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Science 20 October 1995:
Vol. 270. no. 5235, pp. 458 - 461
DOI: 10.1126/science.270.5235.458
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Reports

Superplasticity in Earth's Lower Mantle: Evidence from Seismic Anisotropy and Rock Physics

Shun-ichiro Karato (1),  Shuqing Zhang,  Hans-Rudolf Wenk

In contrast to the upper mantle, the lower mantle of the Earth is elastically nearly isotropic, although its dominant constituent mineral [(Mg,Fe)SiO(3) perovskite] is highly anisotropic. On the basis of high-temperature experiments on fabric development in an analog CaTiO(3) perovskite and the elastic constants of MgSiO(3) perovskite, the seismic anisotropy was calculated for the lower mantle. The results show that absence of anisotropy is strong evidence for deformation by superplasticity. In this case, no significant transient creep is expected in the lower mantle and the viscosity of the lower mantle is sensitive to grain size; hence, a reduction in grain size will result in rheological weakening.


S.-i Karato and S. Zhang, Department of Geology and Geophysics, University of Minnesota, Minneapolis, MN 55455, USA.
H.-R. Wenk, Department of Geology and Geophysics, University of California, Berkeley, CA 94720, USA.
(1) To whom correspondence should be addressed.


THIS ARTICLE HAS BEEN CITED BY OTHER ARTICLES:
Dislocations and Slip Systems of Mantle Minerals.
P. Cordier (2002)
Reviews in Mineralogy and Geochemistry 51, 137-179
   Full Text »    PDF »
Texture and Anisotropy.
H.-R. Wenk (2002)
Reviews in Mineralogy and Geochemistry 51, 291-329
   Full Text »    PDF »
Some mineral physics constraints on the rheology and geothermal structure of Earth's lower mantle.
D. Yamazaki and S.-i. Karato (2001)
American Mineralogist 86, 385-391
   Abstract »    Full Text »    PDF »
Lateral Variations in Compressional/Shear Velocities at the Base of the Mantle.
M. E. Wysession, A. Langenhorst, M. J. Fouch, K. M. Fischer, G. I. Al-Eqabi, P. J. Shore, and T. J. Clarke (1999)
Science 284, 120-125
   Abstract »    Full Text »


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Science. ISSN 0036-8075 (print), 1095-9203 (online)