Sponsor
Portland State University. Department of Earth Science
First Advisor
Marvin H. Beeson
Term of Graduation
Winter 1982
Date of Publication
1-21-1982
Document Type
Thesis
Degree Name
Master of Science (M.S.) in Geology
Department
Earth Science
Language
English
Subjects
Geochemistry -- Oregon -- Mount Hood
DOI
10.15760/etd.3162
Physical Description
1 online resource (2, [vi], 64 pages)
Abstract
The Miocene Rhododendron and Dalles Formations in the Mount Hood area are accumulations of chiefly pyroclastic andesitic material, largely confined to the Dalles-Mount Hood syncline. These very similar units are geographically separated by overlying andesites including the present Mount Hood cone, and past workers have suspected that they may share a common source. Prior to this study, few geochemical data were available for the Rhododendron and the Dalles Formations, compared to the well studied Columbia River basalts underlying them and the overlying Pliocene andesites. This geochemical study was designed to investigate certain aspects of the Rhododendron and Dalles Formations such as their possible common source, how they differ chemically from other andesites in the area, and how they fit into the chemical evolution of the Cascade Mountains.
Sixty-one rocks collected from the Mount Hood area in the field or from drill cuttings were analyzed for trace elements by neutron activation analysis, and twenty-nine were analyzed for major elements by X-ray fluorescence. Several significant aspects of the chemistry of the Rhododendron and Dalles Formations were brought out by the data. The Rhododendron and Dalles Formations are chemically distinct from the overlying andesites and can be typified by rather narrow chemical parameters, and probably do share a common source. The ability to chemically define the top of the Rhododendron Formation is of use in structural modeling in the Mount Hood area. Data reveal definite chemical trends in volcanism in the Mount Hood area during the Neogene, toward a more mafic style of volcanism, and the Rhododendron-Dalles sequence and the Pliocene sequence represent two separate volcanic series along this trend. Trace element evidence suggests that the differences in their chemistry may be attributed to progressive changes in the mechanisms of magma generation in the mantle.
Rights
In Copyright. URI: http://rightsstatements.org/vocab/InC/1.0/ This Item is protected by copyright and/or related rights. You are free to use this Item in any way that is permitted by the copyright and related rights legislation that applies to your use. For other uses you need to obtain permission from the rights-holder(s).
Persistent Identifier
https://archives.pdx.edu/ds/psu/18353
Recommended Citation
Gannett, Marshall W., "A Geochemical Study of the Rhododendron and Dalles Formations in the Area of Mount Hood, Oregon" (1982). Dissertations and Theses. Paper 3166.
https://doi.org/10.15760/etd.3162
Sample locations in the Mt. Hood area
figure1part2.pdf (2299 kB)
Sample locations in The Dalles area
Comments
If you are the rightful copyright holder of this dissertation or thesis and wish to have it removed from the Open Access Collection, please submit a request to pdxscholar@pdx.edu and include clear identification of the work, preferably with URL.