Phanerozoic tectonics of the South China Block: Key observations and controversies

The Phanerozoic tectonic regimes of the South China Block (SCB) hold a key to understanding of its geodynamic evolution with respect to formation of numerous mineral resources. Despite long-time debates in the past three decades, there is still no consensus on the two key points whether the Phanerozoic tectonothermal events were due to subduction of the Pacific plate or intracontinental reworking and whether the three periods of tectonothermal events in the middle Paleozoic (Kwangsian), Triassic (Indosinian) and Jurassic–Cretaceous (Yanshanian) are mainly driven by tectonic transition in subduction of the oceanic crust from Paleotethyan in the west to Pacific in the east. This paper presents an overview of key geological observations in the SCB with respect to its Phanerozoic tectonics. Available data show that there are distinctive sedimentary, magmatic, structural and metamorphic records across the Xuefeng-Jiangnan Domain in the SCB. The geological signatures associated with the Kwangsian and Indosinian tectonothermal events are predominantly preserved in the eastern SCB, including the eastern Yangtze and Cathaysia Blocks to the east of the Xuefeng-Jiangnan Domain. They are characterized by strong thrusting/transpression, anatexic granitic magmatism, high-grade metamorphism and the poor involvement of the juvenile mantle-derived rocks. The two events were dated at ca. 400–460 Ma and ca. 200–250 Ma, respectively. The Yanshanian tectonothermal event is dominantly represented by the development of a wide magmatic belt of exceeding 1300 km (from the coastal province to the Xuefeng-Jiangnan Domain) and a broad deformational belt of more than 2000 km (from the coastal province to the Sichuan basin). The Yanshanian I-, S- and A-type granites, syenite and volcanic rocks display two arrays, which are oblique and parallel to the coastal provinces of the southeast China, respectively. They were mainly formed at the three age-spans of 152–180 Ma, 120–130 and 87–107 Ma with the peak of 158 Ma, 125 Ma and 93 Ma, respectively. The stillstand time of the Yanshanian magmatism was temporally overlapped by the deformation time of the top-to-the-NW progressive transpression or sinistral strike-slip at 132–142 Ma and 95–112 Ma, respectively. In conjunction with the observations and controversies, a geodynamic model is proposed for the Mesozoic tectonic evolution of the SCB.