We analyzed basalt samples from 4 sites at 49.6°E and 50.5°E along the Southwest Indian Ridge,which were collected with television-video guided grab (TVG) or dredge (D) during 2 hydrothermal expeditions of Chinese vessel "Da Yang Yi Hao" in 2008 and in 2010.These samples are fragments of basaltic pillow lavas and sheet flows.These samples are mainly porphyritic with fine-grained,and euhedral to anhedral phenocrysts of plagioclase,olivine and pyroxene.The matrix contains microcrystalline plagioclase,olivine and pyroxene,in which tabular plagioclase microphenocrysts occur with a radical texture.Whole rock major and rare earth elements data of these samples show that ratios of K/Ti range from 0.071 to 0.091,and La/Sm from 0.52 to 0.70,suggesting that they are normal mid-ocean ridge basalt (N-MORB).Plagioclase compositions range from An76-78 to An66,while those of olivine range from Fo86 to Fo84.In comparison of earlier study on basalt samples along SWIR (49°E-70°E),samples in this study are featured with much more depletion in light rare earth elements,Na8 and K/Ti,but higher Fe8.These data indicate that mantle melting in the study area occur in higher degree and at deeper depth.Furthermore,petrologic and mineralogic features of basalts at 49.6°E and 50.5°E suggest that magma activity and source in the study area are complex.%对近年来我国“大洋一号”科考船在西南印度洋中脊(SWIR)多金属硫化物调查区4个站位所获得的玄武岩进行了岩石学及元素地球化学研究.其岩相学特征为以斑状结构为主,斑晶矿物主要由斜长石、辉石和橄榄石组成.基质以间隐结构为主,主要由斜长石、橄榄石和辉石微晶组成.全岩元素地球化学分析结果表明样品属于亏损型洋中脊玄武岩.矿物化学成分表明斜长石主要为倍长石和拉长石,橄榄石为贵橄榄石.研究区玄武岩具低的Na8、K/Ti比值和LREE/HREE以及较高的Fe8值,可整体归入SWIR 49°E-70°E区指示岩浆熔融程度最高、熔融深度最深的区域内.本次研究为探索SWIR洋脊玄武岩和岩浆熔融等相关研究提供了49.6°E和50.5°E区的新资料,也指示了区内岩浆活动或成矿围岩物质来源的复杂性.
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