The ‘‘Taourirt’’ magmatic province, a marker of the closing stage of the Pan-African orogeny in the Tuareg Shield: review of available data and Sr–Nd isotope evidence Abla Azzouni-Sekkal a , Jean-Paul Li  egeois b, * , Faten Bechiri-Benmerzoug a , Safia Belaidi-Zinet a , Bernard Bonin c a Institut des Sciences de la Terre, Universit e des Sciences et de la Technologie Houari Boumediene, B.P. 2, Dar el Beida, Alger, Algeria b Isotope Geology, Africa Museum, B-3080 Tervuren, Belgium c UPS-CNRS-FRE 2566 ‘‘Orsayterre’’, D epartement des Sciences de la Terre, Universit e de Paris-Sud, F-91405 Orsay Cedex, France Received 2 May 2003; accepted 16 July 2003 Abstract The Tuareg Shield, located between the Archaean to Palaeoproterozoic Saharan metacraton and the West African craton, is composed of 23 recognized terranes that welded together during the Neoproterozoic Pan-African orogeny (750–520 Ma). Final convergence occurred mainly during the 620–580 Ma period with the emplacement of high-K calc-alkaline batholiths, but continued until 520 Ma with the emplacement of alkali-calcic and alkaline high-level complexes. The last plutons emplaced in central Hoggar at 539–523 Ma are known as the ‘‘Taourirt’’ province. This expression is redefined and three geographical groups are identified: the Silet-, Laouni- and Tamanrasset-Taourirts. The Silet-Taourirts are cross-cutting Pan-African island arc assemblages while the two others intrude the Archaean–Palaeoproterozoic LATEA metacraton. The Taourirts are high-level subcircular often nested alkali- calcic, sometimes alkaline, complexes. They are aligned along mega-shear zones often delimiting terranes. Mainly granitic, they comprise highly differentiated varieties such as alaskite (Silet-Taourirts) and topaz–albite leucogranite (Tamanrasset-Taourirts). Different subgroups were defined on the basis of REE patterns and major and other trace elements. The Taourirt province displays a wide transition from dominant alkali-calcic to minor alkaline granite varieties. Sr isotopes indicate that these complexes were affected by fluid circulation during the Ordovician along shear zones probably contemporaneous to the beginning of the Tassilis sandstone deposition. Nd isotope systematic indicates a major interaction with the upper crust during the emplacement of highly differentiated melts, particularly in samples showing seagull wing-shaped REE patterns. On the other hand, all Taourirt plutons are strongly contaminated by the lower crust: e Nd vary from )2to )8 and T DM from 1200 to 1700 Ma. This implies the presence of an old crust at depth, also below the Silet-Taourirts, which are emplaced within Pan-African island arc assemblages. A model is proposed for the genesis of the Taourirt province where reworking of the mega-shear zones, which dissected the LATEA metacraton, pro- voked a linear delamination of the lithospheric mantle, asthenosphere uprise and partial melting of the lower crust (or strong interaction with), giving rise to a mixed source. Ó 2003 Elsevier Ltd. All rights reserved. Keywords: Granite; Taourirt; Pan-African; Hoggar; Tuareg Shield 1. Introduction The end of a major orogenic episode is often marked by a sequence of post-collisional, or post-orogenic, magmatic events, displaying successively: (i) K-rich suites, that can comprise shoshonitic to ultrapotassic compositions; (ii) less potassic alkali-calcic (as defined by Peacock, 1931) or alkaline series, with metaluminous, slightly peraluminous and peralkaline end-members (for reviews, Li egeois, 1998). The sequence is observed in Proterozoic and in Phanerozoic orogenic belts during their subsequent consolidation. It seems to have been active at least since 2.6 Ga, i.e. as early as the Late Archæan (Bonin et al., 1998). The Tuareg Shield (Fig. 1) resulted, during the Pan- African orogeny (850–520 Ma), from the welding of ophiolite-bearing juvenile terranes along or onto * Corresponding author. Tel./fax: +32-2-6502252. E-mail addresses: asazzouni@hotmail.com (A. Azzouni-Sekkal), jean-paul.liegeois@africamuseum.be (J.-P. Li egeois), bbonin@geol.u- psud.fr (B. Bonin). 0899-5362/$ - see front matter Ó 2003 Elsevier Ltd. All rights reserved. doi:10.1016/j.jafrearsci.2003.07.001 Journal of African Earth Sciences 37 (2003) 331–350 www.elsevier.com/locate/jafrearsci