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Abstract

The Appalachian orogen represents the Paleozoic amalgamation of Laurentian and Gondwanan terranes; however, the suture of the interstitial early Paleozoic Iapetus Ocean has not been identified in the southern Appalachians. In the western Piedmont of Virginia, the Potomac and Chopawamsic terranes are separated by the Chopawamsic fault, which has been hypothesized to represent the main Iapetan suture. We have conducted new mapping, geochemistry, and geochronology on rocks from these terranes to gain insight into their origin and interaction. Detrital zircon geochronology across correlative units of the metaclastic Potomac terrane is consistent with the interpretation that they are chiefly derived from Laurentian Mesoproterozoic rocks and they were deposited sometime between 500 and 470 Ma. Detrital zircon geochronology and plutonic and volcanic crystallization ages in the metavolcanic Chopawamsic terrane show that the Chopawamsic arc was active between 474 and 465 Ma. Stops on this field trip will highlight key outcrops that help further our understanding of the tectonic development of the Potomac and Chopawamsic terranes prior to their amalgamation in the Late Ordovician. Based on the data presented in this field guide, it remains plausible that the Chopawamsic fault represents either the main Iapetan suture or the closure of a smaller seaway.

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