25 New Research in the Appalachian-Ouachita Orogen: Integrated studies from the Foreland to the Hinterland (Posters)

This session welcomes research from the Ouachita-Appalachian foreland, Blue Ridge, and Piedmont, focusing on old paradigms and new problems. Contributions across scales that utilize mapping, petrology, paleontology, geochemistry, geophysics, and/or geochronology are welcome.

Tuesday, 10 March 2026
9:00 AM - 5:00 PM
RCC, Lower Level Hall

Silurian Resetting of Monazites from the Mineral Bluff Group: Implications for the Paleozoic Evolution of the Western Blue Ridge Terrane

Paper number: 25-2
Program: Technical Sessions
Time: 9:00 AM – 9:00 AM

Authors

Abstract

The Appalachian Orogen records succeeding tectonic events associated with accretion of various terranes, evolving throughout the Paleozoic and leading to the assembly of the Pangea. Multiple stages of deformation and/or metamorphism of these terranes complicate the decipher of their tectonothermal evolution. The timing and driver of metamorphism of the Western Blue Ridge (WBR) terrane stands as a long-lasting debate. Within the WBR, the Murphy synclinorium folds a stratigraphy including the remnants of a Proterozoic to early Paleozoic Laurentian passive margin that was overlain by a shelf carbonate bank, which was then succeeded unconformably by turbiditic clastic successions of the Mineral Bluff Group. At the base of this unconformity lies a key amphibolite marker, the Marble Hill Hornblende Schist (MHHS), which originated as basaltic volcanics with ocean-island-basalt geochemistry and zircon crystallization ages of ca. 437 Ma, recording their emplacement in a remnant Silurian Iapetan Ocean basin. The emplacement age of the MHHS amphibolite protolith conflicts with the previously suggested interpretations – based on detrital mineral ages, inclusion phases within porphyroblasts, and discordant or mixed age results – of Ordovician Taconic metamorphism of the Mineral Bluff Group. Instead, it indicates metamorphism and folding of the Murphy synclinorium and associated regions of the WBR, is Silurian or younger.

We present new U-Pb ages of monazites from a garnet-biotite-muscovite schist sample of the Mineral Bluff Group in contact with the MHHS amphibolite. The separated monazites are sub-rounded to rounded and interpreted to have a detrital origin. EDS analysis yielded their variety to be Ce-monazite. The LA-MC-ICPMS analysis yielded a U-Pb concordia age of 434±2 Ma (n=53; MSWD=0.69) and weighted mean 206Pb/238U age of 435.8±2.2 Ma (n=53; MSWD=0.99). This age strongly agrees with the crystallization age of the MHHS amphibolite protolith and is interpreted to indicate resetting of these monazites during basaltic magmatism. This explanation requires the monazites to have been deposited at the Laurentian margin prior to Silurian magmatism, a scenario that further challenges interpretations of Ordovician Taconic metamorphism in the WBR but can be interpreted to indicate their derivation from a Taconic source.

Additional geo- and thermo-chronological analysis of this sample will be integrated with thermobarometric modeling to further the understanding of tectonothermal evolution of the WBR terrane and the Appalachian Orogen.

Geological Society of America Abstracts with Programs. Vol. 58, No. 1

doi: 10.1130/abs/2026SE-411585

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