Provenance of the Middle–Late Triassic Successions in the Eastern Sichuan Basin, South China: Implications for the Evolution of the Qinling Orogenic Belt

The Qinling orogenic belt in central China underwent long-term tectonic evolution during an amalgamation between the North China and South China cratons. However, intense compressional deformation and uplift erosion resulted in the transformation and disappearance of much geological record from the Qinling orogenic belt, and the tectonic evolution of this belt remains poorly constrained during the Triassic. Located in the northernmost margin of the South China Craton, the Sichuan Basin preserves the complete Triassic sedimentary succession, and can provide significant information for understanding the Triassic tectonic evolution of the Qinling orogenic belt. We present detrital zircon U-Pb dating, trace element and in situ Lu-Hf isotope data for the Middle Triassic Leikoupo Formation and the Late Triassic Xujiahe Formation samples from the eastern Sichuan Basin, South China. The detrital zircon U-Pb ages of the Leikoupo Formation show seven age clusters of 280–242, 350–300, 500–400, 1000–800, 2000–1750, 2100–2000 and 2600–2400 Ma, while those of the Xujiahe Formation show five age clusters of 300–200, 500–350, 1050–950, 2000–1750 and 2600–2400 Ma. Combined with published paleocurrent and paleogeographic data, the sediments of the Leikoupo Formation are interpreted to be sourced from the North China Craton, Yangtze Craton and North Qinling orogenic belt, and the potential main source regions of the Xujiahe Formation included the South and North Qinling orogenic belts. Provenance analysis indicates that the North Qinling orogenic belt was in inherited uplift and coeval denudation in the Middle Triassic. The proportion of the detritus formed in the South Qinling orogenic belt increases gradually from the Leikoupo to Xujiahe formations. This significant provenance change indicates that rapid tectonic uplift and extensive denudation of the South Qinling orogenic belt occurred in the early Late Triassic, which is related to the collision between the North China and South China cratons during the Triassic.