A limited role for metasomatized subarc mantle in the generation of boron isotope signatures of arc volcanic rocks

• Published in: Geology
• Main Authors: Tomanikova, Lubomira, Savov, Ivan P., Harvey, Jason, de Hoog, Jan C.M., Churikova, Tatiana G., Yogodzinski, Gene M., Gordeychik, Boris N.
• Format: Article in Journal/Newspaper
• Language: English
• Published: 2019
• Subjects: Kamchatka
• Online Access: https://resolver.sub.uni-goettingen.de/purl?gro-2/76851; https://resolver.sub.uni-goettingen.de/purl?gs-1/16295; https://doi.org/10.1130/G46092.1

Metasomatized subarc mantle is often regarded as one of the mantle reservoirs enriched in fluid-mobile elements (FMEs; e.g., B, Li, Cs, As, Sb, Ba, Rb, Pb), which, when subject to wet melting, will contribute to the characteristic FME-rich signature of arc volcanic rocks. Evidence of wet melts in the subarc mantle wedge is recorded in metasomatic amphibole-, phlogopite-, and pyroxene-bearing veins in ultramafic xenoliths recovered from arc volcanoes. Our new B and δ11B study of such veins in mantle xenoliths from Avachinsky and Shiveluch volcanoes, Kamchatka arc, indicates that slab-derived FMEs, including B and its characteristically high δ11B, are delivered directly to a melt that experiences limited interaction with the surrounding mantle before eruption. The exceptionally low B contents (from 0.2 to 3.1 μg g–1) and low δ11B (from –16.6‰ to +0.9‰) of mantle xenolith vein minerals are, instead, products of fluids and melts released from the isotopically light subducted and dehydrated altered oceanic crust and, to a lesser extent, from isotopically heavy serpentinite. Therefore, melting of amphibole- and phlogopite-bearing veins in a metasomatized mantle wedge cannot alone produce the characteristic FME geochemistry of arc volcanic rocks, which require a comparatively large, isotopically heavy and B-rich serpentinite-derived fluid component in their source