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

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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.