Isotope geochemistry provides much of our understanding of the workings of the Earth s system from core to clouds. This proposal requests funds to develop and apply new MC-ICPMS methods to tackle geochemical issues that are poorly understood and for which new archives and techniques should lead to significant breakthroughs. We will focus on 3 areas. First, we will study vanadium (V), which is analytically challenging because of its extreme composition but which could be immensely powerful for tracing changes in oxidation. The V isotopic composition of magnetite will be investigated as a proxy for oxidation state and to provide new constraints on the cause of precipitation of V rich magnetite ores in the world s biggest deposits. We will also measure V isotopic compositions of hydrocarbons to address (a) the origin of vanadyl-porphyrins with studies of soils and their associated plant material, (b) subsurface geoporphyrin transformations and the fate of V locked within sedimentary organic matter as it becomes buried and (c) the degree to which degradation in crude oils changes isotopic composition. Second, we will develop isotope geochemistry of fluid immobile elements. Titanium will be used to elucidate: (a) the fate of the lithosphere in convecting mantle; (2) mobility of immobile elements in sedimentary to metamorphic systems and (3) the scavenging history of seawater recorded in marine Fe-Mn crusts. Zirconium will be used with Ti to evaluate changes in physical weathering over time. Lastly, we will develop new kinds of detectors based on photon burst spectroscopy and resonance ionisation spectroscopy, to detect rare isotopes in the Earth. This will be of relevance to the measurement of cosmogenic nuclides and the record of putative supernova events in our galaxy.
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