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MORB是玄武岩中研究得最详细的玄武岩类,可分为N-MORB和E-MORB两类.通常认为,N-MORB和OIB都是独立的端元,分别来自亏损和富集的地幔源岩,而E-MORB则是N-MORB与OIB混合的结果.本文研究表明,E-MORB具复杂的成因,洋脊深度、洋脊扩张速率及源区部分熔融程度及压力不是造成E-MORB富集的主要原因.压力及部分熔融程度对玄武岩成分的影响远小于地幔不均一性的影响.推测E-MORB可能有两个主要的形成方式:1)由较深处略富集的地幔发生部分熔融而成;2)由N-MORB与OIB混合形成.玄武岩微量元素频率直方图表明,N-MORB基本上保持了来自亏损地幔源区的特征;OIB则多多少少受到外来物质加入或与N-MORB混合的影响;E-MORB则是N-MORB受OIB影响的产物.OIB与E-MORB似乎没有本质上的区别,仅仅是受影响和混合程度的不同而已.OIB富集LILE,可能既有继承了来自源区的特征(深部富集地幔、循环的古洋壳、循环的陆壳、大陆岩石圈地幔、LVZ熔体层或早期交代岩脉等),也可能有外来物质加入的影响(与N-MORB发生不同程度的混合作用).3类玄武岩的87Sr/86Sr和143Nd/144Nd同位素频率分布与早先的结论一致,但206pb/204pb、207pb/204pb和208pb/204pb同位素频率分布显示OIB具有更加复杂的特征.“,”At present,MORB is the most detailed basanitoid,can be divided into two categories,N-MORB and E-MORB.It is generally considered that both N-MORB and OIB are independent end-members from depleted and enriched mantle-derived rocks,while E-MORB is the result of mixing N-MORB with OIB.The main causes of E-MORB enrichment are not because of the ridge depth,the ridge expansion rate,the partial melting degree and pressure of the source region,The results show that the E-MORB has the complex cause.The influence of pressure and partial melting degree on basalt composition is much less than that of mantle heterogeneity.It is speculated that the E-MORB may have two main forms of formation:One is partially melted by a slightly enriched mantle;another is formed by mixing N-MORB with OIB.The frequency histogram of trace elements in basalts shows that N-MORB basically maintains the characteristics from the depleted mantle source region.The trace elements histograph in basalts shows that N-MORB basically maintains the characteristics from the depleted mantle source area,but OIB is more or less affected by the addition of foreign material or mixed with N-MORB;E-MORB is the product of N-MORB affected by OIB.OIB and E-MORB,only the impact and the degree of mixing is different.It seems to have no essential difference.OIB enrichment LILE,may inherit the characteristics from the source area.OIB enrichment LILE,may have inherited from the source area characteristics,including deeply enriched mantle,circulating ancient oceanic crust,recirculating continental crust,continental lithosphere mantle,LVZ melt layer or early metasomatic veins etc;may also have the impact of the addition of foreign material,including in varying degrees of mixing with N-MORB.The distribution of 87Sr/86Sr and 143Nd/144Nd isotopic frequencies of the three basal basalts is consistent with the previous conclusion,but the 206Pb/204Pb,207Pb/204Pb and 208Pb/204Pb isotopic frequency distributions show that OIB has more complex characteristics.