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Experimental test of the viscous anisotropy hypothesis for partially molten rocks.

ABSTRACT: 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.

SUBMITTER: Qi C

PROVIDER: S-EPMC4611659 | biostudies-literature | 2015 Oct

REPOSITORIES: biostudies-literature

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Experimental test of the viscous anisotropy hypothesis for partially molten rocks.

Qi Chao C Kohlstedt David L DL Katz Richard F RF Takei Yasuko Y

Proceedings of the National Academy of Sciences of the United States of America 20150928 41

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 mod ...[more]

PMID: 26417107

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Experimental test of the viscous anisotropy hypothesis for partially molten rocks.

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Experimental test of the viscous anisotropy hypothesis for partially molten rocks.

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