Detrital zircon U-Pb dating of low-grade metamorphic rocks in the Sulu UHP belt: evidence for overthrusting of the North China Craton onto the South China Craton during continental subduction

摘要

The Shiqiao-Pingshang low-grade metasedimentary rocks sporadically crop out in the Sulu ultrahigh-pressure (UHP) belt in east-central China. Major and trace element data indicate that they were deposited in a passive margin basin, probably located at the southern margin of the North China Craton. Sensitive high-resolution ion microprobe (SHRIMP) U-Pb dating of detrital zircons from a quartzite (SD53) from Pingshang and a quartz schist (SD54) from Shiqiao records ages ranging from 2800 to 1900 Ma. Three age populations are defined: at 2660-2500, 2350-2150 and 2100-1900 Ma, with peak ages at 2522, 2212 and 2020 Ma, respectively. Muscovite Ar-Ar dating of the quartz schist (SD54) yields a plateau age of 265.9 +/- 1.2 Ma. These data support the view that the Shiqiao-Pingshang low-grade metasedimentary rocks originated from the North China Craton, and underwent deformation in the Permian during subduction of the South China Craton (Yangtze block) beneath the North China Craton. This requires that the low-grade metasedimentary rocks were overthrust for several tens of kilometres onto the South China Craton, explaining why source materials from the North China Craton are common in Triassic to Jurassic sedimentary basins adjacent to the Dabie-Sulu orogenic belt.