CAREER: Tracing sulfur in subducting slabs with apatite oxybarometry

构造板块边界是地球系统中物质传递的重要场所。挥发性元素从地球内部深处转移到俯冲带的表面和大气层，使地球成为一个可居住的星球。位于俯冲带的弧火山喷发的岩浆比大洋中脊喷发的岩浆氧化程度更高。弧火山是大陆地壳的基础，是经济矿床的主要赋存场所。量化俯冲带中岩浆氧化的过程对于理解大陆和矿石的形成至关重要。本项目将调查硫在整个俯冲系统中的转移是弧岩浆氧化态升高的原因这一假设。将进行高压实验，以测量俯冲带条件下岩石中硫的行为。实验结果将被用于通知自然俯冲相关岩石的观测。该项目包括一名博士后助理，一名博士生和两名来自代表性不足群体的本科生的研究和指导经验。项目成果将纳入新的开放获取地球科学教育内容。将举行一次混合顶石外联活动，向公众传播研究成果。这项研究将检验弧岩浆的氧化特征是由于硫酸盐从下行板片上的变质洋壳转移到上覆弧地幔的假设。将进行高压实验，根据矿物磷灰石中硫的结合和价态，校准与俯冲有关的岩石的氧化状态的新代用品。实验磷灰石将与硫化物或硫酸盐相共结晶，使得磷灰石中硫的行为可用于提供关于俯冲洋壳中硫化物与硫酸盐的相对稳定性的间接信息。实验结果将用于确定磷灰石的氧化态，该奖项反映了NSF的法定使命，并通过利用基金会的智力价值进行评估，更广泛的影响审查标准。

Tectonic plate boundaries are important loci of mass transfer in the Earth system. The transfer of volatile elements from Earth’s deep interior to its surface and atmosphere at subduction zones enables a habitable planet. Magmas erupted at arc volcanoes, located at subduction zones, are more oxidized than magmas erupted at mid-ocean ridges. Arc volcanoes are the basis of the continental crust and host economic ore deposits. Quantifying the processes that lead to the oxidation of magmas in subduction zones is then critical for understanding the formation of continents and ores. This project will investigate the hypothesis that the transfer of sulfur throughout the subduction system is responsible for the elevated oxidation state of arc magmas. High-pressure experiments will be executed to measure the behavior of sulfur in rocks at subduction zone conditions. Experimental results will be used to inform observations of natural subduction-related rocks. This project includes research and mentoring experiences for a postdoctoral associate, a PhD student and two undergraduate students from underrepresented groups. Project results will be assimilated into new open access Earth science educational content. A hybrid capstone outreach event will be held to disseminate research outcomes to the public.This study will examine the hypothesis that the oxidized signature of arc magmas is due to the transfer of sulfate from metamorphosed oceanic crust on the down-going slab to the overlying arc mantle. High-pressure experiments will be executed to calibrate a new proxy for the oxidation state of subduction-related rocks based on the incorporation and valence state of sulfur in the mineral apatite. Experimental apatite will be co-crystallized with sulfide or sulfate phases such that the behavior of sulfur in apatite can be used to provide indirect information on the relative stabilities of sulfide vs. sulfates in subducted oceanic crust. Results from the experiments will be applied to determine the oxidation states of suites of apatite-bearing metabasites to determine if subducting slabs record an increase in oxidation state concurrent with the increase in dissolved oxygen in the deep oceans and rise in seawater sulfate in the Early Phanerozoic.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.