Fine lithospheric structure controlling Meso-Cenozoic tectono-magmatism in the South China Block: Inference from a multidisciplinary analysis

As an important tectonic block in East China, the South China Block (SCB) plays a key role in coordinating the subduction of the Paleo-Pacific Plate and the plate reconstruction in the Asian-Pacific region. Studying the lithospheric structure and composition of the SCB is important for deeper understanding of its multi-phase reworking and regional geodynamic processes. In this study, we compile satellite gravity and magnetic observation data, and conduct a multidisciplinary analysis to reveal the deep lithospheric structure that strongly controlled the tectonic evolution and Mesozoic magmatism of the SCB. Meanwhile, seismic tomography, terrestrial heat flow and sedimentation data are utilized to uncover the relationship between tectono-magmatism and alternating contractional and extensional events in the SCB. To further explore the relationship between the Mesozoic tectonic transition and the mechanism of the intra-continental deformation on a regional scale, we conduct a comprehensive analysis on regional tectonics, geophysical anomalies and geometric-kinematic characteristics of major structural systems and their Meso-Cenozoic evolutionary geodynamics. The results show that the distribution of low effective elastic thickness (Te) values, low velocity anomalies, thinner thermal lithosphere and lower rheological strength in the eastern SCB represents a reworked continental lithosphere by long-term magmatism and oceanic plate subduction, which is the final outcome of crust-mantle interaction and isostatic adjustment. According to a multidisciplinary analysis on the deep geophysical anomalies and lithospheric structure, we show a new dynamic model of asthenospheric upwelling, lithospheric thinning, melting of enriched mantle and lower-crustal thickening and delamination beneath the eastern SCB. Our model differs from other pre-existing tectonic models suggesting that the subducting Pacific slab was torn along the transform fault of the Pacific-Izanagi Ridge during the latest Mesozoic or earliest Cenozoic. Hence, we consider that the subduction of the Paleo-Pacific Plate beneath the SCB triggered intraplate shortening and transtension, propagating deformation, magmatic migration, and large-scale mineralization throughout the advance, tearing, rollback, and break-off of the subducting slab. The upwelling of the hot asthenosphere in the eastern SCB triggered partial melting of the mantle lithosphere in a transtensional tectonic setting. Meanwhile, the upward heat conduction and mantle material advection caused lower crust underplating, resulting in the uplift of Moho and Curie surfaces, as well as the rise of surface heat flow. Both the asthenospheric upwelling in the mantle wedge and large amounts of magma underplating provided favorable conditions for the formation of large-scale magmatic rocks and polymetallic deposits within the eastern SCB.