration with age standards (zeta-calibration) 6 1.4.1 Age standards 7 1.5 The thermal stability of fission tracks 8 1.5.1 Kinetic parameters influencing annealing behaviour 8 1.6 Fission tracks and thermochronology 9 1.6.1 Track length distribution and its geological significance 9 1.6.2 Closure temperature, cooling ages and the apatite partial annealing zone 10 1.7 Geological interpretation of apatite fission track age data 12 1.7.1 Cooling rate 12 1.7.2 Denudation, exhumation and uplift 12 1.7.3 Horizontal and vertical sampling profiles 12 1.8 Multi-method approach: AFT and zircon (U-Th)/He 13 1.9 Thermochronological modelling 14 1.9.1 Introduction to QTQt 15 1.9.2 Modelling with QTQt 16 1.9.3 RadialPlotter and DensityPlotter 19 CHAPTER 2: DETRITAL THERMOCHRONOLOGY 21 2.1 Introduction to detrital thermochronology 21 2.2 Erosion and sediment generation estimations 24 2.2.1 Quantification of erosion rates with thermochronology 25 2.3 Thermal maturity estimation 28 2.3.1 Thermal maturity estimations in sedimentary basins based on organic material 28 2.3.2 Thermal maturity estimations in sedimentary basins based on low-temperature thermochronology 28 CHAPTER 3: FROM SAMPLING TO AFT ANALYSIS 30 3.1 Report of field work 30 3.2 AFT sample preparation 31 3.2.1 Heavy mineral separation 31 3.2.2 Heavy mineral selection 31 3.2.3 Mounting procedure 32 3.2.4 Irradiation at nuclear reactor BR1 33 3.3 Zeta-factor age calibration 34 3.3.1 AFT counting procedure 34 3.3.2 AFT length measurements 35 3.3.3 AFT-analysis: calibration by glass dosimeters 35 3.3.4 AFT-analysis: calibration by age standards 37 III CHAPTER 4: GEOLOGICAL CONTEXT 38 4.1 Introduction to the Central Asian Orogenic Belt 38 4.2 Precambrian and Palaeozoic evolution of the CAOB 38 4.2.1 Precambrian geodynamical evolution 38 4.2.2 Palaeozoic evolution: assembly of the Kyrgyz Tien Shan 39 4.3 Mesozoic evolution 42 4.3.1 Late Triassic – Early Jurassic event 43 4.3.2 Middle-Jurassic peneplanation 44 4.3.3 Late-Jurassic – Cretaceous cooling 44 4.3.3.1 A short note on AFT ages in fault zones 47 4.3.4 Mesozoic intramontane basins in the Kyrgyz Tien Shan 49 4.3.4.1 East of TFF: Kavak and Issyk Kul basin 50 4.3.4.2 West of the TFF: Tash Kumyr 51 4.3.4.3 West of the TFF: East Fergana basin 52 4.4 Mesozoic volcanism in the Tien Shan region 54 4.4.1 Early-Jurassic volcanism 54 4.4.2 Mantle plume activity in the CAOB? 54 4.5 Cenozoic evolution 57 4.6 Evolution of the Talas-Fergana Fault (TFF) 59 4.6.1 Late Palaeozoic and Mesozoic activity 59 4.6.2 Cenozoic reactivation 60 4.7 Jurassic and Cretaceous climate 61 CHAPTER 5: RESULTS 62 5.1 Sample overview 62 5.2 Sedimentary logs 64 5.2.1 Paleosol occurence 66 5.3 Apatite fission track (AFT) data on basement rocks 67 5.3.1 Track length measurements 69 5.3.2 Thermal history modelling results with QTQt 72 5.4 AFT data on detrital rocks 76 5.4.1 Track length distributions 80 5.5 Zircon(U-Th)/He data 83 CHAPTER 6: DISCUSSION 85 6.1 Basement AFT and zircon (U-Th)/He data 85 6.1.1 Thermal history model compilation 87 6.1.2 Mesozoic basement cooling in the NTS 88 6.1.3 Mesozoic activity of the TFF based on basement AFT and zircon (U-Th)/He data 90 6.2 Detrital apatite fission track thermochronology 91 6.2.1 East Fergana basin samples (west of TFF) 91 6.2.1.1 KS13-22 91 6.2.1.2 KS 13-19 and KS 13-20 91 6.2.2 Lower-Jurassic samples of Minkush (east of TFF) 92 6.2.3 Issyk Kul sections (east of TFF) 93 6.2.3.1 SK 46 93 6.2.3.2 SK 47 94 6.2.3.3 KS 136, KS 137, KS 138 and KS 139 95 6.3 Geodynamic events and thermochronology in the Kyrgyz Tien Shan 96 IV CHAPTER 7: CONCLUSION 99 REFERENCES I APPENDICES: XIII A. Geological Map of Central Asia and Adjacent areas (version 2008): xiii B. International Chronostratigraphic chart (version 2016) xv C. Complete AFT dataset of basement samples of the Kyrgyz Tien Shan xvi V Introduction The 2000km long Talas-Fergana fault (TFF) represents the largest strike-slip fault in Central Asia. The TFF is mainly located in Kyrgyzstan and divides the country in two distinct domains that are displaced over a large distance. The TFF is one of the ancient Palaeozoic inherited faults of the ancestral Tien Shan mountain belt that is reactivated today and makes of Kyrgyzstan one of the most mountainous countries in the world. The Tien Shan has mountain peaks up to 7400m and is located in the countries of Kazakhstan, Kyrgyzstan and China. It represents an ideal study area for intracontinental deformation in the Central Asian Orogenic Belt (CAOB). Tectonic movements of the TFF are recorded as early as the Late Palaeozoic, continued during the Mesozoic and are reactivated in the Late Cenozoic (Bande et al., 2015) as response to ongoing India-Eurasian convergence.