Document generated on 10/02/2021 7:42 p.m. Geoscience Canada Journal of the Geological Association of Canada Journal de l’Association Géologique du Canada Igneous Rock Associations 15. The Columbia River Basalt Group A Flood Basalt Province in the Pacific Northwest, USA Stephen P. Reidel Volume 42, Number 1, Spring 2015 Article abstract The middle Miocene Columbia River Basalt Group (CRBG) is the youngest, URI: https://id.erudit.org/iderudit/1029230ar smallest, and best-preserved continental flood-basalt province on Earth. The CRBG covers ~ 210,000 km2 of the Pacific Northwest, USA near the British See table of contents Columbia border. CRBG consists of ~ 210,000 km3 of basalt that began erupting ~ 16.7 Ma in the southern part of the province with younger eruptions progressively migrating northward; the last eruption occurred at ~ 5 Ma. The Publisher(s) CRBG consists of seven formations. The Steens Basalt is the oldest but the next oldest, the Imnaha Basalt, began erupting near the end of the Steens volcanic The Geological Association of Canada episode. After a short hiatus at the end of the Imnaha Basalt, the Grande Ronde Basalt began to erupt. Both the Picture Gorge Basalt and Prineville Basalt ISSN erupted simultaneously with the Grande Ronde Basalt. The Steens, Imnaha, and Grande Ronde Basalts are the main phase of the eruptions representing ~ 0315-0941 (print) 94% of the CRBG volume. The Wanapum Basalt followed the Grande Ronde 1911-4850 (digital) Basalt, which in turn was followed by the Saddle Mountains Basalt, the final phase of the eruptions. The formations, members and many flows of the CRBG Explore this journal can be identified by using a combination of major, minor and trace element compositions, lithology, magnetic polarity, and stratigraphic position. This allows the aerial extent and volume of the individual flows and groups of flows Cite this article to be calculated and correlated with their respective dykes and vents. The eruption and emplacement rate of the flows has been controversial, with Reidel, S. P. (2015). Igneous Rock Associations 15. The Columbia River Basalt various lines of evidence suggesting that some flows erupted very rapidly and Group: A Flood Basalt Province in the Pacific Northwest, USA. Geoscience others probably erupted over much longer periods of time. The CRBG was Canada, 42(1), 151–168. probably derived from a mantle plume, although this conclusion is controversial. Compositions indicate the CRBG magmas underwent varying degrees of recharge, contamination, and fractionation prior to each eruption. Although the peak eruptions occurred during the middle Miocene Climatic Optimum, at present no significant extinction or environmental consequence has been correlated with the CRBG. All Rights Reserved © The Geological Association of Canada, 2015 This document is protected by copyright law. Use of the services of Érudit (including reproduction) is subject to its terms and conditions, which can be viewed online. https://apropos.erudit.org/en/users/policy-on-use/ This article is disseminated and preserved by Érudit. Érudit is a non-profit inter-university consortium of the Université de Montréal, Université Laval, and the Université du Québec à Montréal. Its mission is to promote and disseminate research. https://www.erudit.org/en/ GEOSCIENCE CANADA Volume 42 2015 151 SERIES Basalt is the oldest but the next oldest, SOMMAIRE the Imnaha Basalt, began erupting near Le Groupe de basaltes du fleuve the end of the Steens volcanic episode. Columbia (CRBG), du Miocène After a short hiatus at the end of the moyen, est la plus jeune, la plus petite Imnaha Basalt, the Grande Ronde et la mieux préservées des provinces de Basalt began to erupt. Both the Picture basaltes de plateau de la planète Terre. Gorge Basalt and Prineville Basalt Le CRBG couvre une superficie d’env- erupted simultaneously with the iron 210 000 km2 dans la portion nord- Grande Ronde Basalt. The Steens, ouest des États-Unis du Pacifique près Imnaha, and Grande Ronde Basalts are de la frontière avec la Colombie-Bri- the main phase of the eruptions repre- tannique. Le CRBG, c’est environ 210 senting ~ 94% of the CRBG volume. 