Active evaporite tectonics and collapse in the Eagle River valley and the southwestern flank of the White River uplift, Colorado

Abstract

This field trip presents field evidence for Neogene evaporite tectonism, dissolution of evaporites, and related collapse in Eagle River valley and along the southwestern flank of the White River uplift. In the Eagle collapse center, Pennsylvanian evaporite flowed to form anticlinal diapirs, dissolved, and disrupted a lower Miocene basaltic plateau originally at elevations as high as 3.35 km by tilting, faulting, and sagging to elevations as low as about 2.1 km. Also in the Eagle collapse center, the 30 × 10-km, homoclinal Hardscrabble Mountain sank into evaporite during Triassic and Permian collapse followed by Neogene(?) tilting and collapse, based on seismic reflection data. Along the southwestern flank of the White River uplift in the northwestern part of the Carbondale collapse center, parts of the Grand Hogback monocline have collapsed northeastward toward a series of strike-elongate extrusive diapirs. The volume of evaporite removed from the Eagle and Carbondale collapse centers during the Neogene (about 2,250 km3 from an area of roughly 4,500 km 2) was calculated by measuring the departure of collapsed basalts from an assumed original basalt plateau. Regional Neo-gene uplift and incision of the Rocky Mountains, which locally began about 8-10 Ma, probably triggered dissolution and collapse. Presently the Colorado River removes a dissolved-solids load of about 1.4 × 109 kg per year from the two collapse centers. © 1999 Geological Society of America.