Thesis
Petrology of Pleistocene andesites and basaltic andesites at Mountain Lakes Wilderness, Oregon
Washington State University
Master of Science (MS), Washington State University
2012
Handle:
https://hdl.handle.net/2376/100949
Abstract
The Mountain Lakes Wilderness Area of southern Oregon encompasses an overlapping cluster of Pleistocene (1.36 – 0.48 Ma) Cascade shield volcanoes. The wilderness area is located west of the Upper Klamath Lake on the boundary of the Klamath Graben, and is contained within the Aspen Lake 7.5’ and Lake of the Woods South 7.5’ Quadrangles. The overlapping shield volcanoes are made up of two distinct groups of lavas defined by major and trace element data as well as 87Sr/86Sr ratios: basaltic andesites enriched in incompatible trace elements, Qbaa and Qbag; and andesites comparatively less enriched, Qag, Qah, Qacm. A third basaltic andesite, Qbak, is similarly depleted and may be parental to the andesites. Andesites are distinguished by the presence of orthopyroxene, occasional clinopyroxene, and high-An plagioclase, while the basaltic andesites have orthopyroxene, occasional olivine, and lower-An plagioclase. The mineral abundances seen are indicative of a drier and hotter basaltic andesite melt and a wetter, cooler andesite melt. This study focuses on whole-rock compositions of the volcanic rocks and detailed textural study and microanalysis of mineral phases, and reaches new conclusions about sources and evolution. The data provide clear evidence for accumulation of plagioclase, and late stage, post-crystallization contamination of andesites by radiogenic continental crust. The identity of the contaminant is not well constrained. The data do not support crystallization of amphibole during evolution of the andesites although a role for amphibole in basaltic andesite genesis cannot be ruled out.
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Details
- Title
- Petrology of Pleistocene andesites and basaltic andesites at Mountain Lakes Wilderness, Oregon
- Creators
- Mathew Clifton Engle
- Contributors
- John A. Wolff (Degree Supervisor)
- Awarding Institution
- Washington State University
- Academic Unit
- Environment, School of the (CAHNRS)
- Theses and Dissertations
- Master of Science (MS), Washington State University
- Publisher
- Washington State University; Pullman, Wash. :
- Identifiers
- 99900524869001842
- Language
- English
- Resource Type
- Thesis