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A tensile, flexural model for the initiation of subduction

Kemp, David V. and Stevenson, David J. (1996) A tensile, flexural model for the initiation of subduction. Geophysical Journal International, 125 (1). pp. 73-94. ISSN 0956-540X. doi:10.1111/j.1365-246X.1996.tb06535.x.

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We argue that subduction may be initiated at passive continental margins without shortening the lithosphere. Overcoming the lithosphere's high compressive strength requires special circumstances, and these make it difficult to explain the nearly complete recycling of old sea-floor. Instead, we present a model that predicts tensile decoupling of the continental and oceanic lithosphere, passive rifting, and foundering of the seafloor beneath material welling up in the rift. This occurs because the lithosphere in a new ocean basin establishes mechanical continuity with the continent at a depth comparable to mid-ocean ridges. Later subsidence at the margin is therefore inhibited by flexure, which implies shear stresses that promote fault slip and tensile stresses necessary to balance the component of the plate's weight directed down the margin slope. We show that this tension can more than offset ridge push. In our model, an important additional tension arises from basal shear tractions resisting the plate's motion away from the mid-ocean ridge, although these tractions cannot be evaluated with confidence. Slip on a high-angle fault decouples the oceanic and continental lithosphere when shear stresses arising from flexure and the applied tension exceed the lithosphere's shear strength under these loads. A passive rift then forms, allowing a mantle column to rise to the height of mid-ocean ridges, over 3 km above the old seafloor, and flow onto the surface in a gravity current. This load flexes the plate downwards, which enhances the flow and lets the old oceanic lithosphere founder. This model is consistent with the presence of oceanic material in continental forearcs and the youth of ophiolites when they are obducted, as both might be explained by rifting a margin and underthrusting the juvenile crust formed there. Boninites in ophiolite complexes and tectonites at their bases show depleted and hydrated geochemistries consistent with the melting of rifted mantle lithosphere that receives volatiles from foundering oceanic crust.

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Stevenson, David J.0000-0001-9432-7159
Additional Information:© 1996 RAS. Accepted 1995 October 11. Received 1995 October 10; in original form 1994 December 5. This work benefited from discussions with numerous colleagues, including Peter Burgess, John Davidson, Jim Dolan, Mike Gurnis, Brad Hacker, Slava Solomatov, Joel Ita, Louis Moresi, and David Peate. Hong-Kie Thio helped us search the Harvard CMT catalogue. Thoughtful reviews were provided by s. Mueller, R. J. Phillips, and s. Stein. This work was generously supported by the James Irvine Foundation. Contribution No. 5481, Division of Geological and Planetary Sciences, California Institute of Technology.
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James Irvine FoundationUNSPECIFIED
Subject Keywords:continental margins; flexure of the lithosphere; ophiolites; rifts; stress distribution; subduction
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Caltech Division of Geological and Planetary Sciences5481
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ID Code:39066
Deposited By: Tony Diaz
Deposited On:25 Jun 2013 16:22
Last Modified:09 Nov 2021 23:42

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