School of Earth, Energy & Environmental Sciences
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Professor of Geological Sciences
Current Research and Scholarly InterestsMy research focuses on the exploration & exploitation of geological resources, from data acquisition to decision making under uncertainty and risk assessment.
Professor of Geological Sciences
Current Research and Scholarly InterestsResearch
I use stable and radiogenic isotopes to understand Earth system history. These studies examine the link between climate, tectonics, biological, and surface processes. Projects include: 1) examining the terrestrial climate history of the Earth focusing on periods of time in the past that had CO 2-levels similar to the present and to future projections; and 2) addressing how the chemical weathering of the Earth's crust affects both the long- and short-term carbon cycle. Field areas for these studies are in the Cascades, Rocky Mountains, Sierra Nevada, the European Alps, Tibet and the Himalaya and the Southern Alps of New Zealand.
I teach courses at the undergraduate and graduate level in isotope biogeochemistry, Earth system history, and the relationship between climate, surface processes and tectonics. I also teach a three-week field course each September in the Wind River Mountains of Wyoming for sophomores and GES majors. This course covers topics in environmental and geological sciences.
Editor American Journal of Science; Co-Director Stanford Stable Isotope Biogeochemistry Laboratory (present);Chair, Department of Geological and Environmental Sciences (2004-07); Co-Director Stanford/USGS SHRIMP Ion microprobe facility (2001-04)
Phys Sci Res Assoc, Geological Sciences
BioI co-manage the SHRIMP-RG ion-microprobe at Stanford University, where I oversee operation of the laboratories and work closely with Stanford scientists and students as well as visiting scientists to undertake measurements on the SHRIMP-RG. This includes training users in SIMS methods, assisting with sample preparation/characterization, data acquisition, reduction, interpretation, and publication of results. I also contribute to the development and refinement of new techniques and standard development efforts on the SHRIMP-RG.
My research focuses on understanding the timescales of magmatic processes and the sources of crystal diversity in magmatic systems. To accomplish this, I use radiometric dating (238U-230Th, 238U-206Pb, 40Ar-39Ar, and U-Th/He) and chemical analysis of minerals to investigate the temporal and compositional history of magmas. I integrate these results to better understand how magmas evolved in the crust leading up to eruption, and the geology of these deposits exposed on Earth’s surface today. The methods I utilize involve electron microprobe (EMP), secondary ion mass spectrometry (SIMS), nanoSIMS, and inductively coupled plasma mass spectrometry (ICP-MS).
One of the exciting and challenging components of my research is finding analytical techniques to answer complicated petrogenetic questions. To do this, one of the main tools I employ is the high spatial resolution of SIMS in order to measure trace elements and isotopic ages simultaneously, often in-situ, from the same analyte volume (~4 ng). Additionally, using the relatively slow sputter rate of the SIMS method (10’s of nm/min), I have applied this approach to depth profiling into fresh, unpolished mineral surfaces to target the last phase of mineral growth. This have been extremely useful for dating zircons with complicated histories. For example, I have been working on radiometrically dating geologically young volcanic zircons (Quaternary in age) where the outermost micron of grain yields crystallization ages that agree with Ar-Ar and U-Th/He eruption ages, whereas the interiors contain older inherited portions of the grains. Another example is applying this technique to dating thing (<2 micron) metaphoric rims surround an older protolith core, which would be impossible to analyze using traditional techniques of polishing zircon to expose the interiors of the grains.
I am always interested in new dating and trace element applications, analytical approaches, or methodology that can utilize the high-spatial resolution and high mass-resolution of the SHRIMP-RG. Please contact me if you are interested in new method development ideas to tackle specific Earth science questions.
Please visit https://shrimprg.stanford.edu/ for more information about the SHRIMP-RG and SIMS.