Date of Award
4-24-2008
Degree Type
Thesis
Degree Name
Master of Science (MS)
Department
Geosciences
First Advisor
Dr. Timothy E. LaTour - Chair
Second Advisor
Dr. Hassan A. Babaie
Third Advisor
Dr. Eirik J. Krogstad
Fourth Advisor
Dr. William J. Fritz
Abstract
Intermediate igneous rocks exposed in the Badger Pass area and 3.5 km away in the McDowell Springs area of Beaverhead County, Montana, previously mapped as Cretaceous intrusive (Ki), and Cretaceous undifferentiated volcanics (Kvu) respectively, exhibit little geochemical variation. Trace element, and lead isotope analyses provide strong evidence allowing for a single source. REE patterns, obtained through ID-ICP-MS, are essentially identical. Mineral/melt Eu analyses reveal that Eu behaved predominantly as a divalent cation, refuting an earlier study asserting that trivalent Eu dominated. Data suggest rocks were formed under low oxygen activity conditions, not oxidizing conditions as previously reported. Geochemical data combined with field mapping allow us to establish the temporal relationship between late Cretaceous thrusting, intrusion, and volcanism in this locale. Folding, faulting and thrusting were significantly, if not entirely, completed prior to the commencement of volcanism. Volcanism included contemporaneous thrust plate intrusion, foreland extrusion, and hypabyssal foreland intrusion.
DOI
https://doi.org/10.57709/1059596
Recommended Citation
Gallagher, Brookie Jean, "A Comparative Study of the Badger Pass Igneous Intrusion and the Foreland Volcanic Rocks of the McDowell Springs Area, Beaverhead County, Montana: Implications for the Local Late Cretaceous Sequence of Events." Thesis, Georgia State University, 2008.
doi: https://doi.org/10.57709/1059596