Thermochemical Structure and Melting Distribution of the Upper Mantle Beneath Intraplate Volcanic Areas in Eastern South China Block

The Eastern South China Block (SCB) has experienced complex Mesozoic-Cenozoic tectonism and intraplate volcanism. However, due to a lack of exhaustive exploration of the upper mantle's thermochemical structure, it is difficult to determine the extent of the lithospheric modification and the mechanisms by which the volcanism generate. Here, we jointly invert Rayleigh wave dispersion, surface heat flow, geoid height, and elevation data to provide a comprehensive thermal and compositional structure of the upper mantle beneath eastern SCB and infer regions of partial melting. Our model reveals widespread lithospheric thinning in the eastern SCB and large variations of lithospheric composition with a more fertile eastern Lower Yangtze lithosphere than the lithosphere elsewhere, suggesting the lithosphere of the eastern Lower Yangtze is more severely modified than the rest of the SCB. Moreover, two high-temperature anomalies are revealed: one beneath the eastern Lower Yangtze and the other beneath the Pearl River Delta region, associated with the Pacific plate subduction and Hainan plume, respectively. The high-degree partial melting (similar to 6%) in the asthenosphere beneath the Lower Yangtze is responsible for the strong ongoing lithospheric modification and the young intraplate volcanism in the Nvshan and Subei areas. Small-scale upper mantle convections triggered by the large mantle upwellings created a low value of similar to 3% melts, possibly responsible for the intraplate volcanism in the coastal CB and less severe lithospheric modification. We demonstrate that the lithospheric thickness and its thermochemical state are the key factors that influence the composition and evolution of intraplate volcanism in the eastern SCB. The Eastern South China Block is an important part of the Eurasian plate, but we still don't know much about the lateral variations of its lithosphere composition and why it has intraplate volcanism. In this study, we use geophysical data to figure out the thermochemical structure of the lithosphere and sublithosphere and see if there is any partial melting. Our model shows that the lithospheric mantle beneath the eastern Lower Yangtze is more fertile, which means it has been recently rejuvenated like the North China Craton, while the lithospheric mantle beneath the Middle Yangtze and Cathaysia Block is more depleted, which means it still has an ancient cratonic mantle. We think that large-scale upwelling of the mantle is causing high-degree partial melting in the Lower Yangtze and small-scale convection is causing low-degree partial melting in the coastal CB. Finally, combining independent geochemical data from young basalts, we find that the lithospheric thickness and its thermochemical state are the key factors that influence the composition and evolution of intraplate volcanism in the eastern SCB. We construct a thermochemical model and estimate the melt fraction beneath the eastern South China BlockThe thermochemical model reveals a fertile lithospheric mantle beneath the Lower Yangtze and a depleted one underneath the Cathaysia BlockThe origin and composition of intraplate volcanism are controlled by the lithospheric thickness and its thermochemical state