NSFGEO-NERC: Sulfur Cycling at Subduction Zones

该项目由美国国家科学基金会地球科学理事会（NSF/GEO）和英国国家环境研究委员会（NERC）通过NSF/GEO-NERC牵头机构协议共同资助。该协议允许美国/英国提交一份联合提案，并由其调查员拥有最大比例预算的机构进行同行评审。在成功地共同确定一项奖励后，每个机构为预算的比例和与本国有关的调查人员提供资金。硫是地球环境中的关键元素。当火山爆发时，硫被喷射到大气中，起到冷却作用。硫也是铅和锌等经济金属的运输剂和宿主。控制火山和金属沉积物可获得多少硫的一系列因素仍然是科学上的一个主要问题，也是这个项目试图回答的问题。硫的一个可能来源包括海底的沉积物，这些沉积物被俯冲到岩浆形成的深处。该项目通过首次测量不同俯冲带火山系统中硫的形态和通量来验证这一假设。来自美国（哥伦比亚大学）、英国（牛津大学）和意大利（巴勒莫大学）的科学家团队将与德克萨斯a&m大学的海洋钻探项目和爱丁堡大学的NERC离子微探针设备合作，对沉积物和火山物质中的硫及其同位素进行新的测量。大部分项目预算将用于支持哥伦比亚大学的博士生，哥伦比亚大学的本科生和牛津大学的博士后。由Mather、Aiuppa和Plank组成的PI团队将在国际会议上策划特别会议，并出版一期关于深层硫的特别期刊。该项目旨在研究岩浆系统中硫的起源，可能会导致矿床硫供应与会聚边缘火山排放物之间的新联系。这个国际项目的目标是在俯冲带硫磺循环的主要未知数。美国国家科学基金会对该项目的关注将填补俯冲带地幔S输入方面的关键知识空白。它将涉及对汤加、马里亚纳、阿留申群岛、阿拉斯加和中美洲海沟沉积剖面的广泛分析，这些海沟被选为硫沉积、成岩作用和极端同位素变化的末端海洋环境的代表。海洋钻探计划的岩心将通过XRF岩心扫描进行分析，这是一种量化非均质浸染的黄铁矿和重晶石的战略方法，它们是沉积物中硫的主要寄主。岩心扫描结果将指导Palermo大学通过耦合元素分析仪-质谱法进行散装硫和硫同位素分析的离散采样，重点关注可能出现在单个沉积剖面中的硫化物与硫酸盐主导的制度。结果将是对S进入端元海沟的通量和同位素组成的第一次综合估计（具有不确定性）和改进的全球估计。该项目的UK-NERC部分将采用一种新的方法来理解火山弧S输出。它将首次测量未脱气的含橄榄石的电弧熔体包裹体中的硫同位素组成。计划中的工作将包括对来自与上述沉积物目标相同的俯冲系统的熔融包裹体套件进行充分研究。这将确保该项目的美国、英国和意大利部分之间的密切合作，并允许首次直接追踪从沉积物输入到电弧输出的硫同位素。该项目不仅将首次为任何俯冲带提供全面的沉积物输入硫通量和弧同位素组成，而且还将验证弧火山硫浓度和同位素组成反映a)俯冲输入或b)俯冲带硫种类和同位素分异的竞争性假设。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

This is a project that is jointly funded by the National Science Foundation's Directorate of Geosciences (NSF/GEO) and the National Environment Research Council (NERC) of the United Kingdom (UK) via the NSF/GEO-NERC Lead Agency Agreement. This Agreement allows a single joint US/UK proposal to be submitted and peer-reviewed by the Agency whose investigator has the largest proportion of the budget. Upon successful joint determination of an award, each Agency funds the proportion of the budget and the investigators associated with its own country.Sulfur is a critical element in Earth's environment. When volcanoes erupt, sulfur is ejected into the atmosphere with cooling effects. Sulfur is also the transport agent and host of economic metals such as lead and zinc. The cluster of factors that control how much sulfur is available to volcanoes and metal deposits is still a major question in science, one that this project seeks to answer. One possible source of sulfur includes the sediments on the seafloor, which are subducted into the Earth to the depths where magmas form. This project is testing this hypothesis by measuring for the first time the sulfur forms and fluxes that feed volcanic systems at different subduction zones. A team of scientists from the US (Columbia University), the UK (Oxford University) and Italy (University of Palermo) will partner with the Ocean Drilling Program at Texas A&M University and the NERC Ion Microprobe Facility at the University of Edinburgh to make novel measurements of sulfur and its isotopes in sediments and volcanic material. Most of the project budget will support a Columbia Ph.D. student, a Columbia undergraduate, and an Oxford postdoc. The PI Team of Mather, Aiuppa and Plank will incubate special sessions at international meetings and a special journal issue focused on Deep Sulfur. This project, aimed at the very origins of sulfur in magmatic systems, may lead to novel connections between the sulfur supply to ore deposits and volcanic emissions at convergent margins. This international project targets major unknowns in the sulfur cycle at subduction zones. The US-NSF focus of this project will fill a key knowledge gap in terms of S inputs to the mantle at subduction zones. It will involve extensive analysis of sedimentary sections at the Tonga, Marianas, Aleutians, Alaska and Central America trenches, chosen to represent end-member oceanic environments for sulfur deposition and diagenesis and extreme isotopic variations. Ocean Drilling Programs cores will be analyzed by XRF core scanning, a strategic approach to quantify heterogeneously disseminated pyrite and barite, major hosts of sulfur in sediment. Core scanning results will guide discrete sampling for bulk sulfur and sulfur isotope analyses at the University of Palermo by coupled Elemental Analyzer-Mass Spectrometry with a focus on the sulfide- vs. sulfate-dominated regimes that may occur in a single sedimentary section. The outcome will be the first comprehensive estimates (with uncertainties) for the fluxes and isotopic compositions of S into end-member trenches and improved global estimates. The UK-NERC part of this project will take a novel approach to understanding volcanic arc S outputs. It will measure for the first time the sulfur isotopic composition in undegassed olivine-hosted arc melt inclusions. Planned work will include well-studied melt inclusions suites from the same subducting systems as the sediment targets above. This will ensure close collaboration between the US, UK and Italian parts of this project, and allow for the first-time direct tracing of sulfur isotopes from sediment input to arc output. This project will not only provide the first comprehensive sediment input sulfur fluxes and arc isotopic compositions for any subduction zone, but also test the competing hypotheses that the concentrations and isotopic compositions of arc volcanic sulfur reflect a) the subducted inputs or b) the fractionation of sulfur species and isotopes in the subduction zone.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.