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Geochronologic age constraints on tectonostratigraphic units of the central Virginia Piedmont, USA

February 7, 2020

New geologic mapping coupled with uranium-lead (U-Pb) zircon geochronology (sensitive high-resolution ion microprobe-reverse geometry [SHRIMP-RG] and laser ablation-inductively coupled plasma-mass spectrometry [LA-ICP-MS]) analyses of 10 samples, provides new constraints on the tectonostratigraphic framework of the central Virginia Piedmont. Detrital zircon analysis confirms that the Silurian-Devonian Quantico Formation is a postorogenic successor basin, with zircons derived primarily from Ordovician Chopawamsic Formation volcanic rocks. Detrital zircons from strata of the Long Island syncline, previously mapped as a separate successor basin, have a peri-Gondwanan component distinct from Laurentian-sourced rocks of the Potomac terrane to the west. Volcanism of the Chopawamsic Formation spanned at least 14 million years during the Ordovician. The Chopawamsic Formation contains sheet-like Late Ordovician-Silurian granodioritic and tonalitic intrusions that were once mapped as Carboniferous. Biotite-muscovite migmatitic paragneiss, which borders the Chopawamsic Formation on its southeast side and also occurs east of the Lakeside fault, preserves evidence of Silurian deformation and metamorphism, with a Carboniferous (Alleghanian) overprint. Limited SHRIMP-RG analysis of detrital zircons from this paragneiss yields a Laurentian (Mesoproterozoic) signature, which suggests that the structurally concordant contact between volcanic rocks of the Chopawamsic Formation and paragneiss is either a pre-Alleghanian fault or an unconformity.

Publication Year 2020
Title Geochronologic age constraints on tectonostratigraphic units of the central Virginia Piedmont, USA
DOI 10.3133/pp1861
Authors Mark W. Carter, Ryan J. McAleer, Christopher S. Holm-Denoma, David B. Spears, Sean P. Regan, William C. Burton, Nick H. Evans
Publication Type Report
Publication Subtype USGS Numbered Series
Series Title Professional Paper
Series Number 1861
Index ID pp1861
Record Source USGS Publications Warehouse
USGS Organization Eastern Geology and Paleoclimate Science Center