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Journal of Petrology Advance Access published online on November 22, 2007
Journal of Petrology, doi:10.1093/petrology/egm069
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© The Author 2007. Published by Oxford University Press. All rights reserved. For Permissions, please e-mail: journals.permissions@oxfordjournals.org

Insights into Petrological Characteristics of the Lithosphere of Mantle Wedge beneath Arcs through Peridotite Xenoliths: a Review

Shoji Arai* and Satoko Ishimaru

Department of Earth Sciences, Kanazawa University, Kanazawa 920-1192, Japan

Received December 8, 2006; Revised typescript accepted October 12, 2007


  Abstract

The petrological characteristics of peridotite xenoliths exhumed from the lithospheric mantle below the Western Pacific arcs (Kamchatka, NE Japan, SW Japan, Luzon–Taiwan, New Ireland and Vanuatu) are reviewed to obtain an overview of the supra-subduction zone mantle in mature subduction systems. These data are then compared with those for peridotite xenoliths from recent or older arcs described in the literature (e.g. New Britain, Western Canada to USA, Central Mexico, Patagonia, Lesser Antilles and Pannonian Basin) to establish a petrological model of the lithospheric mantle beneath the arc. In currently active volcanic arcs, the degree of partial melting recorded in the peridotites appears to decrease away from the fore-arc towards the back-arc region. Highly depleted harzburgites, more depleted than abyssal harzburgites, occur only in the frontal arc to fore-arc region. The degree of depletion increases again to a degree similar to that of the most depleted abyssal harzburgites within the back-arc extensional region, whether or not a back-arc basin is developed. Metasomatism is most prominent beneath the volcanic front, where the magma production rate is highest; silica enrichment, involving the metasomatic formation of secondary orthopyroxene at the expense of olivine, is important in this region because of the addition of slab-derived siliceous fluids. Some apparently primary orthopyroxenes, such as those in harzburgites from the Lesser Antilles arc, could possibly be of this secondary paragenesis but have been recrystallized such that the replacement texture is lost. The Ti content of hydrous minerals is relatively low in the sub-arc lithospheric mantle peridotites. The K/Na ratio of the metasomatic hydrous minerals decreases rearward from the fore-arc mantle as well as downward within the lithospheric mantle. The lithospheric mantle wedge peridotites, especially metasomatized ones from below the volcanic front, are highly oxidized. Shearing of the mantle wedge is expected beneath the volcanic front, and is represented by fine-grained peridotite xenoliths.

KEY WORDS: mantle wedge; lithospheric mantle; peridotite xenoliths; melting; metasomatism

*Corresponding author. Telephone: 81-76-264-6521. Fax: 81-76-264-6545. E-mail: ultrasa{at}kenroku.kanazawa-u.ac.jp


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