RECORDS FROM COAST TO COAST: NEW TOPOGRAPHIC INSIGHTS ACROSS THE PALEOGENE CORDILLERAN HINTERLAND PLATEAU
Volcanic glass from samples proximal to the Sevier thrust front in western Wyoming have δD values ~30‰ lower than other western U.S. locations. Glass from 48-44 Ma samples record progressive δD value decreases totaling 91–102‰ from the paleo-Pacific coast to the southern Absaroka province, a much larger change than we observe today. These substantially D-depleted waters indicate a major topographic culmination in the northern Rockies, coincident with regions of early Eocene volcanism. To the west, from Utah to eastern Nevada, δD values from 42–28 Ma glasses do not change significantly (±3‰) for over 220 km paleo-distance, suggesting substantial moisture recycling on a long-lived high-elevation plateau. To the east, δD values from 35-28 Ma samples decrease by 20-28‰ to the northwest of Florissant, CO, while a comparison of paleo-Gulf coast and central Rockies δD values suggests air mass mixing across the Laramide province. Our data show that 1) a high-elevation plateau existed across the Cordilleran hinterland by early Eocene and controlled regional moisture transport, 2) the plateau edge was defined by a topographic apex near the Sevier thrust front, and 3) hinterland elevations increased by ~500 m due to slab rollback and delamination and remained high throughout the Paleogene.