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Formation of the Rocky Mountains, Western United States: A Continuum Computer Model

Peter Bird
Science
New Series, Vol. 239, No. 4847 (Mar. 25, 1988), pp. 1501-1507
Stable URL: http://www.jstor.org/stable/1701852
Page Count: 7
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Abstract

One hypothesis for the formation of the Rocky Mountain structures in Late Cretaceous through Eocene time is that a plate of oceanic lithosphere was underthrust horizontally along the base of the North American lithosphere. The horizontal components of the motion of this plate are known from paleomagnetism, and the edges of the region of flat slab can be estimated from reconstructed patterns of volcanism. New techniques of finite-element modeling allow prediction of the thermal and mechanical effects of horizontal subduction on the North American plate. A model that has a realistic temperature-dependent rheology and a simple plane-layered initial condition is used to compute the consequences of horizontal underthrusting in the time interval 75 million to 30 million years before present. Successful predictions of this model include (i) the location, amount, and direction of horizontal shortening that has been inferred from Laramide structures; (ii) massive transport of lower crust from southwest to northeast; (iii) the location and timing of the subsequent extension in metamorphic core complexes and the Rio Grande rift; and (iv) the total area eventually involved in Basin-and-Range style extension.

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