Natural examples of olivine lattice preferred orientation patterns with a flow-normal a-axis maximum

Tomoyuki Mizukami, Simon R. Wallis, Junji Yamamoto

研究成果: Contribution to journalArticle査読

119 被引用数 (Scopus)

抄録

Tectonic plate motion is thought to cause solid-state plastic flow within the underlying upper mantle and accordingly lead to the development of a lattice preferred orientation of the constituent olivine crystals. The mechanical anisotropy that results from such preferred orientation typically produces a direction of maximum seismic wave velocity parallel to the plate motion direction. This has been explained by the existence of an olivine preferred orientation with an 'a-axis' maximum parallel to the induced mantle flow direction. In subduction zones, however, the olivine a axes have been inferred to be arranged roughly perpendicular to plate motion, which has usually been ascribed to localized complex mantle flow patterns. Recent experimental work suggests an alternative explanation: under conditions of high water activity, a 'B-type' olivine preferred orientation may form, with the a-axis maximum perpendicular to the flow direction. Natural examples of such B-type preferred orientation are, however, almost entirely unknown. Here we document widespread B-type olivine preferred orientation patterns from a subduction-type metamorphic belt in southwest Japan and show that these patterns developed in the presence of water. Our discovery implies that mantle flow above subduction zones may be much simpler than has generally been thought.

本文言語英語
ページ(範囲)432-436
ページ数5
ジャーナルNature
427
6973
DOI
出版ステータス出版済み - 1 29 2004
外部発表はい

All Science Journal Classification (ASJC) codes

  • 一般

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