Exhumation history of the metal-rich Chinese Altai: insights from apatite fission track thermochronology

Abstract

The Chinese Altai is located in northern China and represents a section of the Altai Mountain range that extends through Mongolia to the east, Kazakhstan to the west and Siberia to the north. The Altai is one of the key structures of the Central Asian Orogenic Belt, which is the world’s largest intracontinental orogen. This study uses apatite U-Pb and fission track analysis on granitoid samples to constrain the post-magmatic cooling and exhumation history of the Chinese Altai. The apatite samples yield Lower Devonian-Jurassic U-Pb dates, which reflect cooling contemporaneous with (1) the subduction and closure of the Palaeo-Asian Ocean (2) regional oroclinal bending and (3) the Qiangtang collision. Apatite fission track data record varying thermal histories with respect to faults and shear zones that dissect the study area. The analysed samples preserve three cooling histories; (1) fast cooling in the Early Jurassic in response to the Qiangtang collision; (2) slow cooling or thermal quiescence during the Jurassic and Early Cretaceous; and/or (3) fast cooling in the mid-late Cretaceous in response to distant tectonic events such as mountain building in the Mongol Okhotsk Orogenic Belt or extension in the Tethys Ocean. Additionally, all models show rapid Neogene cooling (since ~ 30 Ma) which can be interpreted as a far-field response to the India-Eurasia collision and convergence. Cretaceous rapid cooling is primarily recorded to the east and along fault-splays of the Fuyun Fault, a major NNW-SSE strike slip fault in the study area. The results obtained in this study within the Chinese Altai are consistent with those of previous studies further west along other NW-SE orientated shear zones and contribute to our understanding of stress propagation throughout Central Asia in response to far-field tectonic stress tensors.