Secular lithospheric delamination controls Late Mesozoic magmatism and basin evolution in South China

Abstract

The South China Block underwent complex tectonic activities in the Late Mesozoic, forming the Basin and Range-style magmatic province and widespread lithosphere thinning. However, mechanisms for magmatism and basin evolution remain controversial. Here, we utilize a 2-D geodynamic model to show how lithospheric delamination controls magmatism and related surface responses in South China. The initial delamination occurred in the form of downwelling drip at the convergent boundary between two amalgamated continental blocks triggered by the subduction of oceanic plate. Around the descending drips, the induced mantle upwelling provided enough heat and extensional settings for the formation of felsic magmatism. Also, the downwelling drips pulled down the lithosphere and caused the subsidence relative to surrounding uplift caused by upwelling mantle flows, which accounted for the formation of the Basin and Range-style province. Due to dynamic perturbation of upwelling mantle flows, continuous drips gradually migrated to the coastal areas and led to the formation of extensive magmatism and surface topography change triggered by upwelling mantle flow. As a result, the lower part (>70 km) of the lithospheric mantle of South China has been removed and replaced by hot asthenosphere. The secular migration of drips is consistent with the spatial-temporal distribution of magmatism and the basin evolution in South China. The lithospheric thinning was eventually finished through secular lithospheric delamination. The secular lithospheric delamination model explains why the extensive Basin and Range-style magmatic province formed by the long-time subduction of the Izanagi Plate.