Chemical And Thermal Analysis of Zircons in the Cerro Toledo Rhyolite, New Mexico Hunter England Mentor: Mary Reid Northern Arizona University

Using Zircons Zircons create distinct compositional bands (zoning) Zoning records changes in temperature and composition Magma Evolution (Woudloper, 2009) Zoning in Zircons (Mt. St. Helen’s) (Claiborne et al., 2010) Normal Evolution Reversal More evolved magma

Cerro Toledo Rhyolite (CTR) Set of silicic lava domes and associated tephras (Stix and Gorton, 1993) Emplaced between two supervolcanic eruptions (Phillips et al., 2007) Contains quartz with Ti-rich rims (Campbell et al., 2009) May record evidence for intrusion of hotter, less evolved magma Valles Caldera, source of CTR (red) (Smith et al. 1970) CTR quartz reversals imaged with cathodoluminescence (Campbell et al., 2009) High-Ti Rim Low-Ti Core

Known Volcanic History Phases of Bandelier magma chamber (C) (Campbell et al., 2009) Caldera-forming supereruption (LBT) – may have been triggered by melt intrusion CTR eruptions – show evidence of gradual cooling and normal evolution CTR eruptions Gradual cooling and evolution High-Ti Rim Low-Ti Core CTR quartz rim reversals imaged with cathodoluminescence (Campbell et al., 2009)

Why? Does CTR zircon data also indicate a mafic intrusion? Implications for: Resurgent caldera behavior Affects of melt intrusion Predicting catastrophic eruptions Whether zircons detect magma intrusion Zircon high-Ti rims imaged with cathodoluminescence (Reid, 2011) Form topics into questions  Phases of Bandelier magma chamber (C) (Campbell et al., 2009) How do resurgent calderas behave? How does an intrusion of melt affect a magma system? Help better predict catastrophic eruptions Are zircon data more definitive? Valles Caldera (NASA Earth Observatory, 2002)

Sample Collection and Preparation Pueblo Canyon, near Los Alamos Pumice clasts collected from ash and pumice beds (Oct. 2011) Quartz imaged with cathodoluminescence (CL) to confirm reversals in chemistry Quartz imaged with CL (2012) Low Ti High Ti Glass (not quartz)

Ion Microprobe Zircons mounted in indium Ion microprobe analysis performed at UCLA (at depth intervals into zircon) Obtained trace element data for zircons UCLA’s ion microprobe ~1 cm

Low Zr/Hf indicates greater evolution Feldspar and allanite crystallization trend linearly with evolution Rim values generally less evolved Zr/Hf zircon cryst. Magma Evolution More Evolved Less Evolved

Temperature Variations 778°C 761°C 741°C 684°C 716°C 632°C Zircon high-T rims imaged with CL (Reid et al., 2011) Ti-in-zircon geothermometer used to calculate temperature (Watson et al. 2006) Rim T’s clustered compared to interior domains Campbell et al. (2009) Data Cores Rims

Conclusions CL images of quartz showed reversals in chemistry Zircon chemical data confirms this reversal Reversals indicate the intrusion of a less evolved melt However, further work is required to explain the apparent lack of temperature reversal at the rims Cooler, More evolved Hotter, Less evolved CL image of quartz showing a reversal in chemistry

Questions???

Acknowledgements Mary Reid, Professor, Program Chair of Geology, NAU James Wittke, Geologic Materials Analyst, NAU Northern Arizona University Geology Department at UCLA NASA Space Grant Consortium Nadine Barlow Kathleen Stigmon

Work Cited Campbell, M.E., Hanson, J.B., Minarik, W.G., and Stix, J., 2009, Thermal history of the Bandelier magmatic system; evidence for magmatic injection and recharge at 1.61 Ma as revealed by cathodoluminescence and titanium geothermometry: Journal of Geology, v. 117, p , doi: / Claiborne, Lily L; Miller, Calvin F; Flanagan, Daniel M; Clynne, Michael A; Wooden, Joseph L.Geology (Boulder) (Nov 2010): Phillips, E.H., Goff, F., Kyle, P.R., McIntosh, W.C., Dunbar, N.W., and Gardner, J.N., 2007, The (super 40) AR/ (super 39) Ar age constraints on the duration of resurgence at the Valles Caldera, New Mexico: Journal of Geophysical Research, v. 112, doi: /2006JB Reid, M.R., Vazquez, J.A., and Schmitt, A.K., 2011, Zircon-scale insights into the history of a Supervolcano, Bishop Tuff, Long Valley, California, with implications for the Ti-in-zircon geothermometer: Contributions to Mineralogy and petrology/Beitrage Zur Minerologie Und Petrologie.Berlin and New York NY, v. 161, p , doi: /s Stix, J., and Gorton, M.P., 1993, Replenishment and crystallization in epicontinental silicic magma chambers; evidence from the Bandelier magmatic system: Journal of Volcanology and Geothermal Research, v. 55, p Three Dimensional View of the IMS N.d. Graphic. Department of Earth and Space Sciences, UCLA Watson, E.B., Wark, D.A., and Thomas, J.B., 2006, Crystallization thermometers for zircon and rutile: Contributions to Mineralogy and Petrology, v. 151, p , doi: /s Woudloper. Fractional Crystallization Graphic. Wikipedia es/people/faculty/CalvinMill er.php Magma evolution ( s.us/ree_in_space) Woudloper. Fractional Crystallization Graphic. Wikipedia