Hebert, Laura Baker and Antoshechkina, Paula and Asimow, Paul and Gurnis, Michael (2009) Emergence of a low-viscosity channel in subduction zones through the coupling of mantle flow and thermodynamics. Earth and Planetary Science Letters, 278 (3-4). pp. 243-256. ISSN 0012-821X http://resolver.caltech.edu/CaltechAUTHORS:20090409-112119432
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We use a petrological model (pHMELTS), coupled with a 2D thermal and variable viscosity flow model (ConMan), to describe and compare fundamental processes occurring within subduction zones. We study the thermal state and phase equilibria of the subducting oceanic slab and adjacent mantle wedge and constrain fluid flux. Using a Lagrangian particle distribution to perform thousands of thermodynamically equilibrated calculations, the chemical state of the domain is continuously updated. Compositionally and thermally dependent buoyancy and viscosity terms provide a consistent linkage between the effect of water addition to and flow within the mantle wedge. We present seven model cases that span normal ranges in subducting slab age, convergence velocity, and slab dip angle. In all models, the coupling between chemistry and dynamics results in behavior previously unresolved, including the development of a continuous, slab-adjacent low-viscosity channel (LVC) defined by hydrous mineral stability and higher concentrations of water in nominally anhydrous minerals (NAM). As the LVC evolves to fluid saturation, slab-derived components are able to migrate vertically upwards to the water-saturated solidus, forming a melting region that bounds the top of the LVC. The LVC develops due to fluid ingress into the mantle wedge from the dehydrating slab, and can be responsible for slab decoupling, large-scale changes in the wedge flow field, and a mechanism by which hydrated slab-adjacent mantle material can be transported to the deep mantle. Varying model parameters indicates that slab age and slab dip angle exert primary control over LVC shape and thickness, due to changing fluid release patterns within the slab. Younger slabs tend to have thinner, more uniform LVCs, while older slabs tend to have a thinner LVC at shallow depths with a large increase in LVC thickness at ~100 km depth. Slab convergence velocity appears to have a secondary role in controlling LVC shape.
|Additional Information:||© 2008 Elsevier B.V. Received 15 August 2008. Received in revised form 4 December 2008. Accepted 5 December 2008. Available online 25 January 2009. Editor: R.D. van der Hilst. The authors would like to especially thank Chad Hall for his substantial early work on code and concept development. This work benefited from helpful discussion with V. Manea, M. Chen, B. Hacker, and S. Kidder and from very constructive comments by two anonymous reviewers and editors C. Jaupart and R. van der Hilst. Support provided through the Caltech Tectonics Observatory by the Gordon and Betty Moore Foundation. All calculations carried out on the Caltech Geosciences Supercomputer Facility partially supported by NSF EAR-0521699.|
|Group:||Caltech Tectonics Observatory|
|Subject Keywords:||subduction; low-viscosity channel; coupled models; Costa Rica; Izu-Bonin; Mariana|
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|Usage Policy:||No commercial reproduction, distribution, display or performance rights in this work are provided.|
|Deposited By:||Tony Diaz|
|Deposited On:||23 Apr 2009 21:32|
|Last Modified:||26 Dec 2012 10:56|
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