Research

Thermochronology Research

Cosmogenic noble gas paleothermometry

Helium and neon isotopes are produced in common minerals like quartz and feldspars by interactions with cosmic ray particles. Helium and neon also experience thermally-activated diffusive loss in these minerals at Earth surface temperatures. We utilize the production-diffusion systematics of these noble gas-mineral pairs to quantify the temperatures rocks have experienced while they’ve been exposed at Earth’s surface to cosmic rays. Ongoing work involves use these surface thermal histories of rocks to understand how local climates has varied in the recent geologic past, when rocks have experienced thermal disturbances due to fire, and when landscapes transitioned from different thermo-erosional regimes. Recent work includes quantifying the thermal sensitivities of these noble gas-mineral systems with experiments, and applying these systems in to formerly glaciated regions of the European Alps to quantify temperature changes since the last glacial maximum.

Sampling in the Sierra Nevada, CA.
Sampling in the Sierra Nevada, CA, for cosmogenic noble gas paleothermometry.
Cosmogenic 3He data Dry Valleys
Depth profile of cosmogenic 3He in a bedrock core from the Dry Valleys, Antarctica, compared to model depth profiles for different thermal histories. Data are from Lindsay Schoenbohm’s 2004 PhD thesis at MIT.

Tectonics and geomorphology

Our group uses noble gas thermochronology, in particular apatite 4He/3He, apatite (U-Th)/He, and zircon (U-Th)/He, as well as cosmogenic nuclide geochemistry, to study the interaction of tectonic and geomorphic processes in a variety of geologic environments. Ongoing work involves studying the exhumation histories of passive margins, continental interiors that have recently become tectonically ‘quiescent’, and regions affected by hot spot magmatism. Recent work includes studying the evolution of topography and rivers in southern Tibet.

4He/3He data from southern Tibet
Apatite 4He/3He dataset from a granitic bedrock sample in southern Tibet, which shows rapid cooling at the end of the Middle Miocene.
Field work in southern Tibet
Collecting bedrock samples in southern Tibet.

Thermochronology of planetary materials

Through a combination of noble gas measurements and numerical modeling, our group studies a number of processes that affect the thermal histories of planetary materials, including impact events, space transit, and aqueous alteration. Ongoing work includes determining the age of alteration minerals in Martian meteorites, reconstructing the thermal histories of lunar meteorites, and modeling how impact events shape the distribution of geochronological information of planetary surfaces through time. We are also studying the noble gas diffusion kinetics in jarosite as an analog material for samples returned by Mars 2020 and working on the geochronology of several terrestrial impact craters.

SEM image of NWA 11444
Backscattered electron image of lunar meteorite NWA 11444 with a compositional overlay from energy-dispersive x-ray spectroscopy. Orange = Al, Blue = Mg, Green = Fe.
40Ar/39Ar thermochronology data, NWA 11444
Example of an 40Ar/39Ar dataset from lunar meteorite NWA 11444, collected from the circled clast in the BSE image on the left.

Processes and rates in volcanic systems

We are studying rates of volcanic eruptions, both in deep time and in the very recent geologic past, using a combination of cosmogenic nuclide exposure dating, high-precision geochronology, and numerical modeling. Our work particularly focuses on the interactions of volcanism with the Earth’s climate system. This is a relatively new area of research for our group, so stay tuned for more information as initial projects get spun up.

Landscape view of Deccan Traps
View of the Deccan Traps, India. Credit: Courtney Sprain
Osorno Volcano
Osorno Volcano in the Chilean Andes. Credit: Lilli Freda (distributed via imaggeo.egu.eu)

Noble gas diffusion kinetics

Understanding the kinetics of noble gas diffusion in minerals is essential to all of the scientific questions our group pursues. To this end, we use experiments and theoretical calculations to quantify noble gas diffusion kinetics and understand the underlying phenomena that control noble gas diffusion rates. Ongoing work involves studying how point defects influence helium diffusion in quartz. Recent work includes quantifying the variability of helium and neon diffusion kinetics in quartz and feldspars of different geologic origins.

Gem-quality and synthetic quartz
Gem-quality quartz crystal (top) and synthetic quartz crystal (bottom) that we use to conduct helium diffusion experiments.
Arrhenius plot for gem-quality and synthetic quartz.
Comparison of helium diffusion in gem-quality (blue) and synthetic (orange) quartz crystals.

Geochronology and archaeology