HINTS OF THE MID-CONTINENT BEYOND THE GRENVILLE OROGEN AND GONDWANAN INHERITANCE IN APPALACHIAN TERRANES

Appalachian crust is largely the product of Neoproterozoic rifting and several Paleozoic contractional events. Each orogenic event incorporated earlier "basement". Located west of the central Piedmont suture, rifted-margin metasedimentary rocks of the western southern Appalachian (WSA) terranes are dominated by Grenvillian detrital zircons. In the southern Appalachian Blue Ridge these rift-and-drift facies are nonconformably deposited on Grenvillian and older basement. The Laurentian Grenville orogen located west of the Appalachians is the most obvious source for these rocks. Zircon cores and whole-rock Nd isotopic data from several southern Appalachian internal terranes provide evidence of inheritance from, and recycling of, still older crust from either the Mid-Continent or elsewhere. The most external basement massifs, as well as several internal terranes, from the WSA contain 1.3-1.6 Ga detrital zircon cores and have T_DM ages of ~1.5-1.6 Ga perhaps indicating an eastern granite-rhyolite province connection. These components are also present in the more isotopically evolved Mars Hill terrane, a 1.6-1.8 Ga paragneiss crustal block in the most external WSA massif. Still older detrital zircons are present in the Dahlonega gold belt (lowest thrust sheet in the eastern Blue Ridge) with components of 1.6, 2.0, and 2.7-2.8 Ga. Eastern Blue Ridge Ordovician and Devonian plutons also have older inherited cores with ages of 1.4 and 2.6-2.9 Ga. Eastern Inner Piedmont (Cat Square terrane) detrital zircons record a broad range of ages 2.7 Ga to 1.8, 1.4 to 0.9, and 0.6 to 0.45 Ga, probably reflecting terrane accretion and derivation from both recycled Laurentian margin and Panafrican sources. In contrast to other WSA marginal terranes, reported detrital zircon ages in the Pine Mountain window contain 2.0-2.4 Ga zircons (in addition to 1.1 Ga) and are suggested to have a Gondwanan (Rondonian) source. Easternmost Appalachian terranes contain crust with clear Gondwanan affinities and Neoproterozoic to early Paleozoic (Panafrican) assemblages.