Mid-ocean ridge basalts （MORBs） from East Pacific Rise （EPR） 13°N are analysed for major and trace elements, both of which show a continuous evolving trend. Positive MgO-Al2O3 and negative MgO-Sc relationship...Mid-ocean ridge basalts （MORBs） from East Pacific Rise （EPR） 13°N are analysed for major and trace elements, both of which show a continuous evolving trend. Positive MgO-Al2O3 and negative MgO-Sc relationships manifest the cotectic crystallization of plagioclase and olivine, which exist with the presence of plagioclase and olivine phenocrysts and the absence of clinopyroxene phenoerysts. However, the fractionation of clinopyroxene is proven by the positive correlation of MgO and CaO. Thus, MORB samples are believed to show a “clinopyroxene paradox”. The highest magnesium-bearing MORB sample E13-3B （MGO=9.52%） is modelled for isobaric crystallization with COMAGMAT at different pressures. Observed CaO/Al2O3 ratios can be derived from E13-3B only by fractional crystallization at pressure 〉4±1 kbar, which necessitates clinopyroxene crystallization and is not consistent with cotectic crystallization of olivine plus plagioclase in the magma chamber （at pressure -1 kbar）. The initial compositions of the melt inclusions, which could represent potential parental magmas, are reconstructed by correcting for post-entrapment crystallization （PEC）. The simulated crystallization of initial melt inclusions also produce observed CaO/Al2O3 ratios only at 〉4±1 kbar, in which clinopyroxene takes part in crystallization. It is suggested that MORB magmas have experienced clinopyroxene fractionation in the lower crust, in and below the Moho transition zone. The MORB magmas have experienced transition from clinopyroxene＋plagioclase＋olivine crystallization at 〉4±1 kbar to mainly olivine＋plagioclase crystallization at 〈1 kbar, which contributes to the explanation of the “clinopyroxene paradox”.展开更多
东南印度洋中脊(Southeast Indian Ridge, SEIR)是印度洋中扩张速度最快的洋中脊,由SEIR增生的洋壳占印度洋总面积的50%以上,它是塑造印度洋现今构造格局的关键要素.相对西南印度洋中脊和西北印度洋中脊, SEIR具有更复杂的地质构造特征...东南印度洋中脊(Southeast Indian Ridge, SEIR)是印度洋中扩张速度最快的洋中脊,由SEIR增生的洋壳占印度洋总面积的50%以上,它是塑造印度洋现今构造格局的关键要素.相对西南印度洋中脊和西北印度洋中脊, SEIR具有更复杂的地质构造特征和演化过程.综合SEIR及邻区海底高原的地形地貌特征、重磁异常特征和玄武岩地球化学特征,探讨了SEIR的分段、洋中脊演化过程和地幔不均一性,以及板内火山作用与洋中脊的成因关系等.本文将有助于深入理解东南印度洋区域的构造演化历史,全面理解整个印度洋的洋中脊系统和大地构造格局,增进对冈瓦纳大陆裂解和印度洋演化过程的认识.初步研究认为东南印度洋区是多期洋中脊演化的结果,经历了北西向扩张、南北向扩张直至北东向扩张的三期洋壳增生过程.东南印度洋脊下的地幔源区存在不均一性,尤其是阿姆斯特丹-圣保罗海底高原和澳大利亚-南极错乱带两个区域.东南印度洋中的海底高原与热点火山作用密切相关,同时部分存在热点-洋脊相互作用或残留陆壳物质的影响.展开更多
基金supported in part by the Pilot Project of Knowledge Innovation Project,Chinese Academy of Sciences(n.:KZCX3-SW-223 and KZCX2-YW-211)the Special Foundation for the Eleventh Five Plan of COMRA(no.:DYXM-115-02-1-03).
文摘Mid-ocean ridge basalts （MORBs） from East Pacific Rise （EPR） 13°N are analysed for major and trace elements, both of which show a continuous evolving trend. Positive MgO-Al2O3 and negative MgO-Sc relationships manifest the cotectic crystallization of plagioclase and olivine, which exist with the presence of plagioclase and olivine phenocrysts and the absence of clinopyroxene phenoerysts. However, the fractionation of clinopyroxene is proven by the positive correlation of MgO and CaO. Thus, MORB samples are believed to show a “clinopyroxene paradox”. The highest magnesium-bearing MORB sample E13-3B （MGO=9.52%） is modelled for isobaric crystallization with COMAGMAT at different pressures. Observed CaO/Al2O3 ratios can be derived from E13-3B only by fractional crystallization at pressure 〉4±1 kbar, which necessitates clinopyroxene crystallization and is not consistent with cotectic crystallization of olivine plus plagioclase in the magma chamber （at pressure -1 kbar）. The initial compositions of the melt inclusions, which could represent potential parental magmas, are reconstructed by correcting for post-entrapment crystallization （PEC）. The simulated crystallization of initial melt inclusions also produce observed CaO/Al2O3 ratios only at 〉4±1 kbar, in which clinopyroxene takes part in crystallization. It is suggested that MORB magmas have experienced clinopyroxene fractionation in the lower crust, in and below the Moho transition zone. The MORB magmas have experienced transition from clinopyroxene＋plagioclase＋olivine crystallization at 〉4±1 kbar to mainly olivine＋plagioclase crystallization at 〈1 kbar, which contributes to the explanation of the “clinopyroxene paradox”.
文摘东南印度洋中脊(Southeast Indian Ridge, SEIR)是印度洋中扩张速度最快的洋中脊,由SEIR增生的洋壳占印度洋总面积的50%以上,它是塑造印度洋现今构造格局的关键要素.相对西南印度洋中脊和西北印度洋中脊, SEIR具有更复杂的地质构造特征和演化过程.综合SEIR及邻区海底高原的地形地貌特征、重磁异常特征和玄武岩地球化学特征,探讨了SEIR的分段、洋中脊演化过程和地幔不均一性,以及板内火山作用与洋中脊的成因关系等.本文将有助于深入理解东南印度洋区域的构造演化历史,全面理解整个印度洋的洋中脊系统和大地构造格局,增进对冈瓦纳大陆裂解和印度洋演化过程的认识.初步研究认为东南印度洋区是多期洋中脊演化的结果,经历了北西向扩张、南北向扩张直至北东向扩张的三期洋壳增生过程.东南印度洋脊下的地幔源区存在不均一性,尤其是阿姆斯特丹-圣保罗海底高原和澳大利亚-南极错乱带两个区域.东南印度洋中的海底高原与热点火山作用密切相关,同时部分存在热点-洋脊相互作用或残留陆壳物质的影响.
