From Pan-African Transpression to Cadomian Transtension at the West African Margin: New U–Pb zircon Ages from the Eastern Saghro Inlier (Anti-Atlas, Morocco)

Abstract

Abstract New U–Pb zircon ages from the Eastern Saghro massif in the Anti-Atlas of Morocco demonstrate a link between Pan-African transpressive collision at c. 600 Ma and transtension caused by the onset of Cadomian subduction and arc development from c. 570 Ma onwards. We present new U–Pb laser ablation inductively coupled plasma mass spectrometry ages of detrital and magmatic zircon from the Saghro, M'Gouna, and Ouarzazate Groups. The siliciclastic deposits of the Saghro Group were deposited in a back-arc setting developed on stretched continental crust of the West African margin. Collision with the Atlas–Meseta domain led to the closure of the back-arc basin before 600 Ma. Time of exhumation and surface exposure of the newly formed Pan-African basement is bracketed to c. 30 Ma owing to the maximum depositional age of 571 ± 4 Ma of the overlying M'Gouna Group. The U–Pb age of 567 ± 4 Ma for the lowermost ignimbrite of the Ouarzazate Group limits the time for the deposition of the M'Gouna Group to less than 4 Ma. The Pan-African orogeny was finished at c. 600 Ma whereas the onset of transtension related to Cadomian back-arc formation was very much younger from c. 570 Ma onwards.