Wenbin Jiang

and 6 more

The Xuefengshan tectonic belt in South China is generally regarded as the collisional zone between the Yangtze and Cathaysia blocks in the Neoproterozoic. Recent studies suggest a buried Paleoproterozoic orogenic belt in the Xuefengshan belt, but its distribution and deep structure are still not clear. The 2.4-km-deep Xuefengshan pilot borehole in the Yuanma Basin penetrates the unconformity between the Cretaceous and Cambrian strata and reveals the Neoproterozoic Nanhua rifting formations. By employing the Kirchhoff prestack depth migration, we obtain the SE-trending depth migrated sections of two 30-km-long seismic profiles at the drilling site and a 550-km-long SinoProbe seismic profile across the Xuefengshan belt. The folded strong reflectors beneath the seismically transparent Neoproterozoic strata confirm the existence of the Paleoproterozoic orogen in the chevron-type syncline zone and the Xuefengshan belt. The Xuefengshan belt was then reactivated by collision between the Yangtze Block and the Wuyi terrane in 860–830 Ma, the intracontinental rifting in 820–690 Ma, and Early Paleozoic and Mesozoic intracontinental orogeny. Subduction of the Izanagi Plate beneath South China triggered crustal shortening in the eastern Yangtze thrust-fold belt in the Middle Jurassic, which was accommodated by a SE-dipping décollement to the Moho and a crustal root to a depth of 44 km beneath the Baimashan pluton in the eastern Xuefengshan belt. The Cretaceous crustal extension was limited in the upper crust in the Yuanma Basin. Therefore, the Xuefengshan belt provides a classic example how an ancient orogenic belt was repeatedly reworked in response to multiphase thermal-tectonic events.