T228 The Columbia River Flood Basalts: New Insights into the Volcanism, Petrology, and Tectonism of a Large Igneous Province: Dedicated to Peter Hooper on His Retirement (Posters)
Wednesday, 5 November 2003
8:00 AM - 12:00 PM
TRANSITION FROM THOLEIITIC FLOOD BASALT MAGMATISM TO CALC-ALKALINE AND ALKALINE VOLCANISM ALONG AN ERUPTIVE AXIS COINCIDENT WITH THE EAST MARGIN OF THE GRANDE RONDE VALLEY, NORTHEASTERN OREGON
Paper number: T228-2
Program: Technical Sessions
Time: 8:00 AM – 12:00 PM
Authors
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Vicki McConnellOregon Department of Geology and Mineral Industries, Portland, OR
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Ian MadinOregon Department of Geology and Mineral Industries, Portland, OR
Abstract
Detailed mapping supplemented by geochemical analysis and Ar/Ar age dates indicate that the east side of the modern Grande Ronde Valley is part of a large volcanic complex that first produced tholeiitic flood basalt (Columbia River Basalt Group lavas) and later evolved to produce calc-alkaline andesite and dacite flows and alkalic trachyandesite and basanite flows (Powder River Volcanic Field lavas). Columbia River Basalt eruptive centers are marked by spatter mounds, diatremes, dikes, and fringing hydrovolcanic breccias. Powder River Volcanic Field calc-alkaline eruptions formed small composite and shield volcanos that largely buried the older CRB vents. About a 3 million year hiatus separates the last flood basalt eruption (the evolved, high silica, iron-rich ferro andesite of Fiddlers Hell) from the first eruption of calc-alkaline andesite and dacite flows.