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    Grain-size distribution in the mantle wedge of subduction zones

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    2011JB008294.pdf (2.379Mb)
    Date
    2011-10-20
    Author
    Wada, Ikuko  Concept link
    Behn, Mark D.  Concept link
    He, Jiangheng  Concept link
    Metadata
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    Citable URI
    https://hdl.handle.net/1912/4893
    As published
    https://doi.org/10.1029/2011JB008294
    DOI
    10.1029/2011JB008294
    Keyword
     Grain-scale permeability; Mantle wedge flow; Mineral grain size; Seismic attenuation; Subduction zone thermal structure 
    Abstract
    Mineral grain size plays an important role in controlling many processes in the mantle wedge of subduction zones, including mantle flow and fluid migration. To investigate the grain-size distribution in the mantle wedge, we coupled a two-dimensional (2-D) steady state finite element thermal and mantle-flow model with a laboratory-derived grain-size evolution model. In our coupled model, the mantle wedge has a composite olivine rheology that incorporates grain-size-dependent diffusion creep and grain-size-independent dislocation creep. Our results show that all subduction settings lead to a characteristic grain-size distribution, in which grain size increases from 10 to 100 μm at the most trenchward part of the creeping region to a few centimeters in the subarc mantle. Despite the large variation in grain size, its effect on the mantle rheology and flow is very small, as >90% of the deformation in the flowing part of the creeping region is accommodated by grain-size-independent dislocation creep. The predicted grain-size distribution leads to a downdip increase in permeability by ∼5 orders of magnitude. This increase is likely to promote greater upward migration of aqueous fluids and melts where the slab reaches ∼100 km depth compared with shallower depths, potentially providing an explanation for the relatively uniform subarc slab depth. Seismic attenuation derived from the predicted grain-size distribution and thermal field is consistent with the observed seismic structure in the mantle wedge at many subduction zones, without requiring a significant contribution by the presence of melt.
    Description
    Author Posting. © American Geophysical Union, 2011. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research 116 (2011): B10203, doi:10.1029/2011JB008294.
    Collections
    • Geology and Geophysics (G&G)
    Suggested Citation
    Journal of Geophysical Research 116 (2011): B10203
     

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