Abstract by Danielle Spencer
CANNIBALIZATION AND MIXING PROCESSES IN HOTSPOT RHYOLITES: ANOMALOUS TEXTURES AND GEOCHEMISTRY OF THE KIMBERLY MEMBER OF THE CASSIA FORMATION, YELLOWSTONE HOTSPOT TRACK, IDAHO
The 7.7 Ma Kimberly Member of the Cassia Formation is part of a succession of A-type rhyolites associated with the Yellowstone hotspot track, sampled by the Kimberly core, drilled on the Snake River Plain as part of Project HOTSPOT (Shervais et al., 2013). The Kimberly Member is a 170 m thick high-silica rhyolite with Qz, Pl, Ano, Sa, Aug, Pgt, Fe-Ti oxides, Zrn, and Ap. There are three chemically distinct feldspars: anorthoclase, sanidine, and a continuum from oligoclase (An66Or26Ab8) to andesine (An61Or34Ab5). Pl, Ano, and Sa each lie on solvus lines with different temperatures. Pl is commonly surrounded by pitted Ano that is mantled by Sa. Pgt (Mg # 0.15) is complexly mantled by Aug (Mg # 0.19). Pgt cores are often inverted. Qz is intensely resorbed. The Kimberly Member has low δ18O values (3 per mil in feldspar, 0-3 per mil in zircons; Colon et al., 2017). U-Pb zircon ages, acquired through TIMS and LA-ICPMS span one million years. εHf values in zircon are likewise diverse and range from -8 to 1.The unique textures and geochemistry of the Kimberly rhyolite may be caused by cannibalism of a previous generation of rhyolite or granite, and magma mixing.