A review of studies on the magmatism at Southwest Indian Ridge from petrological and geochemical perspectives
SUN Guohong
,
TIAN Liyan
,
LI Xiaohu
,
ZHANG Hanyu
,
CHEN Lingxuan
,
LIU Hongling
作为超慢速扩张脊的代表，西南印度洋中脊(SWIR)因其独一无二的地形地貌特征、洋壳结构、洋壳增生机制、岩浆和热液活动以及深部动力学过程，近30年来成为国内外研究的热点区域。基于近年来对SWIR玄武岩、辉长岩及橄榄岩的岩石学和地球化学研究成果总结，重点探讨了沿SWIR轴向（大尺度）以及单个洋脊分段（小尺度）的岩石地球化学变化特征及其影响因素，阐述了SWIR的岩浆供应及洋壳增生模式。其中，在9°～16°E斜向扩张脊，以构造作用为主的洋脊扩张模式导致了更宽的洋壳增生带和显著的地球化学异常；而在50°～51°E脊段，发育了强烈的火山活动，其成因机制包括克洛泽热点与洋中脊相互作用、微热点、古老熔融事件的残留地幔再熔融等几种观点。此外，西南印度洋中脊龙旂热液区（～49.7°E）的最新研究表明，其热液循环路径与拆离断层的发育密不可分，热液流体循环最深可达莫霍面以下6 km。因此，在今后的一段时间，应进一步加强SWIR不同空间尺度地幔源区性质、洋中脊构造与岩浆作用过程、热点-洋中脊相互作用和岩浆-热液活动与成矿等主要科学问题的研究。
Abstract:
The Southwest Indian Ridge (SWIR), as an ultraslow spreading ridge, has attracted great attentions from the geo-society of the world in the past three decades due to its unique morphology, crustal architecture, crustal accretion mode, volcanism, hydrothermal activities and deep mantle processes. This paper is devoted to the recent research progress on the petrology and geochemistry of basalt,gabbro and mantle peridotite collected from the SWIR. The geochemical data well revealed the variations of the whole ridge and ridge segments. Based on the data mentioned above, we described and discussed the main factors, which control the geochemical variations, magma supply and crustal accretion. In the oblique spreading ridge segment of 9°～16°E, the tectonics-dominated ocean ridge spreading patterns resulted in the wider oceanic crust accretion zone with significant geochemical anomalies; in the 50°～51°E ridge segment, strong volcanic activities occur, and its genetic mechanism includes different points of view, such as the interaction between the Crozet hotspot and SWIR, the micro hotspot, and the remelting of the residual mantle left behind by the former melting events. The latest research about the Longqi hydrothermal area (～ 49.7° E) suggests that the hydrothermal circulation is closely related to the development of detachment faults, and the maximum depth of hydrothermal circulation may reach 6 km below the Moho boundary. Therefore, it is suggested that the future study be strengthened in such issues as the mantle heterogeneity in different spatial scales, the tectonic-magmatic processes in the ridge system, ridge-plume interaction, and the seafloor hydrothermal activity and deposits.
