Influence of Compaction Length on Radial Melt Segregation in Torsionally Deformed Partially Molten Rocks

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Abstract

To investigate the influence of compaction length on radial melt segregation during torsional shear deformation of partially molten rocks, experiments were performed on samples composed of olivine plus ∼7 vol.% of either an albite, alkali basalt, or lithium silicate melt. These three melts cover a range of three orders of magnitude in viscosity, yielding samples that vary by approximately two orders of magnitude in compaction length. Samples were deformed in torsion at 1,473 K and 300 MPa in constant strain rate experiments to outer-radius shear strains of up to 14.3. Radial melt segregation occurred toward the axial center in all three types of samples that were sheared to γ(R) ≥ 4. At the same strain, samples with the largest compaction length exhibited the highest segregation rate, while samples with intermediate and smallest compaction lengths exhibited similar segregation rates. The experimental observations qualitatively agree with previously published results from two-phase flow theory for base-state melt segregation with anisotropic viscosity; specifically, the segregation rate for radial melt segregation increases with increasing compaction length. However, quantitatively, the segregation rate in experiments is smaller than the rate predicted by simulations for the same compaction length. This discrepancy may, for example, reflect the difference in rheological behavior between that observed in our experiments (non-Newtonian, dislocation-accommodated creep) and that incorporated into the numerical models (Newtonian, diffusion-accommodated creep). Our results thus provide a baseline for testing current and future models of two-phase flow, particularly as applied to understanding melt migration, segregation, and extraction from Earth's deeper interior.

Original languageEnglish (US)
Pages (from-to)4400-4419
Number of pages20
JournalGeochemistry, Geophysics, Geosystems
Volume19
Issue number11
DOIs
StatePublished - Nov 2018

Bibliographical note

Funding Information:
Richard Katz provided insightful comments that significantly improved this paper. The authors are very thankful to Mark Zimmerman, Lars Hansen, Yong-hong Zhao, and Mateˇj Pecˇ for their help with experiments and analyses, to Yasuko Takei for stimulating discussions, and to Yan Liang and Clint Conrad for providing the alkali basalt. Reviews by John Rudge and Marc Spiegelman helped significantly to improving this manuscript. Support from NSF grant EAR-1520647 is gratefully acknowledged. Electron microprobe analyses were carried out with help from Anette von der Handt on JEOL JXA-8900R at the Electron Microprobe Laboratory, Department of Earth Sciences, University of Minnesota-Twin Cities. Full-size optical micrographs are available on the data repository of University of Minnesota (https://doi.org/10.13020/D67D5M).

Funding Information:
Richard Katz provided insightful comments that significantly improved this paper. The authors are very thankful to Mark Zimmerman, Lars Hansen, Yong-hong Zhao, and Mat?j Pe? for their help with experiments and analyses, to Yasuko Takei for stimulating discussions, and to Yan Liang and Clint Conrad for providing the alkali basalt. Reviews by John Rudge and Marc Spiegelman helped significantly to improving this manuscript. Support from NSF grant EAR-1520647 is gratefully acknowledged. Electron microprobe analyses were carried out with help from Anette von der Handt on JEOL JXA-8900R at the Electron Microprobe Laboratory, Department of Earth Sciences, University of Minnesota-Twin Cities. Full-size optical micrographs are available on the data repository of University of Minnesota (https://doi.org/10.13020/D67D5M).

Publisher Copyright:
©2018. American Geophysical Union. All Rights Reserved.

Copyright:
Copyright 2019 Elsevier B.V., All rights reserved.

Keywords

  • compaction length
  • melt segregation
  • partial melts
  • torsion

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