Abstract

Radiometric dating of late Cenozoic igneous rocks of the central Oregon Cascade Range has shown that volcanic activity has been strongly episodic, with most lavas erupting during short intervals of 1 or 2 m.y. The strongest activity occurred during middle Miocene time concurrently with eruption of the Columbia River Basalt. Subsequent episodes followed at about 5-m.y. intervals. Preliminary data from other parts of the circum-Pacific area suggest that these same episodes occurred in unison over a large part of the Earth.

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