Mesozoic exhumation of the northern West Junggar, NW China: Insights from low-temperature thermochronometers

Abstract

As an important component of the Central Asian Orogenic Belt (CAOB), the West Junggar represents a natural laboratory to explore intracontinental deformation in a complex terrane. Although some low-temperature thermochronological studies have been conducted in this range, the number of exhumation stages and the corresponding driving forces behind exhumation remain highly debated. In particular, the exhumation history of the northern West Junggar remains poorly studied owing to a lack of data. Here, we present a study that integrates apatite fission track (AFT) and (UTh)/ He (AHe) dating from the igneous rock in the Sawur Mountains in northern West Junggar to further constrain the exhumation history of the region. AFT dating of the samples dominantly yields Late Triassic ages (200–227 Ma) with mean track lengths (MTLs) varying between 13.33 and 14.98 μm, while AHe dating produced widely dispersed Late Triassic to Late Cretaceous single grain ages (73–215 Ma), with sample mean ages between 100 and 195 Ma. Inverse thermal history modeling of our results and analysis of age-elevation relationships reveal that the Sawur Mountains experienced an extended period of rapid cooling related to local exhumation during the Middle–Late Triassic. A gradual reduction in surface relief following rapid erosion is related to peneplanation processes. The timing and patterns of this exhumation indicate it was caused by reverse oblique-lip reactivation of older strike-slip faults, and it can be explained as the response to the far-field effects of the final closure of the Paleo-Asian Ocean.