Presenter: Chun-Jung Lin
Date: 2015/11/05
Abstract
Geochemical, petrologic and seismological observations indicate that there may be high concentrations of water in the region above a subducting slab,causing dehydration of subducting lithosphere and is likely to transport fluid into the mantle wedge, which could decrease the viscosity of the mantle locally by several orders of magnitude on top of the subducting slab. Using numerical models, the influence of low viscosity wedges and channels on subduction zone structure can be investigated. An isolated low viscosity region in the wedge influences the pressure field and pattern and vigor of flow within the wedge and slab, which in turn affects topography and gravity. Two parameters of the LVW strongly affect the slab's geometry: the viscosity reduction and its maximum depth. The deeper the LVW and the larger the viscosity reduction, the steeper the slab dip; the shallower the LVW and the smaller the viscosity reduction, the shallower the slab dip. With time-dependent models, Manea et al.(2007) used time-dependent models to show that LVWs and LVCs have a significant influence on slab evolution. A LVW with a viscosity an order of magnitude smaller than the upper mantle produces different slab geometries for different LVW maximum depths. On the other hand, upper mantle viscosity or the thickness of the overriding plate does not influence slab structure greatly.
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