268-2 Spatiotemporal Source Heterogeneity in Cenozoic Basalts along the Colorado Plateau-Basin and Range Transition

Session: Old and the New, Long and the Short: Perspectives on Integration of Timescales of Magmatic Processes: Special Session Related to MGPV Awards to Madison Myers and Anita Grunder (Posters)

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Abstract:

Utah hosts numerous monogenetic volcanoes with recent erupted mafic lavas ranging from Pleistocene to present. These volcanoes and their lavas have historically been separated into subfields on the basis of spatial and temporal affinities along with chemical differences. Whole rock major and trace element geochemistry, isotopic data (Pb, Sr, Nd), and new high-precision ⁴⁰Ar/³⁹Ar eruption ages are used to investigate mantle heterogeneity and petrogenesis of basalt to basaltic andesite lava samples from a north-south transect along the Colorado Plateau to Basin and Range transition. The north-south transect includes the localities Curlew Valley (northern), Black Rock Desert subfields (central) and the Santa Clara and Cedar City (southern) volcanic areas. With over 60 samples in total, the sampling resolution of this study is sufficient to identify potential spatiotemporal mantle heterogeneity at the transition between two physiographic provinces. Preliminary results suggest that the northern Curlew Valley lavas were sourced from an isotopically different mantle reservoir than the lavas to the south. The central and southern lavas appear to have origins from isotopically variable mantle pockets, and geochemical data indicate that wall rock assimilation may have occurred during their ascent. Isotopes for Beaver Ridge, Burnt Mountain, and Cove Creek subfields from Black Rock Desert suggest signatures dissimilar to common mafic sources which increase the likelihood of crustal contamination accounting for this disparity. This study seeks to resolve the source variation of these Utah lavas in both space and time and looks to investigate potential contamination sources using thermodynamic models in the future. Geochemical comparisons are made with other Quaternary basalts from volcanic fields along the Colorado Plateau to Basin and Range outside of Utah as well.

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

doi: 10.1130/abs/2025AM-6418

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