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A re-evaluation of basalt-obsidian relations at East Lake Fissure, Newberry Caldera, Oregon

September 1, 1970

Andesite scoria, agglutinate, and small flows formed by thin lava gushes that erupted from East Lake Fissure on the north wall of Newberry Caldera carry numerous inclusions of platy rhyolite, partly melted platy rhyolite, and frothy obsidian. This association of obsidian and “basalt” has been interpreted as the result of intermingling of mafic and siliceous magmas. The locality has been repeatedly cited as an example of a mixed intrusion of the “basalt-rhyolite association.” Field, petrographic, chemical, and experimental evidence suggest, however, that the inclusions of frothy and massive obsidian are melted fragments of platy rhyolite which were ripped from a rhyolite unit forming part of the caldera wall by uncontaminated andesite magma which rose and fountained from the fissure.

Publication Year 1970
Title A re-evaluation of basalt-obsidian relations at East Lake Fissure, Newberry Caldera, Oregon
DOI 10.1130/0016-7606(1970)81[2835:AROBRA]2.0.CO;2
Authors Michael W. Higgins, Aaron C. Waters
Publication Type Article
Publication Subtype Journal Article
Series Title Bulletin of the Geological Society of America
Index ID 70226484
Record Source USGS Publications Warehouse