The Suwannee suture: Significance for Gondwana-Laurentia terrane transfer and formation of Pangaea

In southeastern Laurentia the Suwannee suture separates the undeformed part of the Gondwanan Suwannee terrane (SWT) from crust of Laurentia and previously accreted Gondwanan terranes that were deformed during the Alleghanian orogeny. Undeformed early Paleozoic sedimentary rocks of the SWT are considered of Gondwanan-African derivation on the basis of various considerations, including a lack of Mesoproterozoic (Grenville) detrital zircons. The cratonic heritage of Suwannee lithosphere is complicated, however, because Sm-Nd depleted mantle model ages from both Neoproterozoic and Alleghanian (Carboniferous-Permian) granites north and south of the suture zone are Mesoproterozoic. Mesoproterozoic lithosphere has not been reported in conjugate West Africa, but is present in Amazonia, suggesting that the SWF: 1) may be a composite terrane, containing both African upper crust and Amazonian lower crust/lithosphere, 2) was separated from Gondwana during Atlantic Ocean rifting along a Mesoproterozoic-Neoproterozoic suture, and/or 3) contains Laurentian Grenville-age lower crust and lithosphere that must also underlie other accreted proximal Gondwanan terranes (e.g., Uchee terrane). In addition, the similar to 300 Ma, syn- to post-tectonic granitoids emplaced across the Suwannee suture zone are the product of crustal anatexis, not supra-subduction magmatism, on the basis of Mesoproterozoic Sm-Nd T-dm and zircon xenocrysts. The lack of documented similar to 300 Ma, supra-subduction magmatism in both Laurentian and Gondwanan components in southern Laurentia (e.g., southernmost Appalachian and Ouachita orogens) strongly suggests that accretion of the SWT and related Gondwanan terranes occurred during dextral transpressional convergence between Laurentia and a combined African-Amazonian craton, a characteristic shared with conjugate crust in southwestern Europe. In this interpretation, intervening oceanic lithosphere and contemporary volcanic arcs (if any) were largely removed by disaggregation and dispersion along the transpressional boundary possibly combined with highly oblique overthrusting and/or partly subducted at the leading edge(s) of other blocks of Gondwanan lithosphere that were accreted to southern Laurentia in the late Paleozoic (e.g., Wiggins, Sabine, Coahuila, Maya, etc.). Mesozoic opening of the Gulf of Mexico has subsequently and variably altered the original configuration of these terranes. (C) 2013 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved.