HR: 13:40h
AN: V23D-01    [Abstracts]
TI: Magmatic MORB Volatiles, Seafloor Hydrothermal Systems and Abiotic Organic Synthesis
AU: * Holloway, J R
EM: john.holloway@asu.edu
AF: School of Earth & Space Science, Arizona State University, Tempe, AZ 85287-1404, United States
AU: * Holloway, J R
EM: john.holloway@asu.edu
AF: Department of Chemistry & Biochemistry, Arizona State University, Tempe, AZ 85281-1604, United States
AB: A plausible model for the origin of the observed C-O-H volatiles observed in MORB glasses is that they were incorporated in primary melts of the upwelling mantle. Based on the observed ferric/ferrous ratios in MORB glass, it is probable that the MORB source mantle contained diamond or graphite, depending on pressure. If true, then during partial mantle melting the graphite/diamond would react with FeO1.5 in garnet/spinel and clinopyroxene to form CO2 which would dissolve in the melt as carbonate ion. Using equation of state models for CO2 activity and ferric/ferrous ratios in the magma it is possible to model the amount of carbonate dissolved in the basaltic magma as a function of the degree of melting (Holloway and O'Day, 2000). The results require that rising MORB magma will become saturated in CO2 at depths much greater than those proposed for MORB magma chambers. Conversely H2O values observed in MORB glasses are far below saturation. However as CO2 reaches saturation and exsolves from the melt the low fO2 imposed by the low ferric/ferrous ratio results in a high H2/H2O ratio in the exsolving supercritical fluid. We have shown that fluids with this composition produce methanol (CH3OH) in the presence of magnetite at seafloor hydrothermal P-T conditions in a flow-through system (Voglesonger, et al., 2001) and that aqueous methanol solutions react in montmorillonite clay interlayers to form a wide variety of complex hydrocarbon molecules, the most abundant being hexamethyl benzene (Williams, et al., 2005). Methyl stearate (C17H35COOCH3) was also observed in moderate amounts. Holloway, J. R. and P. A. O'Day (2000). "Production of CO2 and H2 by Diking-Eruptive Events at Mid-Ocean Ridges: Implications for Abiotic Organic Synthesis and Global Geochemical Cycling." International Geology Review 42: 673-683. Voglesonger, K. M., J. R. Holloway, E. E. Dunn, P. J. Dalla-Betta and P. A. O'Day (2001). "Experimental Abiotic Synthesis of Methanol in Seafloor Hydrothermal Systems." Chemical Geology 180: 129-139. Williams, L. B., B. C. Canfield, K. M. Voglesonger and J. R. Holloway (2005). "Organic molecules formed in a primordial womb." Geology 33: 913-916.
DE: 1011 Thermodynamics (0766, 3611, 8411)
DE: 1012 Reactions and phase equilibria (3612, 8412)
DE: 1032 Mid-oceanic ridge processes (3614, 8416)
DE: 1034 Hydrothermal systems (0450, 3017, 3616, 4832, 8135, 8424)
DE: 1037 Magma genesis and partial melting (3619)
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2007 Fall Meeting