Experimental Investigation of Mantle Heterogeneity: Behavior of Ga, Ge, and First-row Transition Elements (FRTE) During Partial Melting of Pyroxenite and Spinel Peridotite

地幔非均质性的实验研究：辉石岩和尖晶石橄榄岩部分熔融过程中 Ga、Ge 和第一排过渡元素 (FRTE) 的行为

• 批准号: 1624691
• 负责人: Frederick Davis
• 金额: $ 15.61万
• 依托单位: University of Minnesota Duluth
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2016
• 资助国家: 美国
• 起止时间: 2016-09-01 至 2021-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1624691&HistoricalAwards=false
• 关键词: Experimental; Investigation; Mantle; Heterogeneity; Behavior

Earth's mantle is its largest layer by mass and volume and is ultimately the source of most of the magmas generated near Earth's surface. The chemistry and mineral composition of the rocks in Earth's mantle also serve as a time capsule that records events from the time of Earth's formation and its subsequent evolution caused by the recycling of near-surface materials back into the mantle through the processes of plate tectonics. This project is an experimental investigation of the chemistry of magmas that can be generated in Earth's mantle by different types of rocks that are likely to be found there. High pressure and high temperature experiments will be performed to investigate how the first-row transition elements (FRTE; Sc-Zn on the periodic table) and Ga and Ge behave during the formation of magmas in Earth's mantle. These elements are particularly useful for identify the types of rocks that may be melting to generate magmas. The results of this project will increase scientific knowledge of how magmas are formed on Earth and, through comparison with the chemistry of natural samples, will increase our understanding of the distribution of different rock types in Earth?s interior. Broader impacts of this research include support for an early-career researcher at a primarily undergraduate institution. The project will support training of a female graduate student who will gain expertise in formulating scientific questions, designing and performing experiments, analysis using several analytical methods, and interpretation and dissemination of experimental results. This project will also foster collaboration between the experimental lab at the University of Minnesota Duluth and the geochemistry and cosmochemistry lab at Florida State University, where analyses will be performed.This research is an experimental study of the partitioning of FRTE between mantle minerals and melts, which will improve geochemical tools for identifying the source lithology of basaltic magmas. Experiments containing melts and either peridotite or pyroxenite mineral residues will be performed in a piston cylinder apparatus at conditions of mantle melt generation (pressures of 1.5 and 3 GPa and temperatures from 1270 to 1450 °C). These experiments will be doped with FRTE and Ga and Ge. The concentrations of these elements in the experimental run products (quenched melts and minerals) will be analyzed by laser ablation inductively-coupled plasma mass spectrometry (LA-ICP-MS). These analyses will yield partition coefficients for each element of interest between each mineral and coexisting melt. The project will aim to improve constraints on the concentrations and ratios of FRTE in melts generated by partial melting of peridotite and pyroxenite in Earth's mantle. Model melt compositions will be generated using these new experimental constraints and compared with the chemistry of natural basalts to better understand how lithological heterogeneity in the mantle is expressed in the chemistry of basaltic magmas. Better constraints on the source lithology of natural basalts will improve estimates of the abundance and distribution of recycled lithologies in Earth's upper mantle.

按质量和体积计算，地幔是地球最大的一层，最终也是地球表面附近产生的大部分岩浆的来源。地幔中岩石的化学和矿物组成也是一个时间胶囊，记录了地球形成时间及其随后的演变，这些事件是通过板块构造过程将近地表物质循环回到地幔而引起的。这个项目是对地幔中可能发现的不同类型岩石所产生的岩浆化学的实验研究。将进行高压和高温实验，以研究第一排过渡元素(FRTE；元素周期表中的Sc-Zn)和Ga、Ge在地幔岩浆形成过程中的行为。这些元素对于识别可能正在熔化以产生岩浆的岩石类型特别有用。该项目的成果将增加对地球上岩浆形成的科学知识，并通过与自然样品的化学成分进行比较，将增加我们对地球内部不同类型岩石的分布的了解？S。这项研究的更广泛影响包括支持以本科为主的机构的早期职业研究人员。该项目将支持对一名女研究生的培训，她将在提出科学问题、设计和执行实验、使用几种分析方法进行分析以及解释和传播实验结果方面获得专门知识。该项目还将促进明尼苏达大学德卢斯大学的实验实验室和佛罗里达州立大学的地球化学和宇宙化学实验室之间的合作，在那里将进行分析。这项研究是关于地幔矿物和熔体之间FRTE分配的实验研究，这将改进识别玄武岩岩浆来源岩性的地球化学工具。含有熔体和橄榄岩或辉石岩矿物残留物的实验将在活塞筒装置中进行，条件是地幔熔体产生(压力为1.5和3 Gpa，温度从1270℃到1450℃)。这些实验将掺入FRTE和Ga、Ge。这些元素在实验运行产物(淬火熔体和矿物)中的浓度将用激光烧蚀电感耦合等离子体质谱(LA-ICPMS)进行分析。这些分析将得出每种感兴趣的元素在每种矿物和共存熔体之间的分配系数。该项目旨在改善对地球地幔中橄榄岩和辉石岩部分熔融产生的熔体中FRTE浓度和比率的限制。将使用这些新的实验约束生成熔体成分模型，并与天然玄武岩的化学进行比较，以更好地了解地幔中的岩性不均质性是如何在玄武岩岩浆的化学中表达的。对天然玄武岩来源岩性的更好限制将改善对地球上地幔再循环岩性丰度和分布的估计。