Abstract

The Laramide orogeny had a spatially variable lifespan, which we explain using a geodynamic model that incorporates onset and demise of flat-slab subduction. Laramide shortening and attendant uplift began in southeast California (USA) at ca. 90 Ma, swept to the northeast to arrive in the Black Hills of South Dakota (USA) at ca. 60 Ma, and concluded in South Dakota within ∼10 m.y. During subsequent slab rollback, the areal extent of Laramide deformation decreased as the eastern edge of active deformation retreated to the southwest rapidly from ca. 55 to 45 Ma and more slowly from ca. 45 to 40 Ma, with deformation ultimately ceasing in the southwestern part of the orogen at ca. 30 Ma. Geodynamic modeling of this process suggests that changes in the strength of the North America plate and densification of the Farallon plate played important roles in controlling the areal extent of the Laramide orogen and hence the lifespan of the orogenic event at any particular location in western North America.

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