000 km3 de basaltes dont les premiers Igneous Rock Associations The Wanapum Basalt followed the épanchements se sont produits il y a 15. Grande Ronde Basalt, which in turn environ 16,7 Ma dans la portion sud de was followed by the Saddle Mountains la province, les éruptions plus jeunes The Columbia River Basalt Basalt, the final phase of the eruptions. migrant progressivement vers le nord, Group: A Flood Basalt The formations, members and many la dernier s’étant produit il y a environ Province in the Pacific flows of the CRBG can be identified 5 Ma. Le CRBG est constitué de sept by using a combination of major, formations. La formation de basalte de Northwest, USA minor and trace element compositions, Steens est le plus ancienne, mais la lithology, magnetic polarity, and strati- suivante, celle du basalte d’Imnaha est Stephen P. Reidel graphic position. This allows the aerial entrée en éruption près de la fin de extent and volume of the individual l’épisode volcanique de Steens. Près School of the Environment flows and groups of flows to be calcu- une courte pause à la fin de l’épisode Washington State University – Tri-Cities lated and correlated with their respec- du basalte de la formation d'Imnaha, 2710 Crimson Way tive dykes and vents. The eruption and l’éruption du basalte de Grande Ronde Richland, Washington, 99354, USA emplacement rate of the flows has a commencé. Et le basalte de Picture E-mail: [email protected] been controversial, with various lines Gorge et le basalte de Prineville ont of evidence suggesting that some fait éruption en même temps que le SUMMARY flows erupted very rapidly and others basalte de Grande Ronde. Les basaltes The middle Miocene Columbia River probably erupted over much longer de Steens, d’Imnaha, et de Grande Basalt Group (CRBG) is the youngest, periods of time. The CRBG was prob- Ronde forment la principale portion smallest, and best-preserved continen- ably derived from a mantle plume, des éruptions avec environ 94 % du tal flood-basalt province on Earth. The although this conclusion is controver- volume du CRBG. Le basalte de Wana- CRBG covers ~ 210,000 km2 of the sial. Compositions indicate the CRBG pum a succédé au basalte de la Grande Pacific Northwest, USA near the magmas underwent varying degrees of Ronde, puis ce fut le basalte de Saddle British Columbia border. CRBG con- recharge, contamination, and fractiona- Mountains, la phase finale des érup- sists of ~ 210,000 km3 of basalt that tion prior to each eruption. Although tions. Les formations, les membres et began erupting ~ 16.7 Ma in the the peak eruptions occurred during the le nombre de coulées du CRBG peu- southern part of the province with middle Miocene Climatic Optimum, at vent être définis par analyse de leur younger eruptions progressively present no significant extinction or composition en éléments majeurs, migrating northward; the last eruption environmental consequence has been mineurs et traces, leur lithologie, leur occurred at ~ 5 Ma. The CRBG con- correlated with the CRBG. polarité magnétique, et leur position sists of seven formations. The Steens stratigraphique. Ce qui permet d’es- Geoscience Canada, v. 42, http://dx.doi.org/10.12789/geocanj.2014.41.061 © 2015 GAC/AGC® 152 timer l’étendue et le volume de coulées status of the CRBG focusing on the ley region, and through the Coast individuelles, de groupes de coulées, et stratigraphic framework, the areal Range, eventually reaching the Pacific de les relier avec leur cheminée et dikes extent and volume of the lava flows, Ocean where they continued to respectifs. Le taux des flux éruptifs their eruptive history, mode of lava advance onto the continental shelf ainsi que le leur mise en place ont été flow emplacement, current thoughts (Beeson et al. 1979; Niem and Niem sujet à controverse étant donné que on the petrogenesis of the basalt, and 1985). certaines indications suggèrent que cer- finally the impact of these lavas on the The area covered by the taines éruptions ont été très rapides Miocene environment. CRBG is divided by the Blue Moun- alors que d'autres se seraient produites tains into the Oregon Plateau and the sur des périodes beaucoup plus REGIONAL SETTING Columbia Basin (Fig. 1) based on sig- longues. Le CRGB est probablement The CRBG erupted in a back-arc set- nificant differences in the style of issus d’un panache mantellique, mais ting between the Cascade volcanic arc post-CRBG deformation. The Oregon cela demeure controversé. Les compo- and the Rocky Mountains (Fig. 1). The Plateau contains four structural-tecton- sitions relevées indiquent que les mag- flood-basalt lavas cover basement ic regions: (1) the northern Basin and mas du CRBG ont subi à des degrés rocks that record a long and complex Range, (2) the High Lava Plains, (3) the divers, des recharges, des contamina- geologic history beginning in the Pro- Owyhee Plateau, and (4) the Oregon- tions et du fractionnement par cristalli- terozoic with the breakup of the Idaho graben. The Columbia Basin sation avant chaque éruption. Bien que supercontinent Rodinia, followed by covers a broader region and consists les plus fortes éruptions se soient pro- the suturing of Mesozoic accreted ter- mainly of the Yakima Fold Belt and duites durant la période climatique ranes, and deposition and deformation the Palouse Slope. optimum du Miocène moyen, jusqu’à of Paleogene and Neogene sedimenta- présent, aucune extinction significative ry and volcanic rocks. These basement STRATIGRAPHIC FRAMEWORK OF ou répercussion environnementale ont structures became the template for THE COLUMBIA RIVER BASALT été mises en corrélation avec le CRBG.