Mantle Melt Contribution and Crustal Contamination of Volcanic Rocks in the Black Rock Desert and Markagunt Plateau, Utah

Abstract:

Subalkaline intraplate volcanic rocks of the Black Rock Desert (BRD) and Markagunt Plateau (MP) of south-central Utah are a diverse suite of rocks that show marked geochemical differences with other intraplate volcanic suites. Previous studies of major and trace element bulk rock geochemistry show a diverse range of geologic settings operating in the region including pre-rift, oceanic (mid ocean ridge), and continental plate subduction. These studies have also established the MP and BRD to be a complicated ‘transition zone’. Previous bulk rock studies suffer from homogenization of phenocrysts/xenocrysts with the melt/groundmass eliminating the subtle differences of these unique chemical markers. In situ analyses of glass and individual crystals have never been carried out for this suite of rocks, to this end we have carried out in situ analysis of olivine grains and basaltic glass for samples throughout the region. Our initial results show there are quantifiable differences between major, trace, and REE distributions for both crystals and glass across both fields, as well as variability within individual fields. Additionally, our results suggest differences in mantle redox conditions exist below the MP and BRD. These preliminary results also demonstrate that in situ analysis allows for better interpretation of complex geochemical settings, like the MP and BRD of Utah. Continual work with this suite of rocks will improve our understanding of the mantle and history of intraplate volcanism within this region including the possibility of slab windows, plumes, and/or enriched mantle sources. Additionally this research will direct future studies ranging from volcanic hazard potential of Utah, to locating and developing geothermal resources.