We have carried out numerous projects related to lithospheric extension in the Basin and Range province--from the study of metamorphic core complexes to the slip histories of normal faults that cut the brittle crust, producing the corrugated topography of the province today. Read more about our specific projects listed under "research" and in the papers listed under publications.
Fission track thermochronology is a geochronologic method that yields the time when rock rose through the 2 to 5 km depth window or ~80°-120°C (for apatite). This low-temperature thermochronometer allows us to collect data at the regional scale to study time-space patterns of mountain building and their uplift or on detailed scales to understand the slip history of faults in the brittle crust. The best studies utilizing low temperature thermochronology involve careful integration of field-based structural studies and balanced cross-sections with laboratory-collected thermochronology data. Transects of ten or more samples are keyed to detailed structural cross-sections. Because the thermal histories of samples in a specific transect must be linked, such data arrrays provide a solid measure of the cooling history of the structural section sampled. The Fission Track Laboratory at Stanford has applied these approaches in a variety of tectonic settings, including reconstructing time-space patterns of extension across the Basin and Range province, analyzing margin-wide shortening across the San Andreas fault system, reconstructing mountain-building in China during the India-Asia collision, and analyzing exhumation of high-pressure rocks within the Franciscan subduction complex. This work has been funded by a series of grants from the NSF Tectonics Division including EAR9417939, EAR-9725371, EAR-029854 and EAR-0809226.
(U-Th)/He thermochonology is a more recently developed and highly complimentary method for dating exhumation from even shallower depths (~40-85°C) intervals. The (U-Th)/He laboratory resides in our Noble Gas Laboratory. The two methods paired together provide a powerful means of solving many tectonic questions about the P-T path of the upper 10 km of the crust. This laboratory was initially funded through NSF's Instrumentation Division.
Understanding the deep crustal processes that drive active faulting and earthquakes in continental settings is viewed as a top scientific challenge in the earth sciences but is an inherently difficult problem to work on because of the minimum 5-10 km depth to the seismogenic base of the elastic crust. It's too deep to drill! Normal fault systems in the Basin and Range province are unusual in that they often provide an opportunity for detailed investigation of faults to great depths in the crust, even into the Elastico-Frictional to Viscous (EFV) (or brittle-ductile) transition zone .
One of the notable disagreements about the evolution of the western U.S. Cordillera centers on how thick its underlying continental crust became during regional folding and thrusting in the Mesozoic. Some think it became 60-70 km thick like the crust beneath the Andes, bringing up the questions of how, where and why it was thinned to its present 30 km. Metamorphic core complexes (rare exposures of the deep crust exhumed during stretching of the crust) are one of the places that provide evidence for a very thick crust. Late Cretaceous metamorphic mineral assemblages suggest thermodynamic equilibration at 35 km depths while geologic mapping and field relationships suggest these same rocks were never buried more than 15 km. When disagreements such as these exist between data sets provided by different disciplines, we usually get to work to try to understand what the problem is.
Knowledge of the thermal and chemical evolution of the deep continental crust beneath the interior of the North American Cordillera is invaluable for understanding how plate tectonic processes lead to mountain building these deeper levels of the crust, however are buried tens of kilometers, accessible to study only by geophysical means.