geometry & rates of 3d mantle flow in subduction zones
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Geometry & Rates of 3D Mantle Flow in Subduction Zones. Magali I. Billen U.C. Davis Dept. of Geology MARGINS Successor Program Workshop, Feb. 15-17, 2010. MARGINS & Geodynamic Modeling. Models of wedge convection Rheology (deformation mechanisms, fabrics, LPO directions, dynamics) - PowerPoint PPT PresentationTRANSCRIPT
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Geometry & Rates of 3D Mantle Flow in Subduction ZonesMagali I. BillenU.C. DavisDept. of Geology
MARGINS Successor Program Workshop, Feb. 15-17, 2010
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MARGINS & Geodynamic Modeling Models of wedge convectionRheology (deformation mechanisms, fabrics, LPO directions, dynamics)Fluids, petrology...Mostly kinematic slabs & mostly 2D
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How will Geodynamics fit into a MARGINS Successor Program?Develop better tools for...3D & time-dependent modelsDynamic slabs (evolving trench & slab geometry)Coupling & tracking fluid & melt migration flowUnderstanding of special processes ie., subduction initiation, slab detachment, flat slabs...
Were making progress here but it takes time to develop and test the required numerical methods.
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How will Geodynamics fit into a MARGINS Successor Program?2. Integrate modeling with all stages of MARGINS researchGuide deployment of seismic stations, sample collection, etc...Region specific modelsAnalyze/interpret results from various focus sitesGeneric (process-related) & regional models Integrate & interpret multi-disciplinary observations
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Two Illustrative Examples
Ridge-Trench InteractionPhD candidate Erin Burkett
3D Mantle Flow at a Slab EdgeMargarete Jadamec (PhD 2009)
... illustrate two ways in which geodynamic modeling can be even better integrated into a MARGINS successor program.
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Ex. 1: Ridge-Trench InteractionBurkett & Billen, JGR 2009
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Detachments & Plate StrengthDetachment: integrated strength of subducted lithosphere => less than stress from sinking slabplate age & rock yield strength.
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Regions With Slab Detachment?Costa Rica (continued sub.) & Baja Calif. (halted sub.)What are effects of 3D geometry?
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3D Ridge-Trench Interaction TemperatureisosurfaceSlabviscosityisosurfaceridgetrench
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3D Ridge-Trench InteractionSide viewFront view
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3D Ridge-Trench InteractionSlab sinking induces complex 3D flow & interaction with approaching ridge & small-scale instabilities.
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Ex. 2: 3D Flow Models of Alaska Detailed regional model (2 km resolution).Slab shape constructed from seismic observations.
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Geometry of 3D Flow at a Slab Edge Corner-flow dominates away from slab edge.Slab is steepening (sinking back & down).Toroidal flow around slab edge (slab-parallel flow).
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Decoupling of Plate & Mantle Flow Pacific plate motion matches observations. Speed and direction.Mantle flows at rates of up to 90 cm/yr.Slab-parallel component near slab edge ~ 10 cm/yr.Significant decoupling of mantle flow from plates.
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Evidence For Fast Mantle FlowCosta Rica: tracking isotopic signature transport along arc.6.5 - 19.0 cm/yrSub. Rate: 8.5 cm/yrHoernle et al., Nature 2008.
If slab-parallel component is fraction (10 %) of mantle flow, predicts mantle flow rates of > 65 cm/yr
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ISA orientation, LPO & SKS Fast-Axis ISA can be non-parallel to mantle flow wedge, slab edge. -- need B-type fabric in wedge nose.ISA match observations of SKS fast-axis orientations (from Christensen & Abers, 2009).
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ISA Sensitive to Rheology & Geometry Need broad (strategic) distribution of observationsCan distinguish successful models from unsuccessful
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3D Geometry of ISA OrientationHighly variable orientations in the mantle wedge: shallow horizontal, dipping slab-parallel, middle dipping and...
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3D Geometry of ISA OrientationsNeed: Better calculation of LPO from flow (A,B...)3D analysis of seismic anisotropy data & model results.Slab-parallelstretching
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ConclusionsMany opportunities to use dynamic modeling to integrate observations & test hypothesis,to help plan other experiments & observations.
Need to create a strategy for development of better numerical methods for future MARGINS sceince.What tools do we need most now?How do we create these tool in tandem with collection & interpretation of data (field or laboratory-based)? How do we leverage work being done by CIG (Computational Infrastructure for Geodynamics)?