东马努斯弧后盆地中酸性火山岩岩浆演化中的锂同位素特征

Lithium isotopic composition of intermediate volcanic rocks in eastern Manus Basin during magma evolution

通过分析东马努斯海盆中酸性火山岩的全岩主量、微量元素以及锂同位素组成,并结合前人数据,讨论盆地岩浆体系的演化过程。分析数据显示,东马努斯海盆主、微量元素与SiO_(2)含量之间呈线性变化关系,表明岩浆结晶分异过程控制东马努斯海盆岩浆演化过程。东马努斯弧后盆地火山岩富集流体相关元素,指示东马努斯弧后盆地岩浆源区可能经历了俯冲流体的交代作用。在岩浆移出源区之后的演化阶段,岩浆体系演化以结晶分异过程为主。锂同位素与流体示踪指数具相关性,δ^(7)Li随俯冲流体加入呈现升高趋势,而与岩浆结晶分异程度无相关性,表明锂同位素分馏受控于流体交代作用。

Major and trace elements and the Li isotopic composition were analyzed for intermediate volcanic rocks in the eastern Manus Basin.Previous data were combined to explore the origination and evolution process.The variation of major and trace elements with the content of SiO_(2)increases,and the ratio of La/Sm remains stable as the differentiation of magma,indicating that the volcanic rocks were controlled by fractional crystallization.According to the characteristics of trace elements,the rocks were enriched with fluid mobile elements and were affected by the metasomatism of subduction fluids.Along with the increase of slab fluids,δ^(7)LiLi showed an increasing trend,indicating that the variation of the lithium isotope was caused by fluid metasomatism.No significant correlation between the lithium isotopic composition and the extent of fractional crystallization was observed.Hence,crystallization was not the main factor that controlled the fractionation of lithium isotopes.