Resolving the timing of orogenesis in the Western Blue Ridge, southern Appalachians, via in situ ID-TIMS monazite geochronology

P – T constraints and timing of Barrovian metamorphism in the Shetland Islands, Scottish Caledonides: implications for the structural setting of the Unst ophiolite

“…Pressure estimates of 7.5-10 kbar for Grampian metamorphism in Shetland are similar to those reported from the North Mayo Inlier in western Ireland (Yardley et al 1987) and the SW Scottish Highlands (Graham 1985). From a wider perspective, the ages presented here are also similar to granulites-facies metamorphism of the Taconic arc-accretion event in the Appalachians (Karabinos et al 1998;van Staal et al 1998) dated at c. 450-460 Ma (Moecher et al 2004;Corrie & Kohn 2007). The new data reported here from Shetland thus confirm the near-synchroneity of Grampian-Taconic metamorphism along the eastern margin of Laurentia.…”

Insights into southern Appalachian tectonics from ages of detrital monazite and zircon in modern alluvium

“…Based on U-Pb zircon and monazite geochronology from localities elsewhere in the Blue Ridge of western North Carolina, peak Paleozoic amphibolite, granulite, and eclogite facies metamorphism is Middle Ordovician in age (Moecher et al, 2004aCorrie and Kohn, 2007;Miller et al, 2010). Hornblende 40 Ar-39 Ar plateau ages in the study area range from 410 to 450 Ma (Dallmeyer, 1975;Kunk et al, 2006), but variably disturbed hornblende isotopic systematics are widespread (Goldberg and Dallmeyer, 1997).…”

“…However, the timing of metamorphic and magmatic events, based on high precision and high spatial resolution U-Pb geochronometers, has only recently been determined (Miller et al, 2000;Moecher et al, 2004a;Miller et al, 2006Miller et al, , 2010Corrie and Kohn, 2007), and then only from scattered outcrops. There is also considerable ambiguity in the extent and intensity of each phase of metamorphism that has affected the southern Appalachians due to a series of overprinting Paleozoic collisional events.…”

“…Some monazite grains contain late Neoproterozoic to early Paleozoic cores, and there are scattered younger ages within the distribution, similar to the pattern of French Broad monazite. Corrie and Kohn (2007) interpreted high mean square of weighted deviate values for U-Pb ID-TIMS analysis of monazite extracted from Great Smoky Group schists by microdrilling, spanning ages from 440 to 470 Ma, as not representing a single population of monazite growth. Corrie and Kohn (2007) established 450 ± 5 Ma as most closely representing the time of the majority of monazite growth, and by extension, the thermal peak of regional metamorphism in the Great Smoky Mountains region.…”

“…Corrie and Kohn (2007) interpreted high mean square of weighted deviate values for U-Pb ID-TIMS analysis of monazite extracted from Great Smoky Group schists by microdrilling, spanning ages from 440 to 470 Ma, as not representing a single population of monazite growth. Corrie and Kohn (2007) established 450 ± 5 Ma as most closely representing the time of the majority of monazite growth, and by extension, the thermal peak of regional metamorphism in the Great Smoky Mountains region. These relations constitute preliminary evidence that Taconian regional metamorphism in the Appalachian Blue Ridge consisted of more than one tectonometamorphic pulse.…”