Sedimentary provenance constraints on the Jurassic to Cretaceous paleogeography of Sichuan Basin, SW China

摘要

The provenance of Jurassic to Cretaceous sediments in the Sichuan Basin is constrained by sandstone petrology and detrital zircon U-Pb geochronology, which provide critical insights into the mid-late Mesozoic paleogeography of the Sichuan Basin. The petrography of 22 sandstone samples suggests moderately-to-highly mature sediments, which are primarily derived from cratonic or recycled sources. Detrital zircon U-Pb ages from Middle Jurassic to Late Cretaceous are classified into age groups of 130-200 Ma, 200-330 Ma, 400-490 Ma, 680- 890 Ma, 1730-1960 Ma, and 2360-2600 Ma. The Middle Jurassic sediments contain a relatively high density of ~260 Ma, ~1.85 Ga, and ~2.5 Ga zircons aswell as a lowdensity of ~800 Ma zircons, consistentwith the derivation fromthe Emeishan large igneous province, the Songpan-Ganzi terrane, and the South Qinling Belt, and to a lesser extent, from the Western Jiangnan Orogen. The Late Jurassic and Early Cretaceous sediments with scattered age distribution share common multiple source-to-sink systems, which were predominantly draining toward the south and southeast, with southward drainage being higher; subsequently, they were disrupted by a synchronous northeastward drainage capture. Late Cretaceous sediments have a distinct reduction in zircons younger than 213 Ma, suggesting southeastward and southwestward transport of sediments that were likely derived from the Songpan-Ganzi terrane, the Sanjiang Orogen, the south segment of the Longmenshan thrust belt and the western Yangtze Craton, and areas of uplift in the northern and northeastern Sichuan Basin. Changes in the provenance during the mid-late Mesozoic coincide with the spatiotemporal variations in the depocenter migration and paleogeographic evolution of the Sichuan Basin, which are closely related to the multistage intracontinental subduction associated with the clockwise rotation of the South China Block.