The Cathaysia Block (CAB) and its surrounding areas experienced intensive magmatism and mineralization in the Yanshanian period (ca. 200–90 Ma), but their mechanism and deep geodynamics are still debated. In addition, the origin and structures of the Hainan mantle plume are still unclear. To resolve these issues and investigate the large-scale lithospheric thinning and extension in the eastern South China Block, we determine a detailed 3-D S-wave velocity (Vs) model down to 700 km depth by collecting 24,190 S-wave teleseismic data recorded at 164 permanent stations and 125 portable stations deployed in the CAB and surrounding areas. Our results show that high-Vs anomalies exist separately in the study volume. Two high-Vs anomalies appear in the shallow upper mantle and the mantle transition zone, which may reflect the present thin lithosphere and the stagnant Paleo-Pacific slab, respectively. Two other high-Vs anomalies exist in the upper mantle, which may reflect the detached lithosphere and subducting slabs. In contrast, low-Vs anomalies appear widely beneath the CAB, which reflect a tilting magmatic conduit beneath the Wuyishan metallogenic belt (WYMB) and magmatic chambers beneath the Nanling metallogenic belt (NLMB). In addition, our results show that the Hainan plume has a double-layered appearance. Combining our tomographic results with previous multidisciplinary findings, we consider that (1) the subduction and rollback of the Paleo-Pacific Plate may have played different roles in the Yanshanian mineralization of the WYMB and the NLMB; (2) the double-layered appearance of the Hainan plume may be formed due to the influence of plume self-evolution dynamics and pre-existing deep structures; and (3) lithospheric delamination triggered by gravity instability may have occurred beneath the Xuefengshan Mountain in the late Mesozoic.

中文翻译：

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Cathaysia Block 及其周边地区的上地幔剪切速度结构：对深部地球动力学的新见解


Cathaysia Block （CAB） 及其周边地区在燕山时期（约 200-90 马）经历了强烈的岩浆作用和矿化作用，但它们的机制和深层地球动力学仍然存在争议。此外，海南地幔羽流的起源和结构尚不清楚。为了解决这些问题并研究华南东部区块的大规模岩石圈变薄和延伸，我们通过收集 24,190 个 S 波遥震数据，确定了深至 700 公里深的详细 3-D S 波速度 （Vs） 模型部署在 CAB 及周边地区的 164 个永久站和 125 个便携式站。我们的结果表明，高 Vs 异常在研究卷中单独存在。浅层上地幔和地幔过渡带出现两个高 Vs 距平，可能分别反映了目前的薄岩石圈和停滞的古太平洋板块。上地幔中存在另外两个高 Vs 异常，这可能反映了分离的岩石圈和俯冲板块。相比之下，低 Vs 异常广泛出现在 CAB 下方，这反映了武夷山成矿带 （WYMB） 下方的倾斜岩浆管道和南岭成矿带 （NLMB） 下方的岩浆室。此外，我们的结果表明，海南羽流具有双层外观。 结合我们的层析结果和以前的多学科发现，我们认为 （1） 古太平洋板块的俯冲和回滚可能在 WYMB 和 NLMB 的燕山期成矿中发挥了不同的作用;（2）海南羽流的双层外观可能是由于羽流自演动力学和预先存在的深层结构的影响而形成的;（3） 重力不稳定引发的岩石圈分层可能发生在中生代晚期雪峰山下方。