195-1 Tectonic and Metamorphic Evolution of the Southern Teton Gneisses, Wyoming: Insights into Crustal Rheology, Partial Melting, and Craton Assembly during the Neoarchean

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

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In Earth’s ancient history, fragments of thickened crust stabilized and collided to form orogenic ranges that now support modern-style plate tectonics. The Teton Range in Wyoming provides evidence of one such collision, the oldest known Himalayan-style continent-continent-type collision, where the Northern and Southern Gneiss blocks fused along the Moran Deformation Zone ~2.6 Ga. The northern block of the Moran Deformation Zone records 2.70 Ga high-pressure granulite facies metamorphism. Much less is known about the Southern Teton Gneisses, the tectonic counterpart to the unique Northern Gneisses. The southern part of the Teton Range includes the Southern Teton Gneisses, the Rendezvous metagabbro, and the Mount Owen batholith, which were formed between 2.8 and 2.6 Ga. Both the Northern and Southern Gneisses formed during a transitional period in the rheology of Earth’s crust (transition from ~3.0-2.5 Ga) that generated unique tectonic styles. This same period is when the building blocks of modern continents were assembled, suggesting that the evolution of Earth’s tectonic styles was required for stable continent formation. Rocks in the southern Teton range have ages spanning from 2.8 to 2.6 Ga, recording 200 million years of tectonic activity and allowing us to assess changes in the crust during this transitional period in tectonic behavior. This study integrates detailed fieldwork, thin-section petrography, whole-rock and mineral geochemistry, thermodynamic modeling, and U-Pb geochronology to unravel the tectonic and metamorphic history of the Southern Gneisses. The most recent deformation episode occurred at approximately 2.62 Ga under moderate pressure (~4 kbar) and temperature (~550°C) conditions. However, signs of partial melting and garnet-rich mineral assemblages indicate earlier high-pressure, high-temperature events not attributable to this final metamorphic phase. The presence of garnets, which typically form at pressures above 4 kbar, and their melt textures suggest a more complex tectonic and metamorphic evolution than previously recognized. In most samples, gneissic and schistose textures are noticeable, suggesting moderate- to high-grade metamorphism. Continuous sphene-clinopyroxene-amphibole reaction rims are seen in some samples, suggesting a metamorphic environment where a mineral grain, likely a parent mineral such as olivine or another ferromagnesian silicate, was changed by high temperatures and pressures. Overall, results presented here will contribute to understanding the tectonic history of the Teton Range, Wyoming Craton, and transition to modern tectonic behavior.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-8577

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