John
Ayers
Ph.D.
Rensselaer Polytechnic Institute, 1991
Geochemistry
and Experimental Petrology
General
Interests
John
Ayers conducts studies in the lab and field of a wide range of problems in
geochemistry and igneous and metamorphic petrology, with a focus on the
behavior of hydrothermal fluids and “accessory minerals,” including
monazite, apatite, rutile, and zircon.
Current
Research
Ayers is taking several approaches to
study the effects of interaction between hydrothermal fluids and rocks. In the
laboratory, he uses a piston-cylinder apparatus to duplicate the
high-pressure, high-temperature conditions of the continental lower crust and
upper mantle. Ayers then uses sensitive techniques to chemically analyze the
products of the experiments. The results help define the behavior of trace
elements and the stability of minerals in fluid-bearing rocks. Ayers hopes to
establish a framework for understanding how aqueous fluids dissolve and
transport rock material, a process that can affect the mineralogy and
composition of rocks and result in ore formation.
Ayers’
research has focused on the aqueous solubility and partitioning behavior of
accessory minerals, and the behavior of deep fluids in subduction zones. New
studies of the growth kinetics and textural development of zircon and monazite
in fluid-bearing rocks are aimed at explaining the development of growth
zoning evident in “in-situ” U-Pb age dating of these minerals. Ayers plans
to use a hydrothermal diamond anvil cell to observe the growth of these
crystals in real time. These studies will aid in his interpretation of zircon-
and monazite-bearing UHPM rocks collected in China, including diamond-bearing
eclogites that were subducted to ~180 km depth during the final suturing of
the north and south China blocks.
What Students Do
Ayers’ students
typically perform high P-T experiments using a piston cylinder apparatus. They
then characterize experimental run products using petrographic examination and
by analyzing them using an X-ray diffractometer, electron microprobe and ion
microprobe. In the process, students learn general problem solving and
laboratory skills, and a better understanding of the earth and how to simulate
earth processes in a creative way. This experience, besides being academically
fruitful and providing an excellent entry point into Ph.D. research, is highly
relevant to environmental problems in aqueous geochemistry and to the
understanding of ore deposits. It is thus very practical, leading to job
opportunities, as well as contributing to the understanding of large-scale
earth processes.
Selected Publications
Ayers J.C., *Dunkle S., Gao S., Miller C. (submitted) Triassic
zircon U-Pb and monazite Th-Pb ages recorded in Maowu ultramafics and Shuanghe
jadeite quartzite, Dabie Shan Ultrahigh Pressure Metamorphic Belt,
east-central China. Tectonophysics.
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.
*Larrieu,
T.L., Ayers, J.C. (1997).
Measurements of the pressure-volume-temperature properties of fluids to 20
kbars and 1000 oC: A new approach demonstrated on water. Geochim.
Cosmochim. Acta, 61:3121-3134.
Ayers,
J.C., *DeLaCruz, K.J., *Gorisch,
E.B., Miller, C.F. (1996). Experimental measurement of the growth rate of
zircon: an assessment of the importance of Ostwald Ripening during high-grade
metamorphism, with implications for U-Pb chronology. GSA Abstracts with
Programs 28, A-357.
*student
