中国海—西太平洋莫霍面深度分布特征及其地质意义

中国海—西太平洋位于欧亚板块、印澳板块和太平洋板块的交汇处,构造运动剧烈,地质情况复杂,是认识板块运动、洋陆相互作用、物质交换和能量传递不可多得的窗口,而莫霍面深度对于研究壳幔结构以及深部动力过程有着重要的意义.本文使用最新的覆盖全球的重力和地形数据,收集了深地震测深、多道地震测深等剖面183条,数字化得到2982个控制点,使用带控制点的三维界面反演方法来约束反演过程,得到中国海—西太平洋莫霍面深度,由莫霍面形态分析可知大洋板块的俯冲和印澳板块与欧亚板块的碰撞对西太平洋边缘海的形成演化有着重要作用.结合地热、岩石圈厚度、地震活动等地质地球物理资料,分析得知研究区内各个海域莫霍深度和地壳性质的变化是处于不同构造演化阶段的表现.并在马里亚纳沟弧盆拟合一条重力2.5维剖面,结果表明热物质上涌导致了马里亚纳海槽处地幔密度减小,马里亚纳海槽以及帕里西维拉海盆到西马里亚纳海岭的下地壳高密度异常是由残留的岩浆岩引起的.

The Moho depth in the China Sea-West Pacific and its geological implications

The China Sea-West Pacific is the junction among Eurasian Plate, Indo-Australian Plate and Pacific Plate. The intense interaction produces many trenches and marginal seas. The various geological structures such as the active continental margins(Ryukyu Trench and Okinawa Trough) and passive continental margins(the northern South China Sea) make it an important place to study the tectonic movement and interaction between ocean and continent. So we calculate the Moho depth as it has always been one of major issues in research on the structure of lithosphere and tectonic movement.We collect last satellite gravity and terrain data, as well as 183 control profiles, including multichannel seismic(MCS), oceanbottom seismometer(OBS) and so on. To get the gravity anomaly which is caused by the Moho interface, we deal with the satellite data by means of complete Bouguer correction, Glennie correction and other procedures. Then we digitalize these profiles to obtain 2982 control points which restrain the inversion result, using the method of three-dimensional density interface with control points. Considering that the geological structure changes a lot in the research area, we divide the whole area into 5 partitions and use different inversion parameters in each partition to calculate the Moho depth. After suturing the 5 partition inversion results together, we get the Moho depth in the China Sea-West Pacific. Combining the structure from the seismic result, we calculate a 2.5D gravity profile in the Mariana trench-arc-basin system finally.According to the crustal structure and the distribution of the Moho depth, we summarize the characteristics of the Moho depth in each region and conclude that the oceanic plate subduction plays a major role in west Pacific marginal seas formation and the Moho lifting of east Asian continent. The collision between the Indo-Australian Plate and Pacific Plate is also an important factor for the evolution of the marginal sea in east Eurasian Plate, but it has little influence on the Philippine Sea Plate. Combining the heat flow, lithosphere depth and historic earthquakes, we think the change of Moho depth and crustal properties are due to different era of tectonic evolutions which includes newborn, childhood, youth, mature and extinct era. From the gravity profile, we conclude that the mantle density in the Mariana Trough decreases because of the hot material upwelling, and the high-density lower crust in the Mariana Trough and Parece Vela basin is due to the remains of arc magmatic.