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SUMMARY:Grain size and rheology as a control for melt transport beneath mi
 d-ocean ridges - Andrew Turner (University of Oxford)
DTSTART:20160606T134500Z
DTEND:20160606T143000Z
UID:TALK66357@talks.cam.ac.uk
CONTACT:INI IT
DESCRIPTION:Authors: A. J. Turner\, R. F. Katz\, and M. D. Behn <br> Abstr
 act: Grain size is a fundamental control on the rheology and permeability 
 of the mantle. These properties\, in turn\, shape the transport and extrac
 tion of melt from the mantle source. It is therefore important to model th
 e continuum grain-size field as a part of two-phase flow calculations that
  aim to capture the full spatial variability of melt transport in the uppe
 r mantle. <br> We first consider a two-dimensional\, single-phase model to
  predict the steady-state grain size beneath a mid-ocean ridge.&nbsp\; The
  model employs a composite rheology of diffusion creep\, dislocation creep
 \, dislocation accommodated grain boundary sliding\, and a brittle stress 
 limiter. Grain size is calculated using the paleowattmeter model of Austin
  & Evans (2007). We investigate the sensitivity of the grain size model to
  parameter variations. Our model predicts that permeability varies by two 
 orders of magnitude due to the spatial variability of grain size within th
 e expected melt region of a mid-ocean ridge. <br> We then consider a two-p
 hase model to test the influence of spatially varying grain size on melt t
 ransport. We find that the rheological coupling of grain size has a greate
 r influence on melt transport than the coupling through permeability. The 
 model predicts that a spatially variable grain-size field can promote focu
 sing of melt towards the ridge axis. This focusing is distinct from the co
 mmonly discussed sub-lithospheric decompaction channel. Furthermore\, our 
 model predicts that the shape of the partially molten region is sensitive 
 to rheological parameters associated with grain size. The comparison of th
 is shape with observations may help to constrain the rheology of the upper
  mantle beneath mid-ocean ridges.
LOCATION:Seminar Room 1\, Newton Institute
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