Regional correlation of Grande Ronde Basalt flows, Columbia River Basalt Group, Washington, Oregon, and Idaho

Abstract

Research Article| November 01, 1986 Regional correlation of Grande Ronde Basalt flows, Columbia River Basalt Group, Washington, Oregon, and Idaho MARGARET T. MANGAN; MARGARET T. MANGAN 1U.S. Geological Survey, M.S. 959, Reston, Virginia 22092 Search for other works by this author on: GSW Google Scholar THOMAS L. WRIGHT; THOMAS L. WRIGHT 2U.S. Geological Survey, Hawaii National Park, Hawaii 96718 Search for other works by this author on: GSW Google Scholar DONALD A. SWANSON; DONALD A. SWANSON 3U.S. Geological Survey, David A. Johnston Cascades Volcano Observatory, 5400 MacArthur Blvd., Vancouver, Washington 98661 Search for other works by this author on: GSW Google Scholar GARY R. BYERLY GARY R. BYERLY 4Department of Geology, Louisiana State University, Baton Rouge, Louisiana 70808 Search for other works by this author on: GSW Google Scholar Author and Article Information MARGARET T. MANGAN 1U.S. Geological Survey, M.S. 959, Reston, Virginia 22092 THOMAS L. WRIGHT 2U.S. Geological Survey, Hawaii National Park, Hawaii 96718 DONALD A. SWANSON 3U.S. Geological Survey, David A. Johnston Cascades Volcano Observatory, 5400 MacArthur Blvd., Vancouver, Washington 98661 GARY R. BYERLY 4Department of Geology, Louisiana State University, Baton Rouge, Louisiana 70808 Publisher: Geological Society of America First Online: 01 Jun 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Geological Society of America GSA Bulletin (1986) 97 (11): 1300–1318. https://doi.org/10.1130/0016-7606(1986)97<1300:RCOGRB>2.0.CO;2 Article history First Online: 01 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn Email Permissions Search Site Citation MARGARET T. MANGAN, THOMAS L. WRIGHT, DONALD A. SWANSON, GARY R. BYERLY; Regional correlation of Grande Ronde Basalt flows, Columbia River Basalt Group, Washington, Oregon, and Idaho. GSA Bulletin 1986;; 97 (11): 1300–1318. doi: https://doi.org/10.1130/0016-7606(1986)97<1300:RCOGRB>2.0.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract The tholeiitic flood basalts of the Columbia River Basalt Group of middle and late Miocene age cover more than 200,000 km2 in Washington, Oregon, and Idaho. The most voluminous formation of the Group, the Grande Ronde Basalt, erupted for 2 m.y. from north-northwest-trending fissure systems concentrated in southeast Washington and adjacent Oregon and Idaho. Four magnetostratigraphic units (designated R1, N1, R2, and N2 from oldest to youngest) 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.Systematic examination of more than 350 analyses from 47 stratigraphic sections show that most flows fall into one of five major chemical groupings, which are distinguished primarily by small but significant variations in MgO, TiO2, and P2O5 content. In addition, four minor chemical types local to the eastern part of the province have been identified. Feeder dikes of each chemical type have also been located.Flows or packets of flows of each chemical type can be correlated between field sections to define specific chemical-stratigraphic subunits. These subunits consist of several flows collectively 30–150 m thick. Subunits of most chemical types are repeated at irregular intervals throughout the formation; no progressive chemical trend occurs within the Grande Ronde.Many of the chemical-stratigraphic subunits extend to the margins of the province, although most are confined to the source region in eastern Washington. Although the total number of subunits is less in the west away from the fissure systems, the total thicknesses of the N2 and R2 magnetostratigraphic units are each as thick or thicker than the corresponding units in eastern Washington. The greatest thicknesses occur in the central part of the province within the Pasco basin.The distribution of basalt relative to the location of vents, as well as the relative east-west thicknesses, suggests that basalt flowed hundreds of kilometres westward during the most voluminous Grande Ronde eruptions, ponding against the irregular margin of the Cascade Range and being diverted through the ancestral Columbia Gorge toward the Washington-Oregon coast. Between these huge sheetflood events, smaller eruptions blanketed areas within the source region, and ongoing regional subsidence created a shallow westward-draining basin in the center of the province. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.