Natural examples of olivine lattice preferred orientation patterns with a flow-normal a-axis maximum
- 1 January 2004
- journal article
- letter
- Published by Springer Science and Business Media LLC in Nature
- Vol. 427 (6973), 432-436
- https://doi.org/10.1038/nature02179
Abstract
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 crystals1,2,3. The mechanical anisotropy that results from such preferred orientation typically produces a direction of maximum seismic wave velocity parallel to the plate motion direction4,5. This has been explained by the existence of an olivine preferred orientation with an ‘a-axis’ maximum parallel to the induced mantle flow direction3,5,6,7,8. In subduction zones, however, the olivine a axes have been inferred to be arranged roughly perpendicular to plate motion9,10,11,12,13, which has usually been ascribed to localized complex mantle flow patterns10,11,12,13. Recent experimental work14 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.Keywords
This publication has 22 references indexed in Scilit:
- Metamorphic evolution of garnet‐bearing ultramafic rocks from the Gongen area, Sanbagawa belt, JapanJournal of Metamorphic Geology, 2003
- Water-Induced Fabric Transitions in OlivineScience, 2001
- A Complex Pattern of Mantle Flow in the Lau BackarcScience, 2001
- Exhuming the Sanbagawa metamorphic belt: the importance of tectonic discontinuitiesJournal of Metamorphic Geology, 1998
- Lattice preferred orientation of olivine aggregates deformed in simple shearNature, 1995
- 40Ar/39Ar mineral age constraints for the tectonothermal evolution of the Sambagawa metamorphic belt, central Shikoku, Japan: a Cretaceous accretionary prismTectonophysics, 1990
- Geology and metamorphic evolution of the Sanbagawa metamorphic belt, JapanGeological Society, London, Special Publications, 1989
- H2OCO2 fluids supplied in alpine-type mantle peridotites: electron petrology of relic fluid inclusions in olivinesEarth and Planetary Science Letters, 1987
- Generation of Seismic Anisotropy in the Upper Mantle along the Mid-Oceanic RidgesNature, 1969
- Seismic Anisotropy of the Uppermost Mantle under OceansNature, 1964