Cenozoic exhumation of the Neoproterozoic Sanfang batholith in South China

Abstract

The 1500-km-long Jiangnan tectonic belt in China is well known for large outcrops of Proterozoic basement rocks, although the exhumation history of the exposed basement is poorly constrained. The thermochronology of the Sanfang batholith in the southernmost section of this belt was used to constrain the timing and mechanism of exhumation using apatite fission track analysis of granite samples collected along three transects. The results show that the ages of single apatite grains are much younger than the Neoproterozoic crystallization age of the Sanfang batholith. The apparent age v. elevation diagram shows two-stage cooling during the Paleogene and Miocene. The cooling stages are coincident with unconformities between the Paleogene and underlying strata, and between the Neogene and the Paleogene, with movement on high-angle normal faults. A compilation of apatite fission track data from this and previous studies suggests that the batholith was exhumed in the Cenozoic and the timing of rapid cooling is progressively younger to the east as a result of slab rollback leading to Cenozoic back-arc extension. The exhumation of the Sanfang batholith therefore indicates that Cenozoic erosion and extensional tectonics played a key part in exhuming the basement rocks and forming the present architecture of the Jiangnan tectonic belt.