首页|Metals in Avachinsky peridotite xenoliths with implications for redox heterogeneity and metal enrichment in the Kamchatka mantle wedge
Metals in Avachinsky peridotite xenoliths with implications for redox heterogeneity and metal enrichment in the Kamchatka mantle wedge
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Peridotite xenoliths from the Avachinsky volcano in southern Kamchatka contain diverse assemblages of native metals and intermetallic compounds associated with primary olivine and orthopyroxene and metasomatic amphibole. Mineral compositions in Avachinsky xenoliths (Mg-rich olivine and low-Al enstatite associated with Cr-spinel) coupled with common absence of primary clinopyroxene and low bulk Al2O3 and CaO contents, suggest a depleted mantle wedge beneath the southern segment of the Kamchatka volcanic arc.Metallic phases in Avachinsky xenoliths occur as euhedral to anhedral grains in fractures andirregularly shaped voids in Fe-Mg silicates as well as micro-particles localized along boundaries between oivine and orthopyroxene. Siderophile metal assemblage is composed of platinum, iron and gold along with Cr-Fe and W-Fe-Mn alloys. Chalcophile metals include native copper, bismuth, lead and zinc along with Cu-Ag, Cu-Sn, Cu-Sn-Au, Ag-Au, Cu-Ag-Au and Ni-Cu-Ag-Au intermetallic compounds. Metals in Avachinsky xenoliths are associated, both spatially and texturally, with magnetite, rutile, galena, cassiterite, Cu-Ag-bearing Sb-Bi-Pb sulfide phase, AgS and non-stoichiometric Cl-bearing silver compound. Siderophile metals were introduced by primitive metasomatizing melts into low fO2 domains in the mantle wedge below the Kamchatka arc. Phase relations in the Cu-Ag-Au system suggest high-temperature (>900 °C) origin for Cu-Ag-Au intermetallic compounds in Avachinsky xenoliths. While Cu-Ag-Au alloys precipitated from metal-rich, mantle-derived silicate melts, low-melting point chalcophile metals and their minerals (Ag, Bi, Sb, Zn, Pb, Sn) were deposited in the sub-Kamchatkan mantle from hydrous slab fluids under reduced conditions. Metal assemblages in Avachinsky xenoliths further attest to reducing conditions in some subduction systems and potentially indicate existence of extreme redox gradients at sufficiently small scales in sub-arc mantle wedge environments.
Kamchatka peridotite xenolithsSiderophile and chalcophile metalsCu-Ag-Au alloysMetal-rich melts and fluidsReduced mantle wedge
Pavel Kepezhinskas、Nikolai Berdnikov、Nikita Kepezhinskas
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PNK Geoscience, Tampa, FL 33647, USA
Yu.A. Kosygin Institute of Tectonics and Geophysics, Far Eastern Branch, Russian Academy of Sciences, Kim Yu Chen Street, 65, Khabarovsk 680000, Russian Federation
Department of Earth and Atmospheric Sciences, University of Alberta, Edmonton, Canada
NSTL
