横穿印度洋重力剖面的基本特征及其地质意义

THE PRIMARY CHARACTERISTICS OF THE GRAVITYPROFILES ACROSS THE INDIAN OCEAN AND ITSGEOLOGICAL INTERPRETATION

本文根据在印度洋实测的重力资料，用ｓｉｎｘ／ｘ反演了一些典型构造的莫氏面深度，对印度洋两种不同类型的大陆边缘、大洋中脊、无震海岭、深海盆地的重力异常特征及地质意义进行了较深入的研究，结果表明，东南非岸外以张性下沉为主，构造活动比较单一，其上的重力异常为单调的正负不对称异常，说明这儿的被动陆缘基本上处于均衡状态；而印度洋东北边缘的太平洋型活动陆缘，为一复杂的火山岛弧系，这里的重力异常面貌复杂，反映了该地区处于非均衡状态；查戈斯－拉克代夫海岭为印度洋中典型的无震海岭，它不应属于印度洋中脊的一部分；印度洋中的大部分深海盆，其上具有典型的大洋重力组合，说明印度洋存在着广大的大洋型原生地壳。

rom October,1986 to May,1987,the third Antarctic Expedition and First Global Scientific Investigation were successfully carried out by Chinese scientists,during which 52 780km continuous gravity profiles of the three oceans-the Pacific,Atlantic and Indian Ocean were obtained.Based on the data obtained during this investigation,the depths of Moho discontinuity in some typical tectonic were inverted by the method of sinx/x.The characteristics of the gravity anomalies of two different types of continental margins,MidOcean Ridges,aseismic rigde,and abyssal basins in the Idian Ocean were analyzed and the geological interpretation for them were presented in this paper.The results showed theat the Atlantic passive continental margin off eastsouthern African coast is characterized by expansion sinking,and monotonous gravity anomalies with positive and negative unsymmetry.All these suggest an equilibrium state here.However,the pacific active continental margin in the northeastern margin of the Indian Ocean consists of complex arcvolcano system.Here the gravity anomalies is very complex,implying that the region is in an unequilibrium state.ChargosLaccadive Ridge is a typical aseismic ridge,not being a part of the MidIndian Ocean Ridge.The fact that most of the abyssal basins have a typical oceanic gravity combination declares the extensive existence of primary oceanic crusts in the Indian Ocean.