Grant: Discovery Grants Program - Individual

Whereas seismology provides an image of the gross structure of the whole Earth, the only available samples of Earth's deep interior - the asthenosphere, transition zone and lower mantle - with which to validate its composition and investigate deep plate subduction, are provided by a class of diamonds known as "super-deep diamonds", that are distinct from those that occur in the lithosphere, Earth's solid outer shell, because they sample the convecting deep mantle. The unique view of the mantle offered by super-deep diamonds allow fundamental questions about the Earth to be addressed such as: How deep do oceanic plates subduct? How far are recycled water and carbon carried into the mantle? What is the composition of the lower mantle? Is there is a signature of core extraction in Earth's mantle? These and other questions will be addressed here using the stable isotopic fingerprints of some of Earth's most abundant elements; Si, Mg and Fe. Stable isotope ratios - the ratios of light and heavy atoms of an element, are controlled by temperature, pressure and mineral structure/chemistry as well as fluid-rock exchange. As such they are powerful tracers of  the interaction between Earth's crust and mantle via plate tectonics. This proposal will create a new framework, verified by high pressure experiments, to be used as a roadmap to show how Si, Mg and Fe isotopes are fractionated between the different minerals that characterise the key parts of the mantle - the asthenosphere, transition zone and lower mantle.  The results will illustrate how plate tectonics and convection of the mantle have redistributed the main elements and their isotopes that comprise our solid Earth. They will yield new direct data on the lower mantle (>670 km), inaccessible other than from diamond inclusions. They will allow us to quantify the exchange between upper and lower mantle, in the search for "primordial regions" untouched by plate subduction. They will allow new, more accurate bounds to be placed on the Bulk Silicate Earth that will, in turn, allow us to quantify key details of the composition of Earth's core. They will illuminate our knowledge of how, and in what components, subducted oceanic slabs cycle volatiles to the deepest parts of the mantle. The data produced will allow new constraints to be placed on the mechanisms and depth of element cycling.  The results will be of  interest to the diamond exploration industry who currently seek methods to enable the early identification - at the exploration and evaluation phase - of deposits that contain large, high-value super-deep gem diamonds. The project will produce a diverse cohort of young researchers trained in cross-disciplinary analytical and experimental techniques with skills relevant to Canada's diamond industry.