Polyphasic tectonic history of the N70° DASA Graben (northern, Niger)

Abstract

Located in northern Niger, the N70° DASA graben is a trough discovered recently in the Tim Mersoï basin. In this study, a tectonic history of the DASA graben was presented based on the combined use of satellite imagery, field observations and measures, available literature and borehole data. These data were used to analyse the sedimentary facies and the tectonic deformations in the DASA graben, and derive their relative chronology. For this purpose, uplift and rift deformations and their interactions with sedimentation were characterized. Overall, the analyses suggest that the DASA graben was affected from the Carboniferous to the Cretaceous by three major tectonic phases: the first phase was an uplifting stage with extension during the Carboniferous to Permian; the second phase was a rifting stage. The mean extension was ~ N160° and dominantly produced ENE-WSW trending normal faults; and the third phase was a postrift stage. It was characterized by a ~ N130° compression. The structural and sedimentological features defined the DASA graben as a particular type of syn-sedimentary basin evolving from a transpressive tectonic regime during the period ranging from Carboniferous to Permian to an extensive tectonic regime during the period ranging from Triassic to Lower Cretaceous. Thus, the second period marked by an extensional regime would probably be related to the initial stage of the opening of the Atlantic Ocean. After this rifting period, the DASA graben was affected by a compressional phase related to the collision between Africa and Europe.

Characterization of the deformation of the Jurassic-Cretaceous deposits of the Toulouk sector (Tim Mersoï basin, North Niger), relation with the uranium mineralizations

“…This structuring has greatly shaped the paleochannels which are very favorable places for the concentration of mineralization. This observation has already been mentioned [12] for the Arlit sector and [18] for the DASA sector. Form [15] these folds would have played a topographic role by creating high zones and depression zones favorable to fluid circulation.…”

“…According to [17], the N70-N80°E and N130-N140°E fault systems would have controlled the sedimentation of the basin during the Carboniferous. At the map scale, the N70° system structures play a dampening role on the operation of N30° trending flexures [10], [18].…”

“…Uranium mineralization in the Tim Mersoï Basin is thought to be hosted in sandstone formations of all series from the Carboniferous to the Lower Cretaceous [18], [19]. It would be directly or indirectly linked to the different volcanic episodes reported by many authors such as [12], [15], [19], [20], [21].…”

“…In the setting of this mineralization, [19], [22], [23] emphasized the circulation of fluids and note that the same mineralizing fluid can be at the origin of post-diagenetic mineralization in Carboniferous and Jurassic formations. Uranium mineralization in the Tim Mersoï Basin is thought to be hosted in sandstone formations of all series from the Carboniferous to the Lower Cretaceous [18], [19]. It would be directly or indirectly linked to the different volcanic episodes reported by many authors such as [12], [15], [19] and [20].…”

“…It should also be noted that this mineralization is often associated with malachite. In the Tim Mersoï Basin, several authors ( [15], [26] and [27] for the Imouraren deposit, [15] for the Tim Mersoï Basin deposits, [18], [19], [24] for the DASA deposit) had shown that Jurassic mineralization (contained in the Tchi2 sandstones) is associated with levels of sandstones rich in organic matter, pyrite or analcime.…”