HR: 1340h
AN: V23A-1243    [Abstracts]
TI: Volcanic CO2 as a major agent of weathering in volcanic regions
AU: * Rive, K
EM: rive@ipgp.jussieu.fr
AF: Lab. Geochimie des Isotopes Stables, tr 54, 4 place Jussieu, Paris, 75252, France, Metropolitan
AU: Gaillardet, J
EM: gaillardet@ipgp.jussieu.fr
AF: La. Geochimie et Cosmochimie, tr 14, 4 place Jussieu, Paris, 75252, France, Metropolitan
AU: Agrinier, P
EM: agrinier@ipgp.jussieu.fr
AF: Lab. Geochimie des Isotopes Stables, tr 54, 4 place Jussieu, Paris, 75252, France, Metropolitan
AU: Rad, S
EM: rad@ipgp.jussieu.fr
AF: La. Geochimie et Cosmochimie, tr 14, 4 place Jussieu, Paris, 75252, France, Metropolitan
AB: According to high erosion rates, weathering of volcanic areas is one of the main processes controlling the atmospheric CO₂ levels (e.g. Louvat, 1997, Dessert et al., 2003). So far, the origin of CO₂ was assumed to be mainly atmospheric. The origin and consumption rates of CO₂ can be estimated using concentration of Dissolved Inorganic Carbon (DIC ~ bicarbonates) in the rivers and carbon stable isotopes. The processes governing the CO₂ consumption by chemical weathering were studied in four volcanic areas, with climates from tropical to sub-polar, in different geodynamic contexts. Lesser Antilles, Reunion, Iceland and French Massif Central are ideal sites for the study of weathering due to the gradients of rainfall (up to 14m/yr), rock ages (tertiary to subactual) and volcanic activities, inducing variable weathering rates (50- 400t/km\²/yr). δ¹³C_DIC and major elements chemistry were studied in streams, springs and soil solutions of these four areas. The δ¹³C_DIC and major elements concentrations are highly variable, and allow us to identify the origin of DIC as a mixing between biogenic CO₂ (average value of δ¹³C ~ - 29.1±2.0‰ in tropical areas, -26‰ in temperate to sub-polar climate) and volcanic CO₂ (δ¹³C_DIC = -5 to 3‰). We found that volcanic CO₂ is a major source of carbon, the highest contribution being for zones with high infiltration of water (up to 100\percent of DIC for Piton de la Fournaise in Reunion). As inferred by Rad et al. (2007) from major elements, this isotopic study of the DIC cycling in the river demonstrates the importance of the volcanic fluids on chemical weathering processes.
DE: 1037 Magma genesis and partial melting (3619)
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2007 Fall Meeting