TESTING THE BASALT-RHYOLITE CONNECTION OF THE BEAVER RIDGE VOLCANIC FIELD, UTAH

The Black Rock Desert volcanic field in central Utah consists of five subfields and covers approximately 840 square miles. Volcanism in the region is attributed to Quaternary Basin and Range extension. The Beaver Ridge subfield is located near Kanosh, covers approximately 30 square miles, and contains both basaltic and rhyolitic lavas. Geochemical analyses and field observations of the <1 Ma lavas identify three suites: basalts of Beaver Ridge 1 (~0.9 Ma), basaltic andesites of Beaver Ridge 2 (~0.5 Ma), and the White Mountain rhyolite dome (~0.4 Ma). In this work, we use the legacy data to evaluate the geochemical processes that could produce the three chemical suites, generating more evolved compositions over time. Assuming a common parental tholeiitic basalt, we use legacy data to test for progressive fractional crystallization versus combined assimilation and fractional crystallization to relate the suites of 0.9-0.4 Ma lavas. Incompatible trace element variation trends suggest possible progressive fractional crystallization, but variations in Sr, Nd, and Pb isotopic ratios suggest possible crustal contamination. This study will help us better understand what processes drive small scale magma evolution over time intervals of ~0.5 million years in rift basins.