Thomas Hoisch: Metamorphic petrology
studies in the area of Metamorphic Petrology with the goal of inferring the
tectonic processes associated with burial and exhumation. I have conducted research throughout the
western US, focusing on problems related to Cordilleran orogenesis. I integrate
several approaches, thermodynamic modeling of mineral chemistries to establish
pressure-temperature (P-T) paths, 2-d numerical thermal modeling of thrusts and
detachments, thermochronology, and field relationships. I utilize thermobarometry to determine the
peak conditions of metamorphism, and Gibbs method calculations involving
Duhem's theorem to determine pressure-temperature paths from growth-zoned
garnets. In order to place P-T paths
into a quantifiable tectonic context, I have written computer codes to simulate
the thermal effect of thrusting and exhumation using planar and listric fault
geometries. Various geochronologic
techniques are employed to determine the timing of garnet growth and the
cooling of an area. Cooling histories
are determined mainly by Ar-Ar thermochronology. Recently, tiny monazite inclusions in garnets
from upper-amphibolite facies rocks from the Grouse Creek Mountains were dated
using the high resolution ion microprobe facility at UCLA, and were interpreted
as occlusion ages, and therefore record the ages of garnet growth. The geochronologic data combine with the P-T
path data to provide the constraints necessary to prepare numerical simulations
of thermal history and infer both rate the rate of slip and dip along faults
that buried the rocks, leading to their metamorphism, and their subsequent
exhumation. To view publications,
courses I teach, more details on research, and graduate research opportunities,
James Wittke: Igneous petrology & meteoritics
I supervise the operations of the electron microprobe laboratory, which houses
a Cameca MBX microprobe. My research interests focus upon petrologic problems
ranging from terrestrial igneous rocks to meteorites. I am collaborating with
Richard Holm on ultra-alkaline volcanics and hypabyssal rocks in central
Arizona, and with Ted Bunch on meteorite classifications and the petrology of
impactites from Meteor Crater, Arizona and Argentina. These form when molten
material ejected during meteorite impacts.
I have just started a comprehensive study of the petrology
of a new lunar meteorite regolith breccia. These breccias are complex and
contain a wide variety of lunar rock types. I am also working on a summary of
mineral chemistry of the howardite-eucrite-diogenite (HED) clan. The NAU
Meteoritics Lab has accumulated one of the most extensive collections of this
clan, which is believed to originate from the asteroid 4 Vesta, as part of our
classification efforts. Among the other meteorites we’ve studied previously are
two lunar samples (NWA 032, NWA 773) and one from Mars (NWA 2046). NWA 773 is a
rare lunar cumulate olivine norite; NWA 2046 is the most primitive (magnesian)
shergottite yet recovered. See “Meteorite Classification Services” at the link
above for more details.
I have also collaborated with archaeologist Kim Spurr of
Navajo Nation Archaeology Department, studying volcanic-ash tempered ceramics.
A.J. Irving, T.E. Bunch, S.M. Kuehner, & J.H. Wittke,
2004, Petrology of Primitive Olivine-Orthopyroxene-Phyric Shergottites NWA 2046
and NWA 1195: Analogies with Terrestrial Boninites and Implications for Partial
Melting of Hydrous Martian Mantle: 35th Lunar and Planetary Science Conference
Abstracts, no. 1444.
T.J. Fagan, G. J. Taylor, K. Keil, T.L. Hicks, M. Killgore,
T. E. Bunch, J. H. Wittke, D.W. Mittlefehldt, R. N. Clayton, T. K. Mayeda, O.
Eugster & S. Lorenzetti, 2003, Northwest Africa 773: Lunar Origin,
Iron-Enrichment Trend, and Brecciation: Meteoritics and Planetary Science
T. J. Fagan, G. J. Taylor, K. Keil, T. E. Bunch, J. H.
Wittke, R. L. Korotev, B. L. Jolliff, J. J. Gillis, L.A. Haskin, E. Jarosewich,
R.N. Clayton, T. Mayeda, V. A. Fernandes, R. Burgess, G. Turner, O. Eugster
& S. Lorenzetti, 2002, Northwest Africa 032: Product of Lunar Volcanism:
Meteoritics and Planetary Science 37:371-394.
J. H. Wittke & R. F. Holm, 1996, The association
basanitic nephelinite-feldspar ijolite-nepheline monzosyenite at House Mountain
volcano, north-central Arizona: The Canadian Mineralogist 34:221-240.