Research
Faults & fluids
Faults likely serve as pathways for fluid movement and heat flow within the Earth's crust, but the timing between magmatism, fluid flow, and faulting is not fully understood.
In the Rio Grande Rift (New Mexico), faults exhibit evidence of past fluid circulation as either silica- or calcite-cemented faults. Many generations of veins and deformation show an interplay between fault motion and fluid flow. We are constraining the age of these veins using U-Pb, which allows us to investigate the temporal relationship between regional magmatic pulses, fluid/heat flow, and faulting.
Botryoidal chalcedony silica surface along Santa Ana Fault in the Rio Grande Rift.
Shocked zircon from Ries impact structure (Ross et al., in prep).
Zircon microstructures
We investigate Chicxulub ejecta at proximal-intermediate K-Pg sites by comparing target rock ages to zircon U-Pb ages in the ejected boundary deposits. These results ground-truth ballistic ejecta models. We found ages that can be attributed to rocks underlying the Chicxulub and shock microstructures within grains from these age modes. Using the shock microstructure as a shock pressure barometer in tandem with the age modes, I suggest a depositional model where the ejecta curtain and rapidly expanding impact plume mix in a dust cloud.
Impact crater thermochronology
I am interested in establishing the relationship between zircon (U-Th)/He (ZHe) ages and shock microstructures. We used the Chicxulub and Ries impact structures as test cases (Ross et al., 2024).
Through step heating fractional release helium diffusion experiments, I quantified the helium diffusion kinetics in shocked zircon. The shock microstructures induce multi-domain diffusion, creating enhanced diffusivity out of the smaller subgrains more easily. Enhanced diffusivity creates lower closure temperatures and thus younger ZHe ages. ZHe thermochronometry within impact structures on well-characterized samples is critical to date impact craters that lack impact melt or other dateable lithologies.
Cartoon and granular shocked zircons from the Ries crater (Ross et al., 2024).
Buckle fold around a small pseudotachylyte injection (Ross et al., in prep).
Ancient earthquake fault geometries & deformation
We tied deformation adjacent to pseudotachylyte veins (fossilized earthquakes) to the seismic cycle by comparing detailed field mapping to modeled stress changes. We compared the stress change distributions from the models to the distribution of small near-fault structures mapped in the field by co-locating the stress changes to our measured strain.
Fault geometric complexities, which are more difficult to model, create stress change patterns that induce deformation away from the fault planes, analogous to what we see in active earthquake-aftershock sequences today.
By mapping pseudotachylyte fault veins in a single outcrop elsewhere in the Norumbega Shear Zone, we found overprinting multi-stranded ruptures suggesting complex multigenerational rupture patterns (Rowe et al., 2018).
<---Sometimes research looks like this!
