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Durham University

Durham Geochemistry Centre

Planetary evolution, mantle geochemistry and recycling

Research in this area is aimed at understanding the formation and differentiation of the Earth and other planets.

Current research interests include:

Early solar system processes.

Constraints on the timing and nature of accretion and core formation on Earth and the other planets. The timing of volatile loss on early planets planetisimals. The nature and origin of stable isotope variations between planets and planetisimals. This has involved the development of new techniques for analysing very small samples to high-precision for both conventional long-lived radiogenic isotopes, linked to short-lived extinct nuclides to provide key information on early solar system processes, such as volatile behaviour of elements or their oxides.

Novel stable isotope constraints on planetary differentiation.

 A major focus of research within the Durham Geochemistry Group is the use of novel stable isotope systems to understand the formation and evolution of the Earth and the other terrestrial planets. Key topics that we are interested in include planetary differentiation and core crystallisation, core-mantle interaction, formation of the Earth’s continental crust and crustal recycling into the deep mantle, and the evolution of the oxidation state of the Earth’s mantle. Novel stable isotope systems can place constraints on these processes as stable isotope effects (fractionation) are driven by changes in bonding environment when isotopic equilibrium is reached. We have exploited the redox-dependence of Fe isotope fractionation within the Earth’s mantle to place constraints on secular variations in mantle redox state and we have are also exploring the possibility of Fe, Zn, Cr and Cu isotope fractionation between the mantle and core using both iron meteorites and high-pressure experiments as analogues of core formation.

Mantle melting and the generation of oceanic lithosphere.

 Understanding of element behaviour during mantle melting and the relationships between the timescales of mantle depletion and the relationships to the formation of the continental crust is fundamental to constraining the chemical evolution of the Earth. A major part of this work is the assessment of the nature and role of source heterogeneities in the mantle and the influence of magmatic processes on the elemental and isotopic evolution of oceanic basalts using isotope systems such as Pb, Os and Fe.

Subduction and mantle redox state

Subduction drives the recycling of surface material into the Earth’s interior. During subduction, fluids and melts released from the subducting slab rise and induce partial melting in the overlying mantle wedge while the residual slab continues into the deeper mantle and may contribute to the long-term geochemical heterogeneity observed in oceanic basalts. The influence of subduction on the chemical evolution of the Earth is still poorly understood and we know little about the nature of the material transferred from the subducting slab to the mantle wedge or the residual material that is recycled into the deep mantle and what the consequences are for mantle compositional heterogeneity and redox state. This can be investigated using a combination of radiogenic and stable isotope tracers (e.g. stable isotopes of Fe, a redox-sensitive element) in rocks sampling the sub-arc mantle (usually brought to the surface as xenoliths) as well as arc volcanic rocks, the subducting slab (typically preserved in obducted oceanic massifs) and the products of melting in the deep mantle (oceanic basalts).