Hydration and Sulfur Metasomatism of Forearc Mantle

在俯冲过程中，蚀变的洋壳和沉积物与上覆的弧下地幔发生反应。 了解这些流体和反应对于理解俯冲带的化学循环以及最终循环到地幔中的物质至关重要。马里亚纳和伊豆-小笠原弧的锥形和鸟岛海山是蛇纹岩突起，是由于下伏俯冲板片脱水导致弧前地幔楔大规模水合作用的结果。拟议项目将分析这两座海山蛇纹化地幔橄榄岩的稳定同位素（O、H、S、C）组成、不透明矿物学和硫含量。 目标是1.确定蛇纹岩化的深部条件;限制了蛇纹流体的成分以及它们与地表取样的成分的关系，以及3.测试从弧火山岩的硫同位素比率的预测，海水硫成分存在于板状流体。 结果将提供一个更好的理解变质过程，水化反应的条件下，在深度和流体成分，以及对弧前地幔楔的热结构的约束。 这项研究将为评价俯冲带的热结构和水化反应模型提供必要的基础数据。

During subduction, altered ocean crust and sediments dehydrate and these fluids react with the overlying sub-arc mantle. Knowledge of such fluids and reactions is critical to understanding chemical cycling in subduction zones, and what is ultimately recycled into the mantle. Conical and Torishima Seamounts in the Mariana and Izu-Bonin forearcs are serpentinite protrusions that result from large scale hydration of the forearc mantle wedge by dewatering of the underlying subducting slab. The proposed project will analyze the stable isotopic (O,H,S,C) compositions, opaque mineralogy, and sulfur contents of serpentinized mantle peridotites from these two seamounts. The objectives are 1. to determine the conditions of serpentinization at depth, 2. constrain the compositions of serpentinizing fluids and how they relate to those sampled at the surface, and 3. test the prediction from the sulfur isotope ratios of arc volcanics that a seawater sulfur component is present in slab-derived fluids. Results will provide a better understanding of metamorphic processes, conditions of hydration reactions, and fluid compositions at depth, as well as constraints on the thermal structure of the forearc mantle wedge. This study will provide fundamental data necessary for the evaluation of models for the thermal structure and hydration reactions in subduction zones.