Thermochronological constraints on the Meso-Cenozoic tectonic evolution of the Haiyuan-Liupanshan region, northeastern Tibetan Plateau

Abstract

The Cenozoic outward growth of the Tibetan Plateau is traditionally considered to be responsible for the arcuate structures in the northeastern Tibetan Plateau. However, it is still unclear how pre-Cenozoic tectonics contributed to this unique geomorphic setting. To decipher the Meso-Cenozoic tectonic evolution, we systematically summarize the published thermochronological data and perform a low-temperature thermochronology study on Paleozoic-Mesozoic samples from the Haiyuan-Liupanshan region. Apatite fission-track ages from the new samples vary widely, ranging from 158.4 Ma to 34.4 Ma. Apatite fission-track and (U-Th-Sm)/He thermal history modeling, constrained by zircon fission-track data and geological evidence, indicate that this area experienced multiple stages of cooling from the Late Triassic to the Cenozoic. These cooling events include (i) Late Triassic-Early Jurassic, (ii) Late Jurassic-Early Cretaceous, (iii) Late Cretaceous-Early Cenozoic, and (iv) Late Cenozoic (~7 Ma). Late Triassic-Early Jurassic cooling was driven by the collision of the Nouth China Plate and the Sorth China Plate. The Late Jurassic-Early Cretaceous tectonothermal event is interpreted as a record of the intracontinental orogeny in East Asia. It is possible that Late Cretaceous-Early Cenozoic exhumation was the far-field response to the Neo-Tethyan subduction under the Lhasa terrane. In addition, Late Cenozoic (~7 Ma) rapid cooling in the Yueliangshan Range (southern part of the Haiyuan-Liupanshan region) was a result of the intense activation of the easternmost Haiyuan fault, in response to the outward growth of the Tibetan Plateau. These findings suggest that pre-Cenozoic tectonics played an important role in the growth of the present-day northeastern Tibetan Plateau edifice.