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Science 3 June 1994:
Vol. 264. no. 5164, pp. 1445 - 1448
DOI: 10.1126/science.264.5164.1445
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Articles

Phase Transitions Between beta and ggr (Mg, Fe)2SiO4 in the Earth's Mantle: Mechanisms and Rheological Implications

D. C. Rubie 1 and A. J. Brearley 2

1 Bayerisches Geoinstitut, Universität Bayreuth, D-95440 Bayreuth, Germany
2 Institute of Meteoritics, Department of Earth and Planetary Sciences, University of New Mexico, Albuquerque, NM 87131, USA.

The mechanisms of the phase transformations between the spinel (ggr) and modified spinel (beta) polymorphs of Mg2SiO4 have been studied experimentally between 15 and 20 gigapascals and 800° to 950°C. The ggr to beta transformation occurs by a shear mechanism, whereas the beta to ggr transformation involves grain-boundary nucleation and interface-controlled growth. These contrasting mechanisms are a consequence of the number of independent slip systems that are available in the respective crystal structures. This result leads to the prediction that in subduction zones and perhaps also rising plumes in the Earth's mantle, the ggr to beta transformation should be accompanied by a transient reduction in strength.

Submitted on January 18, 1994
Accepted on April 11, 1994


THIS ARTICLE HAS BEEN CITED BY OTHER ARTICLES:
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