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为了确定岩浆的来源,我们分析了大洋区内的Mariana和Volcano岛弧近代新鲜火山岩的O和Sr同位素组成.为了比较,也分析了Mariana-Volcano岛弧外围地区的非岛弧新鲜火山岩和一些深海钻探计划沉积物(DSDP sediments).岛弧间熔岩的氧同位索比值显示出较小幅度的变化,这种变化无法完全用分离结晶作用来解释,但其锶同位素组成具显著的均一性(Mariana为0.70332-0.70394).为了解释观察到的同位素特征,我们考虑了三种模式:(1)MORB型地幔与(a)俯冲沉积物,(b)俯冲洋壳(不包括沉积物)的总体混合熔融;(2)沉积物衍生的流体与洋岛型或热点型地幔所组成的混合物的熔融.其中最后一种模式对已得资料吻合得最好.最后的结论是,需要有少许不等量的沉积物衍生流体(≤1%)来解释观察到的岛间氧同位素变异特征,这个观点与其它同行们应用不同的同位素和微量元素方法所得出的结论一致.Mariana-Volcano岛弧岩浆的形成过程中只有很少量的沉积物卷入,Mariana熔岩的源区在同位素方面与热点玄武岩没有什么差别.
In order to determine the origin of the magma, we analyzed the O and Sr isotopic composition of the modern fresh volcanic rocks of the Mariana and Volcano arcs in the Oceania region. For comparison, the non-arc arc fresh volcanic rocks in the periphery of the Mariana-Volcano arc and some deep sea DSDP sediments. The oxygen isotopic ratios of lava between islands show small amplitude changes, which can not be completely explained by segregation but have significant homogeneity of the strontium isotopic compositions (Mariana (0.70332-0.70394) .To explain the observed isotopic characteristics, we consider three modes: (1) the total mixture of MORB mantle with (a) subduction sediment, (b) subducted oceanic crust (excluding sediment) (2) the melting of the mixture of sediment-derived fluids and the ocean-island or hotspot-type mantle, of which the last model is the best fit to the data obtained, and the final conclusion is that a small amount of inequality Of sediment-derived fluids (≤1%) to explain the observed variation in oxygen isotopic variability among islands, in agreement with the conclusions reached by other colleagues using different isotopic and trace element methods. Mariana- Only a small amount of sediment is involved in the formation of volcanic magma in the island of Volcano, and the source of the Mariana lava is no different from that of hot basalts in terms of isotopes.