Paleomagnetic and magnetostructural study of the Gara Djebilet Jurassic magmatic formations (Tindouf Basin, Southwest Algeria)

Abstract

International audienceRecent geochemical analyses and 40Ar/39Ar dating of dolerite sills and dykes and basalt lava flows in southwesternAlgeria (Tindouf, Reggane, Bechar area and Hank basins) showed that these rocks are linked to the CentralAtlantic Magmatic Province (CAMP). The later is one of the largest identified Mesozoic basalt provinces formedapproximately 200 Ma ago as a preamble to the Pangea dismemberment. These data were strong arguments toundertake geological field observations and a sampling for paleomagnetic and magnetic fabric study in CAMPprovince formations. Three long doleritic dykes (198.9 1.8 Ma) in the Tindouf basin were targeted in order topoint out the structural context of their emplacement (magnetic fabric) and to determine a new reliable Mesozoicpole. The magnetic fabric, in almost the whole sampled sections, is defined mainly by clustering of k1 and k2axes on the dyke plane whereas the k3 axis is nearly perpendicular to it. This fabric is therefore interpreted as dueto magma flow. The new Jurassic paleomagnetic pole, of excellent quality, is very close to those obtained fromcoeval detrital Algerian Saharan formations and also close to those recently determined from coeval Morrocan igneousformations. It is very close to the 200 Ma mean NW African pole too. These results represent a considerablecontribution of to a better knowledge of the geodynamical context during this period