HR: 0800h
AN: V31A-1426    [Abstracts]
TI: Halogens and Sulfur Across the Kamchatka Arc
AU: * Churikova, T
EM: churikova@pisem.net
AF: Inst. of Volcanology and Seismology, 9 Piip Ave., Petropavlovsk-Kamch., SC 683006 Russian Federation
AU: W”rner, G
EM: gwoerne@gwdg.de
AF: University of G”ttingen, Geowissenschaftliches Zentrum, G”tingen, CA 37077 Germany
AU: Mironov, N
EM: stup@geo.web.ru
AF: Moscow State University, Leninskiye Gory Moscow, Moscow, WI 119992 Russian Federation
AU: Kronz, A
EM: AKronz@gwdg.de
AF: University of G”ttingen, Geowissenschaftliches Zentrum, G”tingen, CA 37077 Germany
AU: Pletchov, P
EM: pavel@web.ru
AF: Moscow State University, Leninskiye Gory Moscow, Moscow, WI 119992 Russian Federation
AU: Portnyagin, M
EM: mportnyagin@ifm-geomar.de
AF: GEOMAR, Wischhofstr, 1-3, Kiel, NY 2040048 Germany
AB: Volatile (S, Cl, F), major and trace elements across the Kamchatka arc were studied by electron microprobe and SIMS analysis in homogenized melt inclusions in olivine from arc basalts collected along the E-W transect of the Kamchatka arc, from Eastern Volcanic Front (EVF) to back arc region. Halogens show the opposite behavior across the arc. Chlorine concentrations in melts from EVF and Central Kamchatka Depression (CKD) are similar (750 to 1100 ppm) and higher than for Sredinniy Ridge back arc (SR, 500 ppm). In contrast, fluorine increase from EVF and CKD melts (300 to 450 ppm) to the SR region (800 ppm), increasing the F/Cl ratio from arc front to back arc by a factor of five. Sulfur shows the general decrease from the arc front to back arc, but the highest concentrations (2500 ppm) occur in the CKD melts. Volatile element - trace element ratios in general correlate with fluid-mobile elements (B, Li) and suggest successive changes in fluid compositions with increasing slab depth. In detail, we identify three distinct fluid compositions. EVF-fluids are highly enriched in B, Cl and chalkophile elements. This fluid carries additionally LILE (U, Th, Ba, Pb), F, S and LREE (La, Ce). This fluid is dominating EVF sources and is reduced in the CKD melts and is not documented in SR region. The second CKD-fluid affects the Kluchevskaya Group of volcanoes and is enriched in S and U, S/K2O, U/Th and depleted in Cl/S ratio. This fluid unusually enriched in 87Sr, 18O and 11B. The third SR-fluid observed for back arc volcanoes is highly enriched in F, Li and Be, carrying also LILE, LREE and probably some Nb, which results in correlations of F/Ce with Li/Yb, Li/Dy, Sr/Y, Ba/Y, and Nb/Yb. This fluid starts to be released below CKD and becomes the dominant fluid in the back arc region. We argue that the dehydration of different water-rich minerals at different depths from the arc front (low P-T conditions) to back arc (high P-T conditions) explains the difference in fluid composition and the decoupling of B (and Cl) and Li (and F) across the Kamchatka arc. Seawater component could be a significant additional source for chlorine in Kamchatka melts.
DE: 1040 Isotopic composition/chemistry
DE: 1065 Trace elements (3670)
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2004 AGU Fall Meeting