2000 GSA Annual Meeting -- Reno, Nevada
2000 GSA Annual Meeting -- Reno, Nevada
Author(s): BREAM, Brendan R., Geological Sciences, Univ. of Tennessee, Knoxville, TN 37996-1410, bbream@utkux.utk.edu; HATCHER, Robert D., Jr., Geological Sciences, Univ. of Tennessee, Knoxville, TN 37996-1410 & Environmental Sciences Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831; MILLER, Calvin F., Geology, Vanderbilt Univ., Nashville, TN 37235; and FULLAGAR, Paul, D., Geological Sciences, Univ. of North Carolina, Chapel Hill, NC 27599-3315
Keywords: southern Appalachians, crystalline core, geochronology
Recent ion microprobe geochronology and geochemistry of paragneiss samples in areas of detailed mapping within the southern Appalachian Inner Piedmont and Blue Ridge (GA, NC, SC, and TN) provide new age, provenance, and metamorphic constraints for the southern Appalachian crystalline core. Primarily due to the complex tectonic history of the southern Appalachians and paucity of detailed geochemistry, little is known about the origin of most major lithotectonic units. Using preliminary Nd isotope data and U-Pb detrital zircon core ages from paragneiss samples, a comparison of crustal affinities for the eastern Blue Ridge and Inner Piedmont terranes is possible. Psammitic paragneisses in the eastern Blue Ridge and western Inner Piedmont (Chauga belt) have Nd model ages of 1.6-1.7 Ga and are dominated by Mesoproterozoic Grenville (1.0-1.3 Ga) zircon core ages. Late Proterozoic ages are absent from the Blue Ridge and western Inner Piedmont paragneiss samples; however, one central Inner Piedmont paragneiss sample contains detrital zircons (575 to 640 Ma) that may be related to a Neoproterozoic arc terrane (i.e., the Carolina terrane). These data support the interpretation that the paragneisses NW and immediately SE of the Brevard fault zone are correlative and that if a suture with an allochthonous terrane is present within the Inner Piedmont, it must be located in the central or eastern Inner Piedmont. Ion microprobe U-Pb zircon rim ages from the paragneisses are either ~1.0 Ga (Grenville metamorphism) or 320-400 Ma (Paleozoic Acadian metamorphism). Paleozoic rim ages for Inner Piedmont samples are mostly <360 Ma, reconfirming the dominance of an Acadian metamorphism here.
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