The Laramide Orogeny: What Were the Driving Forces?

Abstract

The Laramide orogeny is the Late Cretaceous to Paleocene (80 to 55 Ma) orogenic event that gave rise to the Laramide block uplifts in the United States, the Rocky Mountain fold-and-thrust belt in Canada and the United States, and the Sierra Madre Oriental fold-and-thrust belt in east-central Mexico. The Laramide orogeny is believed to post-date the Jurassic and late Early Cretaceous accre-tion of the terranes that make up much of the North American Cordillera, precluding a collisional origin for Laramide orogenesis. Instead, the deformation belt along much of its length likely devel-oped 700–1500 km inboard of the nearest convergent margin. The purpose of this paper is to show, through a review of proposed mechanisms for producing this inboard deformation (retroarc thrusting, “orogenic float ” tectonics, flat-slab subduction and Cordilleran transpressional collision), that the processes responsible for orogeny remain enigmatic.