地幔矿物和富水流体之间镧分配系数的实验研究

Fluid activities and related island arc volcanism in subduction zones are crucial to the understanding of plate tectonic theory. However, it's still unclear about the properties of subducting slab derived fluids that metasomatize the mantle wedge peritotite and further trigger the arc volcanism, as well as their mobility mechanism for trace elements. Experimental studies on trace elements partition coefficients between aqueous fluid and mantle minerals, such as olivine, garnet, and pyroxene are rare, and the literature data show large variation and uncertainty. This project will focus on the first light rare earth element (REE) Lanthanum, which is the most fluid mobility element in REE. The study will be performed by the novel indirect equilibrium method, in which the Lanthanum silicate was used as medium and the piston cylinder and hydrothermal diamond anvil cell experiments were combined. The results are to acquire the La partition coefficients between olivine, garnet, and pyroxene and aqueous fluid at 1.0-3.0 GPa and 600-1100 ℃, and further to provide constraints on the processes such as dehydration of subducting slab, metasomatism of mantle wedge and generation of island arc magmas.

俯冲带流体活动及相关的岛弧火山作用是板块构造理论的重要内容之一。目前对于交代地幔楔并引发岛弧火山作用的板片来源流体的性质，及其对微量元素的迁移机制还不清楚。前人对地幔矿物橄榄石、辉石和石榴石与含水流体之间的微量元素分配系数的研究非常有限，且现有的数据也存在较大的变化范围和不确定性。因此，我们选择流体活动性元素轻稀土镧（La）作为研究对象，采用新颖的间接平衡方法，以镧硅酸盐作为媒介，将活塞圆筒压机和水热金刚石压腔装置相结合，获得1.0-3.0 GPa，600-1100 ℃条件下，石榴石、斜方辉石、单斜辉石和橄榄石等地幔矿物与含水流体之间镧的分配系数，进而为俯冲带板片脱水，交代地幔楔和岛弧岩浆的形成过程提供更好的约束。