藏南泽当蛇绿岩二辉橄榄岩地幔内脉状纯橄岩形成过程及其效应

在大洋扩张中心地幔源区至洋壳底部的区域内，熔体主要通过由纯橄岩构成的网脉状通道向上迁移汇聚。对蛇绿岩的观察显示这种通道多出现在接近莫霍面的浅部难熔地幔中（方辉橄榄岩为主），而在大洋扩张中心深部的饱满二辉橄榄岩地幔内，纯橄岩脉体通道如何形成？其形成后，熔体在该通道内发生的反应迁移过程如何影响大洋壳幔组成关系？仍是未解决的关键问题。项目将以藏南雅江带泽当蛇绿岩深部二辉橄榄岩地幔内产出的脉状纯橄岩为主要研究对象，在扎实的野外和岩相学研究基础上，通过岩石学、矿物学、元素和同位素地球化学（特别是高精度Sm-Nd、Lu-Hf和Re-Os同位素）的综合研究，查明在大洋扩张中心深部饱满地幔内纯橄岩脉体的成因，揭示熔体属性及其在地幔纯橄岩通道内的复杂反应迁移过程，重点从同位素角度上理清熔体迁移对大洋壳幔组成关系的制约作用。研究结果将为深入理解大洋扩张中心岩浆抽取系统的运行机制和物质循环规律提供新的约束。

Within the mantle portion that connects mantle source and oceanic crust under oceanic spreading centers, melts mainly flow and focus within the tabular channel system made up of dunite veins. Observations based on ophiolites show that such channels mostly occur within the shallow refractory mantle (mainly harzburgitic) close to the Moho. However, within the deep fertile mantle portion (mainly lherzolitic) beneath oceanic spreading centers, how do the tabular dunite channels form? After their formation, how do the reactive migration processes of melts in the channels affect the compositional relationship between oceanic crust and mantle? All these key questions remain unsolved. This project will focus on the vein-like dunites rarely distributed in the deep lherzolitic mantle section of the Zedang ophiolite (Yarlung Zangbo suture, South Tibet). Based on detailed field work and petrographic observations, this study will carry out systematic and combined petrological, mineralogical as well as elemental and isotopic geochemical studies, especially the high-precision Sm-Nd, Lu-Hf and Re-Os isotopic analyses. The aims are to clarify the origin of the dunite veins in the deep fertile mantle portion beneath oceanic spreading centers, to reveal the nature of melts within the mantle dunite channels and their complex reactive migration processes, and to understand the constraints on the compositional relationship between oceanic crust and mantle mainly from the isotopic perspective. The research outcomes will provide novel understanding of the mechanism of the melt plumbing system beneath oceanic spreading centers and the mass cycling processes in Earth.