华南地区地幔过渡带结构及其动力学意义

华南地区同时受特提斯构造域和太平洋构造域影响, 是研究板块相互作用的最佳场所之一.为研究华南地区深部动力学过程, 本文基于国家固定台网30°N以南的宽频带台站数据, 利用接收函数方法开展了华南地区地幔过渡带结构研究, 并结合已有地质、地球物理资料, 讨论了华南地区深部构造单元划分及其浅部构造响应.研究结果表明: (1)扬子克拉通下方地幔过渡带结构接近全球平均水平, 相对稳定; (2)海南岛地区地幔过渡带厚度偏薄, 且410-km和660-km界面分别显著下沉和上升, 可能与海南地幔柱密切相关; (3)太平洋构造域和特提斯构造域深部构造边界显著, 青藏高原东南缘主要受特提斯构造域影响, 其地幔过渡带中可能残留有拆沉的岩石圈板片; (4)雪峰山以东地区的地幔过渡带主要受太平洋构造域影响, 但南北也存在局部差异, 南部华夏地块下方可能不存在滞留板片, 太平洋板块的俯冲、后撤与东南沿海地区地壳减薄和大规模出露的中-新生代岩浆岩密切相关.

Structure of mantle transition zone beneath South China Block and its dynamic significance

South China Block, influenced by both the Tethys tectonic domain and the Pacific tectonic domain, is one of the key areas for studying plate interactions. To study the deep dynamic process beneath South China Block, based on broadband seismic data (south of 30°N) recorded by the national permanent seismic network, we image the mantle transition zone (MTZ) structure beneath the South China Block using receiver function methods, and discuss the division of deep tectonic units and their shallow structural responses combined with the existing geological and geophysical data. Our results indicate: (1) The MTZ structure beneath the Yangtze craton approaches the global average and is relatively stable; (2) The thickness of the MTZ beneath Hainan Island is relatively thin, with significant subsidence and uplift of the 410-km and 660-km interfaces, respectively, possibly related to the Hainan mantle plume; (3) The deep tectonic boundary between Pacific tectonic domain and Tethys tectonic domain is significant. The southeastern margin of the Tibetan Plateau is mainly affected by the Tethys tectonic domain, and delaminated lithospheric slabs may remain in the MTZ; (4) The area to east of the Xuefeng mountain is mainly influenced by the Pacific tectonic domain, with local differences between the north and south part. There may be no stagnated plate under the Cathaysian Block. The subduction and retreat of the Pacific plate are closely related to the crustal thinning and large-scale exposure of Mesozoic-Cenozoic magmatic rocks in the southeast coastal area.