Mesozoic Unroofing History of the Dabie Orogen, Eastern China: Evidence from Detrital Zircon Geochronology of Sediments in the Hefei Basin

Abstract

The Hong’an-Dabie-Sulu orogen in China exposes the largest area of ultrahigh-pressure (UHP) metamorphic rocks in the world. Postcollisional large-scale extension and denudation resulted in the removal of large volumes of high-pressure (HP) and UHP rocks from the Dabie orogen, making it difficult to reconstruct the original distribution of these rocks and analyze the mechanism of exhumation. The Early Jurassic to Cretaceous Hefei Basin formed in response to uplift of the Dabie orogen, and we used detrital zircon age dating to assess the provenance of its sediments. The Lower Jurassic Fanghushan Formation, the oldest rocks in the Hefei Basin, shows a more complex provenance, with source materials from the HP-UHP, Susong Complex, and early Paleozoic arc-magmatic rocks. The Middle Jurassic Sanjianpu Formation shows age clusters mainly in the Triassic and middle Neoproterozoic. By comparing the detrital zircon age frequencies in basins around the orogen, we found that the rocks widely exposed in the Dabie orogen were the Susong Complex in the Early Jurassic; the HP-UHP rocks might have been only locally exposed along the northern margin of the orogen, and extensive outcrops may have occurred after the Middle Jurassic. Rapid uplift occurred at ca. 128 Ma, which caused the HP-UHP rocks to be denuded in the northern Dabie orogen and contributed detrital material to the conglomerates of the Lower Cretaceous Fenghuangtai Formation. Controlled by intense normal movements on a series of faults in the Hefei Basin and northern Dabie orogen, the Hefei Basin extends southward to the north of the Xiaotian-Mozitan Shear Zone.