Bimodal volcanism as evidence for Paleozoic extensional accretionary tectonism in the southern Appalachians

Abstract

Research Article| July 01, 2010 Bimodal volcanism as evidence for Paleozoic extensional accretionary tectonism in the southern Appalachians Christopher S. Holm-Denoma; Christopher S. Holm-Denoma † 1U.S. Geological Survey, Denver, Colorado 80225, USA †E-mail: cholm-denoma@usgs.gov Search for other works by this author on: GSW Google Scholar Reshmi Das Reshmi Das § 2Department of Geological Sciences and National High Magnetic Field Laboratory, Florida State University, Tallahassee, Florida 32306, USA §Current address: Physical Research Laboratory, Ahmedabad 380 009, India Search for other works by this author on: GSW Google Scholar GSA Bulletin (2010) 122 (7-8): 1220–1234. https://doi.org/10.1130/B30051.1 Article history received: 05 Mar 2009 rev-recd: 17 Jul 2009 accepted: 27 Jul 2009 first online: 08 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Christopher S. Holm-Denoma, Reshmi Das; Bimodal volcanism as evidence for Paleozoic extensional accretionary tectonism in the southern Appalachians. GSA Bulletin 2010;; 122 (7-8): 1220–1234. doi: https://doi.org/10.1130/B30051.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract Detailed mapping, U-Pb ages of igneous and detrital zircons, and isotopic and geochemical characterization of a bimodal volcanic sequence from the Appalachian Blue Ridge province provide constraints for the timing and tectonic setting of volcanism along the Early Paleozoic southeastern Laurentian margin. These units, the Pumpkinvine Creek Formation and related rocks, are interpreted as having been deposited along an extended Laurentian margin in a backarc setting during the mid-Ordovician, and tectonically emplaced as late as the late Paleozoic Alleghanian orogeny.Two felsite layers from the Pumpkinvine Creek Formation, a bimodal metavolcanic sequence, have ages of 466 ± 5 Ma and 461 ± 3 Ma. Geochemical analyses of metabasalts indicate compositions derived from a suprasubduction zone, and more specifically a backarc. Furthermore, εNd(460 Ma) = (+)3.3–(+)7.7 and 87Sr/86Sr(initial) = 0.7044–0.7069 indicate a juvenile source. The protoliths of the felsic lithofacies were low-potassium rhyodacite, and have εNd(460 Ma) = (−)3.2–(+)4.65 and 87Sr/86Sr(initial) = 0.709–0.722, suggesting incorporation of an evolved crustal component, which we interpret as Laurentian continental lithosphere. Furthermore, detrital zircons derived from within the Pumpkinvine Creek Formation yielded a majority of ages between 1017 and 1190 Ma, indicating that the source is likely a component of the rifted eastern Laurentian margin.A backarc origin for the Pumpkinvine Creek Formation indicates that the geodynamic setting of the southeastern margin of Laurentia included a retreating subduction zone resulting in extensional accretionary tectonism. These results have implications for the evolution of the southeastern Laurentian margin during a time traditionally linked to collision of an exotic Taconic arc with Laurentia. Additionally, we suggest that there are significant along-orogen disparities that may result from fundamental tectonic boundaries. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.