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Photo of Mount Igikpak

Our faculty employ a broad range of approaches to the petrologic, chemical and mineralogical study of meteorites and the Earth's crust and mantle. Main research emphases include experimental, thermodynamic, physical, geochemical, crystallographic and field-based approaches. Some of the disciplinary approaches are summarized below.

Isotope Geochemistry

We use radiogenic and stable isotope systems (primarily Sr, Nd, Pb, Hf, U-series, oxygen, and lithium) in conjunction with major and trace-element geochemistry to study a wide variety of geological processes. The emphasis of our research is on igneous geochemistry, addressing questions that include the origin and distribution of chemical heterogeneities in the mantle, evolution of continental crust, melt generation processes, and timescales of storage and crystallization of magmas within the crust. In addition, members of our group are using isotopic tracers to study seawater-rock interaction at midocean ridge hydrothermal systems and its effect on both ocean and oceanic crust geochemistry. We also employ isotopic tracers to identify heavy metal and pollutant pathways through the environment. (_Isotope_Geochemistry_Lab_)

Experimental Petrology

We are engaged in experimental studies addressing topics ranging from the thermochemistry of sulfides on Earth to the cooling of pyroxenes on the Moon. The experimental petrology laboratory is well equipped to handle a wide variety of low-pressure high-temperature experimental techniques. Facilities include two vertical quench furnaces designed to perform extremely rapid quench from temperature. These furnaces are equipped for computer assisted control of the furnace gas atmosphere allowing precise control of redox state, sulfur fugacity etc. Instruments are available to perform ultrasonic interferometry and density measurements in silicate and sulfide liquids under controlled-atmosphere conditions at temperatures up to about 1650°C. Lower-temperature furnaces are being used for long-term phase equilibrium experiments designed to address the genesis of an important class of epithermal silver ores.

Volcanic Petrology

Experimental, petrologic and field work are combined to address the important issue of the volatile budget at Popocatépetl, Mexico and Villarrica, Chile. Specifically, we would like to improve our understanding of how gases escape from magmas in relatively non-violent passively degassing volcanoes and how these volcanoes differ from their more destructive counterparts.

Recently we have begun a study of quaternary volcanoes in the Cascade Range. The primary focus is a study of the volatile abundance and speciation by studying the stability of hydrous phenocrysts.

See also: Electron Microprobe Laboratory

Mineralogy and Petrology of extraterrestrial materials

We have a major research program to investigate the thermal histories of lunar rocks, achondritic meteorites, and Martian meteorites. The research involves electron microprobe and ion probe studies of the minerals in these samples coupled with single crystal x-ray and transmission electron microscopic studies of pyroxenes. The goal of this work is to elucidate thermal histories of the lunar rocks and meteorites and to use these data to constrain the petrologic and geochemical evolution of the Moon and the meteorite parent bodies.

See also: Electron Microprobe Laboratory

Field and Laboratory studies of layered intrusions

We have a mature research program in the petrology of layered mafic intrusions, specifically the Stillwater Igneous Complex, Montana. Recent efforts are aimed at understanding the petrogenesis of the Platinum-Palladium ore zones by combining field observation, elemental and isotopic analysis and modeling. Access to the entire Banded series of complex via a 5 km long tunnel provides an unprecedented opportunity to test models of crystal fractionation, magma mixing, compaction, melt migration, and fluid/rock interaction.

See also: Electron Microprobe Laboratory

Faculty Members:

Olivier Bachmann
George Bergantz
Bruce Nelson