NSFGEO-NERC: Sulfur Cycling at Subduction Zones

俯冲带是调节全球S作用和弧火山作用的气候效应、弧岩浆的经济潜力和固体地球储集层的氧化状态的关键阀门。然而，S在整个俯冲系统中的输入、处理和回收仍然不准确。这一国际项目的目标是俯冲带硫循环中的主要未知数。该项目的美国-国家科学基金会重点项目(Pi Plank，LDEO)将填补S在俯冲带向地幔输入方面的关键知识空白。它将涉及对汤加海沟、马里亚纳海沟、阿留申海沟、阿拉斯加海沟和中美洲海沟沉积剖面的广泛分析，选择这些海沟来代表硫磺沉积和成岩作用以及极端同位素变化的终端海洋环境。大洋钻探项目的岩心将通过XRF岩心扫描进行分析，这是一种战略方法，用于量化不均匀分布的黄铁矿和重晶石，这是沉积物中硫的主要宿主。岩心扫描结果将指导巴勒莫大学与Aiuppa教授和Vizzini教授合作进行批量硫和硫同位素分析的离散采样。在巴勒莫收集的试点数据证明了元素分析仪-质谱仪联用技术的质量，以及单一沉积区段中可能出现的以硫化物和硫酸盐为主的清晰区域。其结果将是对S进入末端成员海沟的通量和同位素组成的首次全面估计(具有不确定性)，并改进了全球估计。该项目的英国-NERC部分(牛津大学的Pi Mather)将采取一种新的方法来理解S火山的产出。它将首次测量未脱气的橄榄石寄主弧形熔体包裹体中的硫同位素组成。位于爱丁堡的NERC离子微探测器设备收集的初步数据证明了该技术的可行性，并在富戈火山的熔体包裹体中产生了正增量(34)S。计划中的工作将包括来自与沉积目标相同的俯冲系统的经过充分研究的熔体包裹体套件(上图)。这将确保该项目的美国和英国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弧光输出的硫同位素。

Subduction zones are a key valve mediating global S processing and the climatic effects of arc volcanism, the economic potential of arc magmas, and the oxidation state of solid Earth reservoirs. Yet, the inputs, processing and recycling of S throughout the subduction system are still inaccurately known. This international project targets major unknowns in the sulfur cycle at subduction zones. The US-NSF focus of this project (PI Plank, LDEO) 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, in collaboration with Prof. Aiuppa and Vizzini. Pilot data collected in Palermo demonstrate the quality of the coupled Elemental Analyzer-Mass Spectrometry technique and the clear 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 (PI Mather, Oxford) 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. Pilot data collected at NERC Ion Microprobe Facility at Edinburgh demonstrate the viability of the technique, and yield positive delta(34)S in melt inclusions from Fuego volcano. 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 and UK parts of this project, and allow for the first-time direct tracing of sulfur isotopes from sediment input to arc output.