PRECAMBRIAN CRUSTAL EVOLUTION AS PRESERVED IN THE WYOMING CRATON: INSIGHTS FROM TORREY CANYON AND SOUTH PASS

Tectonomagmatic processes associated with continental crust generation throughout Earth’s history reflect the complex interrelationship between orogenic and accretionary events, as well as the numerous cycles of silicate differentiation, juvenile crust production, and crustal recycling. This study will investigate the timing and nature of continental crust-generating processes as recorded by the Wyoming Craton, which hosts some of the oldest rocks in the US. Specifically, the igneous and metamorphic rocks at two sites: Torrey Canyon and South Pass, will be studied.

Lithologies at these locations include various granites, pegmatites, schists, amphibolites, and gneisses. All samples have been characterized via polarized light microscopy (PLM) and scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS) for modal proportions of major, minor, and trace mineralogy. Within the context of future U-Pb chronological study, titanite, apatite, and zircon have been specifically documented as minor and trace phases. Amphibole and apatite will be characterized for their major element and trace element compositions via electron probe microanalysis (EPMA) and trace element compositions via laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) respectively. This data will be used to determine amphibole crystallization conditions and evaluate the tectonomagmatic environment in which apatite crystallized. Zircon mineral separates from bulk samples will be imaged via cathodoluminescence (CL). These CL images will inform the location of LA-ICP-MS analysis for in-situ U-Pb chronology. Preliminary data has yielded zircon U-Pb ages from 2.7 Ga to 2.8 Ga from one biotite schist sample in Torrey Canyon. From one cross cutting granite unit, zircon U-Pb ages are clustered at ~1.6 Ga.

Future work will focus on in-situ mineral analysis via EPMA and LA-ICP-MS, and significantly expanding the U-Pb chronological dataset at both field sites. Collectively, the petrochronology of the igneous and metamorphic lithologies at Torrey Canyon and South Pass aims to provide new chemical and temporal constraints on the tectonomagmatic processes recorded in the Wyoming Craton.