The Role of History-Dependent Rheology in Plate Boundary Lubrication for Generating One-Sided Subduction |
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Authors: | Michio Tagawa Tomoeki Nakakuki Masanori Kameyama Fumiko Tajima |
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Institution: | (1) Department of Earth and Planetary Systems Science, Graduate School of Science, Hiroshima University, 1-3-1 Kagami-yama, Higashi-Hiroshima 739-8526, Japan;(2) The Earth Simulator Center, Japan Agency for Marine-Earth Science and Technology, 3173-25 Showa-machi, Kanazawa, Yokohama 236-0001, Japan |
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Abstract: | We have developed a two-dimensional dynamical model of asymmetric subduction integrated into the mantle convection without
imposed plate velocities. In this model we consider that weak oceanic crust behaves as a lubricator on the thrust fault at
the plate boundary. We introduce a rheological layer that depends on the history of the past fracture to simulate the effect
of the oceanic crust. The thickness of this layer is set to be as thin as the Earth's oceanic crust. To treat 1-kilometer
scale structure at the plate boundary in the 1000-kilometer scale mantle convection calculation, we introduce a new numerical
method to solve the hydrodynamic equations using a couple of uniform and nonuniform grids of control volumes. Using our developed
models, we have systematically investigated effects of basic rheological parameters that determine the deformation strength
of the lithosphere and the oceanic crust on the development of the subducted slab, with a focus on the plate motion controlling
mechanism. In our model the plate subduction is produced when the friction coefficient (0.004–0.008) of the modeled oceanic
crust and the maximum strength (400 MPa) of the lithosphere are in plausible range inferred from the observations on the plate
driving forces and the plate deformation, and the rheology experiments. In this range of the plate strength, yielding induces
the plate bending. In this case the speed of plate motion is controlled more by viscosity layering of the underlying mantle
than by the plate strength. To examine the setting of the overriding plate, we also consider the two end-member cases in which
the overriding plate is fixed or freely-movable. In the case of the freely-movable overriding plate, the trench motion considerably
changes the dip angle of the deep slab. Especially in the case with a shallow-angle plate boundary, retrograde slab motion
occurs to generate a shallow-angle deep slab. |
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Keywords: | Mantle convection plate motion rheology subduction |
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