“Rock gives reality to the otherwise abstract notion of transhuman time.”
The thermal histories recorded in rocks represent the integrated effects of numerous geologic, tectonic, and climatic processes, acting on a variety of spatial and temporal scales. My research primarily uses multiple techniques, namely geo- and thermo-chronology, in concert with detailed field, structural, petrographic, geochemical, and numerical modeling studies to understand the thermal evolution of rocks and minerals and place absolute constraints on the timing and rate of a range of a whole range of geologic processes. My current projects include work on Cordilleran tectonics, lunar impacts, Rocky Mountain geology, Pyrenean uplift and exhumation, and new ways to dissolve zircons.
RuGGEd (Ruby Mountains Geochronology and Geoscience Education): Documenting the transition from contraction to extension in the Southwestern U.S. Cordillera, NSF Award #1728537 with Co-PI’s Allen McGrew and Carrie Meisner
This recently-funded project in Northeastern Nevada focuses on a well-exposed and tilted crustal section in the Ruby Mountains – East Humboldt Range – Wood Hills Metamorphic Core Complex. The core complexes of the northeastern Great Basin yield fundamentally different interpretations of the timing and tectonic significance of exhumation depending on whether the data derive from deeper or shallower structural levels. In each case, lines of evidence drawn primarily from higher temperature thermochronometry, integrated Pressure-Temperature-time paths, and structural analyses of mid- to deep-crustal rocks suggest older, more protracted and often more complex exhumational histories while low-temperature thermochronometry and syntectonic sedimentation commonly record a simpler and more youthful record of widespread Miocene extensional unroofing. This study will use multiple low- and medium-temperature thermochronometers sampled within a well-defined structural framework to reconcile these disparate interpretations and fully constrain the complete exhumation and deformation history of the mid- to upper-crust. This project also embeds substantial outreach and educational components. The world-class geology of the study area provides an ideal stage for direct community engagement through strategic and comprehensive outreach to local science educators and geoscience professionals by forging an innovative collaboration between two R1 Research institutions and Great Basin College–the institution primarily responsible for training science educators across most of rural Nevada. Undergraduate research projects form a central part of this proposal; students from both CU – Boulder and The University of Dayton will participate in both field and lab work, complete undergraduate research projects, present their results at national meetings, and collaborate with the rest of the group to publish manuscripts.
For more information on this project, including links to the YouTube and virtual field trip pages, please click here.
Coupled U-Pb and (U-Th)/He Geochronology of Lunar Zircons, with collaborators Nigel Kelly, Becky Flowers, and Steven Mojzsis (CU – Boulder)
This project has produced the first (U-Th)/He dates ever reported on lunar material, and the first extraterrestrial zircon (U-Th)/He dates. Thirty-two single-grain zircon (U-Th)/He dates from lunar breccia sample 14311 yielded dates negatively correlated with eU (U + 0.235*Th) ranging from ~4.0 Ga to as young as 6 Ma. The (U-Th)/He date – eU pattern of these data is consistent with models that describe the effects of radiation damage on He retentivity, and have allowed us to evaluate different thermal histories and impact scenarios. Specifically, the thermal models that best fit the data require that sample 14311 must have experienced a significant, late thermal event at ~110 Ma. In addition, a cluster of low-eU (i.e. low radiation damage) grains record evidence of the Imbrium (~3.95 Ga) impact, and demonstrate the ability of zircon to retain He over very long timescales. Finally, thermal modeling of the data also places strict limits on the maximum temperatures that the sample experienced, both during and preceding the ~100 Ma heating event, and suggests that other potential impact events (e.g. Copernicus at ~800 Ma) did not significantly heat this sample. The results from Apollo 14 zircons are now in press in Earth and Planetary Science Letters.
Documenting multiple phases of uplift, exhumation, and burial throughout the Rocky Mountains
Fundamental questions persist surrounding the formation and evolution of the Colorado Rockies, despite being one of the most studied and visited mountain ranges in the world. In particular, there is significant debate surrounding when topography and relief formed, the relative influence of inherited structures, and whether or not there was significant post-Laramide uplift, exhumation, or deformation. I’ve recently been mentoring undergraduate research projects throughout Colorado designed to help answer these questions by integrating thermochronology with regional tectonics and field geology. These projects have formed the core of CU undergraduate honors theses or RESESS summer internship projects. These projects include a study of the northern Wet Mountains that uses zircon, apatite, and titanite (U-Th)/He data, along with field relationships, to develop a continuous, ~500 Myr thermal history for the range, specifically highlighting the importance of multiple burial and exhumation events in the evolution of the Wet Mountains. Other projects include determining the uplift and exposure history of some of the Tertiary paleochannels that drained the Laramide Rockies and constraining the exhumation of very young plutons in the Elk Mountains that allow us to focus on more recent uplift and cooling events.
Uplift and Exhumation of the Pyrenean Orogen
My postdoc at Syracuse University focused on the evolution of the Pyrenean orogen, an asymmetric doubly-vergent collisional orogen developed in previously thinned continental crust between the Iberian and European lithospheric plates beginning in the Late Cretaceous. By applying a range of thermochronologic techniques, in concert with field, structural, petrologic, and numerical modeling studies, we have spatially and temporally constrained multiple phases of crustal shortening, erosional exhumation, and fault activity throughout the orogen. Along with collaborators Paul Fitzgerald and Suzanne Baldwin (Syracuse University) and Josep-Anton Muñoz (University of Barcelona) we published our original set of findings in 2009, and are in the process of publishing the final papers from this project.
I am also involved with a variety of other ongoing research projects, including both the methodological development of (U-Th)/He techniques. Please feel free to contact me if you have any questions!