Cenozoic cooling history of the North Qilian Shan, northern Tibetan Plateau, and the initiation of the Haiyuan fault: Constraints from apatite- and zircon-fission track thermochronology

Abstract

The growth of the Tibetan Plateau resulted primarily from India-Asia convergence since initial collision at 65–55 Ma. The Cenozoic Qilian Shan thrust belt and the left-slip strike Haiyuan fault system together define the northeastern margin of the plateau. Although these thrust and strike-slip fault systems play an important role in accommodating continental convergence, our knowledge of the temporal and spatial distribution of upward and outward growth of the northeastern Tibetan Plateau is still lacking. In this study, we integrate new geologic mapping and low-temperature themochronometry (apatite- and zircon-fission-track ages) to provide constraints on the uplift and cooling history of the North Qilian Shan and the initiation of the Haiyuan fault. Cooling ages and thermal history modeling from a traverse across a prominent restraining bend on the Haiyuan fault suggest the North Qilian Shan experienced a three-phase cooling history, including: (1) broad cooling during the Late Triassic to early Cenozoic, (2) long-term tectonic quiescence from late Cretaceous to middle Miocene, and (3) rapid cooling and exhumation from ~15–10 Ma to present. We relate this most recent local cooling (~15–10 Ma) to the initiation of strike-slip faulting along the central Haiyuan fault, which corroborates other recent studies, suggesting a middle Miocene activation of strike-slip deformation along the Haiyuan fault in northern Tibet.