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Plutons and dikes of the eastern Blue Ridge, North Carolina and northeasternGeorgia, were emplaced syntectonically ca. 400 Ma in the evolving southern Appalachian orogen. These intrusive rocks are uniformly felsic and peraluminous, ranging continuously from trondhjemitic to granodioritic in composition with no associated mafic or intermediate rocks. The trondhjemites are very low in K and in incompatible and high field strength trace elements; are rich in Al, Na, and Sr; and have low 87 Sr/ 86 Sr and δ 18 O and high ε Nd . Granodiorites are less extreme, having elemental and isotopic compositions that are more typical of continent margin granitoids.Their compositions require that the rocks near the trondhjemitic end of the spectrum had a relatively mafic source that was young and derived from depleted mantle. Trace-element modeling and isotopic constraints suggest that this source had the geochemical characteristics of a primitive arc basalt, and that the residue of melting was garnet amphibolite. The granodiorite end of the compositional continuum was derived in large part from the Proterozoic continental basement of the region. The most plausible genetic model involves development of an early Paleozoic magmatic arc, underthrusting of arc rocks during subsequent orogeny, heating of the deep crust as a consequence of crustal thickening, and anatexis within a heterogeneous lower crust. Magmas generated within this crust ranged from trondhjemite to granodiorite, depending upon the source rock, and coalesced in the source region or during ascent to yield the observed compositional continuum.