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Late Cenozoic regional collapse due to evaporite flow and Dissolution in the Carbondale Collapse Center, West-Central Colorado

Mountain Geologist

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Abstract

Dissolution and flow of Pennsylvanian evaporitic rocks in west-central Colorado created the Carbondale Collapse Center, a 450 mi2 structural depression with about 4,000 ft of vertical collapse during the late Cenozoic. This paper describes evidence of collapse in the lower Roaring Fork River valley. Both the lateral extent and amount of vertical collapse is constrained by deformed upper Cenozoic volcanic rocks that have been correlated using field mapping, 40Ar/39Ar geochronology, geochemistry, and paleomagnetism. The Carbondale Collapse Center is one of at least two contiguous areas that have experienced major evaporite tectonism during the late Cenozoic. Historic sinkholes, deformed Holocene deposits, and modern high-salinity loads in the rivers and thermal springs indicate the collapse process continues today. Flow of evaporitic rocks is an important element in the collapse process, and during initial stages of collapse it was probably the primary causative mechanism. Dissolution, however, is the ultimate means by which evaporite is removed from the collapse area. As the Roaring Fork River began to rapidly down-cut through a broad volcanic plateau during the late Miocene, the underlying evaporite beds were subjected to differential overburden pressures. The evaporitic rocks flowed from beneath the upland areas where overburden pressures remained high, toward the Roaring Fork River Valley where the pressures were much lower. Along the valley the evaporitic rocks rose upward, sometimes as diapirs, forming or enhancing a valley anticline in bedrock and locally upwarping Pleistocene terraces. Wherever the evaporites encountered relatively fresh ground water, they were dissolved, forming underground voids into which overlying bedrock and surficial deposits subsided. The saline ground water eventually discharged to streams and rivers through thermal springs and by seepage into alluvial aquifers.

Additional Publication Details

Publication type:
Article
Publication Subtype:
Journal Article
Title:
Late Cenozoic regional collapse due to evaporite flow and Dissolution in the Carbondale Collapse Center, West-Central Colorado
Series title:
Mountain Geologist
Volume
38
Issue:
4
Year Published:
2001
Language:
English
Larger Work Type:
Article
Larger Work Subtype:
Journal Article
Larger Work Title:
Mountain Geologist
First page:
193
Last page:
210
Number of Pages:
18