Experimental constraints on the dynamics of the partially molten upper mantle 2. Deformation in the dislocation creep regime

G. Hirth, D. L. Kohlstedt

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Abstract

Experiments have been conducted to investigate the effect of melt on the creep behavior of water-free olivine aggregates deformed in the dislocation creep regime. The influence of the melt phase is modest at melt fractions less than ~0.04. However, at melt fractions >0.04, the creep rate of melt-added samples is enhanced by more than an order of magnitude relative to melt-free aggregates. This unexpectedly large influence of melt on strain rate arises because deformation occurs by grain boundary sliding accommodated by a dislocation creep process. The results of this study indicate that the viscosity of the upper mantle may decrease by at least an order of magnitude if the retained melt fraction exceeds 0.04 or if the onset of melting results in a reduction in grain size and a concomitant transition from (010)[001] to (010)[100] limited creep. -from Authors

Original languageEnglish (US)
JournalJournal of Geophysical Research
Volume100
Issue numberB8
StatePublished - Jan 1 1995

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