High-MgO lavas from the Keweenawan midcontinent rift near Mamainse Point, Ontario

Abstract

Research Article| November 01, 1988 High-MgO lavas from the Keweenawan midcontinent rift near Mamainse Point, Ontario Jonathan H. Berg; Jonathan H. Berg 1Department of Geology, Northern Illinois University, DeKalb, Illinois 60115 Search for other works by this author on: GSW Google Scholar Kenneth W. Klewin Kenneth W. Klewin 1Department of Geology, Northern Illinois University, DeKalb, Illinois 60115 Search for other works by this author on: GSW Google Scholar Author and Article Information Jonathan H. Berg 1Department of Geology, Northern Illinois University, DeKalb, Illinois 60115 Kenneth W. Klewin 1Department of Geology, Northern Illinois University, DeKalb, Illinois 60115 Publisher: Geological Society of America First Online: 02 Jun 2017 Online ISSN: 1943-2682 Print ISSN: 0091-7613 Geological Society of America Geology (1988) 16 (11): 1003–1006. https://doi.org/10.1130/0091-7613(1988)016<1003:HMLFTK>2.3.CO;2 Article history First Online: 02 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn Email Permissions Search Site Citation Jonathan H. Berg, Kenneth W. Klewin; High-MgO lavas from the Keweenawan midcontinent rift near Mamainse Point, Ontario. Geology 1988;; 16 (11): 1003–1006. doi: https://doi.org/10.1130/0091-7613(1988)016<1003:HMLFTK>2.3.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 SocietyGeology Search Advanced Search Abstract Detailed study of the basal 500 m of the Keweenawan Mamainse Point volcanics in Ontario, Canada, has revealed that the section is dominated by basaltic to picritic lavas with up to 23 wt% MgO. Two stratigraphic suites with distinct chemical characteristics are separated by four flows of high-TiO2 ferrobasalt containing large and abundant plagioclase spherulites. The focus of this study is on the lower suite that contains the most MgO-rich compositions and that generally has lower TiO2 content. Although most of the flows are olivine-phyric, the olivine phenocrysts are skeletal, suggesting in situ crystallization from magmas with high normative-olivine content. Furthermore, the compositional variation of the lavas does not fall along an olivine-only control line. Taken together, the data indicate that the compositional variation of the lavas represents fractionation of high-MgO liquids rather than accumulation of olivine in basaltic liquids. Most of the fractionation apparently involved crystallization of olivine, clinopyroxene, and Cr-spinel, but later fractionation involved olivine, clinopyroxene, and plagioclase. The occurrence of picritic lavas low in the overall volcanic section is similar to relations in other flood-basalt provinces, and should eventually yield important tectonic and magmatic constraints for the development of the Keweenawan midcontinent rift of North America. 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.