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西南印度洋中脊是典型的慢速扩张洋中脊之一。对采自西南印度洋中脊50°E附近的7件玄武岩和蛇纹石化橄榄岩样品所作的分析表明,基性玄武岩类SiO2含量为43.72%～48.40%,TiO2含量较少,为1.14%～1.52%;MgO含量为5.96%～10.98%;TFe2O3含量为4.55%～5.2%;Mg#值为0.53～0.64,里特曼指数σ为2.34～20.10。微量元素Zr/Nb和Y/Nb比值为显示N-MORB的性质,但是其他微量元素的比值(Ba/Nb,Ba/Th,La/Nb,Nb/U,Nb/Pb)均不显示正常洋中脊玄武岩的特征,微量元素原始地幔标准化蛛网图显示强烈富集K和Pb,亏损Nb,稀土元素显示较为平缓的分配模式。超基性蛇纹石化橄榄岩的主量元素特征为SiO2为38.91～45.49;TiO2含量为0.02～0.28;MgO含量很高,为36.87～40.61,TFe2O3含量为2.82～3.91,Mg#值为0.92～0.94。微量元素中Ni,Cr的含量很高,原始地幔标准化蛛网图显示橄榄岩强烈富集K和Pb,Ba,Th,La,Ce,Ti中等程度富集,而亏损Nb,Sr。稀土元素总量较低,标准化曲线显示轻稀土元素富集模式。结合地球化学特征及前人研究资料分析认为,西南印度洋中脊的基性岩和超基性岩属同源性质,其原始地幔物质可能为部分正常洋中脊亏损地幔混染了陆壳或远洋沉积物的结果。
The southwestern Indian Ocean ridge is one of the typical slow-spreading mid-ocean ridges. Analysis of seven samples of basaltic and serpentiniferous peridotites collected from the mid-southwest Indian Ridge near 50 ° E shows that basalts have a SiO2 content of 43.72% -48.4% and a TiO2 content of 1.14% -1.52 %, The content of MgO is 5.96% -10.98%, the content of TFe2O3 is 4.55% -5.2%, the value of Mg # is 0.53-0.64 and the Reiterman index is 2.34-20.10. The trace elements Zr / Nb and Y / Nb ratios are indicative of N-MORB properties, but none of the other trace elements (Ba / Nb, Ba / Th, La / Nb, Nb / U, Nb / Pb) The characteristics of the midrib basalts and the trace element primitive mantle normalized cobweb map show strong enrichment of K and Pb, depletion of Nb, and rare earth elements show a more moderate pattern of distribution. The main elemental characteristics of the ultrabasic serpentinized peridotites are SiO2: 38.91-45.49; TiO2 content: 0.02-0.28; MgO content is 36.87-40.61, TFe2O3 content is 2.82-3.91, Mg # value is 0.92 ~ 0.94. Trace elements in the Ni, Cr content is high, the original mantle normalized cobweb shows strong peridotite enrichment K and Pb, Ba, Th, La, Ce, Ti moderate enrichment, and loss of Nb, Sr. The total amount of rare earth elements is lower, and the normalized curve shows the light rare earth element enrichment pattern. Based on the geochemical characteristics and previous studies, it is considered that the mafic rocks and ultrabasic rocks of the mid-southwest Indian Ridge are of the same-sourced nature, and their mantle materials may be part of the normal mid-ocean ridge depleted mantle that contaminated continental crust or ocean Sediment results.