Assessing the redox state of Mariana forearc

俯冲带(“弧”)是一个构造板块(“板块”)被拖到另一个板块下方进入地球深部(“地幔”)的地质背景。它们是地球表面和内部之间主要的化学交换场所。水和其他挥发物(如硫、氯、氟、碳)以流体的形式从俯冲板块释放出来，并被输送到上覆板块(“弧前地幔”)。这些流体被认为在俯冲带中铜和金等具有重要经济意义的元素的运输和浓缩以及弧岩浆和相关火山气体的化学方面发挥着关键作用。破译这些流体的化学成分对于理解地球的碳和硫循环以及地球大气和海洋的演化也是至关重要的。这些循环依赖于了解俯冲埋藏碳和硫的效率，以及这些元素从俯冲板块到弧前地幔的损失。然而，我们在板坯流体化学方面的知识存在很大差距，特别是与硫、铁和碳的氧化还原循环有关的知识。该项目的目标是限制板坯流体的性质，并使用我们已证明对此目的高度有效的新型化学指纹工具的组合来量化这些流体中硫、碳和铁的预算和氧化状态。在这个项目中，我们将利用IODP探险队366来参观和采样马里亚纳弧区。马里亚纳群岛是研究最深入的弧区之一，也是少数几个我们可以直接接触和采样弧前地幔的地方之一。这次探险为研究流体从俯冲板块释放并与上覆板块的地幔发生反应的区域提供了一个独特的机会。通过对这次考察期间收集的样品进行研究，我们将能够直接研究从俯冲板释放的流体与上覆的前弧地幔之间的反应，并将能够利用我们的结果来确定这些流体的组成和氧化还原预算，并讨论它们在全球碳和硫循环中的作用。

Subduction zones ("arcs") are the geological setting where one tectonic plate ("slab") is dragged underneath another into the Earth's deep interior ("mantle"). They are sites of major chemical exchange between the Earth's surface and interior. Water and other volatiles (e.g. sulfur, chlorine, fluorine, carbon) are released from the subducting slab in the form of fluids and transported to the overlying plate ("fore-arc mantle"). These fluids are considered to play a critical role in the transport and concentration of economically-important elements like copper and gold in subduction zones and the chemistry of arc magmas and associated volcanic gases. Deciphering the chemistry of these fluids is also fundamental to understanding the Earth's carbon and sulfur cycles and the evolution of the Earth's atmosphere and oceans. These cycles rely on knowing both the efficiency of carbon and sulfur burial by subduction, and the loss of these elements from the subducting slab to the fore-arc mantle. However there are major gaps in our knowledge of slab fluid chemistry and especially in relation to the redox cycling of sulfur, iron and carbon. The goal of this project is to constrain the nature of slab fluids and quantify the budgets and oxidation states of sulfur, carbon and iron in these fluids using a combination of novel chemical fingerprinting tools that we have demonstrated to be highly effective for this purpose. In this project we will take advantage of the IODP expedition 366 to visit and sample the Mariana arc. The Marianas are one of the best-studied arcs, and one of the few places where we can directly access and sample the fore-arc mantle. This expedition presents a unique opportunity to study the zone where fluids are released from the subducting slab and react with the mantle of the overlying plate. From working on samples collected during this expedition we will be able to directly study the reactions between the fluids released from the subducting slab and the overlying fore-arc mantle and we will be able to use our results to determine the compositions and redox budgets of these fluids and to address their role in global carbon and sulfur cycles.