Timing and Kinematics of Eburnean Tectonics in the Central Reguibat Shield, Mauritania
Schofield, D. I., Horstwood, M. S. A., Pitfield, P. E. J., Crowley, Q. G., et al., Journal of the Geological Society
The Reguibat Shield of north Mauritania comprises a western Archaean terrane dominated by gneisses and granitic rocks and an eastern Eburnean terrane largely made up of Palaeoproterozoic granitic and metasedimentary rocks. These were juxtaposed during the c. 2.1-2.0 Ga Eburnean Orogeny, which formed an approximately north-trending front contiguous with the Eburnean belt of the Leo Shield in equatorial West Africa. Geological surveying in the Sfariat region of the Reguibat Shield has shown that a metamorphosed Palaeoproterozoic continental margin succession has been intruded by and intercalated with synorogenic granitoids and transported SW onto the Archaean foreland during sinistral oblique collision preserved as strongly partitioned D^sub 1^ shortening and D^sub 2^ strike-slip-dominated transpression within the Sfariat Belt. This was subsequently affected by retrogressive dextral transcurrent deformation and the propagation of the en echelon Imarkene and Tmeimichat fault zones. Laser ablation and conventional thermal ionization mass spectrometry U-Pb geochronology were carried out on five samples of granitic rock and migmatitic gneiss from the region, which reveal that anatexis and sinistral transpression took place between c. 2117 and 2064 Ma. Timing and kinematics of the Eburnean event in the Reguibat Shield are similar to those for the Leo Shield, which underwent SW-directed sinistral transpression at this time.
The Eburnean Orogeny was a c. 2.1 -2.0 Ga tectonothermal event preserved in the West African Craton (Fig. 1 ) and western part of the Congo Craton (not shown). Eburnean belts occur in the Leo Shield of Côte d'Ivoire, Burkina Faso, Guinea, Senegal, western Ghana, southern Mali and western Niger, and the Reguibat Shield of northern Mauritania and western Algeria, within the dominantly Pan-African Hoggar Shield. In all cases juvenile Palaeoproterozoic supracrustal, basaltic and granitic rocks are juxtaposed against Mesoarchaean to Palaeoproterozoic crystalline basement (Fig. 1; e.g. Rocci et al. 1991; Taylor et al. 1992; Zhao et al. 2002).
Owing to the juvenile nature of most of the accreted rocks, the Eburnean Orogeny is thought of as being the culmination of a major episode of crustal growth (e.g. Abouchami et al. 1990; Boher et al. 1992; Taylor et al. 1992) related to the assembly of a pre-Rodinia, Palaeo- to Mesoproterozoic supercontinent termed Columbia (Rogers & Santosh 2002; Zhao et al. 2002). The event has also been interpreted in terms of plate-tectonic processes involving cycles of sedimentary basin development accompanied by subduction-related magmatism and collisional tectonics (Bertrand & Jardim de Sa 1990; Feybesse & Milési 1994; Ledru et al. 1994; Zhao et al. 2002; Lahondère et al. 2003).
Much of the current understanding of the Eburnean Orogeny in the West African Craton, in particular the geochronological and tectonic framework, originates from studies of the Leo Shield (see syntheses of Bessoles 1977; Cahen et al. 1984; Wright et al. 1985; Rocci et al. 1991; Zhao et al. 2002). However, much of the Reguibat Shield has recently been surveyed at the 1:200000 scale by both the Bureau de Recherches Géologiques et Minières (BRGM) and the British Geological Survey (BGS) (Schofield et al. 2003; Thiéblemont et al. 2003; Key et al. 2004) as part of World Bank and European Union-funded research programmes in Mauritania.
This paper presents the results of 1:200 000-scale geological surveying and U-Pb geochronology carried out in the Sfariat region of North Mauritania (Fig. 1; Schofield el al. 2003). The Sfariat region encompasses part of the contact zone between the Mesoarchaean basement and Eburnean volcano-sedimentary sequence and granitoids, and has allowed us to investigate the relationships between these two domains, including the timing and kinematics of their juxtaposition, which is discussed in the context of the Leo …
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Publication information: Article title: Timing and Kinematics of Eburnean Tectonics in the Central Reguibat Shield, Mauritania. Contributors: Schofield, D. I. - Author, Horstwood, M. S. A. - Author, Pitfield, P. E. J. - Author, Crowley, Q. G. - Author, et al. - Author. Journal title: Journal of the Geological Society. Volume: 163. Publication date: May 2006. Page number: 549+. © Geological Society Publishing House Jan 2009. Provided by ProQuest LLC. All Rights Reserved.