U-Pb baddeleyite ages and geochemistry of dolerite dykes in the Bas Draa Inlier of the Anti-Atlas of Morocco: Newly identified 1380 Ma event in the West African Craton

• Published in: Lithos
• Main Authors: El Bahat, Abdelhakim, Ikenne, Moho, Söderlund, Ulf, Cousens, Brian, Youbi, Nasrrddine, Ernst, Richard, Soulaimani, Abderrahmane, El Janati, M'hamed, Hafid, Ahmid
• Format: Article in Journal/Newspaper
• Language: English
• Published: Elsevier 2013
• Subjects: Geology; West African Craton; Anti-Atlas (Morocco); Mafic dykes; U-Pb; geochronology; Mesoproterozoic; Columbia (Nuna); Anabar; Greenland; Siberia
• Online Access: https://lup.lub.lu.se/record/3975587; https://doi.org/10.1016/j.lithos.2012.07.022

In the Bas-Draa Inlier (Anti-Atlas, Morocco), the Paleoproterozoic basement which is cut by the Ediacaran Taourgha granite is also crosscut by numerous dykes of a variety of trends, mostly of uncertain age. Two doleritic dykes are dated by the ID-TIMS U-Pb method on baddeleyite and yield emplacement ages of 1381 +/- 8 Ma (MSWD = 0.84) and 1384 +/- 6 Ma (MSWD = 1.4) determined for a N135 degrees E and a N40 degrees E trending dyke, respectively. These dates represent the first geochronological evidence of a Mesoproterozoic magmatic event in the Anti-Atlas. This magmatic event falls in the previously considered ca 1.7-1.0 Ga (Mesoproterozoic) gap in geological activity in the Anti-Atlas. The poorly dated Taghdout and Taarotihate sequences could represent remnants of the ca. 1380 Ma magmatism and rift-related sedimentation. The Mesoproterozoic sedimentary succession of the Atar Group in the Taoudeni basin (Mauritania) could also represent a good candidate for rift-related sedimentation but it postdates the 1380 Ma magmatic event by 270 Ma. The dated 1380 Ma dykes are transitional to mildly alkaline basalts, not unlike some Hawaiian lavas. However, these dykes have a distinct negative Nb anomaly (a common features in many Large Igneous Provinces, LIPs), and this requires interaction with the lithosphere. This interaction may have occurred at the level of the lithospheric mantle or the crust. These newly dated 1380 Ma dykes may converge to the north, speculatively suggesting a magmatic center (associated with a 1380 Ma mantle plume?) along the northern margin, and possibly linked to rifting and possible breakup on that margin, and also to a regional uplift that largely removed the evidence of a 1380 Ma cover sequence. Contemporaneous 1380-1390 Ma magmatism is reported elsewhere on other crustal blocks, and that in northeastern Laurentia (northern Greenland), northern Siberia (Anabar shield), and Baltica (southern Urals) can be reconstructed with that of the Bas Draa Inlier (Anti Atlas region of the West African ...