MINERALOGICAL CHARACTERIZATION OF REJUVENATED MAGMATISM AT BURTON GUYOT, LOUISVILLE SEAMOUNT TRAIL

The summit of Burton Guyot of the Louisville Seamount trail shows clear evidence for a post-erosional, rejuvenated magmatic phase that was sampled by drilling during IODP Expedition 330 (Koppers et al., 2012). Rejuvenated magmatism is documented by primary and reworked volcaniclastic deposits that emplaced in a deep (< 100 m) marine environment following erosion and subsidence of a volcanic island. The island stage of the guyot is documented by underlying post-shield shallow-marine limestones and volcanic delta deposits of the shield volcanic phase (Buchs et al., 2018). Rejuvenated deposits include abundant crystal cargo with phenocrystic (magmatic) clinopyroxene and two types of clinopyroxene from ultramafic xenoliths. Unlike glass in the rejuvenated volcaniclastic deposits that are more alkaline than glass of shield volcanic deposits (Nichols et al., 2014), the phenocrysts of the rejuvenated deposits (this study) have the same compositional range of phenocrysts in the shield deposits (Dorais, 2015). This suggests an overlap in shield – rejuvenated magma compositions. The dominant type of clinopyroxene from disaggregated ultramafic xenoliths is very similar to clinopyroxene in Hawaiian pyroxenites thought to represent high pressure cumulates. Their relatively low Mg/(Mg+Fe), Cr, and Sc contents, as well as similar trace element abundances to Hawaiian cumulates indicates that they are also cumulates. These clinopyroxene grains equilibrated along the pressure-temperature array defined by their Hawaiian counterparts. A minor subset of Louisville clinopyroxenes are Mg-rich, and plot along the same compositional trends as clinopyroxene in Hawaiian peridotites. These clinopyroxenes are fragments of mantle xenoliths and show intermediate amounts of incompatible element depletion, between more enriched Hawaiian peridotites and strongly depleted abyssal peridotites. Despite Louisville seamounts being approximately one order of magnitude smaller than Hawaiian volcanoes and they have a very dissimilar stratigraphy, our results suggest close similarities of the magma plumbing system of these two volcanic systems.