ABSTRACT The Appalachian Mountains expose one of the most-studied orogenic belts in the world. However, metamorphic pressure-temperature-time ( P-T-t ) paths for reconstructing the tectonic history are largely lacking for the southernmost end of the orogen. In this contribution, we describe select field locations in a rough transect across the orogen from Ducktown, Tennessee, to Goldville, Alabama. Metamorphic rocks from nine locations are described and analyzed in order to construct quantitative P-T-t paths, utilizing isochemical phase diagram sections and garnet Sm-Nd ages. P-T-t paths and garnet Sm-Nd ages for migmatitic garnet sillimanite schist document high-grade 460–411 Ma metamorphism extending south from Winding Stair Gap to Standing Indian in the Blue Ridge of North Carolina. In the Alabama Blue Ridge, Wedowee Group rocks were metamorphosed at biotite to staurolite zone, with only local areas of higher-temperature metamorphism. The Wedowee Group is flanked by higher-grade rocks of the Ashland Supergroup and Emuckfaw Group to the northwest and southeast, respectively. Garnet ages between ca. 357 and 319 Ma indicate that garnet growth was Neoacadian to early Alleghanian in the Blue Ridge of Alabama. The P-T-t paths for these rocks are compatible with crustal thickening during garnet growth.

ABSTRACT The eastern Great Smoky Mountains basement complex consists of the following components: (1) ca. 1350–1325 Ma orthogneiss and mafic xenoliths that represent some of the oldest crust in Appalachian Grenville massifs (similar to “pre-Grenville” basement components in the Adirondack, Green Mountain, Hudson Highland, and Shenandoah massifs); (2) ca. 1150 Ma augen orthogneisses and granitic orthogneisses correlating with the Shawinigan phase of Grenville magmatism; and (3) paragneisses (cover rocks) that have either pre- or syn-Grenville (i.e., Mesoproterozoic) versus post-Grenville (Neoproterozoic) depositional ages, and that experienced Taconian metamorphism and migmatization. Mesoproterozoic paragneisses contain major zircon age modes that require a component of Proterozoic crust in the source region. The Neoproterozoic paragneisses exhibit the archetypical “Grenville doublet” in detrital zircon age distributions that matches the age distribution of Ottawan and Shawinigan magmatic/metamorphic events in eastern Laurentia. Most zircon U-Pb age systematics exhibit variable lead loss interpreted to result from high-grade Taconian (ca. 450 Ma) regional metamorphism and migmatization. Neodymium mantle model ages (T DM ) for ortho- and paragneisses range from 1.8 to 1.6 Ga, indicating that all rocks were derived from recycling of Proterozoic crust (i.e., they are not juvenile), which is consistent with Proterozoic detrital zircon ages in pre- to syn-Grenville paragneisses. Lead isotope compositions confirm the presence of an exotic (Amazonian) crustal component in the source region for the protoliths of the pre-Grenville orthogneisses and xenoliths, and that this exotic component was incorporated to varying degrees in the evolution of the basement complex. The oldest age component may represent an Amazonian pre-Grenville analog to the ca. 1.35 Ga native Laurentian crust present in Adirondack and northern Appalachian basement massifs.