Open AccessNitrogen systematics and gas fluxes of subduction zones: Insights from Costa Rica arc volatiles
Author(s) -
Zimmer Mindy M.,
Fischer Tobias P.,
Hilton David R.,
Alvarado Guillermo E.,
Sharp Zachary D.,
Walker James A.
Publication year - 2004
Publication title -
geochemistry, geophysics, geosystems
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.928
H-Index - 136
ISSN - 1525-2027
DOI - 10.1029/2003gc000651
Subject(s) - fumarole , subduction , geology , volcano , slab , flux (metallurgy) , nitrogen , volcanic arc , geochemistry , andesite , sulfur , volcanic rock , geophysics , chemistry , paleontology , tectonics , organic chemistry
Volcanic gases are a powerful tool for assessing magmatic processes in subduction zones. We report gas chemistry and nitrogen isotope compositions of fumaroles, bubbling springs, and geothermal wells from the Costa Rican segment of the Central American volcanic segment (CAVS), and new correlation spectroscopy (COSPEC) SO 2 flux measurements of Poás and Arenal volcanoes. N 2 /He ratios (100–8,250) and nitrogen isotope compositions (δ 15 N = −3.02 to +1.69‰) of Costa Rica volatiles are consistent with sources ranging from typical arc‐type end‐members, with nitrogen addition from the subducting slab, to MORB end‐member, having experienced no slab modification. Overall, nitrogen‐helium chemistry of Costa Rican material indicates a diminished slab contribution versus other locations along the arc (e.g., Nicaragua and Guatemala). We use SO 2 flux measurements of Poás and Arenal (1.80*10 5 ± 4.00*10 4 and 8.30*10 3 ± 4.00*10 3 kg/day, respectively, or 1.30*10 5 ± 6.25*10 4 and 2.81*10 6 ± 6.25*10 5 mol/day, respectively) to extrapolate a SO 2 flux for the Costa Rica segment of 1.09*10 9 mol/day. Using CO 2 /S t (S t = total sulfur) of 2.7 and 5.9, we calculate CO 2 fluxes of 1.88*10 8 and 4.11*10 8 kg/yr, respectively (2.94*10 9 and 6.42*10 9 mol/yr, respectively). Other volatile fluxes (N 2 , He, H 2 , Ar, HCl, and H 2 O) are calculated using CO 2 /S t and regional gas chemistry. For Costa Rica, the output/input ratios of nitrogen are less than unity (0.03 to 0.06 for CO 2 /S t of 2.7 and 5.9, respectively), suggesting more N is subducted than released in the subarc, possibly resulting from sediment offscraping, forearc devolatilization, limited fluid availability in the subarc, or subduction past the subarc.