Effects of stress-driven melt segregation on the viscosity of rocks

Benjamin K. Holtzman, Daniel S.H. King, David L. Kohlstedt

Research output: Contribution to journalArticle

18 Scopus citations

Abstract

We present rheological data on samples of partially molten mantle rocks deformed in torsion at 1200 °C and 300. MPa in a gas-medium deformation apparatus. Samples in which stress-driven melt segregation occurs are significantly weaker than those with a homogeneous melt distribution, with strain rate increased by up to a factor of 6. The degree of melt segregation, which is influenced by the permeability of the sample material (and hence the compaction length), is controlled by changing chromite fraction as a minor solid second phase. In general, a higher degree of melt segregation causes a greater strain rate enhancement. Although we focus here on the steady-state rheological properties, a simple model of the evolution of melt segregation and rheological properties is presented. This model fits well the latter part of the stress-strain evolution but fails to fit the early, transient stages of deformation. One implication is that weakening occurs very quickly due to the emergence of smaller-scale melt bands. The model (constitutive and evolution equations) is designed to be incorporated into geodynamic-scale continuum models to explore the effects of segregation without resolving the length scales of the process directly.

Original languageEnglish (US)
Pages (from-to)184-193
Number of pages10
JournalEarth and Planetary Science Letters
Volume359-360
DOIs
StatePublished - Dec 5 2012

Keywords

  • Mantle rheology
  • Melt migration
  • Viscosity

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