Geochemical stratigraphy of the Dooley rhyolite breccia and Tertiary basalts in the Dooley Mountain quadrangle, Oregon

Author

David Neale Whitson, Portland State University

Sponsor

Portland State University. Department of Geology

First Advisor

Marvin H. Beeson

Date of Publication

1988

Document Type

Thesis

Degree Name

Master of Science (M.S.) in Geology

Department

Geology

Language

English

Subjects

Breccia -- Oregon -- Dooley Mountain Region, Basalt -- Oregon -- Dooley Mountain Region, Stratigraphic geology -- Tertiary, Geochemistry -- Oregon -- Dooley Mountain Region

DOI

10.15760/etd.5787

Physical Description

1 online resource (137 p.)

Abstract

The Dooley Rhyolite Breccia in northeast Oregon was erupted between 12 and 16 million years ago, from central vents and linear feeder dikes within the Dooley Mountain quadrangle. The peraluminous, high-silica rhyolites of the formation were erupted over an irregular highland of eroded pre-Tertiary metamorphic rocks locally overlain by intracanyon, Eocene Clarno-type basalt flow(s) . The Dooley Rhyolite Braccia is exposed in a tectonically disrupted, north-south trending graben across the Elkhorn Range. The formation is variable in thickness with maximum thickness exceeding 660 meters in the south and 600 meters in the north half of the quadrangle. Volumetrically the formation is dominated by block lava flows with lessor associated volcaniclastic and pyroclastic rocks. Although initial and waning phases of eruption of the formation produced ash-flow tuffs which extend well beyond the quadrangle boundaries, volcanism within the quadrangle appears to have been primarily effusive. At least nine geochemically distinct rhyolite subunits belonging to four related chemical groups have been identified in the formation stratigraphy which appear to represent unique eruptive episodes. Chronologic geochemical patterns within the formation are consistent with a petrogenetic model of repeated partial melting and eruption from multiple silicic magma chambers in an attenuated continental crust. Basalts correlative with the Powder River Basalt and the Strawberry Volcanics overlie the Dooley Rhyolite Braccia on the north flank of Dooley Mountain. Cale-alkaline basalts correlative with the Strawberry Volcanics are overlain by thoeliitic basalts of uncertain affinity on the south flank of the mountain. These basalt flows on respective flanks of the mountain were not continuous across the quadrangle. Rhyolitic volcanism in the Dooley Mountain quadrangle is contemporary with the strawberry Volcanics and the Picture Gorge Basalt of the Columbia River Basalt Group.

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Comments

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Persistent Identifier

http://archives.pdx.edu/ds/psu/21797

Recommended Citation

Whitson, David Neale, "Geochemical stratigraphy of the Dooley rhyolite breccia and Tertiary basalts in the Dooley Mountain quadrangle, Oregon" (1988). Dissertations and Theses. Paper 3902.
https://doi.org/10.15760/etd.5787