Subducting Slabs Stay Shallow

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Science  10 Nov 2000:
Vol. 290, Issue 5494, pp. 1053
DOI: 10.1126/science.290.5494.1053a

Subduction of crust occurs at plate boundaries and is driven by the pull of the subducting slab into the convective mantle. The gravitational pull, combined with plate collision, creates a subduction zone typically at angles of 30° to 60° relative to horizontal.

In some regions, such as the west coasts of North and South America, the sinking slab levels off at a shallow depth near the crust-mantle boundary and extends horizontally for tens to hundreds of kilometers. Slab pull cannot explain this flat geometry, but van Hunen et al. suggest that a continent overriding a young oceanic crust can. They developed numerical models of a thick continent overriding a passive oceanic crust and, after considering the effects of several parameters, found that mantle strength and viscous heating were particularly important in creating a flat slab. Their models provide a good fit with observations of shallow, flat slabs and define an allowable range of plate velocities, rheological properties, and boundary conditions. — LR

Earth Planet. Sci. Lett. 182, 157 (2000).

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