Focusing of upward fluid migration beneath volcanic arcs : effect of mineral grain size variation in the mantle wedge
Behn, Mark D.
MetadataShow full item record
We use numerical models to investigate the effects of mineral grain size variation on fluid migration in the mantle wedge at subduction zones and on the location of the volcanic arc. Previous coupled thermal-grain size evolution (T-GSE) models predict small grain size (<1 mm) in the corner flow of the mantle wedge, a downdip grain size increase by ∼2 orders of magnitude along the base of the mantle wedge, and finer grain size in the mantle wedge for colder-slab subduction zones. We integrate these T-GSE modeling results with a fluid migration model, in which permeability depends on grain size, and fluid flow through a moving mantle matrix is driven by fluid buoyancy and dynamic pressure gradients induced by mantle flow. Our modeling results indicate that fluids introduced along the base of the mantle wedge beneath the fore arc are initially dragged downdip by corner flow due to the small grain size and low permeability immediately above the slab. As grain size increases with depth, permeability increases, resulting in upward fluid migration. Fluids released beneath the arc and the back arc are also initially dragged downdip, but typically are not transported as far laterally before they begin to travel upward. As the fluids rise through the back-arc mantle wedge, they become deflected toward the trench due to the effect of mantle inflow. The combination of downdip migration in the fore arc and trench-ward migration in the back arc results in pathways that focus fluids beneath the arc.
Author Posting. © American Geophysical Union, 2015. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geochemistry, Geophysics, Geosystems 16 (2015): 3905–3923, doi:10.1002/2015GC005950.
Showing items related by title, author, creator and subject.
Behn, Mark D.; Hirth, Greg; Elsenbeck, James R. (2009-03-04)We construct a 1-D steady-state channel flow model for grain size evolution in the oceanic upper mantle using a composite diffusion-dislocation creep rheology. Grain size evolution is calculated assuming that grain size ...
Wada, Ikuko; Behn, Mark D.; He, Jiangheng (American Geophysical Union, 2011-10-20)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, ...
Influence of grain size evolution and water content on the seismic structure of the oceanic upper mantle Elsenbeck, James R. (Massachusetts Institute of Technology and Woods Hole Oceanographic Institution, 2007-06)Grain size is an important material property that has significant effects on the viscosity, dominant deformation mechanism, attenuation, and shear wave velocity of the oceanic upper mantle. Several studies have investigated ...