CHARACTERIZATION OF AN ERUPTIVE SEQUENCE OF CINDER AND SPATTER CONES IN THE ICE SPRINGS VOLCANIC FIELD OF THE BLACK ROCK DESERT, UTAH

The ~20 km² Ice Springs Volcanic Field comprises at least four centrally located basaltic cinder/spatter cones surrounded by lava flows in south-central Utah on the eastern boundary of the Basin and Range Province. The field contains the youngest known volcanoes in Utah ( 660 +/- 170 years; Valastro et al., 1972). Although the development of the field has been described by previous workers (e.g., Hoover, 1974), the timing of lava emplacement and vent formation in the area of the cones remains uncertain. The main goal of this project is to map and geochemically characterize outcrops within the nested cones in order to establish an eruption sequence.

We recognized four morphologic features in the study area: cones with complete or partial crater rims, remnant crater rims, breaches in crater rims, and lava outflow channels. The study area includes three cinder/spatter cones: Crescent, Miter, and Pocket. Crescent includes a large partial crater rim that encompasses the smaller Miter and Pocket cones. Miter is a well-developed cone, with a 200 m diameter circular crater rim, while Pocket is the smallest and youngest cone, with a 100 m crater rim. Outcrops were correlated based on field characteristics and associations, including outcrop geometry, bomb and bed orientations, and lithofacies. Based on field mapping we hypothesize the following sequence of events: 1. emplacement of the Crescent crater; 2. formation of older Miter crater and possibly the destruction of the western wall of Crescent crater; 3. emplacement of the nested younger Miter crater within the older crater rim; 4. breaching of the northern rim of the younger Miter crater and lava flow effusion; 5. breaching of the western rim of Miter crater and lava effusion; and 6. emplacement of Pocket cinder cone within the Crescent crater.

Eighteen samples were collected to characterize the petrology and geochemistry of the study area rocks. Ongoing thin section and XRF geochemical analyses will be used to assess field correlations and the hypothesized event sequence. Geochemical and mineral data will be also used to correlate more distant lava flows to the crater sequence. Preliminary analysis of trace element data shows similarities of different mapped units, suggesting that it will be difficult to distinguish and correlate units based on geochemical signatures.