Abstract
The Kyzylkum-Nurata region represents a key area in understanding the tectonic evolution of the western Tian Shan. In this study, we present new thermochronological data (apatite fission track and apatite (U-Th-Sm)/He) and associated thermal history models for 45 igneous samples from the Kyzylkum-Nurata Segment of South Tian Shan on the territory of Uzbekistan and Tajikistan. Our data show that the Kyzylkum-Nurata Segment experienced a multi-phase Mesozoic thermal history that differs from previously studied segments of the Tian Shan. A Triassic (~220–200 Ma) cooling signal is widespread throughout the Tian Shan and is interpreted as being associated with exhumation following the closure of the Palaeo-Asian Ocean. Following this period of fast cooling, the Kyzylkum-Nurata Segment experienced a period of slow cooling and erosion in the Early Jurassic (~190–160 Ma). However, in contrast to other parts of the Tian Shan, our study area preserves evidence for rapid cooling during the Late Jurassic–Early Cretaceous (~160–120). Given that this rapid cooling signal was only recorded for samples in association with major structures (e.g., relic suture-shear zones), we interpret this event as a period of fault reactivation related with tectonic processes at the Eurasian margin of the Tethys Ocean. Subsequently, the Late Cretaceous–early Palaeogene (~100–50 Ma) is characterised by slow cooling and erosion. Since the late Palaeogene, the basement of the Tian Shan experienced cooling related to the India-Eurasia collision. The thermal signal of this collision has been extensively recorded in the high-altitude Kyrgyz Tian Shan. Within the low-relief Kyzylkum-Nurata Segment, this Cenozoic overprint is not recorded, allowing for a detailed assessment of the Mesozoic thermal and landscape evolution of the western Tian Shan. Our study demonstrates that the Cretaceous Uzbek Tian Shan was characterised by a series of parallel, linear mountain belts that formed along suture zones during fault reactivation.
Highlights
Central Asia hosts one of the world’s largest active orogen, the intracontinental mountain range of the Tian Shan
Mean track lengths are referred to their relative length following the outline established in Figure 5, with samples that produce mean track length (MTL) 12.9-13.5 μm refered to as “long”, MTLs of 12.6-12.8 μm are “moderate”, and MTLs of 11.4-12.5 μm are refered to as “short”
Detailed tables and figures for all single-grain apatite fission track (AFT), mean track length (MTL) data, individual thermal history models, and modelling parameters are available in Supplementary files (Supplementary files 1, 2, 3, and 4)
Summary
Central Asia hosts one of the world’s largest active orogen, the intracontinental mountain range of the Tian Shan. Throughout the Mesozoic and Cenozoic, progressive ocean closure along the southern margin of Eurasia generated regional deformation and the reactivation of existing structures (Bullen et al 2001, 2003, De Grave et al 2007, Glorie et al 2010, 2011, Jepson et al 2018) As a result, these intracontinental structures in the Tian Shan have been the focus of many geo- and thermochronological studies in order to generate a model for the formation of the Tian Shan intracontinental orogenic system These intracontinental structures in the Tian Shan have been the focus of many geo- and thermochronological studies in order to generate a model for the formation of the Tian Shan intracontinental orogenic system (e.g. Sobel & Dumitru 1997, Dumitru et al 2001, Bullen et al 2001, De Grave et al 2007)
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