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