Tracing Lithosphere formation and evolution with highly siderophile elements and Os isotopes

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Highly siderophile elements (HSE) in combination with Os isotopes have revealed themselves as powerful tracers of mantle formation and secondary overprint (mantle metasomatism). It was owing to the advent of precise Re-Os geochronology in the early 90ies that the co-evolution of continental crust and underlying lithospheric mantle was first broadly demonstrated. The formation and evolution of continents is one of the most fundamental aspects of Earth Sciences that is closely related to questions of the evolution of life, ore genesis, the Earth’s material cycle, among many others. Despite decades of intensive research, the details of how the earliest continental nuclei formed, when crust-mantle coupling occurs and how the continental lithosphere evolves have yet to be determined. This is an ongoing research effort at Frankfurt University where the Lu-Hf isotope system is increasingly used as a promising tool to obtain precise isochron ages on crust and mantle samples. However, this approach is restricted to mantle portions where melt-metasomatism can be shown to be minimal. Because of the compatibility of Os in the mantle and much lower abundances in fluids and melts, Os isotopes can be singularly able to “weather” secondary overprints. The severity and the effects of such overprints can be monitored by HSE abundance patterns. I am applying for funds to bring the measurement of Os isotopes and HSE abundances to Frankfurt University, using facilities and instrumentation already available. Once instituted, I will apply the technique to a small suite of peridotite xenoliths from Namibia whose age is so far ill-constrained and which are the subject of an ongoing project on crust mantle coupling.