The evolution of the Central Atlantic Magmatic Province (CAMP) plumbing system and its possible environmental effects during the Triassic-Jurassic transition: Insights from doleritic pipes of the Tindouf basin, SW Algeria

Abstract

Exposed parts of the Central Atlantic Magmatic Province (CAMP) plumbing system, including huge doleritic sills and numerous dykes, are widespread in the northern flank of the Tindouf basin (Algeria). Doleritic pipes, that have never been studied so far, are spatially associated with these sills and dykes and thus supposed of CAMP origin. We present new field, petrographic and geochemical data on the pipe dolerites and other components of the CAMP plumbing system of the northern flank of the Tindouf basin. According to petrographic investigations, doleritic sills and dyke display homogeneous mafic petrographic features, typical of CAMP tholeiites, whereas doleritic pipes show more chemically evolved characteristics with granophyric texture containing an abundance of K-feldspar and quartz. Furthermore, we report for the first time the presence of abundant carbonatitic xenoliths in the pipe dolerites. Geochemically, all the investigated rocks are low-Ti tholeiites that can be subdivided into four groups, three of them correlate well with three (Intermediate, Upper and Recurrent units) of the four units defined in the High Atlas of Morocco, whereas the fourth group, represented by pipe dolerites, show geochemical features that have never been reported before. However, their tholeiitic nature, their association in the field at the same geographic location with CAMP sills, and their trace element patterns, all indicate that pipe dolerites are of CAMP origin, representing the evolved products of Recurrent magmas. Our study suggests that the small anticlines of the northern flank of the Tindouf basin that host doleritic pipes in its cores can be explained as forced folds above igneous intrusions. Finally, the high CO2 and sulfur contents of the pipe dolerites, combined with the emplacement of large sills within Upper Devonian organic-rich shales of Tindouf basin indicate an important emanation of CO2 and sulfuric gases that have contributed to climate change at the Triassic-Jurassic boundary.