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Cenozoic Tectonics of Western North America Controlled by Evolving Width of Farallon Slab

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Science  16 Jul 2010:
Vol. 329, Issue 5989, pp. 316-319
DOI: 10.1126/science.1190366

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Abstract

Subduction of oceanic lithosphere occurs through two modes: subducting plate motion and trench migration. Using a global subduction zone data set and three-dimensional numerical subduction models, we show that slab width (W) controls these modes and the partitioning of subduction between them. Subducting plate velocity scales with W2/3, whereas trench velocity scales with 1/W. These findings explain the Cenozoic slowdown of the Farallon plate and the decrease in subduction partitioning by its decreasing slab width. The change from Sevier-Laramide orogenesis to Basin and Range extension in North America is also explained by slab width; shortening occurred during wide-slab subduction and overriding-plate–driven trench retreat, whereas extension occurred during intermediate to narrow-slab subduction and slab-driven trench retreat.

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