Paleoproterozoic collision to Mesozoic crustal reworking in central
South China: evidence from drilling data and seismic crustal structure
Abstract
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.