Constraints on mantle melting and composition and nature of slab components in volcanic arcs from volatiles (H2O, S, Cl, F) and trace elements in melt inclusions from the Kamchatka Arc

Abstract

New and published data on the composition of melt inclusions in olivine ) from volcanoes of the Kamchatka and northern Kurile Arc are used 1) to evaluate the combined systematics of volatiles (H 2 O, S, Cl, F) and incompatible trace elements in their parental magmas and mantle sources, 2) to constrain thermal conditions of mantle melting, and 3) to estimate the composition of slabderived components. We demonstrate that typical Kamchatkan arc-type magmas originate through 5-14% melting of sources similar or slightly more depleted in HFSE (with up to ∼ 1 wt.% previous melt extraction) compared to MORB-source mantle, but strongly enriched in H 2 O, B, Be, Li, Cl, F, LILE, LREE, Th and U. Mean H 2 O in parental melts (1.8-2.6 wt.%) decreases with increasing depth to the subducting slab and correlates negatively with both 'fluid-immobile' (e.g. Ti, Na, LREE) and most 'fluid-mobile' (e.g. LILE, S, Cl, F) incompatible elements, implying that solubility in hydrous fluids or amount of water does not directly control the abundance of 'fluid-mobile' incompatible elements. Strong correlation is observed between H 2 O/Ce and B/Zr (or B/LREE) ratios. Both, calculated H 2 O in mantle sources (0.1-0.4%) and degrees of melting (5-14%) decrease with increasing depth to the slab indicating that the ultimate source of water in the sub-arc mantle is the subducting oceanic plate and that water flux (together with mantle temperature) governs the extent of mantle melting beneath Kamchatka. A parameterized hydrous melting model [Katz et al. 2003, G 3 , 4(9), 1073] is utilized to estimate that mantle melting beneath Kamchatka occurs at or below the dry peridotite solidus (1245-1330°C at 1.5-2.0 GPa). Relatively high mantle temperatures (yet lower than beneath back-arc basins and ocean ridges) suggest substantial corner flow driven mantle upwelling beneath Kamchatka in agreement with numerical models implying non-isoviscous mantle wedge rheology. Data from Kamchatka, Mexico and Central America indicate that b 5% melting would take place beneath continental arcs without water flux from the subducting slab. A broad negative correlation appears to exist between crustal thickness and the temperature of magma generation beneath volcanic arcs with larger amounts of decompression melting occurring beneath thinner arc crust (lithosphere). In agreement with the high mantle temperatures, we observe a systematic change in the composition of slab components with increasing slab depth from solute-poor hydrous fluid beneath the volcanic front to solute-rich hydrous melt or supercritical liquid at deeper depths beneath the rear arc. The solute-rich slab component dominates the budget of LILE, LREE, Th Earth and Planetary Science Letters 255 (2007) and U in the magmas and originates through wet-melting of subducted sediments and/or altered oceanic crust at ≥ 120 km depth. Melting of the upper parts of subducting plates under water flux from deeper lithosphere (e.g. serpentinites), combined with high temperatures in the mantle wedge, may be a ...

First volatile inventory for Gorely volcano, Kamchatka

“…The H 2 O, S, Cl and F contents of K parental magmas have recently been quantified by Portnyagin et al [2007]. By combining their parental melt S content (0.07-0.27%) with our inferred CO 2 /SO 2 ratio (1.2) in Gorely's volcanic gas, a CO 2 content of 0.13-0.45% in these parental melts is inferred.…”

Sources of post-orogenic calcalkaline magmas: The Arrochar and Garabal Hill–Glen Fyne complexes, Scotland

“…to the mantle wedge at the shallower depths (e.g., Gill, 1981;Kushiro, 1990;Plank and Langmuir, 1993;Elliott et al, 1997;Tatsumi and Kogiso, 1997) and that slab melts (if they occur) may be the metasomatic agents at greater depths (e.g., Beard et al, 1993;Rapp et al, 1999;Killian and Stern, 2002;Kelemen et al, 2004), perhaps producing more sodic metasomatic products. Portnyagin et al (2007) The experiments of Rapp et al (1999) and the geochemical and theoretical studies of Xiong et al (2006) suggest that fertile mantle, metasomatised by high-T melts, would consist of sodic amphibole pyroxenite, with phlogopite pyroxenite formed by interaction with lower-T melts. Kessel et al (2005) measured the compositions of fluids and melts that had been experimentally equilibrated with a basaltic eclogite at P-T conditions relevant to subduction zones.…”

Constraints from melt inclusions and their host olivines on the petrogenesis of Oligocene-Early Miocene Xindian basalts, Chifeng area, North China Craton

“…(2) Now that being trapped at relatively high pressure, melt inclusions could preserve volatile components (such as H 2 O, S, Cl and CO 2 ) of magmas well, which could be measured directly (e.g., Sobolev and Chaussidon 1996;Kovalenko et al 2000;Walker et al 2003;Portnyagin et al 2007). (3) Melt inclusions within resistant phenocrysts would survive from alteration if they remain closed all the time (e.g., McDonough and Ireland 1993).…”