| 摘要: |
| 利用全球岩石地球化学数据库(PetDB)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。 |
| 关键词: 西北印度洋中脊 玄武岩 沿脊轴变化 地幔不均一性 |
| DOI：10.11759/hykx20150514002 |
| 分类号: |
| 基金项目:国家重点基础研究发展计划项目(2013CB429702); 中国大洋矿产资源研究开发协会“十二五”重大项目(DY125-11-R-01, DY125-12-R-03) |
|
| Mantle source features of basalts in the Northwest Indian Ridge |
|
CHUN Ming-hao,YU Zeng-hui,LI Huai-ming,ZHAI Shi-kui
|
| Abstract: |
| The geochemical features and variation in major elements, trace elements, and isotopic compositions of CR, NCIR, and SCIR MORBs, collected from the PetDB database, are examined to investigate mantle source heterogeneity and the variation in magmatic processes along a ridge axis. The trace element and isotopic composition of the basalts are nearly identical to that of N-MORB, except for an anomaly in some segments, and are different from typical Indian Ridge basalts. The basaltic magma is a product of spinel lherzolite mantle melting, and the mantle source comprises two mantle domain components, namely DMM and EMⅡ, which contribute 69% and 27%, respectively. The enrichment of the EMⅡ-type component may be a result of ancient crustal contamination. The isotopic composition of Sr, Nd, and Pb is heterogeneous, reflecting that the composition of mantle source is similar for the basalts from the CR, NCIR, and SCIR. The basalts show that there is heterogeneity in the mantle source near the SCIR 19°S segment. In addition, it shows that the significant feature of the EMⅡ-type component mixed. There is enrichment of K, Ba, La, and U in the basalts near the CR 3.5°N segment; however, the features of the mantle source need to be further studied because of the lack of isotopic composition data. Based on these research results, we define large-scale mapping, intensive survey sampling, and laboratory analysis as a basis for further research the CR. An extensive isotopic analysis of Sr, Nd, Pb and Re, Os, and Be could provide evidence on the mantle heterogeneity of the CR. Furthermore, clarification on the degree of influence of Indian Ocean Mantle on the CR could contribute to a better understanding of the causes of mantle heterogeneity and its dynamic processes. |
| Key words: the Northwest Indian Ridge basalt variation along ridge axis mantle heterogeneity |
