195 Evolution of Orogenic Belts Through Time: Insights from Sedimentation, Deformation, Magmatism, and Metamorphism (Posters)

This session explores the evolution of orogenesis on Earth, encompassing applications of sedimentology, petrology, geochemistry, paleomagnetism, geochronology, and structural geology. We encourage studies combining field observations with laboratory and modeling techniques to unravel tectonic processes.

Tuesday, 21 October 2025
8:00 AM - 5:30 PM
HBGCC, Hall 1

Unraveling the Tectonic History of the eastern Blue Ridge: Petrochronologic and Microstructural Analysis of the Ashe Metamorphic Suite in northwestern North Carolina

Paper number: 195-8
Program: Technical Sessions
Time: 8:00 AM – 8:00 AM

Authors

Abstract

A belt of ultramafic rocks in the eastern Blue Ridge mountains near Peden, North Carolina (the Rocky Ridge and Peden ultramafic bodies) are interpreted to be dismembered ophiolites. The ultramafic bodies are highly altered and composed of chlorite-amphibole and talc-tremolite schists. The bodies are hosted in the Ashe Metamorphic Suite, a suite of metasediments suggested to have formed in an accretionary wedge. Rankin et al. (1993) hypothesized that these ultramafic bodies might represent a cryptic suture between continental margin and accretionary rocks of the Ashe Metamorphic Suite. To test this hypothesis, preliminary petrologic, microstructural, and monazite U-Pb data are used to evaluate the P-T-t-D history of rocks on either side of the ultramafic bodies and compare their tectonic histories. Samples of schist and paragneiss (metagraywacke) from both sides of the ultramafic bodies have similar peak assemblages including kyanite, sillimanite, staurolite, garnet, and biotite. Rocks on both sides display multiple deformation fabrics. The dominant foliation to the southeast of the ultramafic bodies (068º/65º SE) is generally steeper than the foliation to the northwest of the bodies (067º/41º SE). Preliminary data indicates that mineral lineations to the southeast may have a different orientation (60º=>194º) than the mineral lineations to the northwest (37º=>126º). Microstructures and textures include curved inclusion trails in garnet and staurolite, crenulation cleavage, and garnet included in staurolite. Preliminary electron-probe micro analysis of monazite was completed at UMass Amherst for samples on both sides of the ultramafic bodies. In two locations, monazite cores yielded Ordovician (Taconic?) dates. In several other locations, most monazite grains had Late Devonian to Early Mississippian cores and rims that are interpreted to be associated with the Acadian-Neoacadian orogeny. There is a younger subset of Mississippian monazite rims that are likely related to the Alleghanian orogeny. The goal of our ongoing work is to tightly constrain the P-T-t-D path using monazite petrochronology to resolve the complex tectonic history of the eastern Blue Ridge and highlight any differences that might indicate a cryptic tectonic boundary residing along the ultramafic bodies.

Geological Society of America Abstracts with Programs. Vol. 57, No. 6

doi: 10.1130/abs/2025AM-414078

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