I am NERC GW4+ funded researcher in the Bristol Isotope Group. My research focuses on using high precision stable isotope mesurments of Uranium to study the evolution of the Earth's surface and mantle. My project will use multi-collector inductively coupled plasma mass spectrometry measurements to investigate and trace the fate of subducted material as it is mixed into the mantle, with the goal of improving our understanding of mantle convection.
The enrichment of Uranium (U) in the upper portions of the altered mafic oceanic crust (AMOC) can be associated with isotopic fractionation of U. In the upper AMOC U6+ can be absorbed onto secondary mineral surfaces, leading to low ẟ238U, while partial reduction of U6+ from deep circulating fluid results in high ẟ238U. Both cases require U6+ in deep oceans, and thus oxygenated deep oceans. Identifying when in the geological past AMOC shows isotopic heterogeneity in U therefore constrains the timing of deep ocean oxygenation and informs on how long isotopically distinct U has been recycled into the mantle.
Timing the oxygenation of the deep oceans - By measuring ophiolites (preserved ancient oceanic crust) spaning the Phanerozoic we can investigate past U alteration processes and look for when isotopic heterogeneity in U was first generated. This will allow us to narrow the time window for deep ocean oxygenation.
Global variation in U isotopes in MORB - By measuring fresh unaltered MORB for its U isotope composition we can examine the chemical heterogeneity in the upper mantle. We can use this information to better understand how crustal recycling can pollute the upper mantle. Combined with an understanding of how long isotopically distinct U has been recyled into the mantle, we aim to improve our understanding on the timescales over which chemical heterogeneity developed.
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