Hydration and Sulfur Metasomatism of Forearc Mantle

在俯冲过程中，蚀变的洋壳和沉积物脱水，这些流体与上覆的弧下地幔发生反应。了解这种流体和反应对于了解俯冲带中的化学循环以及最终循环到地幔中的物质至关重要。马里亚纳海前弧和伊豆-博宁前弧的锥形和托里什马海山是弧前地幔楔体通过下伏俯冲板脱水而大规模水化的蛇纹岩突起。拟议的项目将分析这两个海山蛇纹岩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。其目的是：1.确定深部蛇纹岩化的条件；2.限制蛇纹岩化流体的成分及其与地表取样的成分之间的关系；3.从弧形火山岩的硫同位素比值中检验板条成因流体中存在海水硫成分的预测。这些结果将有助于更好地了解变质过程、水化反应条件和深部流体成分，以及对弧前地幔楔热结构的限制。这项研究将为评估俯冲带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.