Volatile (H2O, CO2, Cl, S) budget of the Central American subduction zone

• Published in: International journal of earth sciences : Geologische Rundschau 2014-10, Vol.103 (7), p.2101-2127
• Main Authors: Freundt, A., Grevemeyer, I., Rabbel, W., Hansteen, T. H., Hensen, C., Wehrmann, H., Kutterolf, S., Halama, R., Frische, M.
• Format: Article
• Language: English
• Subjects: Carbon dioxide; Carbonates; Earth and Environmental Science; Earth Sciences; Electrical resistivity; Geochemistry; Geology; Geophysics/Geodesy; Magma; Mineral Resources; Multidisciplinary research; Original Paper; Sedimentology; Structural Geology; Sulfur; Sulfur dioxide; VOCs; Volatile organic compounds; Water budget
• ISSN: 1437-3254; 1437-3262
• DOI: 10.1007/s00531-014-1001-1

After more than a decade of multidisciplinary studies of the Central American subduction zone mainly in the framework of two large research programmes, the US MARGINS program and the German Collaborative Research Center SFB 574, we here review and interpret the data pertinent to quantify the cycling of mineral-bound volatiles (H 2 O, CO 2 , Cl, S) through this subduction system. For input-flux calculations, we divide the Middle America Trench into four segments differing in convergence rate and slab lithological profiles, use the latest evidence for mantle serpentinization of the Cocos slab approaching the trench, and for the first time explicitly include subduction erosion of forearc basement. Resulting input fluxes are 40–62 (53) Tg/Ma/m H 2 O, 7.8–11.4 (9.3) Tg/Ma/m CO 2 , 1.3–1.9 (1.6) Tg/Ma/m Cl, and 1.3–2.1 (1.6) Tg/Ma/m S (bracketed are mean values for entire trench length). Output by cold seeps on the forearc amounts to 0.625–1.25 Tg/Ma/m H 2 O partly derived from the slab sediments as determined by geochemical analyses of fluids and carbonates. The major volatile output occurs at the Central American volcanic arc that is divided into ten arc segments by dextral strike-slip tectonics. Based on volcanic edifice and widespread tephra volumes as well as calculated parental magma masses needed to form observed evolved compositions, we determine long-term (10 5 years) average magma and K 2 O fluxes for each of the ten segments as 32–242 (106) Tg/Ma/m magma and 0.28–2.91 (1.38) Tg/Ma/m K 2 O (bracketed are mean values for entire Central American volcanic arc length). Volatile/K 2 O concentration ratios derived from melt inclusion analyses and petrologic modelling then allow to calculate volatile fluxes as 1.02–14.3 (6.2) Tg/Ma/m H 2 O, 0.02–0.45 (0.17) Tg/Ma/m CO 2 , and 0.07–0.34 (0.22) Tg/Ma/m Cl. The same approach yields long-term sulfur fluxes of 0.12–1.08 (0.54) Tg/Ma/m while present-day open-vent SO 2 -flux monitoring yields 0.06–2.37 (0.83) Tg/Ma/m S. Input–output comparisons show that the arc water fluxes only account for up to 40 % of the input even if we include an “invisible” plutonic component constrained by crustal growth. With 20–30 % of the H 2 O input transferred into the deeper mantle as suggested by petrologic modeling, there remains a deficiency of, say, 30–40 % in the water budget. At least some of this water is transferred into two upper-plate regions of low seismic velocity and electrical resistivity whose sizes vary along arc: one