MESOPROTEROZOIC DETRITAL ZIRCONS FROM NEOPROTEROZOIC STRATA IN WEST AFRICA AND IMPLICATIONS FOR APPALACHIAN TERRANES

Detrital zircon results are reported from Mesoproterozoic to Ordovician strata from the West African craton (Taoudeni Basin, n =1287) and the Mauritanide orogen (n = 1052). The Taoudeni Basin samples show four distinctive, sequential age distributions ("barcodes"): the Char, Assabet, Téniagouri, and Oujeft barcodes. Age maxima are as follows, with the largest in bold. The Char barcode, from ca. 1150-1100 Ma strata, has maxima at 2941, 2871, 2703, 2447, 2076, and 2041 Ma—all traceable to West African basement. The Assabet barcode, from strata deposited between ca. 870 and ca. 635 Ma, has maxima at 2137, 2053, 1510, 1212, 1021, and 936 Ma; the youngest populations cannot have come from West Africa. The Téniagouri barcode, from strata deposited at ca. 600 Ma, has maxima at 1983, 1872, 1522, 1215, 1109, 988, and 601 Ma. The Oujeft barcode, from strata deposited between about 543 and 444 Ma, has maxima at 2124, 2053, 1197, 624 and 579 Ma. The youngest Téniagouri and Oujeft zircon populations were probably derived from contemporaneous igneous sources in the Mauritanides. All of the major map units in the Mauritanides have yielded detrital zircon age spectra that can be matched with one of the Taoudeni Basin barcodes, suggesting that these rocks are ultimately of West African affinity. Previous reconstructions of Rodinia have placed West Africa in various peripheral positions, far from the Grenville or other broadly coeval collisional orogens. These reconstructions fail to account for 1.5 to 0.9 Ga detritus on West Africa. In a possible alternative Rodinia reconstruction, West Africa restores to a position opposite the Grenville orogen of Laurentia, but with Oaxaquia, Ganderia, and Avalonia in between. Age distributions of detrital zircons from some Ganderia and West Avalonia samples are clear matches with cratonic West Africa, calling into question the putative Amazonian origin for at least some rocks in these dispersed prei-Gondwanan fragments.