Distant effects of India–Eurasia convergence and Mesozoic intracontinental deformation in Central Asia: Constraints from apatite fission-track thermochronology
Section snippets
Introduction and location
In Central Asia, north of the India–Eurasia collision zone (north of the Tibetan Plateau), a vast array of active intracontinental mountain belts extends deep into the interior of the Eurasian continent (Fig. 1A): this is the Central Asian Deformation Zone (CADZ) or the Central Asian orogenic belt. In Russian literature the CADZ is often labeled as the Ural-Mongolian Fold Belt, while Sengör et al. (1993) refer to it as the Altaids. The CADZ stretches for over 5000 km, comprising the Tien Shan
Paleozoic
The CADZ basement was formed during the Paleozoic evolution of the Paleo-Asian Ocean (PAO) that extended amid Mesoproterozoic and older continental blocks (Baltica, Siberia, Tarim, Kazakhstan and North China) in the Early Neoproterozoic–Middle Paleozoic (Dobretsov et al., 1995, Khain et al., 2003). The PAO evolution marks an important phase in the formation, accretion and growth of Eurasia, leading to the present-day, complex blocky-mosaic architecture of the CADZ (Sengör et al., 1993).
Sampling areas
In the Tien Shan Mountains several E-W trending ranges in the vicinity of the intramontane Issyk–Kul Basin in northeastern Kyrgyzstan were sampled: (1) the central Terzkey Range; (2) the central Kungey Range; (3) the west Kungey Range (and Boom Canyon area); and (4) the Kindil Las Range (Fig. 5). All these ranges are formed by Ordovician granitoids that intruded the Precambrian basement of the CTS or Ili Microcontinent. The large (over 200 km long and up to 80 km wide) Issyk–Kul Basin is situated
Methodology and analytical procedures
For this study 75 crystalline basement rock samples yielded sufficient high-quality apatite crystals for apatite fission-track (AFT) analysis. Apatite was separated using conventional heavy liquid and magnetic techniques, embedded in epoxy resin, polished and dated with the external detector (ED) method (muscovite ED). Spontaneous tracks in the apatite were etched with a 2.5% HNO3 solution (70 s at 22 °C). Induced tracks in the muscovite ED were etched with a 40% HF solution (40 min at 22 °C).
Results and models
In this paper we focus on the general trends observed in the modeled cooling paths from the apatite samples of the Kyrgyz Tien Shan and Siberian Altai Mountains in the context of the geodynamic and tectonic evolution of Central Asia as a whole. In particular, we focus on the effects of Mesozoic Tethyan subduction and accretion events, and the subsequent Cenozoic India–Eurasia collision and ongoing convergence. Detailed description and analysis of the AFT results are reported elsewhere (De Grave
Interpretation and discussion
We interpret the various stages in the thermal histories of the Kyrgyz Tien Shan and Siberian Altai samples in the context of the Meso-Cenozoic accretionary tectonics and geodynamics affecting intracontinental Central Asia as outlined earlier. Our AFT data and models reconstruct a consistent thermotectonic evolution for Central Asia.
Mesozoic reactivation
Our AFT data and models show that the interior part of the Eurasian continent experienced important Mesozoic activity. After the Paleozoic assembly of Eurasia and its Permo-Triassic consolidation, growth and accretion of the continent continued throughout much of the Mesozoic. Convergence between northward drifting peri-Gondwanan fragments and the southern Eurasian margin, produced a large-scale subduction-accretion belt, ranging from the Okhotsk Sea in far eastern Siberia, all the way to the
Acknowledgements
We wish to thank Dr. R. Jonckheere, Prof. F. De Corte and A. De Wispelaere for help at various stages in the AFT research. Drs. B. Dehandschutter, D. Delvaux, R. Hus, J. Klerkx, L. Smirnova, K. Theunissen, E. Vassilieva, E. Vysotsky, and others are acknowledged for assistance during fieldwork and sampling. A critical review and comments by Dr. Mark Allen were greatly appreciated. Review comments by Dr. C. Johnson undoubtedly enhanced the quality of both contents and form of this paper. This
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