Post on 24-Jan-2016
description
Chemical And Thermal Analysis of Zircons in the Cerro Toledo Rhyolite, New Mexico
Hunter EnglandMentor: Mary ReidNorthern 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
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-T
i RimLow-T
i 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 R
imLow-Ti C
ore
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
Phases of Bandelier magma chamber (C) (Campbell et al., 2009)
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
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
MoreEvolved
LessEvolved
Temperature Variations
778°C
761°C
741°C
684°C
716°C
632°C
Ti-in-zircon geothermometer used to calculate temperature (Watson et al. 2006)
Rim T’s clustered compared to interior domainsCampbell 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. 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