Mantle Flow and Dynamics Beneath Central‐East China: New Insights From P‐Wave Anisotropic Tomography

Abstract

The present study region, central-east China, is composed of the southeastern North China block (NCB) and the eastern South China block (SCB), which are separated by the Qinling-Dabie orogen (QDO) and the Sulu orogen (Figure 1). This region is one of the largest ultra-high pressure (UHP) metamorphic belts in the world due to the Triassic collision between the NCB and the SCB (Ling et al., 2011). The NCB has an Archean to Paleoproterozoic metamorphosed basement and a Mesoproterozoic to Cenozoic sedimentary cover (G. Zhao & Zhai, 2013). Unlike other Archean cratons, the eastern NCB experienced widespread tectono-thermal reactivation and crustal melting during the late Mesozoic and Cenozoic, followed by lithospheric delamination (Wu et al., 2019). The SCB is composed of the Yangtze block and the Cathaysia block assembled at about 860 Ma (X. Wang et al., 2007). The eastern SCB has undergone thinning of lithosphere in the Mesozoic, but more weakly than the eastern NCB (C. Y. Zhang, Chen, et al., 2018).Two intense activities during the Yanshanian movement occurred in eastern China. One was from the Middle Jurassic to the Late Cretaceous (H. Zhang et al., 2004) and the other in the Cenozoic (X.-H. Li, 2000). The magmatism during the Permian-Early Cretaceous trended younger eastward in the Cathaysia block (Z. X. and was westward younging to the east of the Cathaysia block (X.-H. . The prominent magmatism in the NCB is characterized with a westward younger trend in the Jurassic and with an eastward trend in the Early Cretaceous (Wu et al., 2019). A flat-slab subduction model was proposed to explain the age trend of the Mesozoic magmatism in the SCB (

Crustal Structure and Anisotropy in the Lower Yangtze Region and its Metallogenic Implications

“…During the early Cretaceous, the direction of back arc extension of the eastern continental margin of China was controlled and changed by the direction of Pacific subduction, resulting in strong NW-SE stretching and the formation of numerous related extensional basins in the eastern part of South China (Zhu et al, 2012). The crustal thinning zone (Li et al, 2013;Han et al, 2019;Shahzad et al, 2021) and upper-mantle low-velocity anomalies (Jiang et al, 2014) show a consistent distribution in the NE-SW direction, which is consistent with that of the crustal anisotropic fast directions revealed in this study and approximately parallel to the strike of the adjacent fault, indicating the direction of migration with ore-forming fluid (or magma) (Jiang et al, 2021). At the block scale, various layers of the lithosphere are dominated by coupling deformation.…”

“…Moreover, we observed an obvious low velocity zone 70 km below the Dexing and Tongling ore deposits (Figures 7F, L, Ye et al, 2019). The P-wave tomography results revealed recognizable low-velocity anomalies in the depth range of 150-400 km beneath the LYB (Jiang et al, 2014(Jiang et al, , 2021. These velocity anomalies have been interpreted as the source of hot magma injected into the lithosphere (Jiang et al, 2021;Lü et al, 2021).…”

“…Moreover, wide-angle reflection profiles revealed uplifting of the Moho beneath this belt and lowvelocity anomalies zone extending from the upper mantle to the crust of the metallogenic area (Xu et al, 2014;Zhang et al, 2015). Seismic tomography results indicated a "sandwich" structure of velocity anomalies in the upper mantle of the metallogenic area (Jiang et al, 2014(Jiang et al, , 2021, and the ambient noise tomography results suggested that the upper and lower crusts are characterized by relatively low velocities, whereas the middle crust is characterized by relatively high-velocities (Meng et al, 2021). The joint inversion results of receiver functions analyses and surface wave dispersions suggested that low-velocity anomalies exist in the upper mantle of the Lower Yangtze Block, several of which occur beneath the Dexing and Tongling ore deposits, and have been attributed to the ponding of relic (still cooling) mantle magma chambers (Ye et al, 2019).…”

Structural boundary and deep contact relationship between the Yangtze and Cathaysia Blocks from crustal thickness gradients

“…Tomography results reveal the presence of extensive lowvelocity anomalies in the upper mantle of southeastern China to the north of F1, along with near-horizontal high-velocity bodies in the mantle transition zone (MTZ), which are similar to those in the North China and Northeast China Blocks. High-velocity anomalies are speculated to be caused by the Pacific subduction plate remaining in the MTZ (Huang and Zhao, 2006;Li and Van Der Hilst, 2010;Huang et al, 2014;Jiang et al, 2021). However, the MTZ in the CB, south of F1, showed no obvious high-velocity anomalies (Figure 9D; Li and Van Der Hilst, 2010;Huang et al, 2021).…”

Seismic Anisotropy Tomography and Mantle Dynamics

“…P-wave AAN tomography has been also applied to study the 3-D structure and dynamics beneath continental regions (Figs. 5, 6 and 7), including Mainland China (Tian and Zhao 2013;Huang et al 2014;Wei et al 2016;Jiang et al 2021;Jia et al 2022), the Tibetan Plateau (Wei et al 2013;Zhang et al 2017;Yang et al 2022a), western and central USA (Huang and Zhao 2013;Yu and Zhao 2018;Wang and Zhao 2019a;Wang et al 2022a;Yang et al 2022b), Africa (Yu et al 2020a), Turkey (Wang et al 2020), and Greenland (Toyokuni and Zhao 2021). Figure 5 shows Vp AAN tomography beneath China (Wei et al 2016), revealing that the northern limit of the subducting Indian plate has reached the Jinsha River suture in eastern Tibet.…”