Grain-size dynamics beneath mid-ocean ridges : implications for permeability and melt extraction
MetadataShow full item record
Grain size is an important control on mantle viscosity and permeability, but is difficult or impossible to measure in situ. We construct a two-dimensional, single phase model for the steady state mean grain size beneath a mid-ocean ridge. The mantle rheology is modeled as a composite of diffusion creep, dislocation creep, dislocation accommodated grain boundary sliding, and a plastic stress limiter. The mean grain size is calculated by the paleowattmeter relationship of Austin and Evans (2007). We investigate the sensitivity of our model to global variations in grain growth exponent, potential temperature, spreading-rate, and mantle hydration. We interpret the mean grain-size field in terms of its permeability to melt transport. The permeability structure due to mean grain size may be approximated as a high permeability region beneath a low permeability region. The transition between high and low permeability regions occurs across a boundary that is steeply inclined toward the ridge axis. We hypothesize that such a permeability structure generated from the variability of the mean grain size may focus melt toward the ridge axis, analogous to Sparks and Parmentier (1991)-type focusing. This focusing may, in turn, constrain the region where significant melt fractions are observed by seismic or magnetotelluric surveys. This interpretation of melt focusing via the grain-size permeability structure is consistent with MT observation of the asthenosphere beneath the East Pacific Rise.
© The Author(s), 2015. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Geochemistry, Geophysics, Geosystems 16 (2015): 925–946, doi:10.1002/2014GC005692.
Suggested CitationGeochemistry, Geophysics, Geosystems 16 (2015): 925–946
The following license files are associated with this item:
Except where otherwise noted, this item's license is described as Attribution-NonCommercial-NoDerivatives 4.0 International
Showing items related by title, author, creator and subject.
Depth‐dependent permeability and heat output at basalt‐hosted hydrothermal systems across mid‐ocean ridge spreading rates Barreyre, Thibaut; Olive, Jean-Arthur; Crone, Timothy J.; Sohn, Robert A. (John Wiley & Sons, 2018-04-20)The permeability of the oceanic crust exerts a primary influence on the vigor of hydrothermal circulation at mid‐ocean ridges, but it is a difficult to measure parameter that varies with time, space, and geological setting. ...
Magmatic focusing to mid-ocean ridges : the role of grain-size variability and non-Newtonian viscosity Turner, Andrew J.; Katz, Richard F.; Behn, Mark D.; Keller, Tobias (John Wiley & Sons, 2017-12-06)Melting beneath mid-ocean ridges occurs over a region that is much broader than the zone of magmatic emplacement that forms the oceanic crust. Magma is focused into this zone by lateral transport. This focusing has typically ...
Poroelastic response of mid-ocean ridge hydrothermal systems to ocean tidal loading : implications for shallow permeability structure Barreyre, Thibaut; Sohn, Robert A. (John Wiley & Sons, 2016-02-26)We use the time delay between tidal loading and exit-fluid temperature response for hydrothermal vents to model the poroelastic behavior and shallow upflow zone (SUZ) effective permeability structure of three mid-ocean ...