Research Interests
Epidote: magmatic vs. subsolidus?
Laser probe measurements of oxygen isotope ratios of epidote and adjacent minerals suggest that oxygen isotope fractionations may provide a tool for distinguishing magmatic from subsolidus epidote. Textural criteria (Zen and Hammarstrom, 1984) have been used to make the distinction, but textures alone can be misleading. In the Mt. Lowe intrusion of S. California, oxygen isotopic compositions confirm that large euhedral epidote crystals are magmatic in origin. Texturally ambiguous coarse anhedral epidotes have also been shown to be magmatic in origin. Surprisingly, intergrowths of epidote with biotite and/or hornblende are subsolidus. These textures were thought to be indicative of crystallization from a magma. Work is continuing on many of the classic "magmatic" epidote occurrences to assess the reliability of oxygen isotopes in distinguishing magmatic from subsolidus epidote.
Fluids in metamorphic core complexes
The role of fluids in the evolution of the Whipple Mountains metamorphic core complex (SE California) is a subject of on going research. Our initial studies in the Whipple Mountains have shown that lower-plate lithologies have exchanged with surface-derived or meteoric waters. However, this fluid-rock exchange occurred after the mylonitized lower-plate rocks were brought up to depths of <~4km. There is no evidence to suggest that meteoric fluids circulated down into the zone of ductile deformation, below the brittle-to-ductile transition. Recent work has focused on detailed oxygen isotope analysis of hornblende + potassium feldspar filled tension gashes in lower-plate rocks. These tension gashes are thought to document the earliest stages of extension. Hornblende d18O values range from 5.17 to 6.69 o/oo (average = 5.64 ± 0.35 o/oo). We are currently analyzing coexisting feldspar, and the data will be used to constrain the temperatures of mineralization and the source of the mineralizing fluid
Experience
1996-1997: Visiting Associate Professor, California Institute of Technology
1995-present: Associate Professor, University of Southern California
1988-1995: Assitant Professor, University of Southern California
Education
1980-Colgate University, B.A.
1983-University of Georgia, Athens, M.S.
1988-University of Wisconsin, Ph.D.
Classes taught
Core 103
Mineralogy GEOL 215aL
Petrology GEOL 215bL
Metamorphic Petrology GEOL 568L
Stable Isotope Geochemistry GEOL 567
Seminar in Petrology GEOL 600
Honors & Awards
2001- present. National Science Foundation panelist, Graduate Research Fellowship Program
2001-present. University of Wisconsin, Department of Geology & Geophysics Board of Visitors
2000. Sigma Chi Professor of the Year
2000. Sigma Gamma Epsilon, Excellence in Teaching Award
1998, declined. National Research Council Post-doctoral Fellowship Award
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