DISTINCTIVE AFRICAN AND NON-AFRICAN DETRITAL ZIRCON SOURCES IN THE MAURITANIAN BELT

Remnants of a late Paleozoic Mauritanian Orogenic Belt crop out along northwest Africa's coast. This belt overlays the West African Craton (WAC) to the east, though main tectonometamorphic imprint age remains uncertain. Pan-African (Neoproterozoic) and/or Variscan (Late Paleozoic) events might overlap, contributing variably to the final orogenic picture. In the northern Mauritanides (Akjoujt area), the belt comprises siliciclastic metasedimentary rocks, with BIFs, metaigneous (felsic to mafic), and volcanoclastic intercalations, loosely attributed to the Neoproterozoic. This study reports detrital zircon U-Pb zircon ages derived from nine quartzite rock samples from the Akjoujt area. Our results yield Ediacaran maximum depositional ages (as shown by the youngest zircon grains) from 615 to 565 Ma. The distribution of the main detrital zircon populations defines two groups of samples with distinctive inherited zircon grains. Group 1 presents main zircon age peaks at c. 2170, 2026, 999, 753, and 614 Ma, notably lacking Mesoproterozoic or late Paleoproterozoic dates (1.8-1.1 Ga). The 2.2-2.0 Ga populations can be related to the Eburnean orogeny, while the 0.8-0.6 Ga can be associated with the Cadomian/Pan-African orogeny. Both orogenies are well-known as primary sediment sources in northwest Africa. Group 2 depicts main peaks at c. 2948, 1907, 1458, 1280, 1031, and 616 Ma, thus being predominant the Mesoproterozoic and late Paleoproterozoic ages (2.0-1.0 Ga). This latter age distribution indicates contributions from sources which are not present in northwest Africa, but well-known in eastern Laurentia, Baltica and Amazonia. According to the available paleogeographic reconstructions for the Ediacaran period, Amazonia would be linked to Gondwana and, hence, it would be located close to west Africa, while Laurentia and Baltica would have been separated from Gondwana by oceanic realms. Consequently, the most probable sediment source for Group 2 samples points to Amazonia. The virtual occurrence in the studied area of the Mauritanides of Group 1 and Group 2 detrital zircon signatures, apparently mixed in the same area and rock sequence, implies either the existence of an Ediacaran depocenter fed by two very different cratons, or a complex tectonic history that juxtaposed different paleogeographic realms.