Professor, Geochemistry and Radiogenic Isotopes
My research is broad, and can be described as evolution of the mantle-crust-hydrosphere of the Earth over geologic time reflected by geochemistry and isotopes. I am involved in collaborations on tectonics of mountain belts, large-scale sedimentary provenance, origin of granitoid batholiths, growth of continental crust through geologic time, development of the Colorado River and Grand Canyon, and evolution of Pleistocene climate in North and South America. Although some papers present models and reinterpretations of existing databases or problems, most of my publications involve major analytical efforts, in which geochemical and/or isotopic data are provided as a constraint on histories and processes. Most projects involve collaboration with other scientists within and beyond our department. Specific broad projects from 1990 onwards (see Current Biography) include: early crust-mantle evolution from Hf and Nd isotopes on meteorites and early crustal rocks; origin of terrane components of orogenic belts; Nd isotopic and geochemical study of sedimentary provenance at continent scale; Sr isotopes applied to the evolution of the Colorado River system; and U-Th disequilibrium geochronology applied to climate evolution in the Bolivian Altiplano and the desert Southwest.
I oversee a suite of laboratories dedicated to chemistry and thermal ionization radiogenic isotope mass spectrometry. Together with rock and mineral processing facilities, and a laboratory housing a Multicollector ICPMS instrument, these areas are broadly shared with George Gehrels, Joaquin Ruiz, Jay Quade and Mihai Ducea. Radiogenic isotopic techniques under my supervision include Sm-Nd, Lu-Hf, Rb-Sr and U-Th (U-series). I apply these, often in collaborative mode with other faculty in our department, to problems and rocks with all ages from 3.8 Ga to Holocene.
Office: Gould-Simpson Bldg. 507