Southeastern Section - 63rd Annual Meeting (10–11 April 2014)

Paper No. 6
Presentation Time: 2:55 PM

EVIDENCE FOR MELT TRANSPORT AND CRYSTALLIZATION BELLOW THE CRUST-MANTLE BOUNDARY IN THE SANTA ELENA OPHIOLITE, COSTA RICA


MADRIGAL, Pilar, Department of Geosciences, Virginia Tech, 4044 Derring Hall (0420), Blacksburg, VA 24060, GAZEL, Esteban, Department of Geosciences, Virginia Tech, 4044 Derring Hall, Blacksburg, VA 24061, SMITH, Ian, Geology, School of environment, University of Auckland, Auckland, 87416, New Zealand and SNOW, Jonathan E., Earth and Atmospheric Sciences, University of Houston, Houston, TX 77204, pilarmq@vt.edu

Constraining the melting generation and transport processes in the mantle is fundamental to the understanding of our planet. Well-preserved ophiolite sections around the globe constitute windows into the fossilized melt transport systems that fed the crust and upper mantle. The Santa Elena ophiolite, located in Costa Rica, is a good example of an ancient plumbing system obducted into the surface. Using a combination of techniques, including structural geology, geochemistry, Ar-dating and petrological modeling, we examined the 120 Ma diabase dike swarm that intrudes the peridotite in the Santa Elena ophiolite. Crystallization models require a MORB magma source containing 0.5 wt% H2O, 53 wt% SiO2, 3 wt% Na2O and yielded pressures between 0.4 and 0.8 GPa below the crust-mantle boundary, at depths ranging between 15 and 30 km. Global geochemical comparisons suggest a tectonic scenario that is compatible with back arc basins and slow spreading ridges. We interpret that these sets of conditions may have been achieved during the Late Jurassic-Early Cretaceous spreading between North America and South America, under the influence of the subduction of the Farallon Plate towards the west.