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Étude structurale du centre de l'Adrar des Iforas (Mali) : mylonites et tectogénèse

Abstract : The Pan-African belt ot the Hoggar and the Adrar des Iforas results from the collision between the West-African Craton and the Pan-African mobile belt. In Mali, the suture zone, an island arc, a batholith and the Adrar des Iforas central zone may be recognized. The latter has been mapped and is the subject of this study. The principal lithostratigraphic units are the following: - the granulitic unit of Iforas (UGI) with eburnéan metamorphism is crosscut by pre-Pan-African doleritic dykes. An unconformable sedimentary cover attests that the UGI was outcropping before the Pan-African orogenesis. - metasediments Middle to Upper Proterozoic in age from passive continental margin. - volcanoclastic metasediments of late Proterozoic age. - a gneissic assemblage (kidalian assemblage) wich results from the deformation and metamorphism in deep conditions of the two first units together with pre-tectonic intrusives. During the D1 deformation phase , the UGI and its autochtonous to allochtonous Upper Proterozoic cover are thrust upon the kidalian assemblage. Structures, microstructures and metamorphic zonation suggest a SSW to NNE direction ofthrusting. The succession of metamorphisms of intermediate pressure (D1a) then high temperature (D1b) is attributed to a mecanism of doubling isotherms associated to thrust tectonics. The other phases are interpreted in terms of contractional folds (D2) and strike-slip faults (D3). Thus, some of the large NS and subvertical mylonitic zones which characterize the Hoggar shield are the result of the superposition of the three phases of deformation. The age of D& is uncertain and could be ca. 700 My. D2 and D3 could have started at 610-600 My and ended at 535 My. A numerical modelling of the collision has been realized. It confirms the relationships between the D2 and D3 phases and the collision between the West-African Craton and the Pan-African mobile belt and reproduces the rotation of shortening direction with time. However, it does not allow to integrate D1 in a continuous process with D2 and D3 and is consistent with the hypothesis of a thrust tectonics prior to the collision. A comparative review of other areas of the Hoggar shield in Algeria indicates that a thrust tectonics took place after the Eburnean and prior to Pan-African. Geochronological and kinematic studies are still necessary to precise the age and shortening directions of these events. Thus, the Hoggar shield remains an ideal area to study the processes of basement reworking.
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Submitted on : Tuesday, January 8, 2013 - 2:50:10 PM
Last modification on : Tuesday, October 19, 2021 - 7:01:25 PM
Long-term archiving on: : Saturday, April 1, 2017 - 1:46:20 AM


  • HAL Id : tel-00771351, version 1


Anne-Marie Boullier. Étude structurale du centre de l'Adrar des Iforas (Mali) : mylonites et tectogénèse. Pétrographie. Institut National Polytechnique de Lorraine - INPL, 1982. Français. ⟨NNT : ⟩. ⟨tel-00771351⟩



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