11-11 Assessing the Potential for Preservation of Shock Features in the “Woodbury-Manchester-Roosevelt Structure", Southern Appalachian Piedmont (USA), Using a Global Database of Terrestrial Impact Structures

Session: Applications of Igneous Petrology, Geochemistry, and Geochronology to Understanding Earth and Other Planetary Systems (Posters)

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Abstract:

Terrestrial impact structures are a common feature across the solar system, but are commonly modified or completely erased by erosion and tectonism on Earth. In fact, ~70% of confirmed astroblemes on Earth with well-constrained ages are Paleozoic or younger, attesting to the effectiveness of systematic destruction of impact structures by erosion and overprinting of shock features during tectonism (e.g., faulting, folding, metamorphism). Here, we incorporate information (e.g., crater size, impact age, location) from comprehensive databases (e.g., Impact Earth Database) of confirmed terrestrial impact structures, and expand on that data by adding information on crater modification, reported hypervelocity impact structures, and the presence/absence of post-impact tectonic modification features using publicly available literature. With this expanded database, we explore the implications for preservation of hypervelocity impact features following post-impact tectonism, with special focus on the purported “Woodbury-Manchester-Roosevelt structure” in the Pine Mountain belt of the southern Appalachians (Georgia, USA). In this region of the western Inner Piedmont, a linear belt of Mesoproterozoic (Grenville) rocks and their Paleozoic cover have been alternately interpreted as an Alleghanian-aged, complexly folded, large-scale (half wavelength >6 km) recumbent antiform – or – as a Neoproterozoic hypervelocity impact structure (“Woodbury-Manchester-Roosevelt structure”) >200 km in diameter. The latter interpretation requires the purported ca. 800 Ma impact structure be overprinted by middle-upper amphibolite facies metamorphism during the Late Paleozoic assembly of Pangea and growth of the Appalachian Mountains. Consequently, the impact model also requires preservation of purported hypervelocity impact features (e.g., shocked quartz, shatter cones) following post-impact burial, metamorphism, and regional deformation. Using our comprehensive database (n>200) of impact structures on Earth, we compare and contrast the purported “Woodbury-Manchester-Roosevelt structure” with confirmed hypervelocity impact structures overprinted by post-impact tectonic processes. That subset (n<30) includes impact structures affected by younger faulting, folding, metamorphism, and other thermal overprints. We focus primarily on 4 confirmed impact structures with potential metamorphic overprints ranging from greenschist to amphibolite facies in order to assess the likelihood that delicate shock features in the “Woodbury-Manchester-Roosevelt structure” were preserved during metamorphism of the Pine Mountain belt. Viewed through the lens of our comprehensive database, and coupled with age and tectonic constraints, we suggest the structural setting for rocks of the Pine Mountain belt is more consistent with a tectonic and not impact origin.

Geological Society of America Abstracts with Programs. Vol. 58, No. 1, 2026

doi: 10.1130/abs/2026SE-13603

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