CHEMICAL COMPOSITION OF THE BASALTS ON EAST PACIFIC RISE (1.5°N~1.5°S) AND SOUTH MID-ATLANTIC RIDGE (13.2°S)
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摘要: 对东太平洋海隆(EPRⅠ区和Ⅱ区)和南大西洋中脊(SMAR)6个站位新鲜的玄武岩样品进行了岩石学及地球化学研究。结果显示,EPR玄武岩样品可分为辉石玄武岩、气孔玄武岩和玻基玄武岩3种类型,SMAR玄武岩样品主要为辉石玄武岩。EPR和SMAR玄武岩样品的标准矿物组合相同,均出现了石英和紫苏辉石标准矿物,为典型的拉斑玄武岩。EPRⅠ区和SMAR玄武岩表现出轻稀土富集的配分模式,可能受到了富集地幔源区(E-MORB)的影响,其玄武岩可能形成于未经历早期熔融事件的富集地幔或部分熔融程度相对较低。EPRⅡ区玄武岩为正常型洋中脊玄武岩(N-MORB),其源区为经历了早期熔融事件的、亏损洋中脊地幔源区(DMM),且源岩部分熔融程度较高。EPRⅠ区与Ⅱ区不同的幔源特征说明东太平洋海隆地幔源区存在不均一性。Abstract: Six samples of fresh basalts collected from the East Pacific Rise (EPRⅠarea and Ⅱarea) and the South Mid-Atlantic Ridge (SMAR) have been studied in petrology and geochemistry. The EPR basalts can be grouped into the categories of pyroxene basalt, vesicular basalt and tholeiitic basalt, and the SMAR are dominated by pyroxene basalts. The mineral composition of the EPR is similar to that of SMAR by the existance of quartz (Q) and hypersthene (Hy).They all belong to the typical tholeiite. Both of the basalt of EPRⅠand SMAR, however,are enriched in LREE possibly due to the constraints of the mantle source (E-MORB). These basalts may be formed by the enriched mantle before partial melting or only having weak partial melting in the early stage of evolution. The basalts from the EPRⅡarea are normal mid-ocean ridge basalts from the classical depleted mantle (N-MORB) partially melted in early stage and the upper mantle magma was differentiated to certain extent. The difference in sources of the basalts at EPRⅠand Ⅱillustrates that the mantle is heterogeneous on the East Pacific Rise.
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Key words:
- basalt /
- petrology /
- geochemistry /
- East Pacific Rise /
- South Mid-Atlantic Ridge
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