Upper Mantle Velocity Structure Beneath the Eastern South China Block and Implications for Late Mesozoic Magmatism

The eastern South China Block (ESCB) is characterized by intense magmatism in the late Mesozoic. To further investigate the mechanism of late Mesozoic magmatism, we apply the tomographic method to construct a P-wave velocity model down to 750 km by using 40,989 P-wave arrival times collected from 687 teleseismic events recorded by 191 stations. Our model shows that (1) a high-Vp anomaly is observed beneath the lower Yangtze Block (YZB) and northern Cathaysia Block (CAB) in the crust and uppermost mantle, which could represent the present lithosphere; (2) two high-Vp anomalies are observed in the upper mantle beneath the YZB, which could be the detached lithosphere and the relict of the subducted SCB; (3) the break-off of the subducted Eurasian Plate has penetrated the 410 km discontinuity beneath central and northern Taiwan Island; (4) the stagnant PaleoPacific Plate in the MTZ is mainly beneath the lower YZB; (5) the low-Vp anomaly in the upper mantle that is immediately above the stagnant Paleo-Pacific Plate may represent the thermal asthenosphere caused by plate dehydration; and (6) the low-Vp anomaly beneath the southern CAB extends from the crust downward to the MTZ, which may represent an 'upward channel' for thermal materials. Based on our results and those of previous studies, we suggest that late Mesozoic magmatism in the ESCB could be highly associated with the subduction of the Paleo-Pacific Plate and its eastward rollback. We also suggest that thermal/chemical erosion may be responsible for lithospheric thinning in the ESCB.