Exhumation of the Qilian Shan and Miocene activity of the Haiyuan Fault: Insights from apatite (U-Th)/He thermochronology in the Laolongwan basin, northeastern Tibetan Plateau

The Tibetan Plateau, which is deformed by the collision between the Indian and Eurasian plates, is a natural laboratory to study intracontinental deformation related to northeastward growth of the Plateau. However, how and when the Tibetan Plateau propagated to its present-day margins remain unclear. The Qilian Shan and Haiyuan fault, which serve as the topographic and geological boundaries of high Plateau, are key to revealing the uplift and expansion of the Tibetan Plateau. Here, we present detrital apatite (U-Th)/He and reverse modelling results from the Laolongwan basin, which is interpreted as a pull-apart basin controlled by activity of the Haiyuan fault in the east portion of the Qilian Shan region. Our results reveal three stage tectono-thermal evolution of Qilian Shan: (a) late Jurassic to Cretaceous rapid exhumation; (b) late Cretaceous to middle Miocene tectonic quiescence period and (c) exhumation after middle Miocene. We suggest that the Jurassic to Cretaceous rapid exhumation might be related to the convergence of the Lhasa block with the Eurasian plate or regional extension during the Mesozoic closure of the Meso-Tethys, and the mid-Miocene accelerated exhumation was driven by Haiyuan fault activation related to the growth of the Tibetan Plateau to its northeastern margin. Thematic collection: This article is part of the Mesozoic and Cenozoic tectonics, landscape and climate change collection available at: https://www.lyellcollection.org/topic/collections/mesozoic-and-cenozoic-tectonics-landscape-and-climate-change Supplementary material: https://doi.org/10.6084/m9.figshare.c.7018149