索罗尔海槽俯冲前缘基底的岩石学和矿物学研究

Petrology and Mineral Geochemistry of Basement Basalts in Sorol Trough Subducting

对从雅浦海沟东南侧处获得的正在俯冲的基底样品(索罗尔海槽的轴部在海沟直接投影位置处的玄武岩样品)进行了岩石学和单矿物原位主微量元素地球化学研究。结果表明,索罗尔海槽正在沿着雅浦海沟俯冲的片段的基底岩石属碱性玄武岩系列,橄榄石斑晶的Fo值为84.97~86.85。根据模拟计算,该片段基底玄武岩的源区地幔为橄榄岩,这些玄武岩可能是由地幔源区的尖晶石二辉橄榄岩经2%~5%部分熔融形成的;由计算的地幔潜在温度可知形成该玄武岩的地幔并不存在热量异常。所以,研究区玄武岩是在卡罗琳海脊裂解形成索罗尔海槽期间被动上涌的相对富集(大离子亲石元素和高场强元素)的地幔岩石组分经过低程度的部分熔融所形成。

In this study,we performed petrological and mineral geochemical(in situ major element compo-sitions and trace element compositions)studies on newly acquired subducting basement basalt samples from the Sorol Trough segment being subducted along the Yap Trench.Our results show that these rocks belong to the alkaline basalt series,and the Fo value of the olivine phenocrysts in these rocks vary from 84.97 to 86.85.The simulation calculation shows that the source mantle of these basement basalt is peridotite,and these Sorol Trough basalts may be formed by 2%to 5%partial melting of mantle spinel lherzolite.The calculated mantle potential temperature beneath the Sorol Trough segment being subducted along the Yap trench shows that there is no thermal anomaly.In conclusion,the basalts in the study area were products of low-degree partial melting of relatively enriched mantle rock components that were passively upwelling during the formation of Sorol Trough separating Caroline Ridge into western-and eastern part.