SOURCE-TO-SINK ANALYSIS OF A TRANSTENSIONAL RIFT BASIN FROM SYN-RIFT TO UPLIFT STAGES

摘要

The Permian-Triassic successions in the Bogda Mountains, northern Xinjiang, northwest China, record a pivotal but poorly constrained tectonic regime of a transtensional rift, which can be subdivided into synrift, post-rift, and uplift stages. Systematic sandstone petrography, whole-rock geochemistry, and detrital-zircon U-Pb dating analysis were conducted to evaluate the source-to-sink process involved, as well as to understand its provenance characteristics and the factors that control the source-to-sink evolution. Comprehensive provenance analytical methods indicate that the sediments in the syn-rift and post-rift stages experienced weak chemical weathering and were compositionally immature, poorly sorted, and mostly acidic, with few basic volcanic rocks from North Tianshan (NTS) and Central Tianshan (CTS). Meanwhile in the uplift stage, the sediments underwent moderate chemical weathering and sedimentary recycling, with a complex age population, containing syndepositional zircon ages, which were likely derived from the volcanic rocks of NTS, CTS, and the Bogda Mountains. Integrated provenance analyses reveal that the syn-rift and post-rift source-to-sink systems of Bogda rift (and probably other rift basins) are controlled mainly by tectonics, the sinks are principally immature, and the sources are derived predominantly from axial volcanic arcs and local rift shoulders, with little input from syndepositional volcanic rocks. Inversely, the source-to-sink system of the uplift stage is rather complex, which is influenced by tectonics, climate, and sedimentary processes. Their sinks are relatively submature to mature, and their sources include detritus, with ages close to the depositional age, along with significant input from surrounding volcanic arcs and initial uplift highlands.