2015 GSA Annual Meeting in Baltimore, Maryland, USA (1-4 November 2015)

Paper No. 210-28
Presentation Time: 9:00 AM-6:30 PM


PERRY, Sarah E.1, SCHELAND, Cullen L.2, CLAIBORNE, Lily L.3, MILLER, Calvin F.4, MCDOWELL, Susanne M.5 and COVEY, Aaron K.3, (1)Department of Earth Science and Geography, Vassar College, Box 2186, Poughkeepsie, NY 12604, (2)Geology and Environmental Geosciences, Lafayette College, Easton, PA 18042, (3)Department of Earth and Environmental Sciences, Vanderbilt University, Nashville, TN 37235, (4)Dept. of Earth and Environmental Sciences, Vanderbilt University, Nashville, TN 37235, (5)Department of Geology, Hanover College, Hanover, IN 47243, sarperry@vassar.edu

The Cook Canyon Tuff (CCT) is a major, ~18.9 Ma (Lidzbarski 2014) ignimbrite exposed in the Cerbat and Black Mountains and adjacent areas of NW Arizona and SE California. It is characterized by abundant plagioclase and biotite phenocrysts (Buesch and Valentine 1986). In many localities it underlies the Peach Spring Tuff (PST), an ignimbrite produced by an 18.8 Ma supereruption (Ferguson et al 2013). AMS data indicates that the CCT may be sourced from the same vicinity as the PST (R. Varga, unpub), suggesting that they may be products of the same magmatic system. Therefore, understanding the CCT’s magmatic history is critical in characterizing the volcanic sequence of the region and understanding the processes leading to a supereruption. We collected light- and dark gray pumice samples from Cook Canyon and nearby Coyote Pass near Kingman, AZ and, combined with data from previous studies (Pratt et al. 2014; Varga unpub.; Scheland et al. 2015, GSA abs), we characterized the geochemistry and mineral assemblage, and modeled eruption temperatures.

Plagioclase is the dominant phenocryst (~20%); relatively homogeneous, high-Ti biotite (6% TiO2, 15% MgO, 13% FeO) is also abundant (~10%). Sanidine is rare (<<5%), as are clinopyroxene and hornblende. Accessory minerals include Fe-Ti oxides, apatite, sphene, and zircon. Bulk rock compositions (XRF) mostly fall within a narrow range (66-67.5 wt% SiO2, 2.5-4% FeOt, 5.3-6.3% K2O), but one dark pumice is less silicic (63 wt% SiO2, 4.2% FeOt, 6.1% K2O), hinting at the possibility of multiple magmas. Glass compositions (SEM-EDS + LA-ICPMS) are heterogeneous within individual samples; SiO2 typically ranges from 69-72 wt%., and Na2O, FeOt, and CaO correlate negatively with SiO2. Heterogeneity is also evident in trace elements (e.g. ~200-400 ppm Sr, 300-650 ppm Zr), further supporting incomplete magma mingling. Zircon saturation thermometry (Boehnke et al 2013) based on glass data indicates a range of temperatures of the mingling magmas from 800-900 °C. MELTs modeling (based on assumption of equilibrium) suggests an eruption temperature of around 875 ⁰C at 2% wt H2O or 815 ⁰C at 4% wt H2O. Our new data suggest that two or more magmas mingled to form the CCT shortly prior to eruption, but it does not reveal a direct petrogenetic relationship between the CCT and PST.

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