西南印度洋中脊地质构造特征及其地球动力学意义

西南印度洋中脊（SWIR）增生的洋壳面积仅占印度洋的15%左右，但其具有比东南印度洋中脊和西北印度洋中脊更悠久而复杂的演化历史.基于已有的地质、地球物理和地球化学等资料，系统总结了SWIR的地质构造特征，并讨论了SWIR的演化过程、洋脊地幔的不均一性、洋脊周边海底高原成因等核心问题.SWIR地形中段高、东西两段低，空间重力异常基本与地形变化一致.按转换断层一级边界可将SWIR划分为20个一级段.SWIR的磁异常条带呈现两端渐进式分布和中段带状分布特征，对应洋脊的三期演化历史.SWIR的地幔源区极不均一，尤其是中新元古代造山带根部集中拆离的中段.源区地幔的不均一性与大陆裂解和洋脊演化过程密切相关.SWIR的东端与西北印度洋中脊和东南印度洋中脊的邻近洋脊段具有地球化学亲缘性，西端与大西洋中脊和南美洲—南极洲洋中脊的邻近洋脊段具有地球化学亲缘性，这与SWIR的渐近式扩张有关.SWIR周边海底高原普遍具有较大的地壳厚度，其成因除了陆壳基底之外，可能与热点火山作用、热点-洋脊相互作用或热点-三联点相互作用有关，目前尚未形成统一的认识.SWIR的形成演化及其作用域内的熔融异常（如海底高原）是冈瓦纳大陆裂解、残留岩石圈地幔、软流圈地幔和深部地幔热柱物质共同作用的结果.了解SWIR的演化过程对揭示冈瓦纳大陆的裂解过程和印度洋的演化具有重要意义.

The geotectonic features of the Southwest Indian Ridge and its geodynamic implications

The Southwest Indian Ridge (SWIR) has a more complex evolution than the Southeast Indian Ridge (SEIR) and the Northwest Indian Ridge (NWIR), even though it takes up only 15% of the total area of Indian Ocean crust. On the base of existing geological, geophysical and geochemical data, we systematically summarized the geotectonic characteristics of SWIR, and tried to address the issues of evolution process of SWIR, the mantle heterogeneity beneath the ridge and the origin of adjacent oceanic plateau. The bathymetry of the ridge shows obvious shoaling up in the Mid-section of SWIR, while the East-section and West-section are relatively deeper. The free-air gravity anomaly is consistent with the topography. Base on the gravimetric and topographic features, SWIR can be subdivided into 20 first-order segments according to the first-order boundaries, like transform faults. The magnetic anomaly of SWIR shows propagating spreading at both ends and horizontal zoning distribution in the Mid-section, suggesting a three-stage evolution history for the ridge. The mantle sources of SWIR are extremely heterogeneous, especially in the Mid-section, where the delamination could most probably happen beneath the Meso- to Neoproterozoic orogenic belt. The heterogeneity of the source is closely related to the continental breakup and ridge evolution. Both ends of SWIR show geochemical affinities with the adjacent ridge segments of Mid-Atlantic Ridge and South America-Antarctica Ridge, SEIR and NWIR, respectively. The oceanic plateaus close to SWIR generally have large crustal thickness, which may be related to the hotspot magmatism, hotspot-ridge interaction, or even hotspot-triple junction interaction, apart from the ghostly stranded continental fragment trapped in the asthenospheric mantle. Understanding the evolution history of SWIR is of great importance for revealing the break-up process of Gondwana supercontinent and the evolution of the Indian Ocean.