Comment Comment on “U–Pb baddeleyite ages and geochemistry of dolerite dykes in the Bas Drâa Inlier of the Anti-Atlas of Morocco: Newly identified 1380 Ma event in the West African Craton” by El Bahat et al. André Michard a, ⁎, Dominique Gasquet b a 10, rue des Jeûneurs, 75002 Paris, France b EDYTEM, Université de Savoie, Campus Scientifique, 73376 Le Bourget du Lac, France ARTICLE INFO Article history: Received 28 September 2012 Accepted 28 November 2012 Available online 8 April 2013 Keywords: Baddeleyite Basic dykes Anti-Atlas West African Craton Two important papers have been recently published in Lithos by the same group of authors, both dealing with the pre-Palaeozoic basic dykes that cut across the basement of the Anti-Atlas mountain belt. Kouyaté et al. (2013) consider the Precambrian inliers of the central part of the belt, namely the Zenaga, Iguerda and Ait Melloul inliers, whereas El Bahat et al. (2013) consider the Bas Draa inlier in the south-westernmost part (Fig. 1). These papers report U–Pb baddeleyite (and scarce zircon) dating on samples from the numer- ous basic dykes crosscutting the Palaeoproterozoic basement of the Central and Western Anti-Atlas. Our comment concerns more partic- ularly El Bahat et al.'s (2013) paper. Surprisingly, the ages obtained from the Bas Draa samples are markedly distinct from those of the Zenaga, Iguerda and Ait Melloul inliers. In the latter group, Kouyaté et al. (2013) obtain one date at 2040 ± 2, three other dates around 1655 Ma (1656 ± 9, ca. 1655 and 1654 ± 16 Ma) and finally two dates at ca. 885 Ma. In contrast, El Bahat et al. (2013) obtain two dates of 1380 ± 9 and 1384 ± 6 Ma in the Bas Draa inlier, although using the same U–Pb TIMS method on structurally and geochemically equivalent material. We will discuss the possible origin of this puzzling contrast — a discussion which is overlooked in El Bahat et al. (2013) study. It is possible that the ca. 1380 Ma-old dykes did not intrude the Central Anti-Atlas inliers or were not sampled by Kouyaté et al. (2013), or conversely that none of the 2040, 1655 and 885 Ma-old basic dykes occur in the Bas Draa inlier or that they were not sampled by El Bahat et al. (2013). We consider such a hypothesis unlikely as, i) sampling of numerous dykes was undertaken in the three large inliers of the Central Anti-Atlas by Kouyaté et al. (2013), and ii) the Bas Draa inlier is only 300 km from the Central Anti-Atlas, whose inliers are exposed within a 100 × 50 km area. Since all these inliers are found in the same region of the West African Craton (El Bahat et al., 2013; Kouyaté et al., 2013) or more precisely in its metacratonic fringe (Gasquet et al., 2008), the same sets of basic dykes should be expected in both locations. However, since the new U–Pb baddeleyite ages suggest different sets of dykes in these two inliers it is possible that the baddeleyite geochronometer has been seriously perturbed in the Bas Draa region, as opposed to that in the Central Anti-Atlas. Furthermore, a 2040 Ma baddeleyite age from the Zenaga inlier (i.e., the same age range as nu- merous U–Pb zircon ages measured in the varied inliers of the Central and Western Anti-Atlas) supports the idea of a poorly perturbed U–Pb baddeleyite geochronometer in the Zenaga inlier. This idea is consis- tent with the fact that, i) during the Pan-African orogeny, the Zenaga inlier as well as the Iguerda and Ait Melloul inliers of the Central Anti-Atlas were located in the low grade metamorphic (upper greenschist facies), external zone of the orogen; and ii) during the Variscan collision they were also located in the external zone of the orogenic prism and only affected by low to very-low grade recrystallisation (Ruiz et al., 2008). In contrast, the Bas Draa inlier was also metamorphosed to a relatively low grade by the Pan-African orogeny, but it was much more affected by the Variscan tectono- metamorphic event since it was located much closer to the front of the high-grade internal zones than the Central Anti-Atlas inliers (Fig. 1; Michard et al., 2010; Soulaimani and Burkhard, 2008). At about 315–330 Ma resetting of the mica geochronometers (Bonhomme and Hassenforder, 1985; Gasquet et al., 2004; Magroum, 2001) indicates that the western Anti-Atlas basement underwent considerable heating at this time (>300 °C). Therefore it is likely that during the Variscan event the Bas Draa baddeleyite reacted with hot, Si-bearing hydrothermal fluids to form polycrystalline zircon, resulting in a significant perturbation of the corresponding geochronometer. In contrast baddeleyites in the Central Anti-Atlas and particularly in the Zenaga inlier are unlikely to have undergone such a reaction, at least at a similar grade. Significantly, El Bahat et al. (2013) and Kouyaté et al. (2013) observe that many baddeleyite grains have “frosty” surfaces, which Lithos 174 (2013) 99–100 ⁎ Corresponding author. E-mail addresses: andremichard@orange.fr (A. Michard), dominique.gasquet@univ-savoie.fr (D. Gasquet). Contents lists available at SciVerse ScienceDirect Lithos journal homepage: www.elsevier.com/locate/lithos 0024-4937/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.lithos.2012.11.029