A mechanism for mode selection in melt band instabilities
Earth and Planetary Science Letters
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Bercovici, D., & Rudge, J. (2015). A mechanism for mode selection in melt band instabilities. Earth and Planetary Science Letters, 433 139-145. https://doi.org/10.1016/j.epsl.2015.10.051
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 between 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.
Magma transport, mantle dynamics, rock deformation
The authors sincerely thank Sam Butler and Ben Holtzman for thoughtful reviews. Support was provided by the National Science Foundation (NSF, grant EAR-1344538), the Natural Environment Research Council (NERC, grant NE/I023929/1) and Trinity College.
External DOI: https://doi.org/10.1016/j.epsl.2015.10.051
This record's URL: https://www.repository.cam.ac.uk/handle/1810/252485
Creative Commons Attribution 4.0 International License
Licence URL: http://creativecommons.org/licenses/by/4.0/
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