 Data suggests throughout the Sevier-Laramide thrusting the crust was also uplifted and extended.The modern Chilean subduction is thought to be a parallel model of the Sevier and Laramide events so there are possibly answers to this question in this modern model.Explanations may include a combination of plate motion rates increasing, the underriding oceanic plate becoming younger as the older portion subducts, and thus the underriding plate being hotter and more buoyant.