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

Christopher S. Holm-Denoma and Reshmi Das
Bimodal volcanism as evidence for Paleozoic extensional accretionary tectonism in the Southern Appalachians
Geological Society of America Bulletin (July 2010) 122 (7-8): 1220-1234


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+ or -5 Ma and 461+ or -3 Ma. Geochemical analyses of metabasalts indicate compositions derived from a suprasubduction zone, and more specifically a backarc. Furthermore, epsilon (sub Nd(460 Ma)) =(+)3.3-(+)7.7 and (super 87) Sr/ (super 86) Sr (sub (initial)) =0.7044-0.7069 indicate a juvenile source. The protoliths of the felsic lithofacies were low-potassium rhyodacite, and have epsilon (sub Nd(460 Ma)) =(-)3.2-(+)4.65 and (super 87) Sr/ (super 86) Sr (sub (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.

ISSN: 0016-7606
EISSN: 1943-2674
Serial Title: Geological Society of America Bulletin
Serial Volume: 122
Serial Issue: 7-8
Title: Bimodal volcanism as evidence for Paleozoic extensional accretionary tectonism in the Southern Appalachians
Affiliation: U. S. Geological Survey, Denver, CO, United States
Pages: 1220-1234
Published: 201007
Text Language: English
Publisher: Geological Society of America (GSA), Boulder, CO, United States
References: 80
Accession Number: 2010-050196
Categories: Structural geologyGeochemistry of rocks, soils, and sediments
Document Type: Serial
Bibliographic Level: Analytic
Annotation: With GSA Data Repository Item 2010042
Illustration Description: illus. incl. sects., 3 tables, geol. sketch maps
N30°00'00" - N35°00'00", W88°30'00" - W85°00'00"
N30°19'60" - N35°00'00", W85°34'60" - W80°45'00"
Secondary Affiliation: Florida State University, USA, United States
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2019, American Geosciences Institute. Reference includes data from GeoScienceWorld, Alexandria, VA, United States. Reference includes data supplied by the Geological Society of America, Boulder, CO, United States
Update Code: 201027
Program Name: USGSOPNon-USGS publications with USGS authors
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