Metasomatized harzburgite xenoliths from Avacha volcano as fragments of mantle wedge of the Kamchatka arc: Implication for the metasomatic agent

Abstract

Abundant peridotite xenoliths have been found in pyroclasitics of Avacha (Avachinsky) volcano, the south Kamchatka arc, Russia. They are mostly refractory harzburgite with or without clinopyroxene: the Fo of olivine and Cr/(Cr + Al) atomic ratio of spinel range from 91 to 92 and from 0.5 to 0.7, respectively. They are metasomatized to various extents, and the metasomatic orthopyroxene has been formed at the expense of olivine. The metasomatic orthopyroxene, free of deformation and exsolution, is characterized by low contents of CaO and Cr2O3. The complicated way of replacement possibly indicates low viscosity of the metasomatic agent, namely hydrous fluids released from the relatively cool slab beneath the south Kamchatka arc. This is a good contrast to the north Kamchatka arc, where the slab has been hot enough to provide slab‐derived melts. High content of total orthopyroxene, 40 vol% on average, in metasomatized harzburgite from Avacha suggests silica enrichment of the mantle wedge, and is equivalent to some subcratonic harzburgite. Some subcratonic harzburgites therefore could have been formed by transportation of subarc metasomatized peridotites to a deeper part of the upper mantle.

Rock seismic anisotropy of the low‐velocity zone beneath the volcanic front in the mantle wedge

“…Based on petrological data, the peridotite xenoliths are thought to have originated from depths shallower than 60 km [Arai et al, 2003]. Given that the depth to the Moho in this area is about 37 km, the peridotite xenoliths are likely to have originated in the uppermost 20 km of the mantle beneath Avacha volcano.…”

Orthopyroxene-enrichment in the lherzolite-websterite xenolith suite from Paleogene alkali basalts of the Poiana Ruscă Mountains (Romania)

“…Kelemen et al 1992;Smith et al 1999;McInnes et al 2001;Santos et al 2002;Arai et al 2003Arai et al , 2004Arai et al , 2006Bali et al 2007Bali et al , 2008Rehfeldt et al 2008;Dantas et al 2009). Most studies explain orthopyroxene-enrichment of the mantle rocks either by reaction with aqueous SiO 2 -rich melts derived from slab dehydration and melting (e.g.…”

“…These interpretations suggest that orthopyroxene-rich lithologies can be (1) products of interaction between mantle wall rock and aqueous SiO 2 -rich melts/fluids derived from slab dehydration or melting (e.g. Kelemen et al 1992;Arai et al 2003Arai et al , 2004, (2) reaction products of interaction between mantle wall rock and silica-rich melts of alkali basaltic origin percolating in the mantle (e.g. Arai et al 2006;Dantas et al 2009), (3) maficultramafic cumulates crystallized at mantle depth (EmbeyIsztin et al 1989;Santos et al 2002;Cvetković et al 2004Cvetković et al , 2007Bali et al 2007) and (4) products of infiltration-crystallization-reaction processes (Wulff-Pedersen et al 1996.…”

Petrography and Geochemistry of the mantle xenoliths: Implications for lithospheric mantle beneath the Japan arcs

“…(Nixon, 1987) 5 6 cm ( ) ( ) ( 1992) (Schiano et al, 1995;Arai et al, 1996Arai et al, , 2004Arai and Kida, 2000) ( Kepezhinskas et al, 1995;Arai et al, 2003a ) (…”