NEW COSMOGENIC AND VML DATES AND REVISED EMPLACEMENT HISTORY OF THE ICE SPRINGS VOLCANIC FIELD IN THE BLACK ROCK DESERT, UTAH

The development of robust dating methods (Cosmogenic Dating & Varnish Microlamination (VML)) makes it possible to date young lava flows in the Ice Springs Volcanic Field (ISVF) in the Black Rock Desert, Utah. ISVF is hypothesized to be a compound polygenetic volcano due to multiple cinder cones (Miter, Terrace, Pocket, & Crescent), eruptions, and magma batches. This study aims to determine the flows’ emplacement sequence and ages in order to place the ISVF in geologic context and improve understanding of its eruption history. Two pahoehoe samples were collected from the Miter/Terrace boundary and within the Miter flow for whole-rock cosmogenic 36Cl dating at the Purdue PRIME Lab. The CRONUS calculator was used to find minimum and maximum ages that are in disagreement with Valastro et al.’s (1972) radiocarbon age of 660 ± 170 years. New cosmogenic ages for the Miter/Terrace boundary range 9.4 (±1.3) - 10.9 (±1.6) kyr and 10.9 (±1.6) - 11.3 (±1.5) kyr for the Miter flow. VML ultra thin sections were made from 3 samples of the Miter/Terrace flows to independently estimate the age, dating the samples as old as ~12.5 kya. Earlier studies found that Crescent and early Miter flows contain high silica (>51 wt.%) while later Miter and Terrace lavas contain low silica (<51 wt.%). Early Miter and Crescent are distinguished by differences in FeO* and TiO₂. New whole-rock geochemical data (XRF, The College of Wooster) show that some “early Miter” samples overlap with the Crescent lavas in their SiO₂, FeO*, and TiO₂ compositions, and may have been erupted from Crescent. Samples collected north of the Miter/Crescent boundary contain low silica, suggesting that the Miter lava flow continues north of the formerly hypothesized boundary. The geochemical boundary corresponds to a change in the lava morphology. Crescent flows form a’a lava with rafted cinder material. Miter lavas comprise slabby, disrupted terrain with a distinct lava channel. Additional geochemical, cosmogenic, and VML work will help clarify the nature of the Miter/Crescent boundary. Our new dates and revised flow boundaries are consistent with the compound polygenetic volcano classification and further enhance our understanding of the ISVF in the geologic history of the Black Rock Desert.