The Mesozoic Tholeiitic Province of Northwest Africa: A Volcano-Tectonic Record of the Early Opening of Central Atlantic

Abstract

Continental tholeiites (CT) have long attracted the attention of geologists all over the world, and were successively described as “plateau basalts” (Geikie 1903) and “flood basalts” (Tyrrel 1937). They consist of large accumulations of basaltic lava piles of fissural origin associated with extensive dyke swarms and hypabyssal sills, overlaying areas up to thousands of square kilometers, and ranging from Precambrian to Tertiary times, so that, except for ocean floor basalts, they represent the most voluminous volcanics on earth. Most of the CT are considered to be relatively uniform in petrography and chemistry, and are dominantly differentiated basalts. They are classically linked to extensional episodes and often occur during preliminary stages of continental breakup and ocean opening, and are consequently reliable indicators of the evolution of rift systems evolving to ocean formation. Among the largest Phanerozoic continental flood basalts (CFB) provinces, the most famous and best studied examples are the Columbia River (USA), Paraná (South America), Deccan (India), the Siberian Platform, Karoo (southern Africa), Antarctica and the North Atlantic.