冲绳海槽地壳结构与性质研究进展和新认识

Study on Crustal Structure and Nature of the Okinawa Trough

冲绳海槽是张裂于东亚大陆边缘的弧后盆地,对其地壳结构性质的研究具有重要的理论和现实意义。本文在总结冲绳海槽重力场、广角反射/折射地震探测、海底磁异常条带以及火山岩和岩浆作用这4个方面研究成果的基础上,对海槽的地壳结构、地壳性质和所处的构造演化阶段进行了探讨。认为冲绳海槽绝大部分地区地壳厚度大于正常洋壳,应属减薄的陆壳,由裂陷作用形成;但海槽中段和南段中央地堑地壳速度结构与洋壳类似,发育条带状磁异常,且已有大量幔源物质参与了地壳的组成,具备初始扩张作用的特征。对于海槽内是否存在洋壳,仍需进一步调查和研究。

The Okinawa Trough is a back-arc basin rifted at the edge of East Asian continent, and the study of crustal structure and nature of this basin are both theoretical and practical significanees. In this work, we summarized the previous research gains in four aspects including gravity anomaly, wide-angle reflection and refraction survey, linear magnetic anomaly and voleanies and magmatism, then discussed the crustal structure, crustal nature and tectonic evolution stage of the Okinawa Trough. We suggest that the crustal nature in most part of the basin belongs to thinned continental crust and was formed by continental rifting because the crustal thickness is large compared with normal oceanic crust. Nevertheless, the velocity structure of the central grabens in middle and southern Okinawa Trough is similar to oceanic crust, the existence of linear magnetic anomalies and extensive mantle source materials emplaced in the crust suggesting the incipient spreading. Further study is needed to assure if there is oceanic crust in the trough.