Petrology

Thomas Hoisch: Metamorphic petrology

Research activities

I pursue 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, click here. 

James Wittke: Igneous petrology & meteoritics

Research activities

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.

Selected references

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 38:529-554.

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.