I 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.
Phys Sci Res Assoc, Geological Sciences
PhD, Stanford University (2012)
BS, Oregon State University (2004)
PGEs and trace metals in Sulfides
I am undertaking analyses of trace elements in sulfides from samples at McDermitt Caldera, NV. The project utilized the Cs+ primary beam on the SHRIMP-RG, and is a new technique in development in the lab, with collaboration Jessica Warren and Megan D'Errico (Stanford GES)
McDermitt Caldera, NV
U-Pb and Trace Elements in Apatite
I am working to measure high precision (better than 5% uncertainties) 206Pb/238U ages on natural apatites. Trace element concentrations in apatites include Li, Cl, S, F, Mg, Fe, Sc, Y, REE, Hf, Th, and U, and are reproducible to better than 5% (1sigma). I have been working with several groups to analyze natural apatites, as well as Jonathan Payne's group analyzing trace elements in conodonts.
U-Pb surface depth profiling
I have several projects in progress using a method by which we target specifically the outer-most unpolished zircon surface. The analyses of the surfaces contain data for the youngest-most mineral growth. I have applied this approach to look at age differences between the rim and core for zircon from the Fish Canyon Tuff. A second projects in collaboration with Mary Leech (SFSU) is targeting the youngest phase of metamorphic zircon growth from samples located in the Great Himalaya Sequence deformed and exhumed along the Zanskar Shear Zone. This is the only approach for targeting thin rims that may be only 2-5 microns in diameter, when viewed in cross section.
Combining zircon U-Th dating on the SHRIMP and U-Th-He on the Noblesse
I am collaborating with Seth Burgess (Mendenhall Postdoc at USGS), Jorge Vazquez and Michelle Coombs (USGS) on combining these two techniques to date young (Holocene-Pleistocene) tephras in Alaska
New applications in Rutile, Baddeleyite, Monazite, and other minerals
I am always interested in new dating ideas, approaches, or methodology that can utilize the high-spatial resolution and high mass-resolution of the SHRIMP-RG. Recently, we have been running Rutile, Baddeleyite, and Apatite for U-Pb ages, but other potential minerals are also an option. Please contact me if you are interested in new method development ideas to tackle specific Earth science questions.
The eruptive and magmatic history of the youngest pulse of volcanism at the Valles caldera: implications for successfully dating late Quaternary eruptions
JOURNAL OF VOLCANOLOGY AND GEOTHERMAL RESEARCH
2016; 310: 50-57
View details for DOI 10.1016/j.jvolgeores.2015.11.021
The Early Paleozoic basite magmatism of Western Transbaikalia: Composition, isotope age (U-Pb, SHRIMP RG), magma sources, and geodynamics
2016; 24: 367–391
View details for DOI 10.1134/S086959111604007X
Chemical abrasion-SIMS (CA-SIMS) U-Pb dating of zircon from the late Eocene Caetano caldera, Nevada
2016; 439: 139-151
View details for DOI 10.1016/j.chemgeo.2016.06.013
Refined deep-water depositional history and dating of the Tongaporutuan reference section, North Taranaki, New Zealand
NEW ZEALAND JOURNAL OF GEOLOGY AND GEOPHYSICS
2016; 59: 313-329
View details for DOI 10.1080/00288306.2015.1132744
Thermochronology of extensional orogenic collapse in the deep curst of Fiordland, New Zealand
2016; 12: 1-31
View details for DOI 10.1130/GES01232.1
Petrogenesis and provenance of distal volcanic tuffs from the Permian–Triassic Karoo Basin, South Africa: A window into a dissected magmatic province
2016; 12: 1-14
View details for DOI 10.1130/GES01215.1
Elucidating the magmatic history of the Austurhorn silicic intrusive complex (southeast Iceland) using zircon elemental and isotopic geochemistry and geochronology
CONTRIBUTIONS TO MINERALOGY AND PETROLOGY
2016; 171 (69): 1-21
View details for DOI 10.1007/s00410-016-1279-z
Geology of the High Rock caldera complex, northwest Nevada, and implications for intense rhyolitic volcanism associated with flood basalt magmatism and the initiation of the Snake River Plain–Yellowstone trend
2016; 12: 58-113
View details for DOI 10.1130/GES01162.1
Constraints on plateau architecture and assembly from deep crustal xenoliths, northern Altiplano (SE Peru)
GEOLOGICAL SOCIETY OF AMERICA BULLETIN
2015; 127: 1777-1797
View details for DOI 10.1130/B31206.1
Influence of radiation damage on Late Jurassic zircon from southern China: Evidence from in situ measurements of oxygen isotopes, laser raman, U–Pb ages, and trace elements
2014; 289: 122–136
View details for DOI 10.1016/j.chemgeo.2014.09.013
- Initial impingement of the Yellowstone plume located by widespread silicic volcanism contemporaneous with Columbia River flood basalts GEOLOGY 2012; 40 (7): 655-658
- Calibration of Nu-Instruments Noblesse multicollector mass spectrometers for argon isotopic measurements using a newly developed reference gas CHEMICAL GEOLOGY 2011; 290 (1-2): 75-87