Geochemistry and origin of basalt of the Columbia River Group, Oregon and Washington

Abstract

Research Article| May 01, 1976 Geochemistry and origin of basalt of the Columbia River Group, Oregon and Washington IAN McDOUGALL IAN McDOUGALL 1U.S. Geological Survey, Menlo Park, California 94025 Search for other works by this author on: GSW Google Scholar GSA Bulletin (1976) 87 (5): 777–792. https://doi.org/10.1130/0016-7606(1976)87<777:GAOOBO>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 MailTo Tools Icon Tools Get Permissions Search Site Citation IAN McDOUGALL; Geochemistry and origin of basalt of the Columbia River Group, Oregon and Washington. GSA Bulletin 1976;; 87 (5): 777–792. doi: https://doi.org/10.1130/0016-7606(1976)87<777:GAOOBO>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 Strontium isotope and major- and trace-element data from the voluminous middle Miocene tholeiitic basalts of the Columbia River Group differentiate the lavas stratigraphically and reflect the origin of the basalt. The Picture Gorge Basalt has relatively low Sr87/Sr86 ratios (0.7035 to 0.7039) and a major- and trace-element composition consistent with an origin from the upper mantle. The Picture Gorge Basalt is clearly distinguished from the Imnaha basalt in northeast Oregon and from the widespread, mainly younger Yakima Basalt. The Yakima Basalt, including lava flows in the Vantage, Grande Ronde, and Imnaha regions, forms a relatively coherent geochemical group with moderate to high initial Sr87/Sr86 ratios (0.7045 to 0.7080), which increase with decreasing age of the lava and show an inverse relation with Sr abundance. Possible explanations include progressive contamination of parental mantle—derived magmas by crustal material or derivation from an inhomogeneous upper mantle.It is suggested that the Yakima Basalt formed during a major readjustment episode related to plate motions in an extensional tectonic regime. This caused diapiric upwelling of upper mantle peridotite with formation of great volumes of olivine tholeiite magma, which underwent extensive olivine fractionation. The Columbia Plateau may be a continental analogue of the marginal seas of the western Pacific Ocean. 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.