U-Pb geochronologic, Nd isotopic, and geochemical evidence for the correlation of the Chopawamsic and Milton terranes, Piedmont Zone, southern Appalachian Orogen

We report U-Pb crystallization ages from four metavolcanic rocks and two gr anitic gneiss samples as well as wholerock chemical analyses and Sm-Nd isot opic ratios from 25 metaigneous and metasedimentary rocks from the Chopawam sic and Milton terranes, southern Appalachian Orogen. A metarhyolite sample from the Chopawamsic Formation and a metabasalt sample from the Ta River F ormation in the Chopawamsic terrane have indistinguishable U-rb crystalliza tion ages of 471.4 +/- 1.3 Ma and 470.0 + 1.3/-1.5 Ma, respectively. A samp le from the Prospect granite that intruded metavolcanic rocks of the Ta Riv er Formation yields a younger U-W date of 458.0 +/- 1 Ma. Metarhyolite and granitic gneiss samples from the northern part of the Milton terrane yield U-Pb dates of 458.5 + 3.8/-1.0 Ma and 450 +/- 1.8 Ma, respectively. Metavol canic and metaplutonic rocks from both terranes span a range in major eleme nt composition from basalt to rhyolite. Trace element concentrations in the se samples show enrichment in large-ion lithophile elements K, Ba, and Rb a nd depletion in high field strength elements Ti and Nb, similar to those fr om island are volcanic rocks. Initial is an element of(Nd) values and T-DM ages of the metaigneous and metasedimentary samples range from 0.2 to -7.2 and from 1200 to 1700 Ma for the Chopawamsic terrane and from 3.7 to - 7.2 and from 850 to 1650 Ma for the Milton terrane. The crystallization ages fo r the metavolcanic and metaplutonic samples from both terranes indicate tha t Ordovician magmatism occurred in both. Similar is an element of(Nd) value s from representative samples hom both terranes suggest that both were gene rated from an isotopically similar source. Xenocrystic zircons from metavol canic rocks in the Chopawamsic terrane have predominately Mesoproterozoic P b-207/Pb-206 ages (600-1300 Ma), but a single Archean (2.56 Ga) core was al so present. The xenocrystic zircons and the generally negative is an elemen t of(Nd) values indicate that both terranes are composed of isotopically ev olved continental crust.