DETERMINING THE IMPACT OF THE MARYSVALE VOLCANIC FIELD ON PRESENT DAY HYDROLOGICAL SYSTEMS IN SEVIER COUNTY, UTAH

The upper reaches of the Sevier river flow through the remnants of the Marysvale Volcanic Field (MVF), a complex of massive calderas that deposited several hundred cubic kilometers of magma erupted to the surface. The MVF became active between 27 and 19 Ma forming at least 5 calderas depositing ashflow units throughout Southwestern Utah. The volcanics of the field are characterized by two different compositions, starting calc-alkaline switching to a bimodal composition near the end of the field’s activity. Dotting the landscape of the MVF are hot springs, heated by remnant cooling magma from a deep composite batholith extending several plutons to the calderas. The springs take advantage of pathways through existing Basin and Range faults such as the Sevier fault or smaller faults related to volcanism. Several samples were taken from the hot springs and the surrounding tributaries in order to determine trace element and isotopic compositions using Ar and a mass spectrometer for identification. The goal of the survey is to characterize the aquifer based on its compositional interaction with the remnant magma system as well as the buried volcanic stratigraphy. We characterized compositions using Pratt diagrams and compared to geologic maps and cross sections of the MVF in order to understand how the magma composition is manifested in the aquifer and spring water.