Geochemical Evolution of the Mantle

这项以成果为基础的更新的首要目标是了解几个已知的非均质地幔区域的位置、成因、演化和岩性，以及从这些地幔区域熔融和熔体提取的动力学。这些领域中有两个领域尚未充分描述其Os同位素组成。为解决这一问题，将对被认为来自EM1地幔区域的洋岛玄武岩(皮特凯恩和圣诞岛)和来自世界上所有主要扩张脊系的深海橄榄岩(MORB区域)中的难熔铬铁矿进行Os同位素研究。地球的几个地幔区域被认为是岩石圈再循环的结果，但这种物质的岩性表现和熔融动力学尚不清楚。这些问题将通过两个途径进行探讨。离子探针研究不同洋岛玄武岩矿物(斑晶)熔融包裹体的铅同位素组成和微量元素特征，将有助于揭示熔融岩性和熔体输运网络。第二种方法将利用Th和Ra同位素数据，结合对加拉帕戈斯群岛一系列历史熔岩的熔体包裹体研究。通过单一地幔来源熔融程度的大范围明显地派生出这些岛屿，将允许对批量熔融与分批熔融、渗流熔体与聚焦熔体输送、高速管道中连续熔体再平衡与逸出以及同质源岩性与小规模(脉状)非均质性的问题施加限制。

9804891HartThis accomplishment-based renewal has, as its overarching goals, the understanding of the placement, genesis, evolution and lithologic nature of the several known heterogeneous mantle domains, and the dynamics of melting and melt extraction from these mantle domains. Two of these domains have yet to be adequately characterized for their osmium isotopic composition. In order to address this, osmium isotope studies will be conducted on ocean island basalts (Pitcairn and Christmas Islands) thought to be derived from the EM1 mantle domain and on refractory chromites in abyssal peridotites (MORB domain) from all of the major spreading ridge systems of the world. Several of Earth's mantle domains are thought to be a result of lithospheric recycling, yet the lithologic expression and melting dynamics of this material are not understood. These issues will be explored via two avenues. Ion microprobe studies of the Pb isotope composition and trace element signatures of mineral (phenocryst) melt inclusions from various ocean island basalts will shed light on the melting lithologies and melt transport networks involved. The second approach will utilize Th and Ra isotope data in conjunction with melt inclusion studies for a series of historic lavas from the Galapagos Islands. The apparent derivation of a number of these islands by a wide range in degree of melting from a single mantle source will allow constraints to be placed on issues of batch versus fractional melting, percolative versus focused melt transport, continuous melt re-equilibration versus escape in high velocity conduits, and homogenous source lithology versus small-scale (veined) heterogeneities.