Collaborative Research: PGE and Pb Systematics in Altered Abyssal Peridotites: Integrating Experiments with Natural Samples

这项拟议的工作将检验这样一种假设，即橄榄岩蚀变过程中硫化物和金属合金矿物学的变化将相对于它们的原始岩浆浓度动员和分馏PGE、Re和Pb。水热实验将限制PGe、Re、Pb在含镍-铁-Ru-Re硫化物和金属合金中的溶解度随温度和氧化还原条件的变化，并评估PGE合金在低硫逸度下的出溶和PGe-Re分馏。研究的自然样品部分将限制PGe、Re、Pb在硫化物、合金和来自特征良好的深海橄榄岩的块状岩石中的分布和分馏，这是氧化还原、蚀变、硫化物矿化和主要成分(富矿与贫化)的函数。通过实验和自然样品数据的整合，这项工作将限制PGe、Re、Pb在蚀变海洋岩石圈再循环时的去向，以及随着时间的推移，蚀变橄榄岩是否会在难熔(金属合金)或流动(硫化物)储层之间形成高度不均匀的187Os/188Os和186Os/188Os比值。该项目是两个美国机构之间的合作努力，将促进将新分析技术的技术和专业知识转移到南加州大学新建立的地球化学设施。研究人员将分享一套最先进的仪器，包括FIB-SEM、FE-EMPA、FE-SEM、LA-ICPMS和同步辐射显微X射线荧光。所有收集的数据将提交给PetDB和IEDA，并将通过CIW托管的数据存储库向公众提供。南加州大学的一名研究生将参与完成他的博士研究。暴露在海底的蚀变地幔岩石(称为蛇纹岩化的深海橄榄岩)含有与次生植物族元素(PGE)、含硫矿物(硫化物)和PGE金属块有关的含镍金属相。PGE具有独特的物理和化学特性，这些特性对许多技术应用至关重要。因此，在包括航空航天和燃料电池技术在内的广泛行业中，它们经常被视为战略金属。这项拟议的研究将极大地促进目前对高温海水变化对深海橄榄岩中植物族元素硫化物分布的影响的有限理解。此外，深海橄榄岩还为了解地球--S地幔的组成和演化提供了重要的记录。拟议的工作是一项协作性的实验和自然样本调查。实验数据将确定与现代深海火山有关的条件下PGE矿物的热力学性质，并评估高温/压力条件下PGE在Fe-Ni-Ru-Re硫化物/合金中的溶解机理的关键细节。结合实验结果和天然样品数据，将对海水蚀变对蚀变橄榄岩亲铁和亲黄成分的影响以及对S地幔中Os、Pb同位素不均一性的影响有一个新的认识。

The proposed work will test the hypothesis that changes in sulfide and metal alloy mineralogy during peridotite alteration will mobilize and fractionate the PGE, Re and Pb relative to their primary magmatic concentrations. Hydrothermal experiments will constrain the solubility of PGE, Re, Pb in mantle Ni-Fe-Ru-Re bearing sulfides and metal alloys as function of temperature and redox conditions, and evaluate PGE alloy exsolution and PGE-Re fractionation under low sulfur fugacity. The natural sample part of the study will constrain the distribution and fractionation of PGE, Re, Pb in sulfides, alloys and bulk rocks from well characterized abyssal peridotites, as function of redox, alteration, sulfide mineralization and primary composition (fertile versus depleted). Through integration of the experimental and natural sample data this work will constrain the fate of PGE, Re, Pb upon recycling of altered oceanic lithosphere and whether altered peridotites can develop, over time, highly heterogeneous 187Os/188Os and 186Os/188Os ratios between refractory (metal alloys) or mobile (sulfide) reservoirs. This project is a collaborative effort between 2 US institutions, and will promote transfer of technology and expertise on novel analytical techniques to a newly established geochemical facility at USC. Researchers will share a suite of state-of-the art instrumentation including FIB-SEM, FE-EMPA, FE-SEM, LA-ICPMS and synchrotron radiation micro-X-Ray fluorescence. All the data collected will be submitted to the PetDB and IEDA, and will be available to the public through a CIW-hosted data repository. A graduate student from USC will participate towards completion of his PhD studies.Altered mantle rocks exposed at the seafloor (called "serpentinized abyssal peridotites") contain Ni-bearing metal phases associated with secondary plantinum-group element (PGE) sulfur-bearing minerals (sulfides) and PGE metal nuggets. PGEs have unique physical and chemical properties that are critical to many technological applications. Thus, they are often regarded as strategic metals in a wide range of industries including aerospace and fuel cell technology. The proposed research will significantly advance the currently limited understanding of the effects of high-temperature seawater alteration on the distribution of plantinum-group element sulfides hosted in abyssal peridotites. Moreover, abyssal peridotites provide an important record for understanding the composition and evolution of Earth?s mantle now and in the past. The proposed work is a collaborative experimental and natural sample investigation. Experimental data will define the thermodynamic properties of PGE minerals at conditions relevant to modern deep-sea volcanoes and assess critical details of PGE solubility mechanisms in Fe-Ni-Ru-Re sulfides/alloys at elevated temperature/-pressure conditions. The combined experimental results and natural sample data will lead to a fundamental new understanding on the effects of seawater alteration on the siderophile and chalcophile composition of altered peridotite and its effect on the Os and Pb isotope heterogeneity in the Earth?s mantle.