Chemical And Thermal Analysis of Zircons in the Cerro Toledo Rhyolite, New Mexico

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

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

3. 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) Low-Ti Core CTR quartz reversals imaged with cathodoluminescence (Campbell et al., 2009) High-Ti Rim

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

5. 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 Form topics into questions  • 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) Zircon high-Ti rims imaged with cathodoluminescence (Reid, 2011) Phases of Bandelier magma chamber (C) (Campbell et al., 2009)

6. 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 High Ti Glass (not quartz) Low Ti Quartz imaged with CL (2012)

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

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

9. 778°C Temperature Variations 761°C 741°C 716°C • Ti-in-zircon geothermometer used to calculate temperature (Watson et al. 2006) • Rim T’s clustered compared to interior domains 684°C Campbell et al. (2009) Data Zircon high-T rims imaged with CL (Reid et al., 2011) 632°C Rims Cores zircon cryst.

10. Conclusions Hotter, Less evolved • 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 CL image of quartz showing a reversal in chemistry

11. Questions???

12. 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

13. http://www.vanderbilt.edu/ees/people/faculty/CalvinMiller.phphttp://www.vanderbilt.edu/ees/people/faculty/CalvinMiller.php 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. 469-485, doi: 10.1086/604744. Claiborne, Lily L; Miller, Calvin F; Flanagan, Daniel M; Clynne, Michael A; Wooden, Joseph L.Geology (Boulder)38. 11 (Nov 2010): 1011-1014. 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, p. @B08201, doi: 10.1029/2006JB004511. 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. 293-311, doi: 10.1007/s00410-010-0532-0. 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. 201-215. Three Dimensional View of the IMS-1270. 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. 413-433, doi: 10.1007/s00410-006-0068-5. Woudloper. Fractional Crystallization. 2009. Graphic. Wikipedia Woudloper. Fractional Crystallization. 2009. Graphic. Wikipedia Magma evolution (http://www.rareearthelements.us/ree_in_space)