Late Paleozoic to Jurassic tectonic evolution of the Bogda area (northwest China): Evidence from detrital zircon U–Pb geochronology

Abstract Since the Cenozoic, the Tian Shan is rejuvenated by crustal shortening related to the ongoing India–Asia collision. However, the tectonic process prior to the Cenozoic remains ambiguous, especially in the Bogda area of the eastern Tian Shan. The continuous Late Paleozoic–Mesozoic sequences in the Bogda area record abundant information about the basin–mountain interaction. U–Pb (LA–ICP-MS) dating of detrital zircons from seven sandstone samples from Permian to Jurassic was used to investigate the changes of provenance and basin–mountain interaction in the Bogda area. During the Permian, proximal and synchronous pyroclastic materials were the major source. The Late Paleozoic magmatic belt in the North Tian Shan (NTS) had gradually become one of the main sources by the Late Permian, which implies the uplift and exhumation in the NTS area. This is interpreted in terms of near-source sedimentation in basin developing in a post-orogenic extension setting. The large range of U–Pb ages of detrital zircons observed in the Early–Middle Jurassic sediments encompasses most of the available sources implying a wide drainage pattern developing on a rather flat topography. Re-emergence of the Early Permian peak in the spectrum implies that the Bogda Mountains has existed as a gentle positive relief and began to provide materials to the submountain regions. The southern Junggar Basin extended towards to the south and evolved as a passively subsiding basin from the Middle Triassic to the Middle Jurassic. However, the synchronous pyroclastic (tuff) and the exhumed late Paleozoic detrital materials from the uplifted Bogda Mountains were the major component of the Upper Jurassic sediments. Associated to the conglomerate in the Kalaza Formation, the basin–range evolution entered a compression uplift stage. The basin pattern evolution of the Bogda area is consistent with that of the southern Junggar Basin.