Date Available
4-28-2017
Year of Publication
2017
Document Type
Master's Thesis
Degree Name
Master of Science (MS)
College
Arts and Sciences
Department/School/Program
Earth and Environmental Sciences (Geology)
Advisor
Dr. Frank Ettensohn
Abstract
The West Elk Breccia has been studied since the late 1800’s with many interpretations regarding its origin. One unrecognized possibility is that parts of it are debris-avalanche deposits. This study has recognized evidence for this interpretation at three scales: volcano scale, outcrop scale, and intra-outcrop scale. At the volcano scale, a scarp in the old volcano reveals underlying Mesozoic bedrock, suggesting sector collapse. At the outcrop scale, megablocks of the original edifice, up to hundreds of meters in length, have atypical orientations and are surrounded by a gravel matrix. At the intra-outcrop scale, jigsaw-fit fracturing and rip-up clasts are common in distal deposits, which are documented in analogous debris-avalanche deposits. Similar to the debris-avalanche deposit at Mt. Shasta, medial-to-distal-matrix volcaniclast content decreases by 23%; Paleozoic and Mesozoic clasts increase by 5%; and the size of megablocks decreases. The geochemical and petrographic signatures reveal breccia blocks composed of pyroxene-andesite, a more silicic matrix facies, and the andesitic-to-dacitic East Elk Creek Tuff, all compositions that corroborate previous work on this northern extension of the San Juan volcanic field. Measured sections in the 100-km² study area allow for an estimation of total formation volume of approximately 8.5 km3.
Digital Object Identifier (DOI)
https://doi.org/10.13023/ETD.2017.162
Recommended Citation
Whalen, Patrick J., "THE OLIGOCENE WEST ELK BRECCIA: EVIDENCE FOR MASSIVE VOLCANIC DEBRIS AVALANCHES IN THE EASTERN GUNNISON RIVER VALLEY, WEST-CENTRAL COLORADO, U.S.A." (2017). Theses and Dissertations--Earth and Environmental Sciences. 47.
https://uknowledge.uky.edu/ees_etds/47
