Volatile (S, Cl and F) and fluid mobile trace element compositions in melt inclusions: implications for variable fluid sources across the Kamchatka arc

Abstract

Volatile element, major and trace element compositions were measured in glass inclusions in olivine from samples across the Kamchatka arc. Glasses were analyzed in reheated melt inclusions by electron microprobe for major elements, S and Cl, trace elements and F were determined by SIMS. Volatile element-trace element ratios correlated with fluid-mobile elements (B, Li) suggesting successive changes and three distinct fluid compositions with increasing slab depth. The Eastern Volcanic arc Front (EVF) was dominated by fluid highly enriched in B, Cl and chalcophile elements and also LILE (U, Th, Ba, Pb), F, S and LREE (La, Ce). This arc-front fluid contributed less to magmas from the central volcanic zone and was not involved in back arc magmatism. The Central Kamchatka Depression (CKD) was dominated by a second fluid enriched in S and U, showing the highest S/K 2 O and U/Th ratios. Additionally this fluid was unusually enriched in 87 Sr and 18 O. In the back arc Sredinny Ridge (SR) a third fluid was observed, highly enriched in F, Li, and Be as well as LILE and LREE. We argue from the decoupling of B and Li that dehydration of different water-rich minerals at different depths explains the presence of different fluids across the Kamchatka arc. In the arc front, fluids were derived from amphibole and serpentine dehydration and probably were water-rich, low in silica and high in B, LILE, sulfur and chlorine. Large amounts of water produced high degrees of melting below the EVF and CKD. Fluids below the CKD were released at a depth between 100 and 200 km due to dehydration of lawsonite and phengite and probably were poorer in water and richer in silica. Fluids released at high pressure conditions below the back arc (SR) probably were much denser and dissolved significant amounts of silicate minerals, and potentially carried high amounts of LILE and HFSE.

Contrasting partition behavior of F and Cl during hydrous mantle melting: implications for Cl/F signature in arc magmas

“…Although the variations of degree of melting and crystallization are likely responsible for some of F and Cl variation within each group of arc melt inclusions, it is unlikely that crystallization is solely responsible for these variations. For instance, Le Voyer et al (2010) (Straub and Layne 2003;Elburg et al 2006;Wysoczanski et al 2006;Churikova et al 2007;Portnyagin et al 2007;Sadofsky et al 2008;Vigouroux et al 2008;Bouvier et al 2008;Le Voyer et al 2008;Sorbadere et al 2011;Shaw et al 2012;Rose-Koga et al 2012). The Cl/F ratio is determined by the slab component, the degree of melting, but also the rate of fluid-induced melting.…”

Late Pleistocene-Holocene volcanism on the Kamchatka Peninsula, Northwest Pacific Region

“…All the SR rocks contain a variable amount of the enriched OIB-like mantle component. The amount of this component changes from low addition on Ichinsky volcano (so called SR (IAB)) to highly enriched (up to 30-35%) in intra-plate basalts (so called SR (WPT)) [Churikova at al., , 2007Münker et al, 2004;Volynets et al, 2006].…”

“…While fluid released in EVF and CKD carries high amounts of B, Cl and S [Portnyagin et al, 2007a], the fluid below SR is enriched in Li and F (Fig. 16), [Churikova et al, 2004[Churikova et al, , 2007. We argue that the dehydration of different water-rich minerals at different depths explains the difference in fluid Fluid mobile trace element concentrations (A-D) and HFSE and REE concentrations (E-H) of single volcanoes in relation to the depth of the slab surface below the volcanoes for the northern Kamchatka transect.…”

“…In Kamchatka, subduction is responsible for most of recent volcanism [e.g. Volynets, 1994;Churikova et al, 2001Churikova et al, , 2007Avdeiko et al, 2006;Portnyagin et al, 2007a, b]. However, its spatial distribution and time patterns are rather complicated.…”

“…The best example of this connection are findings of adakite-like rocks in northern Kamchatka, probably reflecting the edge of the subducting Pacific plate being warmed or ablated by mantle flow [Volynets et al, 1997b[Volynets et al, , 1999b[Volynets et al, , 2000Peyton, 2001;Yogodzinski et al, 2001a]. Research aimed at understanding of the nature of various volcanic zones in Kamchatka and their relation to the changing tectonic environment is currently going on in many areas of Kamchatka [e.g., Avdeiko et al, 2006;Churikova et al, 2001Churikova et al, , 2007Duggen et al, 2007;Perepelov, 2004;Perepelov et al, 2005;Portnyagin et al, 2005Portnyagin et al, , 2007aVolynets et al, 2005] and hopefully will result in the understanding of this dynamic region.…”