Permian post-orogenic terrestrial successions in the western and northern peripheral orogens of the Junggar Basin: Records of sedimentary provenance, paleogeographic and tectonic changes

The Permian terrestrial successions were deposited in peripheral orogens of the main Junggar Basin, including the West Junggar and Chinese Altai orogens. These successions probably marked the termination of the Paleozoic orogeny in the SW Central Asian Orogenic Belt and document paleogeographic and tectonic changes during that time. However, comprehensive research of these successions is still lacking. This study investigated representative sections and outcrops of Permian successions in West Junggar and Chinese Altai, and we present a detailed sedimentological comparison in the specific chronological framework according to new zircon U-Pb ages of syndepositional volcanics. This comparison shows that the Lower Permian successions consist of almost equal amounts of sedimentary rocks (46-56%), characterized by fluvial (meandering river-dominated)-deltaic and lacustrine facies, and volcanic rocks (44-54%). By contrast, the Middle-Upper Permian is dominated by alluvial facies (>79%) with highly reduced fluvial-deltaic and lacustrine facies. Furthermore, detrital modes and detrital zircon dating were applied to sandstones from four selected areas for provenance analysis. As a result, two major provenances were detected by detrital zircon ages, including the syn-depositional volcanics and granitoids (40-65%) and the Devonian-Early Carboniferous subduction-related plutons and arc volcano-sedimentary rocks (31-51%). Samples in Tarbagatay received a certain contribution from the Early Paleozoic arcs, and materials from the metamorphic basement in Chinese Altai localized in the vicinity and northernmost West Junggar. In summary, the Early Permian paleogeographic pattern of West Junggar is proposed as a series of small-scale fluvial plains and lacustrine basins that were separated by syn-depositional volcanoes and uplifted Paleozoic orogenic units under a tectonic setting of active rifting. The great shrinkage of sedimentation and coarsening of deposits during the Middle-Late Permian was triggered by intracontinental deformation rather than regional climate change.