A mechanism for mode selection in melt band instabilities

Bercovici, David and Rudge, John F. (2016) A mechanism for mode selection in melt band instabilities. Earth and Planetary Science Letters, 433. pp. 139-145. ISSN 0012-821X DOI 10.1016/j.epsl.2015.10.051

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Abstract

The deformation of partially molten mantle in tectonic environments can lead to exotic structures, which potentially affect both melt and plate-boundary focussing. Examples of such structures are found in laboratory deformation experiments on partially molten rocks. Simple-shear and torsion experiments demonstrate the formation of concentrated melt bands at angles of around 20° to the shear plane. The melt bands form in the experiments with widths of a few to tens of microns, and a band spacing roughly an order of magnitude larger. Existing compaction theories, however, cannot predict this band width structure, let alone any mode selection, since they infer the fastest growing instability to occur for wavelengths or bands of vanishing width. Here, we propose that surface tension in the mixture, especially on a diffuse interface in the limit of sharp melt-fraction gradients, can mitigate the instability at vanishing wavelength and thus permit mode selection for finite-width bands. Indeed, the expected weak capillary forces on the diffuse interface lead to predicted mode selection at the melt-band widths observed in the experiments.

Item Type: Article
Uncontrolled Keywords: 2015AREP; IA70
Subjects: 02 - Geodynamics, Geophysics and Tectonics
Divisions: 02 - Geodynamics, Geophysics and Tectonics
07 - Gold Open Access
Journal or Publication Title: Earth and Planetary Science Letters
Volume: 433
Page Range: pp. 139-145
Identification Number: 10.1016/j.epsl.2015.10.051
Depositing User: Sarah Humbert
Date Deposited: 21 Jul 2016 11:17
Last Modified: 21 Jul 2016 11:17
URI: http://eprints.esc.cam.ac.uk/id/eprint/3575

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