西南印度洋中脊东段MORB微量元素地球化学及其对地幔源区组成的指示

MORB trace element geochemistry in the eastern of southwest indian ridge and its indication for the composition of mantle source

西南印度洋中脊东段(E-SWIR)处于61°~70°E区域,具有相对匮乏的熔体供给。该区产出的大多数洋中脊玄武岩(MORB)具有富集不相容元素以及大离子亲石元素等特征,属典型E-MORB。基于玄武岩样品的微量元素地球化学资料,通过La/Sm、Zr/Nb和Lu/Tb等分析表明E-SWIR地幔具有明显的不均一性,这种不均一性可能与地幔中辉石岩含量的沿轴变化有关。利用稀土元素Ce、Sm、Lu和Yb含量结合部分熔融计算模拟结果,进一步阐明地幔源区中石榴石的作用与影响,并且认为其可能是以含金红石榴辉岩的形式赋存于地幔之中。对E-SWIR地幔源区榴辉岩性质和赋存形式的识别是探讨EMORB成因、地幔不均一性与洋中脊构造演化等科学问题的关键。

The eastern of the southwest Indian ridge(E-SWIR)is located between 61°and 70°E,with relatively low melt supply.Most of the mid-ocean ridge basalts(MORB)produced in this area is a typical E-MORB with the characteristics of enrichment of incompatible elements and large ion lithophile elements.Based on the trace element geochemical data of basalt samples,the analysis of La/Sm,Zr/Nb and Lu/Tb shows that the E-SWIR mantle has obvious heterogeneity,which may be related to the axial variation of pyroxenite content in the mantle.Using the contents of rare earth elements Ce,Sm,Lu and Yb in combination with the simulation results of partial melting calculation,the role and influence of garnet in the mantle source area are further clarified,and it is believed that it may exist in the mantle as auriferous garnet pyroxene.The identification of the nature and occurrence form of eclogites in the E-SWIR mantle source region is the key to discuss the origin of EMORB,mantle heterogeneity and the tectonic evolution of mid ocean ridge.