AMPHIBOLITE ZIRCON U-PB GEOCHRONOLOGY IN THE ASHE METAMORPHIC SUITE, EASTERN BLUE RIDGE, NORTH CAROLINA

Measuring precise timing of Appalachian metamorphism is critical to understanding the tectonic history of eastern North America. Reliable evidence of early Paleozoic orogenesis is limited in the southern Appalachians compared to the northern Appalachians. Three previous studies employed U-Pb isotope dilution thermal ionization mass spectrometry (ID-TIMS) to find ages consistent with Taconic metamorphism in the North Carolina Blue Ridge – the metamorphic core of the southern Appalachians. Miller et al. (2010) dated zircons from an eclogite sample at 459 +1.5/-0.6 Ma. Moecher et al. (2004) reported a peak metamorphism age of 457.6 ± 1.0 Ma for a migmatite leucosome. Corrie and Kohn (2007) reported an age of 450 ± 5 Ma for metamorphic monazite cores from samples collected in the Western Blue Ridge. Preliminary ID-TIMS work by Bridgeman (2015) dated an amphibolite sample from the Eastern Blue Ridge at 414.5 ± 3.8 Ma.

We applied U-Pb ID-TIMS to metamorphic zircons from amphibolite in the Ashe Metamorphic Suite of the Eastern Blue Ridge. These zircons are assumed to be metamorphic in origin and to not exhibit inheritance due to the zircon-poor tholeiitic protolith. This assumption can be verified by concordant ages younger than the Proterozoic origin of the unit. Previous work by Bridgeman (2015) indicates the sample experienced retrogression from eclogite, and the sample was collected 80 m SW of the eclogite dated by Miller et al. (2010).

Our analysis resulted in a preliminary age of 457 Ma, indicating peak metamorphism of this sample was Taconic and similar in age to the nearby eclogite. The new data corroborate previous findings of Taconic metamorphism in the southern Appalachians, however more investigation is needed to constrain temporal and geographic orogenic variability in the region.