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Interactions between fluids and rocks in the earth’s mid- to lower-crust and upper mantle constitute the focus of John’s research. Deep fluids have played a primary role in the development of earth's crust, atmosphere, hydrosphere and biosphere. They are responsible for explosive volcanic eruptions and for the formation of most ore deposits. John is particularly interested in the effects fluids have on the accessory minerals zircon and monazite. His research has broad relevance in geochemistry and igneous and metamorphic petrology because these minerals are commonly used for dating geologic processes.
John and his students use the ion microprobe and LA-ICP-MS to date zones within individual mineral grains, but it is not always clear what the ages represent. John approaches this problem in a variety of ways, including:
· - characterizing the kinetics of growth of dateable minerals in the presence of fluid.
· - developing methods for using isotope ratios in minerals for identifying hydrothermal alteration events.
· - measuring aqueous solubilities, which serve as a measure of susceptibility to fluid-induced recrystallization.
· - measuring mineral/fluid partition coefficients, which can be used to establish fluid "fingerprints".
· - contrasting the behavior of different minerals to fluid infiltration in well-characterized field settings of various types, including contact metamorphic aureoles in Nevada and California, and ultrahigh-pressure, diamond-bearing rocks in China that were exhumed from earth's mantle.
Results from these studies suggest that measured ages in monazite often correspond to resetting by recrystallization induced by infiltrating fluid. Thus, monazite can be used to characterize, in time and space, the process of open-system fluid infiltration. This will lead to a better understanding of fluid alteration events, including those that form hydrothermal ore deposits.
John’s research projects are based in both the lab and field. Lab experiments performed at high pressure and temperature have yielded important insights into accessory mineral-fluid reactions in nature. Field experiments are designed to test hypotheses that arise from lab experiments. Field observations also raise new questions that may be addressed experimentally, so the two approaches are synergistic.
Students choose whether they want to work in the lab, field, or both. Field studies have been conducted in central China, southern Nevada and eastern California, and generally consist of collecting rock samples, recording locations in a geographic information system, and performing mineral separations to obtain samples of zircon and monazite powders. In lab studies the samples are synthesized at high pressure and temperature. Students then measure the chemical and isotopic compositions of their lab and field samples using a variety of analytical tools: ion microprobe, electron microprobe, laser ablation ICP-MS, x-ray diffractometer, and scanning electron microscope. The information they obtain provides powerful constraints on the timing and style of fluid-rock interactions. For example, we have been able to estimate the rate of exhumation of subducted continental crust in China. Recently we used oxygen isotopes to show unequivocally that monazites in country rock near a pluton had recrystallized in the presence of fluid derived from the magma, and we used Th-Pb geochronology to date that event. In the process, John’s students develop problem solving and laboratory skills and a better understanding of earth processes. This experience is highly relevant to environmental problems and to the understanding of ore deposits. It is thus very practical, leading to job opportunities, as well as contributing to our knowledge of large-scale earth processes.
Eclogite block in metacarbonates, Dabie Shan ultrahigh-pressure metamorphic belt, China.
National Science Foundation, PI (Calvin Miller co-PI), $285,000, 6/1/05-6/1/08, Zr mineral aqueous solubilities and zircon/(fluid-melt) partitioning.
Ayers J.C., *Loflin M., Miller C.F., Barton M.D., Coath C. (2006) Monazite used to determine the extent and timing of fluid infiltration in the Birch Creek Pluton metamorphic aureole. Geology 34(8), 653-8. http://geology.geoscienceworld.org/cgi/content/abstract/34/8/653
Lehner S.W., Savage K., Ayers J.C. (2006) Vapor growth and characterization of pyrite (FeS2) doped with Co, Ni, and As: Variations in semiconducting properties. Journal of Crystal Growth, v. 286, 306-317. doi:10.1016/j.jcrysgro.2005.09.062
Ayers, J.C., *Loflin, M., Miller, C.F., Barton, M.D., and Coath, C. (2004) Dating fluid infiltration using monazite. In R.B. Wanty, and R.R. Seal II, Eds. Proceedings of the Eleventh International Symposium on Water-Rock Interaction, Vol. 1, p. 247-251. A.A. Balkema Publishers.
Bryant D. L., Ayers J. C., Gao S., Miller C. F., and Zhang H. (2004) Geochemical, Age, and Isotopic Constraints on the Location of the Sino-Korean/Yangtze Suture and Evolution of the Northern Dabie Complex, East Central China. Geological Society of America Bulletin 116, 698-717. http://bulletin.geoscienceworld.org/cgi/content/full/116/5-6/698
Ayers J.C., *DeLaCruz K., Miller C.F., *Switzer O. (2003) Experimental study of the growth kinetics of zircon in quartzite ± H2O at 1.0 GPa and 1000oC, with implications for geochronological studies of high-grade metamorphism. American Mineralogist 88, 365-376.
Ayers J.C., *Dunkle S., Gao S., Miller C. (2002) Triassic zircon U-Pb and monazite Th-Pb ages recorded in Maowu ultramafics and Shuanghe jadeite quartzite, Dabie Shan UHP belt, east-central China. Chemical Geology 186:315-331.
Ayers, J.C., Miller, C.F., *Gorisch, E.B., *Milleman, J. (1999). Textural development of monazite during high-grade metamorphism: Implications for U,Th-Pb age dating. American Mineralogist 84:1766-1780.
Ayers, J.C. (1998). Trace element modeling of aqueous fluid – peridotite interaction in the mantle wedge of subduction zones. Contrib. Mineral. Petrol., 132:390-404.
Ayers, J.C., *Dittmer, S.K., Layne, G.D. (1997). Partitioning of elements between peridotite and H2O at 2.0-3.0 GPa and 900-1100 oC, and application to models of subduction zone processes. Earth Planet. Sci. Lett., 150:381-398.
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*student
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