东海中段钓鱼岛隆起的内部结构与演化

The internal structure and evolution of the middleDiaoyudao Uplift in the East China Sea

由于钓鱼岛隆起的地质与地球物理资料相对缺乏,前人对该区域系统研究较少,关于其构造演化存在许多争议。本文通过重磁资料,结合反射地震剖面解释研究了西湖凹陷东侧的中段钓鱼岛隆起的构造与沉积特征,并进一步完善了其演化模式。研究结果表明,隆起内部存在多个残余凹陷,残留地层具有“北多南少”的分布特征,据此以舟山-国头断裂为界,可以将中段钓鱼岛隆起进一步分为南、北两个亚段。南、北亚段边界处在舟山-国头断裂的延长线上。同时,隆起西部的岩浆岩体分布于平坦剥蚀面T20之下,而东部存在岩浆活动引起的“基底尖峰”,空间重力异常的梯度带恰好与“基底尖峰”的西缘对应,以“基底尖峰”的西缘为界,将中段钓鱼岛隆起大致分成东、西两区,其中西区又可以进一步分为发育岩浆岩体的西Ⅰ区和局部残留凹陷的西Ⅱ区。西区由西湖凹陷经构造反转与岩浆活动改造而成,东区保留了古隆起。综合分析推断,中段钓鱼岛隆起是在古隆起的基础上经历多次构造与岩浆活动演化而成。

Due to the lack of geological and geophysical data of the Diaoyudao Uplift,the previous studies on this area are unsystematic,so there are many controversies about its tectonic evolution.Based on gravity,magnetic,and multichannel seismic data,the tectonic and sedimentary characteristics of the middle Diaoyudao Uplift were analyzed,which located to the east of the Xihu Depression,East China Sea Basin.The evolution model of the middle Diaoyudao Uplift was further refined.More residual sags are found in the north than in the south of the middle Diaoyudao Uplift.Accordingly,the middle Diaoyudao Uplift can be divided into the north and south segments.The boundary of the two segments is on the extended trace of the Zhoushan-Guotou Fault.In addition,magmatic intrusions are confined below the T20 unconformity in the west,whereas a basement pinnacle caused by magmatic activity exists in the east.It is found that the gradient zone of gravity anomaly corresponds exactly to the western edge of the basement pinnacle.Taking the west edge of the basement pinnacle as the boundary,the middle Diaoyudao Uplift can be divided into two parts from west to east.And the western zone can be further divided into two subzones,including partⅠwith magnetic rocks and partⅡwith residual sags.The western part of the middle Diaoyudao Uplift is from the strong tectonic and magmatic deformation of the eastern Xihu Depression,whereas the east part retained the original Diaoyudao Uplift.The comprehensive analysis of above features showed that the present-day middle Diaoyudao Uplift was formed by many episodes of tectonic events and magmatic activities around an ancient uplift.