Graduation Term

2022

Degree Name

Master of Science (MS)

Committee Chair

David H. Malone

Abstract

This project has constructed a detailed bedrock geologic map of the Bald Mountain, Wyoming 7.5-Minute Quadrangle (Scale 1:24,000) and analyzed the occurrence of rare-earth elements (REE’s) in the Cambrian age Flathead and Archean basement. This research advances the scientific understanding of the geology of the Bighorn Mountains and Archean geology of the Wyoming Archean Province (WAP). The structure and geochronology of the Bald Mountain inlier, a region of Archean bedrock that occurs 18.6 miles (~30 km) to the northwest of the greater Bighorns Archean massif, was studied using traditional field mapping and U-Pb isotopic age dating. The goals of this research were to map the Bald Mountain quadrangle to study the Bald Mountain inlier, along with identifying REE’s in the Cambrian age Flathead and Archean basement. This was done to bolster previous REE data on the Flathead and subdivide various phases of the 2.8-3.0 Ga Archean rocks based on rock types, isotope ages, and structural features. This research supports the broader efforts of the Wyoming Geological Survey to complete 1:24,000 scale geologic maps of the state. Mapping the Bald Mountain Quadrangle has revealed three different lithologic phases of the Archean basement, amphibolite and diabase dikes, Flathead and Gros Ventre, Bighorn Dolomite, Madison Limestone, Amsden, and Quaternary landslides. U-Pb isotope data of the Archean basement show ages range from 2879.7±6.7 Ga to 2894.7±7.3 Ga. An alkali feldspar granite was the most prominent phase of the Archean basement, which displayed a strong and consistent fabric of N70oE/70oNW. REE data collected on the Flathead and Archean basement using SEM-EDS shows REE proportions (>35% total REE) largely in monazite, with apatite and zircon having significantly less (<10% total REE).

Access Type

Thesis-Open Access

DOI

https://doi.org/10.30707/ETD2022.20220705065054196065.999967

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