TERRANE TRANSFER DURING THE GRENVILLIAN ASSEMBLY OF RODINIA: TRACING THE AMAZONIAN ANCESTRY OF SOUTHERN APPALACHIAN BASEMENT THROUGH PB AND ND ISOTOPES
In order to test for a Rodinian connection between Laurentia and Amazonia, the Pb fingerprint of 54 whole rocks samples from the Grenvillian basement rocks of the SW Amazon craton (Rondônia, Brazil), are compared to those from the Grenville belt of North America and Grenvillian basement inliers in the southern Appalachians. Both the SW Amazon basement and the allochthonous Blue Ridge/Mars Hill terrane are defined by highly radiogenic mu2 values of ~10, well above the crustal average. In contrast, the greater Grenville Province of Laurentia is characterized by lower mu2 values of ~9.5. Published U-Pb zircon ages and Sm-Nd for the Blue Ridge/Mars Hill terrane also suggest an ancient provenance very different from the rest of the adjacent Grenville belt, which is dominated by juvenile, 1.3-1.5 Ga rocks. The presence of mature continental material in rocks older than 1.15 Ga in the Blue Ridge/Mars Hill terrane (Epsilon Nd > 0) is consistent with the signature of Amazon basement rocks. We propose that this portion of the S. Appalachian basement is derived from Amazonia and was transferred to Laurentia during Grenvillian orogenesis at ~1.15 Ga. The presence of these Amazonian rocks in southeastern Laurentia records the northward passage of the Amazon craton along the Laurentian margin, following the original collision with southernmost Laurentia at ca. 1.2 Ga.