Experimental test of the viscous anisotropy hypothesis for partially molten rocks
Chemical differentiation of rocky planets occurs by melt segregation away from the region of melting. The mechanics of this process, however, are complex and incompletely understood. In partially molten rocks undergoing shear deformation, melt pockets between grains align coherently in the stress fi...
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| Published in: | Proceedings of the National Academy of Sciences - PNAS Vol. 112; no. 41; pp. 12616 - 12620 |
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| Main Authors: | , , , , , |
| Format: | Journal Article |
| Language: | English |
| Published: |
United States
National Academy of Sciences
13-10-2015
National Acad Sciences |
| Subjects: | |
| Online Access: | Get full text |
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| Summary: | Chemical differentiation of rocky planets occurs by melt segregation away from the region of melting. The mechanics of this process, however, are complex and incompletely understood. In partially molten rocks undergoing shear deformation, melt pockets between grains align coherently in the stress field; it has been hypothesized that this anisotropy in microstructure creates an anisotropy in the viscosity of the aggregate. With the inclusion of anisotropic viscosity, continuum, two-phase-flow models reproduce the emergence and angle of melt-enriched bands that form in laboratory experiments. In the same theoretical context, these models also predict sample-scale melt migration due to a gradient in shear stress. Under torsional deformation, melt is expected to segregate radially inward. Here we present torsional deformation experiments on partially molten rocks that test this prediction. Microstructural analyses of the distribution of melt and solid reveal a radial gradient in melt fraction, with more melt toward the center of the cylinder. The extent of this radial melt segregation grows with progressive strain, consistent with theory. The agreement between theoretical prediction and experimental observation provides a validation of this theory. |
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| Bibliography: | ObjectType-Article-1 SourceType-Scholarly Journals-1 ObjectType-Feature-2 content type line 23 Author contributions: C.Q. and D.L.K. designed research; C.Q., D.L.K., R.F.K., and Y.T. performed research; C.Q. analyzed data; and C.Q., D.L.K., R.F.K., and Y.T. wrote the paper. Edited by David Walker, Columbia University, Palisades, NY, and approved September 2, 2015 (received for review July 14, 2015) 1Present address: Department of Earth and Environmental Science, University of Pennsylvania, Philadelphia, PA 19104-6316. |
| ISSN: | 0027-8424 1091-6490 |
| DOI: | 10.1073/pnas.1513790112 |