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Subduction zone evolution and low viscosity wedges and channels

Manea, Vlad and Gurnis, Michael (2007) Subduction zone evolution and low viscosity wedges and channels. Earth and Planetary Science Letters, 264 (1-2). pp. 22-45. ISSN 0012-821X. doi:10.1016/j.epsl.2007.08.030.

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Dehydration of subducting lithosphere likely transports fluid into the mantle wedge where the viscosity is decreased. Such a decrease in viscosity could form a low viscosity wedge (LVW) or a low viscosity channel (LVC) on top of the subducting slab. Using numerical models, we investigate the influence of low viscosity wedges and channels on subduction zone structure. Slab dip changes substantially with the viscosity reduction within the LVWs and LVCs. For models with or without trench rollback, overthickening of slabs is greatly reduced by LVWs or LVCs. Two divergent evolutionary pathways have been found depending on the maximum depth extent of the LVWand wedge viscosity. Assuming a viscosity contrast of 0.1 with background asthenosphere, models with a LVWthat extends down to 400 km depth show a steeply dipping slab, while models with an LVWthat extends to much shallower depth, such as 200 km, can produce slabs that are flat lying beneath the overriding plate. There is a narrow range of mantle viscosities that produces flat slabs (5 to 10×10^(19) Pa s) and the slab flattening process is enhanced by trench rollback. Slab can be decoupled from the overriding plate with a LVC if the thickness is at least a few 10 s of km, the viscosity reduction is at least a factor of two and the depth extent of the LVC is several hundred km. These models have important implications for the geochemical and spatial evolution of volcanic arcs and the state of stress within the overriding plate. The models explain the poor correlation between traditional geodynamic controls, subducting plate age and convergence rates, on slab dip.We predict that when volcanic arcs change their distance from the trench, they could be preceded by changes in arc chemistry.We predict that there could be a larger volatile input into the wedge when arcs migrate toward the trench and visa-versa. The transition of a subduction zone into the flat-lying regime could be preceded by changes in the volatile budget such that the dehydration front moves to shallower depths. Our flat-slab models shed some light on puzzling flat subduction systems, like in Central Mexico, where there is no deformation within the overriding plate above the flat segment. The lack of in-plane compression in Central Mexico suggests the presence of a low viscosity shear zone above the flat slab.

Item Type:Article
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Gurnis, Michael0000-0003-1704-597X
Additional Information:© 2007 Elsevier B.V. Received 6 December 2006; revised 2 July 2007; accepted 27 August 2007. Editor: C.P. Jaupart. Available online 17 September 2007. We thank L. Baker, P. Asimow, R. Clayton, D. Helmberger, and M. Chen for discussions. This is contribution number 9159 of the Division of Geological and Planetary Sciences and 55 of the Tectonics Observatory. Principal support provided through the Caltech Tectonics Observatory by the Gordon and Betty Moore Foundation and supplemented by NSF grants EAR-0205653 and EAR- 0609707. All calculations carried out on the Caltech Geosciences Supercomputer Facility partially supported by NSF EAR-0521699.
Group:Caltech Tectonics Observatory, Seismological Laboratory
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Gordon and Betty Moore FoundationUNSPECIFIED
Subject Keywords:low viscosity; mantle wedge; flat subduction; dip angle
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Other Numbering System NameOther Numbering System ID
Caltech Tectonics Observatory55
Caltech Division of Geological and Planetary Sciences9159
Issue or Number:1-2
Record Number:CaltechAUTHORS:20101124-085523011
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:21013
Deposited By: Tony Diaz
Deposited On:24 Nov 2010 18:48
Last Modified:09 Nov 2021 00:05

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