The crustal thickness and composition in the eastern South China Block constrained by receiver functions: Implications for the geological setting and metallogenesis

Abstract

The eastern South China Block is characterized by multi-stage intra-continental collisions and orogeny from the Paleozoic to early Mesozoic, and strong magmatism and metallogenesis since the late Mesozoic. In order to further study the tectonics, magmatism and metallogenesis, we constructed a new model of crustal thickness and Vp/Vs ratio for the crust beneath the eastern South China Block using H-κ stacking of teleseismic P-wave radial receiver functions from 845 broadband seismic stations. New knowledge of the crustal structure and properties pertinent to the tectonics and metallogenesis is as follows: (1) the average crustal thickness beneath the eastern South China Block is 33 km. It is thinner and varies smoothly in the Cathaysia Block and Jiangnan Orogen, and gradually thickens to the northwest and reaches ~40 km in the Yangtze Block; (2) the average crustal Vp/Vs ratio of the eastern South China Block is ~1.72, lower than the global average value ~1.78. This implies an absence of a mafic lowermost crustal layer; (3) the Jiangnan Orogen is characterized by a conspicuous belt of lower Vp/Vs ratios, different from the Yangtze and Cathaysia Blocks on either side. This is interpreted as caused by synorogenic crustal thickening and the subsequent lower crustal delamination; (4) the crustal thickness and the Vp/Vs ratios in the eastern South China Block are negatively correlated, also indicating tectonic thickening of a felsic upper and middle crust. This is consistent with folding and thrusting during orogenesis and the later delamination of the mafic lower crust; (5) the Anhua-Luocheng fault is considered to be the southwestern segment of the boundary between the Yangtze Block and Jiangnan Orogen; (6) lithospheric extension caused by subduction of the Pacific Plate and the corresponding slab rollback during the late Mesozoic can explain the crustal thickness, the Vp/Vs ratio distribution patterns and the metallogenesis in the eastern South China Block.