Initial Cenozoic Exhumation of the Northern Chinese Tian Shan Deduced from Apatite (U-Th)/He Thermochronological Data

Jingxing Yu,Yuqi Hao,Dewen Zheng,Yizhou Wang,Huiping Zhang,Chaopeng Li,Chris Yakymchuk

doi:10.2113/2022/8099539

Abstract

Abstract The present topography of Tian Shan is related to the India-Asia collision, whereas the mechanisms for the topographic growth of Tian Shan remain at the center of debate partly due to the poorly constrained onset timing of the Cenozoic tectonic deformation. Our new apatite (U-Th)/He (AHe) data in the northern Chinese Tian Shan suggest that rapid cooling commenced at 20.2±4.9 Ma along the northern margin, which is consistent with published fission-track data from the same area and confirms that the youngest component of fission-track has been totally annealed. Moreover, AHe data from the interior mountain suggest that enhanced cooling began at 28.0±2.3 Ma, which is slightly older than that from the northern edge of the mountain. Although thermochronological data suggest that both the interior and northern margin of the northern Chinese Tian Shan have undergone rapid cooling since the late Oligocene-early Miocene, well preservation of relict low-relief surfaces along the northern rim of the northern Chinese Tian Shan and published thermochronological data indicate that the northern Chinese Tian Shan may have experienced differential exhumation in the Cenozoic. Combining the thermochronological and geomorphological evidence, we propose a progressive northward growth model for the northern Chinese Tian Shan. During the late Oligocene and early Miocene, compressive deformation derived from the India-Asia collision have arrived at the northern Tian Shan to reactivate both the interior mountain and its northern margin, while intense exhumation was concentrated in the interior mountain range. Then, deformation extended northward into the foreland basin that may be initiated in the middle-late Miocene.

Highlights

The Tian Shan extends east-west for over 2500 km through central Asia (Figure 1(a)) with peaks exceeding 7000 m
Combining the agedepth plot and inverse thermal history modeling results, we suggest that rapid cooling/exhumation in the northern margin of the Chinese Tian Shan began at or slightly prior to 20:2 ± 4:9 Mean age (Ma), which is well consistent with the AFT results from Hendrix et al [15]
New apatite (U-Th)/He data from two sections reveal that enhanced cooling and exhumation commenced at or slightly prior to 20:2 ± 4:9 Ma and 28:0 ± 2:3 Ma for the northern margin and interior mountain of the northern Chinese Tian Shan, respectively

Summary

Introduction

The Tian Shan extends east-west for over 2500 km through central Asia (Figure 1(a)) with peaks exceeding 7000 m. The present-day structures of active faults and folds, surface ruptures of historical or prehistoric large earthquakes, and modern seismicity are widely distributed along the northern and southern flanks of the mountain ranges, and even in the interior mountains, it remains incompletely understood on when the deformation commenced and how it propagated in the Cenozoic. The timing of initiation of deformation in the Chinese Tian Shan is estimated to be ranging from the late Oligocene to Pleistocene (e.g., [2, 8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24]).

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Conclusion