Geochemical Evolution of the Mantle

9804891哈特这一基于证据的更新，作为其首要目标，理解的位置，成因，演化和岩性性质的几个已知的异质地幔域，熔融和熔融提取从这些地幔域的动力学。其中两个领域尚未充分表征其锇同位素组成。为了解决这个问题，将对被认为来自EM1地幔域的洋岛玄武岩（皮特凯恩和圣诞岛）和世界上所有主要扩张脊系统的深海橄榄岩（MORB域）中的耐火铬铁矿进行锇同位素研究。一些地球的地幔域被认为是岩石圈再循环的结果，但这种物质的岩性表达和熔融动力学还不清楚。这些问题将通过两个途径加以探讨。离子探针研究的Pb同位素组成和微量元素的矿物（斑晶）熔融包裹体从各种海洋岛屿玄武岩的签名将阐明熔融岩性和熔体运输网络。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。这些岛屿的数量明显的衍生广泛的程度熔化从一个单一的地幔源将允许限制放在批量与部分熔化，对流与集中熔体运输，连续熔体再平衡与逃逸在高速管道，和均匀的源岩性与小规模（脉）的不均匀性的问题。

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.