Document generated on 09/27/2021 8:53 a.m. Geoscience Canada Journal of the Geological Association of Canada Journal de l’Association Géologique du Canada Detrital Zircon Geochronology Across the Chopawamsic Fault, Western Piedmont of North-Central Virginia: Implications for the Main Iapetan Suture in the Southern Appalachian Orogen K. Stephen Hughes, James P. Hibbard, Jeffrey C. Pollock, David J. Lewis and Brent V. Miller Volume 41, Number 4, 2014 Article abstract The Chopawamsic fault potentially represents the main Iapetan suture, URI: https://id.erudit.org/iderudit/1062257ar previously unidentified in the southern extent of the Appalachian orogen. The DOI: https://doi.org/10.12789/geocanj.2014.41.052 fault trends through the north-central portion of the western Piedmont of Virginia and separates the composite metaclastic Potomac terrane, commonly See table of contents interpreted to be of Laurentian affinity, from the Chopawamsic terrane, the remains of a Middle Ordovician volcanic arc of uncertain crustal affinity. To gain insight on the first-order orogenic significance of the Chopawamsic fault, Publisher(s) we report the results of LA–ICP–MS U–Pb analyses of 1,289 detrital zircons from 13 metasedimentary rock samples collected from both sides of the fault. The Geological Association of Canada The near exclusivity of Middle Ordovician zircon grains (ca. 470 – 460 Ma) in four sampled metasedimentary rocks of the Chopawamsic Formation likely ISSN represents the detrital recycling of syndepositional Chopawamsic volcanic rocks. A subset of Cambrian and older grains hint at one or more additional, 0315-0941 (print) older sources. Samples from the Potomac terrane include mostly 1911-4850 (digital) Mesoproterozoic zircon grains and these results are consistent with previous interpretations that the metaclastic rocks are Laurentian-derived. The Explore this journal youngest zircons (ca. 550 – 500 Ma) and the age of cross-cutting plutons indicate that at least some parts of the Potomac terrane are Late Cambrian – Early Ordovician. The results imply temporally discrete and geographically Cite this article isolated sedimentary systems during deposition of sedimentary rocks in the Chopawamsic and Potomac terranes. Metasedimentary rocks near Storck, Hughes, K., Hibbard, J., Pollock, J., Lewis, D. & Miller, B. (2014). Detrital Zircon Virginia, previously identified as a successor basin, contain detrital zircon Geochronology Across the Chopawamsic Fault, Western Piedmont of populations that indicate they are actually peri-Gondwanan derived North-Central Virginia: Implications for the Main Iapetan Suture in the metasedimentary rocks unrelated to a successor basin system; their geographic Southern Appalachian Orogen. Geoscience Canada, 41(4), 503–522. position between the Laurentian-derived Potomac terrane and the https://doi.org/10.12789/geocanj.2014.41.052 Chopawamsic terrane suggests a peri-Gondwanan affinity for the Chopawamsic arc and geographic separation of the Chopawamsic and Potomac terranes in the Middle Ordovician. Consequently, we tentatively support the hypothesis that the Chopawamsic fault system represents the main Iapetan suture in the southern Appalachian orogen. Most detrital zircons from samples of the Arvonia successor basin crystallized in the Ordovician—Silurian or Mesoproterozoic. These data suggest that the Arvonia basin was deposited in the latest Ordovician to Early Silurian only after the Late Ordovician accretion of the Chopawamsic arc to Laurentia. All Rights Reserved ©, 2014 The Geological Association of Canada This document is protected by copyright law. Use of the services of Érudit (including reproduction) is subject to its terms and conditions, which can be viewed online. https://apropos.erudit.org/en/users/policy-on-use/ This article is disseminated and preserved by Érudit. Érudit is a non-profit inter-university consortium of the Université de Montréal, Université Laval, and the Université du Québec à Montréal. Its mission is to promote and disseminate research. https://www.erudit.org/en/ GEOSCIENCE CANADA Volume 41 2014 503 HAROLD WILLIAMS SERIES Texas A&M University sedimentary systems during deposition College Station, Texas, 77843, USA of sedimentary rocks in the Chopawamsic and Potomac terranes. SUMMARY Metasedimentary rocks near The Chopawamsic fault potentially Storck, Virginia, previously identified represents the main Iapetan suture, as a successor basin, contain detrital previously unidentified in the southern zircon populations that indicate they extent of the Appalachian orogen. are actually peri-Gondwanan derived The fault trends through the north- metasedimentary rocks unrelated to a central portion of the western Pied- successor basin system; their geograph- mont of