DETRITAL ZIRCON BARCODES FROM MESOPROTEROZOIC AND NEOPROTEROZOIC STRATA ON THE WEST AFRICAN CRATON, AND IMPLICATIONS FOR APPALACHIAN TERRANES

The Taoudeni Basin is a Mesoproterozoic to Phanerozoic basin that overlies Archean and Paleoproterozoic basement of the West African craton. Detrital zircons from the Mesoproterozoic Char and Atar Groups show age peaks at 2941, 2871, 2703, 2447, 2076, and 2041 Ma (major populations in bold). Detrital zircons from the overlying early Neoproterozoic Assabet El Hassiane Group and correlatives ("Assabet" for short) show age peaks at 2137, 2053, 1510, 1212, 1021, and 936 Ma. These results point to six broad conclusions. (1) All DZs from the Char and Atar are traceable to igneous rocks in West Africa, but the Assabet's youngest (1.8 to 0.9 Ga) DZ must be exotic; paleocurrents suggest derivation from sources that, before opening and closing of West Africa's later Neoproterozoic Pan-African oceans, were to the east and/or south in present coordinates. (2) Based on age, thickness, fluvial facies, and exotic zircons, the Assabet was most likely deposited in a foreland basin related to the collisional assembly of Rodinia. (3) Published Rodinia reconstructions, which all placed West Africa at the edge of Rodinia, far from the Grenville or coeval orogens, fail to explain the Assabet. (4) West Africa's igneous barcode, with age peaks at 2871, 2726, 2165, 2071, 635, and 570 Ma and an absence of ca. 1.3 to 0.9 Ga "Grenvillian" ages, has long been used to rule out a West African origin for Avalonia or Ganderia. The Assabet DZ record shows this logic to be suspect, as sediment eroded in the late Neoproterozic from West Africa could likely have been partly derived from cover strata. (5) A West African source for putative "Grenvillian" DZs in Appalachian terranes should be entertained. (6) Assabet-like DZ age distributions have been reported from the Mauritanide and Dahomeyide orogens, Brazil, Greece, the Urals, Avalonia, and Ganderia. But remarkably, Char-like age distributions are only known from West Africa. A new Rodinia reconstruction can account for all of these findings.