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Jean-Paul Liégeois
Earth Sciences
Geodynamics and mineral resources
Geodynamics and mineral resources
Publication details
Liégeois, J.P., Latouche, L, Boughrara, M, Navez, J & Guiraud, M. 2003. ‘The LATEA metacraton (Central Hoggar, Tuareg shield, Algeria): behaviour of an old passive margin during the Pan-African orogeny’. Journal of African Earth Sciences 37: 161-190. Amsterdam : Elsevier. I.F. 1.219.
Article in a scientific Journal / Article in a Journal
Historically, the Tuareg shield is divided into three parts bordered by mega-shear zones with the centre, the Central Polycyclic Hoggar, characterized by Archaean and Palaeoproterozoic lithologies. Nearly 10 years ago, the Tuareg shield was shown to be composed of 23 displaced terranes (Black et al., 1994) whose relationships were deciphered in Aïr to the SE (Liégeois et al., 1994). The Polycyclic Central Hoggar terranes were characterized by the presence of well preserved Archaean / Palaeoproterozoic and Neoproterozoic lithologies.
We show here that the terranes from Central Hoggar (Laouni, Azrou-n-Fad, Tefedest, Egéré-Aleksod) belonged to a single old passive margin, to which we gave the acronym name LATEA, which behaved as a craton during the Mesoproterozoic and the Early-Middle Neoproterozoic but was partly destabilized and dissected during the Late Neoproterozoic as a consequence of its involvement as a passive margin in the Pan-African orogeny.
The early Pan-African phase consisted of thrust sheets including garnet-bearing lithologies (eclogite, amphibolite, gneiss) that can be mapped and correlated in three LATEA terranes. In the Tin Begane area, P-T-t paths have been established from >15 kbar - 790°C (eclogite) to 4 kbar - 500°C (greenschist retrogression) through 12 kbar - 830°C (garnet amphibolite) and 8 kbar - 700°C (garnet gneiss), corresponding to the retrograde path of a Franciscan-type loop. Sm-Nd geochronology on minerals and laser ablation ICP-MS on garnet show the mobility of REE, particularly LREE, during the retrograde greenschist facies that affects, although slightly, some of these rocks. The amphibolite facies metamorphism has been dated at 685 ± 19 Ma and the greenschist facies at 522 ± 27 Ma. During the thrust phase, the Archaean-Palaeoproterozoic basement was only locally affected by the Pan-African tectonics. LATEA behaved as a craton. Other juvenile terranes were also thrust early onto LATEA: the Iskel island arc at c. 850 Ma to the west of LATEA, the Serouenout terrane in the 700 - 620 Ma age range to the east. No subduction-related magmas have intruded LATEA during this epoch, which behaved as a passive margin.
During the main Pan-African phase (625-580 Ma), LATEA was dissected by mega-shear zones that induced several hundreds km of relative displacement and allowed the emplacement of high-K calc-alkaline batholiths.