Ordovician–Silurian back-arc silicic magmatism in the southernmost Appalachians

Abstract Ordovician and Silurian siliciclastic, volcanic, plutonic rocks in the southern Appalachian eastern Blue Ridge western Inner Piedmont, formerly interpreted as components of an obducted Taconic arc terrane, are recognized parts paired arc/back-arc system that formed on seaward edge Laurentian plate. New crystallization ages from metamorphosed plutonic-volcanic intruding intercalated with metasedimentary back-arc basin lithologies Wedowee-Emuckfaw-Dahlonega confirm rapid deposition (hundreds meters per million years) Ordovician–Silurian extensional received input continentally derived Mesoproterozoic crust bimodal volcanic components. U-Pb (206Pb/238U) zircon 12 samples Zana Granite yield minimum between 459 Ma 430 Ma, while grains six Kowaliga Gneiss have 452 435 Ma. Zircons a probable metavolcanic unit within Wedowee Group 206Pb/238U age 454 ± 3 depleted mantle model negative initial εhf values zircons metaigneous suggest significant component their genesis. Formation these silicic plutons was likely associated intrusion mantle-derived mafic melts decompression melting lower part tectonically thickened crustal section contribution sub-continental lithosphere during backarc extension. Silicic magma thick successions sedimentary shortly after is typical extension contraction phases above B-type subduction zones (i.e., Benioff oceanic subduction) Lachlan-style orogens, which consistent accretionary orogenic nature orogen.