The Role of the Forearc in Subduction Zone Chemical Cycles: Elemental and Isotopic Signatures of Forearc Serpentinites, ODP Leg 125

俯冲带是地球上唯一一个可以将地表物质（水、沉积物和地壳岩石）带入地球内部深处的地方。为了量化这一俯冲带再循环过程，我们需要了解沉积物和地壳向海沟的输入，以及与俯冲过程相关的所有地球化学输出。虽然以火山弧和弧后环境中的岩浆活动为代表的化学输出已被广泛研究，但对于通过弧前浅层、弧与海沟之间可能存在的与俯冲有关的流出，人们知之甚少。我们试图通过研究在马里亚纳弧-海沟体系中沿弧前地幔和地壳向底端上升的蛇纹岩来表征“弧前通量”。我们的工作将完成几年前开始（在美国国家科学基金会的支持下）的努力，并将对这些样品（以及帮助制造它们的板块衍生流体）的放射性同位素、锂和氧同位素，以及“流体流动”元素Cs、Rb、U、As、Pb和Sb进行表征。我们的工作将使我们能够表征从前缘俯冲板块释放的物种的化学清单，以及这种通量的大小。用于与海沟输入的结果（作为ODP Leg 125的一部分收集）和马里亚纳系统弧火山输出的现有数据进行比较。

Subduction zones are the one place on Earth where materials from the surface (water, sediments and crustal rocks) can be carried into our planet's deep interior. To quantify this process of subduction-zone recycling, we need to understand both the input of sediments and crust to trenches, and all geochemical outputs related to the subduction process. While the chemical outputs represented by magmatism at volcanic arcs and in back-arc settings have been widely studied, little is known about possible subduction-related outfluxes through the shallow forearc, between the arc and the trench. We are attempting to characterize the "forearc flux" by examining serpentinites which are rising diapirically through the forearc mantle and crust in the Mariana arc-trench system. Our work will complete efforts begun (with NSF support) several years ago, and will characterize these samples (and the slab-derived fluids which helped to create them) for radiogenic isotopes, lithium and oxygen isotopes, and the "fluid-mobile" elements Cs, Rb, U, As, Pb, and Sb. Our work will allow us to characterize both the chemical inventories of species that are released from subducting slabs beneath forearcs, and the magnitude of this flux, for comparison with results for trench inputs (being collected as part of ODP Leg 125), and existing data for arc volcanic outputs in the Mariana system.