Collaborative Research: Resolving Mantle, Crustal and Slab Fluxes to Arc Magmatism in Central America Using Geothermal Fluids and Volcanic Rocks

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Hilton/Walker/FischerEAR-0003628/0003664/0003668 This proposal is aimed at producing a volatile mass balance for the Central American subduction zone by quantifying the contributions from the subducting slab, mantle wedge and overlying crust to the overall arc budget. The Central American arc was chosen because it possess a number of unique features which allow explicit linkages to be forged between systematic variations in volcanic output and variations in subduction parameters, specifically slab dip, sediment supply and crustal thickness. Our approach is to couple CO2 and helium measurements (isotopes and relative abundances) which allows for identification and quantitative assessment of the various contributors to the magmatic output. Although a powerful technique, the accuracy of any flux estimates is limited by uncertainties in the effects of magmatic degassing on resultant CO2/3He ratios and on assumptions on the isotopic and abundance characteristics assigned to potential endmember compositions involved in arc magmagenesis. By analyzing and comparing the CO2-He relationships in geothermal fluids with mafic minerals both along and across the Central America arc, we aim to explore the extent of these limitations and to assess approaches with the potential to circumvent any difficulties. Additionally, we will derive present-day CO2 fluxes through combined COSPEC and gas chemistry studies. This offers the further possibility of deriving absolute fluxes for N2 and H2O and for also constraining their provenance in the subduction zone factory.