40Ar/39 Ar ages of late Cenozoic volcanic rocks within and around the Carbondale and Eagle collapse centers, Colorado: Constraints on the timing of evaporite-related collapse and incision of the Colorado River

GSA Special Papers
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Abstract

40Ar/39Ar dating results of 133 samples from 84 late Cenozoic volcanic rocks provide emplacement ages that constrain the timing of evaporite collapse and the incision rates of the Colorado River. Our samples are from areas in west-central Colorado, both within and outside of the Carbondale and Eagle collapse centers. Significant pulses of volcanic activity occurred in the intervals from 24 to 22, 16 to 13, 11 to 9, and 8 to 7 Ma. In addition, small flows, widely spaced in time and space were emplaced during the last 4 m.y. Although individual basaltic flows appear to be chemically and isotopically homogeneous, there are significant geochemical and isotopic differences between flows, even between some flows that apparently have the same age within the limits of analytical precision.

A low-relief early to middle Miocene erosional surface has been postulated in west-central Colorado. Our studies are consistent with the existence of a low-relief paleotopographic surface that is now at a minimum elevation range of 2.9–3.4 km outside areas of collapse. Elevation departures from this range suggest that 1000 m of subsidence due to evaporite removal has locally occurred in the Carbondale and Eagle collapse centers. 40Ar/39Ar ages from downdropped and disrupted basaltic flows in the Carbondale center constrain initial collapse to 13 Ma, the timing of much ofthe evaporite-related collapse to the past 10–8 m.y., and an increase in the rate of collapse during the last 3 m.y.

Ages and elevations of basaltic rocks above the Colorado River in Glenwood Canyon are used to calculate average apparent incision rates for the Colorado River in Glenwood Canyon of 24 mm/k.y. from 7.8 to 3.0 Ma. The average apparent incision rate increased by an order of magnitude to 242 mm/k.y. during the last 3 m.y

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Additional publication details

Publication type Article
Publication Subtype Journal Article
Title 40Ar/39 Ar ages of late Cenozoic volcanic rocks within and around the Carbondale and Eagle collapse centers, Colorado: Constraints on the timing of evaporite-related collapse and incision of the Colorado River
Series title GSA Special Papers
DOI 10.1130/0-8137-2366-3.213
Volume 366
Year Published 2002
Language English
Publisher GSA
Contributing office(s) Florence Bascom Geoscience Center
Description 22 p.
First page 213
Last page 234
Country United States
State Colorado
Other Geospatial Carbondale
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