This implies thinning and shearing of the Cordilleran was confined to the fore-arc region. 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. Crustal shortening A study on calcite twinning and carbonate relationships with the Sevier orogenic belt showed that shortening directions were parallel to the thrust faulting, which was an E-W direction. Differential stress magnitudes determined from calcite twinning showed a decreasing trend exponentially toward the craton. Differential stresses causing compressional deformation in the Sevier thrust were greater than 150 MPa. The E-W contraction during the Sevier changed to roughly N-S oblique during the Laramide orogenic event. Sevier shortening has been recorded throughout much of the western United States as far east as Minnesota in the Cretaceous Greenhorn Limestone as preserved by calcite twinning. The distance of stress transfer is roughly equivalent to more than 2000 km. The E-W shortening shown in calcite twinning of the Sevier is parallel to today's principal stresses in the western interior of the North American plate. Sevier volcanism Voluminous volcanism is also associated with the Sevier Orogeny. Volcanic activity can be observed at modern subduction zones, (such as along the west coast of South America) like the one that caused the Sevier Orogeny. Several volcanic flare-ups occurred in the Sierra Nevada arc, associated with the Sevier Orogeny: one from 170 Ma to 150 Ma, and one from 100 Ma to 85 Ma . Volcanic centers migrated generally eastward during the progression of the Sevier and the transition to Laramide deformation, and by the late Cretaceous volcanism related to Farallon Plate subduction could be found as far east as the Colorado Mineral Belt, east of the leading edge of the Sevier fold and thrust belt. Foreland sedimentation As Sevier thrust faults were uplifted, thrust sheet erosion occurred; those eroded sediments were then deposited where accommodation space existed. Dynamic subsidence and flexure due to crustal loading created space where sediments could accumulate. As the Sevier thrusting migrated eastward, the sedimentary basins also migrated eastward. Balanced cross-sections show that significant erosion of