Magma Differentiation processes and volatile contents in Shatsky Rise oceanic Plateau basalts: constraints from mineral, glass and melt inclusion compositions combined with experimental and thermodynamic modeling

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Oceanic plateaus are giant volcanic constructs whose formation and existence is related to the enormous magma flux from mantle to lithosphere. These Large Igneous Provinces (LIPs) can be important indicators of fundamental processes of mantle convection and geodynamics, as well as major environmental changes and are crucial for advancing understanding of the whole Earth system. It is widely thought that oceanic plateaus arise from massive eruptions resulting from the arrival of a deep mantle plume head at the lithosphere. An alternative hypothesis invokes decompression melting of unusually fusible mantle beneath fast-spreading ridges. Shatsky Rise is a unique oceanic plateau, formed during the Late Jurassic and Early Cretaceous at a rapidly spreading triple junction, with characteristics that could be attributed to either model of formation. The goal of Integrated Oceanic Drilling Program Expedition 324 conducted in 2009 was to core the igneous rocks of Shatsky Rise and the sediments above to examine the age, physical volcanology, geochemistry, and tectonic evolution of the rise. In the proposed project we plan to contribute to the determination of magma storage conditions and to the simulation of differentiation processes in Shatsky Rise oceanic plateau. This information can be gained from (1) the study of recovered samples to determine chemical compositions of natural minerals, glasses and melt inclusions; (2) high pressure crystallization experiments and (3) thermodynamic modelling (COMAGMAT). The Shatsky Rise is also an ideal region to study pristine pre-eruptive volatile abundances in LIP basalts, due to the lack of contamination with continental lithosphere. The quantitative information on volatile budget, composition, oxygen fugacity, and volatile release in Shatsky Rise basaltic magmas will be obtained from a complementary approach combining analysis of natural glasses and melt inclusions, investigation of phase relationships at controlled oxygen fugacity and volatile activities. This is a prerequisite information to quantify the degassing of mantle plume derived melts and the possible climatic impact in Earth’s history.