EAR-PF In-situ and bulk sulfur isotope constraints on crustal recycling: a bridged investigation of superdeep diamonds and ocean island basalts

James W. Dottin III博士获得了美国国家科学基金会EAR博士后奖学金，将在卡内基科学研究所地球与行星实验室（sis - epl）接受Steven Shirey博士和Michael Walter博士的指导，从事研究和教育工作。地壳可以通过板块构造从地球表面转移到地球内部，它提供了许多化学元素，控制着我们星球上生命的可居住性。然而，各种地壳物质的详细性质、相对年龄以及它们最终在地球内部的位置还没有得到很好的了解。在这个项目中，多廷博士将利用从地球深处喷发的岩石和矿物中测量到的化学特征（特别是硫元素的特征）来深入了解板块构造的细节。多廷博士的工作包括分析来自地球内部不同地区的岩石和钻石，以确定地壳中发现的元素如何在全球范围内移动和分布。拟议的研究将利用硫的独特特征来识别通过地球内部循环的特定地壳物质，并提供地壳循环发生的时间尺度的相对限制。多廷博士还将领导一个教育项目，将历史上代表性不足的少数群体的学生直接纳入研究项目。学生的参与将通过与马萨诸塞州女子学院史密斯学院的强有力合作而形成。多廷博士还计划通过CIS-EPL的暑期实习项目，与当地高中和华盛顿特区许多历史悠久的黑人学院和大学积极招募的学生进行接触，作为导师和顾问。地幔的成分是不均匀的，从地壳提取和地壳再循环到地幔的过程中，由地球化学上不同的储层组成。HIMU（高μ=238U/204Pb）地幔储层是一个具有极端pb同位素组成的神秘端元，被认为是由俯冲蚀变洋壳组成的，并伴有碳酸化成分。然而，对构成HIMU地幔的成分的性质、起源和全球分布仍然知之甚少。在这个项目中，Dottin博士将使用微束和体积消解技术，结合来自关键HIMU玄武岩和超深钻石硫化物包裹体的硫同位素信息。Dottin博士的目标是追踪HIMU地幔储层中循环原岩的全球分布和相互作用，这些储层被认为位于地幔底部和/或地幔过渡带内。所提出的分析技术，关键HIMU玄武岩的选择，以及过渡带钻石硫化物的选择，为解决矿物、手工样品和全球尺度之间存在的潜在同位素非均质性提供了机会。从这项工作中，Dottin博士计划通过对HIMU地幔储层之间的源非均质性的限制，以及可能与储层年龄和/或热点位置相关的板层堆积深度，来深入了解板块构造的细节。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。

Dr. James W. Dottin III has been awarded an NSF EAR Postdoctoral Fellowship to pursue research and education endeavors at the Carnegie Institution for Science-Earth and Planets Laboratory (CIS-EPL) under the mentorship of Dr. Steven Shirey and Dr. Michael Walter. The Earth’s crust, which can be transferred from the surface to the interior of Earth through plate tectonics, provides many of the chemical elements that control the habitability of life on our planet. However, the detailed nature, relative ages of the various crustal materials, and where they ultimately reside in the Earth’s interior are not well understood. For this project, Dr. Dottin will use chemical signatures (specifically those of the element sulfur) measured in rocks and minerals erupted from the deep interior of the Earth to provide insight into the finer details of plate tectonics. Dr. Dottin’s work involves analyzing rocks and diamonds that come from different parts of the Earth’s interior to determine how elements found in the crust move around and are distributed across the globe. The proposed research will use unique characteristics of sulfur to identify specific crustal materials that are recycled through the Earth’s interior and provide relative constraints on the timescales on which crustal recycling occurs. Dr. Dottin will also lead an education program that incorporates students from historically underrepresented minority groups directly into the research project. Student involvement will take form through a strong collaboration with Smith College, a women’s college in Massachusetts. Dr. Dottin also plans to engage with students that will be actively recruited from local high schools and the many Historically Black Colleges and Universities in the Washington, D.C. area as a mentor and advisor through a summer internship program at CIS-EPL. The Earth’s mantle is compositionally heterogeneous, comprising geochemically distinct reservoirs from the process of crust extraction and recycling of crust into the mantle. The HIMU (high μ=238U/204Pb) mantle reservoir is an enigmatic endmember with extreme Pb-isotopic compositions, and is postulated to be composed of subducted altered oceanic crust that is associated with a carbonated component. However, the nature, origin, and global distribution of the components that make up the HIMU mantle remain poorly understood. For this project, Dr. Dottin will combine sulfur isotope information from key HIMU basalts and from sulfide inclusions in superdeep diamonds using microbeam and bulk digestion techniques. Dr. Dottin aims to trace the global distribution and interaction of recycled protoliths in HIMU mantle reservoirs that are thought to reside at the base of the mantle and/or within the mantle transition zone. The proposed analytical techniques, choice of key HIMU basalts, and choice of sulfides from transition zone diamonds offers an opportunity to address the potential isotopic heterogeneities that exist among mineral, hand sample, and global scales. From this work, Dr. Dottin plans to provide insight into the finer details of plate tectonics through constraints of source heterogeneity among HIMU mantle reservoirs and the proposed depth of slab accumulation that is possibly linked to the age of the reservoir and/or hotspot location.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.