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churikova

HR: 0830h
AN: T41C-0879
TI: Trace Element Features of Subduction-Related Metasomatism from Ultramafic Xenoliths of the Kamchatka arc
AU: * Yogodzinski, G M
EM: [email protected]
AF: Department of Geological Sciences, University of South Carolina, Columbia, SC 29209 United States
AU: Churikova, T
EM: [email protected]
AF: Institute of Volcanic Geology and Geochemistry, Piip Avenue 9 Petropavlovsk-Kamchatsky, Russian Federation
AU: Koloskov, A V
EM: [email protected]
AF: Institute of Volcanic Geology and Geochemistry, Piip Avenue 9 Petropavlovsk-Kamchatsky, Russian Federation
AU: Roth, J
EM: [email protected]
AF: Department of Geology, Dickinson College, Carlisle, PA 17013 United States
AB: Ultramafic xenoliths from Shiveluch and Kharchinsky volcanoes in Kamchatka appear to provide a unique opportunity to directly observe the effects of subduction-related metasomatism on depleted mantle peridotite. At Shiveluch Volcano, the common xenolith type is a tectonized dunite that contains abundant kink-banded olivine and displays textural variation from protogranular to porphyroclastic and mosaic equigranular. These xenoliths are cut by millimeter-scale veins and are invaded by irregular spots of metasomatic pyroxene and phlogopite (+/- trace amphibole). At nearby Kharchinsky Volcano, the hydrous, metasomatic mineral in the deformed dunite xenoliths is amphibole. All samples are enriched in the light rare-earth elements (REE), with La/Yb from 1.80 to 14.8-times chondritic. Samples with low REE concentrations have concave-upward heavy REE patterns (low Dy/Yb), similar to published data on harzburgite and dunite xenoliths interpreted to be the highly depleted residue left after fractional melting. The most strongly metasomatized xenoliths (based on phlogopite abundance) have relatively high concentrations of incompatible elements and light REE-enriched patterns similar to those in common volcanic rocks from oceanic arcs (e.g., La/Yb=3.5 with Dy/Yb=2.1). Trace element ratios such as Ba/La, Th/La and Ba/Th are widely variable in the xenoliths (e.g., Ba/La=5-100), but most samples fall within the range of common arc rocks (Ba/La= 25-50; Th/La=0.08-0.14; Ba/Th = 250-500). In contrast, relative Sr concentrations in the xenoliths are low (e.g., Sr/Nd=5-21) compared to common arc rocks (Sr/Nd = 20-60). Most of the preliminary trace element data thus appear to support recently reported 3He/4He and CO2/He observations (N. Basu et al., 2001, GSA annual meeting) which point toward subduction-related fluids as the likely metasomatic agent in the dunite xenoliths from Shiveluch and Kharchinsky volcanoes, Kamchatka.
DE: 1025 Composition of the mantle
DE: 1065 Trace elements (3670)
DE: 1749 Volcanology, geochemistry, and petrology
SC: T
MN: 2001 AGU Fall Meeting