Provenance and sedimentary evolution from the Middle Permian to Early Triassic around the Bogda Mountain, NW China: A tectonic inversion responding to the consolidation of Pangea

Abstract

Abstract The tectonic attribute and evolution of the Bogda Mountain are crucial to understand the Palaeozoic development of the Tian Shan and Central Asian Orogenic Belt (CAOB). In this work, we combined sedimentological and geophysical methods such as field section measurements, core analyses, well logs and seismic sections interpretation to study the sedimentary evolution from the Middle Permian to Early Triassic. In addition, provenance analysis was performed for the sediments from both flanks of the Bogda Mountain. This set of data allows to improve the constraint on the tectonic attribute and evolution in this area. The facies studies indicate abrupt changes in depositional environments from the lacustrine-alluvial fan to fan delta during the Middle to Late Permian. The subsidence centers shifted from the Paleo-Bogda Mountain to present Bogda piedmonts. Based on detrital zircon U-Pb geochronology, the North Tian Shan (NTS) Early-Middle Permian post-collisional plutons are identified as the main provenances of the Middle Permian deposits from both flanks. The Upper Permian sample shows a strongly concentrated unimodal age peak of ~305–320 Ma, indicating a single source from the NTS and Bogda Mountain. The Lower Triassic samples in the Chaiwopu Depression (CWD) in the south flank of the Bogda Mountain show obvious sources from the Central Tian Shan (CTS) but these are absent in all samples from the north flank of Bogda Mountain. Meanwhile, the Early Permian ages of ~280–295 Ma which correspond to the bimodal volcanism in the Bogda Mountain occur in both flanks of this mountain. According to the comprehensive geological evidence, the deposition of the Lower Permian–Middle Permian strata probably occurred in a rift extension and expansion setting. A tectonic inversion happened at the beginning of the Late Permian, which resulted in initial uplift of the Bogda Mountain. The uplift also occurred in the NTS and CTS in the Late Permian. This tectonic inversion happened for the whole Junggar Basin and was an important intracontinental tectonic movement, which might result from the consolidation of the Pangea supercontinent.