The lithospheric structure beneath the Indian Ocean is probably the most complicated, but at the same time, the least understood among world’s oceans. Results of tomographic, geochemical, magnetic and other surveys provide the evidence of its complex geological history. Seismic surveys have been a primary source of information about the lithospheric structure beneath the Indian Ocean, but these experiments are mainly concentrated at locations of a high geophysical interest. Marine gravity data obtained from processing the satellite altimetry measurements, on the other hand, deliver a detailed image of the whole seafloor relief, advancing further the knowledge about its formation, tectonism and volcanism. In this study, we use gravitational, bathymetric, marine sediment and lithospheric density structure data to compile the Bouguer and mantle gravity maps. We then use both gravity maps to interpret the lithospheric structure beneath the Indian Ocean. The Bouguer gravity map reveals major tectonic and volcanic features that are spatially correlated with crustal thickness variations. The mantle gravity map exhibits mainly a thermal signature of the lithospheric mantle. Gravity lows in this gravity map mark distinctively active oceanic divergent tectonic margins along the Central, Southeast and Southwest Indian Ridges including also the Carlsberg Ridge. Gravity lows extend along the Red Sea–Gulf of Aden and East African Rift Systems, confirming a connection between mid-oceanic spreading ridges (in the Indian Ocean) and continental rift systems (in East Africa). The combined interpretation of the Bouguer and mantle gravity maps confirms a non-collisional origin of mountain ranges along continental rift systems in East Africa. The evidence of a southern extension of the East African Rift System and its link with the Southwest Indian Ridge in the mantle gravity map is absent. Similarly, the ongoing breakup of the composite Indo-Australian plate is not manifested. A missing thermal signature in the mantle gravity map at these two locations is explained by the fact that the southern Nubian-Somalian plate boundary (i.e., the Lwandle plate) and the Indo-Australian plate boundary (i.e., the Capricorn plate) are diffuse zones of convergence, characterized by low deformation and seismicity due to very slow rates of relative motions accommodated across these boundaries. The clear manifestation of the thermal signature of intraplate hot spots in the mantle gravity map is also absent. This finding agrees with the evidence from direct heat flow measurements that do not indicate the presence of a significant positive temperature anomaly compared to the oceanic lithosphere of a similar age.

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印度洋下方岩石圈结构的重力图

印度洋下方的岩石圈结构可能是最复杂的，但同时也是世界海洋中了解最少的。层析、地球化学、磁力等调查结果为其复杂的地质历史提供了证据。地震勘测一直是有关印度洋下方岩石圈结构信息的主要来源，但这些实验主要集中在具有高度地球物理兴趣的位置。另一方面，通过处理卫星测高测量获得的海洋重力数据提供了整个海底地形的详细图像，进一步促进了对其形成、构造作用和火山作用的了解。在这项研究中，我们使用重力、测深、海洋沉积物和岩石圈密度结构数据，以编制布格和地幔重力图。然后我们使用两个重力图来解释印度洋下方的岩石圈结构。布格重力图揭示了与地壳厚度变化在空间上相关的主要构造和火山特征。地幔重力图主要展示了岩石圈地幔的热特征。这张重力图中的重力低点标志着印度洋脊中部、东南部和西南部（包括嘉士伯海岭）特别活跃的海洋发散构造边缘。重力低沿红海-亚丁湾和东非裂谷系统延伸，证实了洋中扩张脊（在印度洋）和大陆裂谷系统（在东非）之间的联系。布格和地幔重力图的综合解释证实了东非大陆裂谷系统沿线山脉的非碰撞起源。在地幔重力图中没有东非裂谷系统向南延伸及其与西南印度洋脊的联系的证据。同样，印度-澳大利亚板块的持续破裂也没有表现出来。由于努比亚-索马里板块南部边界（即 Lwandle 板块）和印度-澳大利亚板块边界（即摩羯座板块）是扩散区这一事实，这两个位置的地幔重力图中缺失的热特征可以解释由于跨越这些边界的相对运动速度非常慢，因此会聚的特点是低变形和低地震活动。在地幔重力图中也没有明显地显示板内热点的热特征。这一发现与直接热流测量的证据一致，与类似年龄的海洋岩石圈相比，这些证据并未表明存在显着的正温度异常。