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Physical model of source region of subduction zone volcanics

Davies, J. Huw and Stevenson, David J. (1992) Physical model of source region of subduction zone volcanics. Journal of Geophysical Research B, 97 (B2). pp. 2037-2070. ISSN 0148-0227. doi:10.1029/91JB02571.

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The thermal structure of a generic subduction zone is investigated to elucidate the source region of subduction zone volcanics. The steady state thermal field is evaluated for a model subduction zone where the plates are prescribed by kinematic boundary conditions, such that the subducting slab induces a flow in the mantle wedge. The resulting model suggests that the oceanic crust of the downgoing slab is not melted extensively, if at all, and hence is not the source of subduction zone magmatism (with the possible exception of the special case of very young oceanic crust). The temperature in the mantle wedge is high enough to produce melting at the amphibole-buffered peridotite solidus. It is proposed that the combination of vertical motion of water as a free phase and the transport of hydrous phases (e.g., amphiboles) by the slab-induced mantle wedge flow lead to the net transport of water being horizontal, across the mantle wedge from the slab. Provided the subducting oceanic crust enters the asthenosphere at a velocity > 6(±2) cm/yr, the mantle wedge will be hot enough at the limit of the lateral water transport mechanism to generate melting at the amphibole-buffered solidus. The model was then extended to include the effect of localized sources of buoyancy (melt, residue, etc.) as a stationary body force, to investigate the possibility of reversing the slab-induced flow. Best estimates of the buoyancy sources and appropriate viscosity in the wedge suggest that there is likely to be only a weak modulation of the slab-induced flow unless the slab and wedge are locally decoupled, for instance by shear heating, the presence of water, or dehydration/hydration reactions. If there is decoupling, then it is possible for there to be an appreciable reversal of the slab-induced flow. Such an appreciable reversal of flow, if it persists, leads to cooling of the mantle wedge. Hence flow reversal cannot be a steady state mechanism. Instead it would lead to a cycle in the melting with a period of O(1 m.y.). The time dependence of a model with appreciable flow reversal would be reinforced by the need to clear the wedge of infertile material.

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Stevenson, David J.0000-0001-9432-7159
Additional Information:© 1992 by the American Geophysical Union. Received August 7, 1990; revised May 15, 1991; accepted August 30, 1991. This work was supported by grant EAR8618511 and EAR8816268 from the National Science Foundation. We would like to thank P. Wyllie for his detailed discussion of this paper. Also, D. Bell and T. Duffy provided valuable comments and advice that have improved this paper. H.D. would like to thank Don Anderson, Brad Hater, and Bruce Marsh for encouraging him to investigate this problem, and John Holloway and Don Turcotte for introducing him to interesting twists. We should also like to thank M. Baker, M. Fahnestock, O. Gudmundsson, P. Ihinger, S. King, M. Rutter, J. Saleeby, D. Scott, and R. Stead for their help and stimulating discussions. We would also like to thank R. O'Connell, J. Saleeby, H. Sato, Y. Tatsumi, B. Watson, and S. Wdowinski for providing preprints of their papers, and J. Davidson, P. Wyllie, G. Miller, J. Lister, and A. Nur for reprints of their papers. The most important issues in the paper were brought more clearly to the fore as the result of the comments of two anonymous reviewers and the associate editor B. Marsh. H.D. would also like to acknowledge the support of an NERC postdoctoral fellowship and the use of the facilities of ITG and DES at the University of Cambridge during the final stages of writing up. Sam Lal and Hilary Alberti helped with completing the figures. Contribution 5061, Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena.
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Caltech Division of Geological and Planetary Sciences5061
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ID Code:39058
Deposited By: Tony Diaz
Deposited On:24 Jun 2013 21:54
Last Modified:09 Nov 2021 23:42

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