PETROGENESIS AND GEOCHRONOLOGY OF BASALTIC LAVAS FROM BLACK ROCK DESERT, UTAH

The Black Rock Desert Volcanic Field located in central Utah covers ~350 square miles and is subdivided into five subfields. The Twin Peaks subfield is characterized by an early (~2.5 Ma) rhyolitic phase of volcanism followed by the eruption of basaltic lavas (~2.1 Ma). Previous studies termed the basalts the Burnt Mountain lavas and separated them into three groups based on their geochemical signatures. This contribution examines the processes that could produce three groups of chemically distinct lavas within a single volcanic field. New whole-rock major and trace element analyses were acquired and compiled along with a database of geochemical results from previous workers. Additionally, high-precision ⁴⁰Ar/³⁹Ar dates were obtained for several samples to improve upon previously reported K/Ar dates and provide time constraints for the magmatic processes. Thermodynamic modeling using the Magma Chamber Simulator and the FC-AFC-FCA Excel modeling program was conducted to test differentiation processes within and between the groups of basalts (Bohrson et al., 2014; Ersoy & Helvaci, 2010). Preliminary results indicate that several compositions can be reproduced solely through fractional crystallization, while others require a combination of fractional crystallization and assimilation of more silicic material. We use the thermodynamic models to evaluate the genetic relationships between different Burnt Mountain lava flows and place them within a temporal and spatial context.