25 Million Years of Mantle Upwelling below the Mid Atlantic Ridge: The Vema Lithopsheric Section Revisited

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ABSTRACT Bonatti (0551288)Intellectual Merit: This research is the continuation of a project that studies an uplifted sliver of oceanic lithosphere that exposes upper mantle and seafloor crustal units along the Vema Lithospheric Section. This field area provides an opportunity to monitor how processes of seafloor lithospheric generation have changed over the last 25 million years. The project combines multibeam, gravity, magnetics and seismic reflection geophysical data with geochemical and isotopic analyses of closely spaced geochemical samples of the exposed mantle ultramafic basal units and the crustal basaltic units. Samples of peridotites, gabbros, and basalts (including fresh glass) were collected during the April-May 2005 field season augmenting the original study by 32 additional sites and extending the time coverage of the sample suite by 10 million years. Geochemical work includes major and trace element analyses of mantle equilibrated pyroxenes and spinels. These data will be used to refine patterns of mantle thermal properties, composition, and melting processes. Major and trace element analyses of basaltic glasses will be used to obtain independent estimates of the extent of mantle melting. Sr-Nd-Pb isotope compositions of pyroxenes from peridotites and basaltic glasses will be used to determine genetic links between the mantle and crustal basalts. Results will test the idea that short-scale isotopic heterogeneities of upper mantle peridotites are homogenized in the melt that derives from a broad region of the upper mantle. Combined geochemical and geophysical data from the study will permit 3D modeling of lithosphere formation. Broader impacts: This project will fund researchers from New York State, one of whom is a female, early career scientist. Undergraduates will be involved in the research as will faculty and students at the urban Queens College campus of the City University of New York which has a high enrollment of minorities under-represented in the sciences. Analytical data will be archived and made available to the public through the PetDb petrologic database at Lamont-Doherty Earth Observatory.