Chalcophile elements in Shatsky Rise basalts as potential indicators of the mantle plume origin

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Igneous oceanic plateaus, such as Shatsky Rise, represent one of the least understood types of basaltic magmatism on Earth. In the case of Shatsky Rise, two main models were proposed to explain their origin: (1) melting of deep-sourced mantle plume head, (2) melting at a mid oceanic ridge (MOR) with unusual characteristics (e.g., anomalously high dynamics or spreading-induced upwelling of eclogite) . In 2009, Integrated Ocean Drilling Program Expedition 324 has cored an early Cretaceous Shatsky Rise oceanic plateau to test its plume vs. non-plume origin. Consequent post-cruise petrological and geochemical studies including isotope determinations of Sr, Nd, Hf and He in the rocks testified that the majority of the Shatsky Rise magmas originated from a slightly enriched MORB-type source and underwent MORB-like crystal fractionation. The data did not, however, provide unequivocal evidence of the Shatsky Rise formation by one of the two main proposed scenarios (plume vs. non-plume origin). Some hotspot-related magmas were previously recognized to have elevated concentrations of strongly chalcophile elements (Cu, Au) compared to typical MORB, providing potential proxy for a deep mantle plume origin. However, the present dataset available for Shatsky Rise basalts includes only whole-rock Cu contents, whose elevated values in some rock types can also be explained by post-magmatic sulfidization. In the course of our new research project we plan to carry out new geochemical investigations of the Shatsky Rise basaltic glasses with the focus on (1) in-situ analysis of strongly chalcophile elements in pristine glasses (Cu, Ag, Au, Se), and (2) determination of the oxidation state of magmas. The data will be used to test plume vs. non-plume origin of the Shatsky Rise oceanic plateau.