Supervisors: (Earth Sciences), Teal Riley (British Antarctic Survey) and Fin Stuart (Scottish Universities Environmental Research Centre)
Importance of the area of research:
The present-day volatile content of the lithospheric mantle results from potentially billions of years of metasomatic enrichment but a key outstanding issue concerns the relative input of volatiles ‘leaking’ more or less continuously from the MORB source or downgoing slabs, compared with episodic fluxes of primordial volatiles from the deep mantle transported by plumes. Constraints on these fluxes are vital to understanding which branches of Earth’s chemical cycle are losing volatiles to long-term storage in the lithosphere. There is compelling evidence that a substantial volatile flux into the lithospheric mantle occurs more or less contemporaneously with mantle plume activity. More continuous metasomatism may be linked to alkali-carbonate fluids released from down-going slabs in the convecting mantle1.
The project involves the novel analysis of volatile elements and noble gas isotopic ratios in both nominally volatile-free minerals (apatite, clinopyroxene, olivine) and volatile phases (phlogopite, amphibole) present in mantle xenoliths in order to constrain the volatile fux in the mantle2. New analyses of Cl, F, H and C together with 3He/4He and 20Ne/22Ne for samples from a variety of tectonic settings, such as W. Eifel and Tanzania, together with existing data for sub-cratonic lithosphere (e.g. Kaapvaal, Siberian & Slave cratons) will place important constraints on the nature and extent of volatile flux from subducting slabs and the convecting mantle to the overlying lithosphere.
What the student will do:
Micro-analytical techniques will be used to determine trace-element and volatile contents of mantle phases. This data together with noble gas isotope measurements will place important constraints on the provenance of volatiles stored in the lithospheric mantle. We anticipate that elemental ratios that remain relatively constant during melting and crystallisation will be novel diagnostic tracers of volatile provenance in the convecting mantle. An example is H2O/Ce as melt inclusions in arc lavas have much higher ratios than those of MORB and OIB. Another potential provenance tracer is the Cl content of apatite3.
1Kiseeva, E. S., Litasov, K. D., Yaxley, G. M., Ohtani, E. & Kamenetsky, V. S. (2013). Melting and phase relations of carbonated Eclogite at 9–21 GPa and the petrogenesis of alkali-rich melts in the deep mantle. J. Petrol. 54, 1555–1583.
2Matsumoto, T., Honda, M., McDougall, I., Yatsevich, I. & O’Reilly, S. Y. (1997). Plume-like neon in a metasomatic apatite from the Australian lithospheric mantle. Nature 388, 162–164.
3Patiño Douce, A. E., Roden, M. F., Chaumba, J., Fleisher, C. & Yogodzinski, G. (2011). Compositional variability of terrestrial mantle apatites, thermodynamic modeling of apatite volatile contents, and the halogen and water budgets of planetary mantles. Chem. Geol. 288, 14–31.
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