I am NERC GW4+ funded researcher in the Bristol Isotope Group. My reasearch focuses on using high precision stable isotope measurments of Uranium (U) to study the evolution of the Earths surface and mantle. My project will use multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS) and geodynamic code 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 geochemical and redox sensistive cycle of Uranium (U) has evolved over the history of the Earth. A key change occured when the deep oceans became oxygenated, allowing U6+ to exist in deep oceans and be reduced to U4+ and uptaken during alteration of the oceanic crust. This reaction imparts an isotopic fractionation, giving altered mafic oceaninc crust a distinct 238U/235U ratio. We can use therefore use the 238U/235U ratio of mantle rocks (arc rocks, ocean island basalts and mid-ocean ridge basalts (MORB)) to trace fate of subducted mantle and how it is mixed into the mantle.
I will use the U system to tackle three main research areas.
1) Timing the oxygenation of the deep oceans - The distinct isotopic signal of U in altered mafic oceaninc crust could only have been generated when the deep oceans became oxygenated, which likely did not happen until after 600 Ma. By measuring ophiolites (preserved ancient oceanic crust) spaning the Phanerozoic and searching for this distinct isotopic signal in U we can time when the deep oceans became oxygenated. Important for understanding how long the upper mantle has had to become oxygenated by oxidised subducting slabs.
2) Global variation in U isotopes in MORB - By measuring fresh unaltered MORB glass for its U isotopes we can examine the chemical heterogeneity in the upper mantle. Combining the data with Molybdenum isotopic data, will allow us to examine the history of manlte convection, with the aim of reconcillig geochemical, geophysical and geodynamic interpretations to determine if Earth did or did not change mantle convection styles from layered to whole in the last quarter of Earth history.
3) Geodynamic mantle convection code - Use the mantle convection code, Terra, which has been modified to track labelled particles, to integrate our geochemical analyses into geodynamic models, to better understand the history of mantle convection.
High precision (±10ppm 2se) MC-ICP-MS measuments of MORB, petrographic, SEM and microprobe analyses of ophiolite and oceanic crust to understand the uptake of uranium during alteration and geodynamic code to model mantle convection.
An integrated understanding of mantle convection over the last quarter of Earths histroy combing geochemistry and geodynamics.