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Title

Upper mantle can in-situ fracture: an implication from a cataclastic peridotite xenolith from Megata, Northeast Japan arc.

Authors

Takeuchi, Miyuki; Arai, Shoji

Abstract

A peculiar peridotite xenolith with cataclastic texture was found from Ichinomegata crater, Megata volcano, the Northeast Japan arc. This peridotite xenolith is the same in mineral assemblage and mineral chemistry (olivine, Fo; spinel, Cr/(Cr Al) atomic ratio, 0.2) to some fertile mantle lherzolites, but quite different in texture from all the documented mantle peridotite xenoliths from Ichinomegata and other localities on Earth. The peridotite is a mixture of coarse and fine grains of olivine, orthopyroxene, clinopyroxene, chromian spinel. The coarse mineral grains are angular but never elongated like those in mylonite. All minerals have been fragmented, and the fragmented pyroxenes and chromian spinel form thin streaks in fine-grained olivine-rich matrix. These features indicate that brittle fracturing does occur even in the upper mantle possibly along pre-existing deep-seated faults that have been frequent in the Northeast Japan arc. Some of the fine grains (<100 μm across) of olivine and pyroxenes display strong intra-grain and inter-grain chemical variations; some are more refractory and the others are more evolved in chemistry than the coarse grains. This suggests a possibility of very small degree frictional melting of peridotite upon cataclastic fracturing.

Subjects

JAPAN; MYLONITE; INCLUSIONS in igneous rocks; PERIDOTITE; CATACLASTIC rocks; PYROXENE; SURFACE of the earth

Publication

Mineralogy & Petrology, 2015, Vol 109, Issue 2, p283

ISSN

0930-0708

Publication type

Academic Journal

DOI

10.1007/s00710-015-0365-7

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