西北印度洋中脊玄武岩源区地幔特征

发布时间：2018-04-12 19:04

  本文选题：西北印度洋中脊 + 玄武岩　； 参考：《海洋科学》2016年08期

【摘要】：利用全球岩石地球化学数据库(Pet DB)中有关卡尔斯伯格洋脊(CR)、北中印度洋脊(NCIR)及南中印度洋脊(SCIR)玄武岩的微量元素及同位素组成数据,分析了玄武岩的元素地球化学特征及其沿脊轴的变化,旨在探讨玄武岩源区地幔的(不)均一性及岩浆作用过程的差异。初步研究结果表明:CR、NCIR及SCIR玄武岩组成相近,仅在个别脊段表现有微量稀土元素和同位素组成上的差异,玄武岩整体与N-MORB组成特征相近,与先前通常认为的典型印度洋中脊玄武岩不同。玄武质岩浆主要源自尖晶石二辉橄榄岩地幔的熔融,岩浆源区主要由两个地幔端元构成,即以亏损型地幔(DMM)为主(69%),其次为富集型地幔(EMⅡ,27%)。富集组分可能源自古老陆壳物质的混染。自CR经NCIR到SCIR整个印度洋中脊西北分支玄武岩的Sr、Nd及Pb同位素组成表现出均一性,表明岩浆源区地幔组成相近。在SCIR 19°S附近脊段岩浆源区地幔存在有不均一性,有EMⅡ型地幔端元混入的迹象。在CR 3.5°N附近脊段,玄武岩明显富集K、Ba、La及U等微量元素,但由于缺少同位素数据,源区地幔特征有待进一步研究。在上述研究成果的基础上,提出了该区大比例尺的调查填图及密集采样和精细室内分析是CR深入研究的基础,同时加强Sr、Nd、Pb及Re、Os、Be等同位素分析测试,可提供揭示CR地幔不均一性的可靠依据,而厘清印度洋型地幔对CR的影响程度则有助于深入认识地幔不均一性的成因及地幔动力学过程。
[Abstract]:Using the data of trace elements and isotopic compositions of basalts from the global petrogeochemical database (Pet DB) relating to the Karlsberg Ridge, the North Central Indian Ridge (NCIRs) and the South Indian Ridge (SCIRR),The elemental geochemical characteristics of basalts and their variations along the ridge axis are analyzed in order to explore the (inhomogeneity) of mantle and the differences of magmatic processes in basalt source regions.The preliminary results show that the composition of SCIR basalts is similar to that of SCIR basalts, and only shows the differences of trace rare earth elements and isotopic compositions in individual ridges. The basalts as a whole are similar to those of N-MORB rocks.It is different from the typical Indian Ocean ridge basalt.Black Tortoise magma is mainly derived from the melting of the spinel peridotite mantle. The magmatic source region is mainly composed of two mantle endants, namely, the depleted mantle (DMMM) and the enriched mantle (EM 鈪，

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