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

Island Arc - Tập 12 Số 2 - Trang 233-246 - 2003
Shoji Arai1, Satoko Ishimaru1, Victor M. Okrugin2
1Department of Earth Sciences, Kanazawa University, Kanazawa 920-1192, Japan (email: [email protected]) and
2Department of Physical-Chemical Methods of Research and Mineralogy, Institute of Volcanology, Russian Academy of Science, 683006, Petropavlovsk-Kamchatsky, Russia

Tóm tắt

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.

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Island Arc

Tập 12 Số 2

233-246

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