西南印度洋中脊50°E基性超基性岩石地球化学特征及其成因初探  

The Characteristic of Geochemistry and Genesis for Mafic and Utrlmafic Rocks from the 50°E of Southwest Indian Ridge

作　　者：韩宗珠[1] 张贺[1] 范德江[1] 丁蒙蒙[1] 刘明[1] 徐翠玲[1] 

机构地区：[1]中国海洋大学海洋地球科学学院海底科学与探测技术教育部重点实验室,山东青岛266100

出　　处：《中国海洋大学学报（自然科学版）》2012年第9期69-76,共8页Periodical of Ocean University of China

摘　　要：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。Southwest Indian Ridge（SWIR） is one of important slow-spreading mid-ocean ridges.We have analyzed 7 samples of basalt and serpentinized peridotite collected from the vicinity of 50 ° E from SWIR.The SiO2 of basic basalts content is of 43.72%~48.40%,TiO2 content is less of 1.14%~1.52%,MgO content of 5.96%~10.98%,TFe2O3 content of 4.55%~5.2%,Mg # value of 0.53~64 and the Rittmann index σ is 2.34~20.10.Trace element ratios of Zr/Nb and Y/Nb show the nature of N-MORB,but the ratios of other trace elements（Ba/Nb,Ba/Th,La/Nb,Nb/U,Nb/Pb） do not display this feature.Primitive mantle-normalized spider diagram of trace element shows a strong enrichment of K and Pb,loss of Nb.And the REE distribution shows a gentle pattern.The major element characteristics of ultramafic serpentinized peridotite are as follows.The SiO2 content is of 38.91~45.49,TiO2 content of 0.02~0.28,MgO content very high of 36.87~40.61,TFe2O3 content of 2.82~3.91 and Mg # value of 0.92~0.94.The contents of trace elements Ni and Cr are high.And the primitive mantle-normalized spider diagram shows a strong enrichment of K and Pb,moderate enrichment of Ba,Th,La,Ce,Ti,and loss of Nb,Sr.The ∑REE are low,and the chindrite-normalized REE shows LREE enrichment patterns.Combine geochemical characteristics with the former analysis results,we suggest that the mafic and ultramafic rocks Southwest Indian Ridge are products of the homologous origin,and their original mantle material may be the product of the normal depleted mid-ocean ridge mantle mixed with continental crust or pelagic sediments partly.

关 键 词：西南印度洋中脊 50°E 地球化学 

分 类 号：P591[天文地球—地球化学]