CENOZOIC TOPOGRAPHIC EVOLUTION OF WESTERN-CENTRAL US (Invited Presentation)

The western-central U.S. has experienced a dramatic topographic increase since the Late Cretaceous when the region subsided to below sea level. How and when the region's topography reached the present-day elevation remains unclear. We designed several types (adjoint, forward and hybrid) of data assimilation models to evaluate the topographic contributions from past oceanic subduction, intrusion of hot mantle, and the evolving continental lithosphere since the Mesozoic. We find that 1) the Late Cretaceous-early Cenozoic subsidence in the region was mainly due to dynamic topography associated with the flat Farallon subduction; 2) Disappearance of the Western Interior Seaway and early-Cenozoic uplift were due to dynamic rebound associated with the removal of the flat slab, while the present high elevation of the Intermountain West mostly reflect the effect of increased lithospheric buoyancy due to removal of the dense lower mantle lithosphere by the flat slab; 3) Intrusion of hot materials from the Pacific asthenosphere to the western U.S. upper mantle since the middle Miocene helped to partially maintained the collapsing topography of the extending Basin & Range, with the spatial and temporal pattern of this signal of dynamic uplift consistent with that of the widespread intraplate volcanism.