MAPPING YELLOWSTONE HOT SPOT TRACK RHYOLITES IN THE EASTERN SNAKE RIVER PLAIN: A CASE STUDY FROM THE HEISE VOLCANIC FIELD, AMMON 7.5-MINUTE QUADRANGLE, IDAHO

Successive eruptions of explosive large-volume rhyolites define a hot spot track in the Yellowstone-Snake River Plain volcanic province (YSRP). Understanding of the genesis and age of these units has progressed in recent years with the development of single crystal isotopic analyses. In contrast, geologic mapping at scales sufficient to accurately depict details of unit distribution, thickness, and stratigraphic relationships is relatively rare. Here, we present preliminary results of 1:24,000-scale mapping from a key area of the Heise volcanic field (HVF). The HVF is the second-youngest caldera complex in the YSRP with ages ranging from about 6.6 to 4.5 Ma. Exposures in the Ammon quadrangle and adjacent Heise Cliffs and Meadow Creek areas are among the best in the HVF for the large volume Blacktail, Lake Walcott, and Kilgore ignimbrites. Superb exposures of unwelded rhyolitic deposits are also present in pumice mines within the quadrangle. We facilitate access to our mapping with free distribution on the IGS website www.idahogeology.org. New and compiled petrological, geochemical, and paleomagnetic datasets together with geo-located outcrop and thin section images are also provided. Users can access the map, cross section, unit descriptions, and supporting data tables as a single integrated PDF file, or as individual ArcMap GIS shape files, Excel spreadsheets, and KML files. Field guides aimed at K-12 educators and geologic professionals are planned.