KARROO DOLERITES OF THE UNION OF SOUTH AFRICA

Abstract

Research Article| April 01, 1949 KARROO DOLERITES OF THE UNION OF SOUTH AFRICA FREDERICK WALKER; FREDERICK WALKER UNIVERSITY OF CAPE TOWN, RONDEBOSCH, S. AFRICA. Search for other works by this author on: GSW Google Scholar ARIE POLDERVAART ARIE POLDERVAART UNIVERSITY OF CAPE TOWN, RONDEBOSCH, S. AFRICA. Search for other works by this author on: GSW Google Scholar GSA Bulletin (1949) 60 (4): 591–706. https://doi.org/10.1130/0016-7606(1949)60[591:KDOTUO]2.0.CO;2 Article history received: 13 May 1947 first online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation FREDERICK WALKER, ARIE POLDERVAART; KARROO DOLERITES OF THE UNION OF SOUTH AFRICA. GSA Bulletin 1949;; 60 (4): 591–706. doi: https://doi.org/10.1130/0016-7606(1949)60[591:KDOTUO]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 Karroo dolerites represent the intrusive phase of the early Jurassic basalts which built up the Basutoland lava plateau. Those in the Union of South Africa are described.Both basalts and dolerites are of tholeiitic magma type and are characterized by low Fe2O3 and alkalies. Most of the dolerites show little differentiation, but olivine rich types and acidic veins and schlieren are recorded. The differentiation trend was toward moderate iron enrichment. The magma was extremely active toward the associated sedimentary rocks causing widespread rheomorphic and syntectic phenomena. Many of the rocks previously described as "diorite" or "granophyre" were found to be transfused siltstones.The dolerites occur chiefly as sills, dikes, and inclined sheets, but "bell-jar" intrusions occur near the focus of activity southwest of Basutoland.The mechanism of intrusion is discussed. The authors believe that the Karroo dolerites were injected under conditions of tension following the buckling of the Samfrau geosyncline and represent only one phase of the pronounced igneous activity which spread over a large portion of Gondwanaland during Trias-Jura time. 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.