Staff directory
Jean-Paul Liégeois
Earth Sciences
Geodynamics and mineral resources
Geodynamics and mineral resources
Publication details
Azzouni-Sekkal, A, Bonin, B, Benhallou, A, Yahiaoui, R & Liégeois, J.P. 2007. ‘Tertiary alkaline volcanism of the Atakor Massif (Hoggar, Algeria): field, petrological, mineralogical, geochemical, and geodynamical features’. In: Beccaluva, L. Bianchini G. and Wilson M. (eds), Cenozoic volcanism in the Mediterranean area. Series ‘Special Paper’, 418. Boulder : Geological Society of America, pp. 321-340. (PR) DOI: 10.1130/2007.2418(16).
Chapter in an edited book / Article in an edited book
The Atakor massif is a part of the Hoggar volcanic province, which was emplaced on top of a swell initiated during the Cretaceous. Three main episodes of volcanic activity, separated by long-lasting periods of quiescence, are identified since the Miocene. The lava flows and domes were emitted along lithosphere-scale fault zones. With its famous scenery, the Atakor massif is one of the largest (2150 km2) volcanic districts of the province. The distribution of the various rock types is not random. Mafic rocks, abundant in the centre of the massif, become scarce to the south, where only few scarps can be observed. Phonolite occurs only in the Assekrem area, whereas trachyte can be seen everywhere, with a marked enrichment in quartz to the south and the southeast (Tahifet area), where rhyolite is also exposed. From the field and petrological evidence, two magmatic groups are identified. The mafic group is made up of basanite - phonotephrite associations, forming uplifted plateaus, scoria cones and valley-filling lava flows. Mantle amphibole ± mica megacrysts and peridotite enclaves, together with the non-primary chemical compositions, evidence that magmas originate in a HIMU source and that differentiation took place within the upper mantle. The felsic group comprises two diverging trends, a silica-saturated benmoreite - trachyte - rhyolite trend and a silica-undersaturated trachyte - phonolite trend. Sources of the magmas are also of HIMU affinity, but original incompatible trace element compositions are largely modified by feldspar + accessory minerals fractionation. Primary magmas were produced through minor linear delamination along mega-shear zones, mantle decompression and low degrees partial melting at variable depths (110 - 40 km) of upwelling asthenosphere. Discrete volcanic episodes correspond to discrete events of re-activation of fault zones, in response to discrete extensional Neogene events in the ongoing Alpine orogeny in W. Mediterranean induced by Africa-Eurasia collision.