Cretaceous tectonic evolution of South China: A preliminary synthesis

The Cretaceous tectonic evolution of South China is characterized by widespread extensional basin and dome generation, voluminous magma intrusion/eruption and associated polymetallic mineralization, all of which are of world-wide interests that have stimulated the attention of geologists for more than half a century. Due to the lack of a comprehensive understanding of regional tectonic evolution and geodynamics of South China, many controversies regarding the nature and origin of these features remain. This paper attempts to make a review by synthesizing existing structural, petrological, geochronological and geochemical data of the Cretaceous structures and magmas, which guides us to propose a three-stage tectono-thermal evolutionary history of South China during the Cretaceous period. The earliest Cretaceous (145–137 Ma) tectonic stage was characterized by syn-orogenic shortening deformation and metamorphism under a NW–SE compressional setting, which generated voluminous porphyry Cu–Au ore-bearing adakitic rocks in the Lower Yangtze River Belt and gneissic granites in the coastal area. Its geodynamic origin was interpreted as combined effects of the Pacific–Izanagi ridge subduction beneath the Lower Yangtze River Belt and the Pacific subduction beneath the Cathaysia Block. This syn-orogenic shortening stage was followed by a post orogenic stage (136–86 Ma) comprising two episodes of alternate extensional and shortening events. The extension (136–118 Ma) in the earlier episode was dominated by a NW–SE extensional regime, it led to significant taphrogenesis manifested by large-scale extensional basins and voluminous magma intrusion/eruption; this extensional event was associated with a combination of the slab window opening during the ridge subduction and the rollback of the subducted Pacific slab. The subsequent NW–SE transpressional event led to cessation of active marginal magmatism and resulted in tectonic inversion of previous rift basins; this transpression lasted from 117 Ma to 108 Ma, and its driving mechanism was attributed to the collision between the eastern Asian margin and the West Philippine Block. The extension (107–86 Ma) in the later episode was dominated by a WNW–ESE extensional regime, which led to a second phase of basin subsidence and produced numerous A- and I-type granites and bimodal volcanoes. The tectonic regime then changed at ca. 85 Ma to WNW–ESE-oriented transpression, causing inversion of the Late Cretaceous rift basins and cessation of extension-related magmatism. The change of stress field from WNW–ESE extension to WNW–ESE transpression was related to the variations of the subducted slab dynamics, i.e., the transition from either the ESE-ward retreat to WNW-ward subduction of the Pacific slab, or the alternate stress during slab break-off. During the latest Cretaceous, a drastic change of regional tectonic stress orientation from WNW–ESE to N–S occurred in South China, the third stage predominated by N–S extension was developed, which caused a new phase of regional crustal subsidence along the youngest E–W trending extensional structures.