Application of geochemistry to the petrogenesis and geodynamics of komatiites and leucogranites

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Two research projects will be undertaken with the aim of adding to our knowledge of how the Earth's mantle and crust evolved and how and where economic mineral deposits might have been formed. The first project deals with MgO-rich volcanic rocks, komatiites, which provide a window on the composition and thermal regime of the Archean mantle. Komatiites are assumed to represent plumes of unusually hot rock that were ejected from a great depth (plume model). Recently, however, researchers have suggested an alternative model whereby komatiites were formed by the melting of mantle at a relatively shallow depth and at considerably lower temperatures (subduction model). The purpose of this project is to test these two contradictory models by investigating the chemical composition of komatiites in two locations where komatiitic rocks show a wide compositional range. However, as komatiites are usually altered, the focus is to utilize "in situ" analyses of fresh clinopyroxene (major and trace elements) and of pristine melt inclusions trapped in relict primary minerals (major and trace elements, water, Pb and Li isotopes).  From these data, the nature of the magma sources as well as the melting processes can be inferred and used to test the mantle plume komatiite vs. subduction zone komatiite controversy. The second project will focus on granitic rocks that are rich in lithium and fluorine, elements that can help concentrate valuable metals. In some areas, these rocks host deposits of tin, tungsten and uranium. The study will look at granitic rocks of similar ages from Atlantic Canada and Europe. Determining the trace element and isotope compositions of these rocks and their constituent minerals will provide critical information on how the rocks and their deposits formed and will show if the granites could have originally been part of a large geological province enriched in metallic mineral deposits. Thus, this study can improve mineral exploration models.