Regional correlation of Grande Ronde basalt flows, Columbia River basalt group, Washington, Oregon, and Idaho ( USA).

Abstract

The tholeiitic flood basalts of the Columbia River Basalt Group of middle and late Miocene age cover >200 000 km 2 in Washington, Oregon, and Idaho. The most voluminous formation of the Group, the Grande Ronde Basalt, erupted for 2 m.y. from NNW- trending fissure systems concentrated in SE Washington and adjacent Oregon and Idaho. Four magnetostratigraphic units are recognized on the basis of polarity in the Grande Ronde and provide the broad stratigraphic framework for the formation. In this study, major-element chemistry and relative stratigraphic position within the polarity intervals are used to identify and correlate individual flows and sequences of flows within the Grande Ronde Basalt on a regional scale.-from Authors