P‐wave Velocity Structure of Crustal and Upper Mantle beneath South China and its Tectonic Implications

Abstract

The 3D P‐wave velocity structure beneath the South China Block was determined by applying arrival times from 269 teleseismic events recorded by 240 seismic stations within the study region. Our tomographic results reveal the deep structural characteristics of major tectonic units and ore concentration areas. There are distinct high velocity anomalies beneath the ancient Yangtze and Cathaysia blocks, with the lithosphere of the Cathaysia Block being thinner than the Yangtze Block; the Jiangnan orogenic belt, located in the combined zone of two blocks, is a high and low velocity anomaly conversion zone; the famous metallogenic belts of Edongnan, the Youjiang Basin and the Cathaysia Block are obviously low velocity areas with different metallogenic mechanisms. The deep ore‐forming material source in the Edongnan metallogenic belt is different from that of the Cathaysia Block. The low velocity anomaly under the Cathaysia Block related to mineralization results from the upwelling of mantle material, caused by the joint action of the Paleo‐Tethys tectonic domain, the Paleo‐Pacific tectonic domain and the Hainan mantle plume migration and erosion, which has been occurring from northeast to southwest since 80 Ma. The low‐temperature mineralization mechanism of Youjiang Basin should be considered not only in terms of the influence of the Emeishan mantle plume in the west and the Paleo‐Tethys tectonic domain in the south, but also in the context of the influence of the upwelling of asthenospheric material from the Paleo‐Pacific tectonic domain in the east.

New Insights into the Mesozoic Large‐scale Intra‐plate Magmatism and Mineralization in South China from Seismic Tomography

“…It has been enigmatic whether the extensional regime since the Mesozoic was derived from back-arc rifting due to roll-back of the presumed paleo-Pacific subduction plate (Zhou and Li, 2000;Li and Li, 2007) or a mantle plume (Maruyama, 1994;Wang, 1996). Previous tomographic studies show a large-scale P-wave lowvelocity zone atop the 410-km discontinuity beneath Cathaysia (Li and van der Hilst, 2010;Zheng et al, 2022), different from the high velocity anomalies of the stagnant Pacific slab in the MTZ beneath North China (Grand, 2002;Zhao, 2004;Li and van der Hilst, 2010;Tao et al, 2018). However, suffering from limited data coverage, whether the marked low velocity zone beneath Cathaysia extends down to the lower mantle (He et al, 2016;Tao et al, 2018;Han et al, 2020;Jiang et al, 2021) or not (Li and van der Hilst, 2010) and whether there is also a stagnant paleo-Pacific slab in the MTZ beneath Cathaysia (Wang X et al, 2018) remain unresolved.…”