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.

Abstract

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. Kouyate 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 numerous basic dykes crosscutting the Palaeoproterozoic basement of the Central and Western Anti-Atlas. Our comment concerns more particularly 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, Kouyate 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 Kouyate et al. (2013), or conversely that none of the 2040, 1655 and 885 Ma-old