MINERALOGICAL AND GEOCHEMICAL CHARACTERIZATION OF COOK CANYON TUFF NEAR KINGMAN, AZ WITH IMPLICATIONS FOR MAGMATIC PROCESSES
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.