Virginia and separates the ic position between the Laurentian- Detrital Zircon composite metaclastic Potomac ter- derived Potomac terrane and the rane, commonly interpreted to be of Chopawamsic terrane suggests a peri- Geochronology Across the Laurentian affinity, from the Chopa- Gondwanan affinity for the Chopa- Chopawamsic Fault, wamsic terrane, the remains of a Mid- wamsic arc and geographic separation dle Ordovician volcanic arc of uncer- of the Chopawamsic and Potomac ter- Western Piedmont of tain crustal affinity. To gain insight on ranes in the Middle Ordovician. Con- North-Central Virginia: the first-order orogenic significance of sequently, we tentatively support the the Chopawamsic fault, we report the hypothesis that the Chopawamsic fault Implications for the Main results of LA–ICP–MS U–Pb analyses system represents the main Iapetan Iapetan Suture in the of 1,289 detrital zircons from 13 suture in the southern Appalachian Southern Appalachian metasedimentary rock samples collect- orogen. ed from both sides of the fault. Most detrital zircons from Orogen The near exclusivity of Middle samples of the Arvonia successor Ordovician zircon grains (ca. 470 – basin crystallized in the Ordovician – K. Stephen Hughes1*, James P. 460 Ma) in four sampled metasedimen- Silurian or Mesoproterozoic. These Hibbard1, Jeffrey C. Pollock2, David tary rocks of the Chopawamsic For- data suggest that the Arvonia basin J. Lewis3, and Brent V. Miller3 mation likely represents the detrital was deposited in the latest Ordovician recycling of syndepositional Chopa- to Early Silurian only after the Late 1Department of Marine, Earth, and wamsic volcanic rocks. A subset of Ordovician accretion of the Atmospheric Sciences Cambrian and older grains hint at one Chopawamsic arc to Laurentia. North Carolina State University or more additional, older sources. Raleigh, North Carolina, 27695, USA Samples from the Potomac SOMMAIRE terrane include mostly Mesoprotero- La faille de Chopawamsic représente *Department of Geology zoic zircon grains and these results are peut-être la principale suture japéti- University of Puerto Rico—Mayagüez consistent with previous interpreta- enne, non-reconnue dans prolonge- Mayagüez, Puerto Rico, 00681, USA tions that the metaclastic rocks are ment sud de l’orogène des Appalaches. E-mail: [email protected] Laurentian-derived. The youngest zir- La faille traverse la portion nord du cons (ca. 550 – 500 Ma) and the age of centre du piedmont ouest de Virginie 2Department of Earth Sciences cross-cutting plutons indicate that at et sépare le terrane métaclastique de Mount Royal University least some parts of the Potomac ter- Potomac, d’affinité laurentienne pen- Calgary, Alberta, T3E 6K6, Canada rane are Late Cambrian – Early Ordo- sait-on, du terrane de Chopawamsic, vician. The results imply temporally vestige d’un arc volcanique de l’Or- 3Department of Geology and Geophysics discrete and geographically isolated dovicien moyen d’affinité crustale Geoscience Canada, v. 41, http://dx.doi.org/10.12789/geocanj.2014.41.052 © 2014 GAC/AGC® 504 incertain. Afin de mettre en lumière la géographiquement durant le dépôt des INTRODUCTION signification orogénique première de la roches sédimentaires dans les terranes The Chopawamsic fault is a Late faille de Chopawamsic, nous présen- de Chopawamsic et de Potomac. Ordovician structure that bisects the tons les résultats d’analyses U-Pb par Les roches métasédimentaires western Piedmont of Virginia into two ICP–MS par AL sur 1 289 zircons près de Storck en Virginie, jadis inter- distinct crustal tracts known as the détritiques provenant de 13 échantil- prétées comme bassin successeur, ren- Potomac and Chopawamsic terranes lons de roches métasédimentaires ferment des populations de zircons (Fig. 1; Pavlides 1989, 1990, 1995; Hor- prélevés de chaque côté de la faille. détritiques qui indiquent qu’ils provien- ton et al. 1989; Virginia Division of L’existence quasi-exclusive de nent en fait de roches métasédimen- Mineral Resources 1993; Pavlides et al. grains de zircon de l’Ordovicien moyen taires péri-gondwaniennes sans rapport 1994; Mixon et al. 2000, 2005; Hughes (env. 470 – 460 Ma) dans quatre roches avec un système de bassin successeur; et al. 2013a; Hibbard et al. 2014). métasédimentaires de la Formation de leur localisation géographique entre le Whereas the majority of previous Chopawamsic représente vraisem- terrane de Potomac issu des Lauren- research involving the Chopawamsic blablement le recyclage détritique des tides et le terrane de Chopawamsic fault has been focused on identifying roches volcaniques synsédimentaires de porte à penser que l’arc de Chopawam- the local feature and its timing Chopawamsic. Un sous-ensemble de sic est d’affinité péri-gondwanienne, et (Pavlides