MKohn Research Interests

Rocks – Research Projects

Pressure-temperature-time evolution of metamorphic rocks in the Himalaya

In these collaborative projects primarily with Profs. D Robinson, Nadine McQuarrie, and Sean Long, we are determining P-T conditions and timing of metamorphism to better understand the tectonic evolution of the Himalaya. We have numerous samples from NW India, central and eastern Bhutan, and central Nepal. These span sub-garnet grade rocks of the Lesser Himalayan Sequence and the Tethyan Himalaya, to partially melted rocks of the Greater Himalayan Sequence. The metamorphic and chronologic evolution of these rocks has implications for tectonic models of the Himalaya, particularly whether the Greater Himalayan Sequence flowed (in a pipe-flow sense) towards the Indian foreland. Currently, graduate student Jesse Walters is working on these projects.

Titanite geochemistry and geochronology

Using our laser-ablation ICP-MS system, we discovered that Greater Himalayan titanite appears to preserve both its growth temperature (Zr thermometry) and age (U-Pb geochronology). Graduate student Jesse Walters is further exploring the utility of titanite for retrieving T-t paths in medium- to high-grade rocks.

Trace element thermometry and speedometry

The application of new trace element thermobarometers (e.g. Ti-in-zircon/quartz, Zr-in-sphene) require either the presence of rutile, or an estimate of the activity of rutile. We are investigating new methods of constraining parameters relevant to these systems (e.g. the activity of rutile in rocks that lack rutile, based on Ti equilibria), and in constraining element transport during cooling and its impacts on diffusion profiles. We work closely with Sarah Penniston-Dorland, at the University of Maryland, using rocks from Santa Catalina Island.

Subduction zone metamorphism and tectonics

In this ongoing project with Sarah Penniston-Dorland, we are determining P-T-t histories from the Santa Catalina Island subduction complex in southern California. This work involves close evaluation of trace element thermometers, as well as U-Pb geochronology. In addition, we are involved in a 5-year project to investigate Alpine subduction metamorphism under the auspices of the ExTerra (EXhumed TERRAnes) working group. In this project, called E-FIRE (ExTerra Field Institutes and Research Endeavor) we are collaborating with the ZIP (Zooming-In-between-Plates) consortium in Europe to constrain P-T-fluid-deformation evolution of the subduction interface. Boise State is leading this multi-million dollar, 9-institution project together with the University of Maryland (Sarah Penniston-Dorland) and Penn State University (Maureen Feineman).

Fossils Research projects

Eocene – Miocene climate and ecological change in southern Argentina

In this collaborative project with Prof. Caroline Strömberg at the University of Washington, and Dr. Richard Kay at Duke University, we are investigating the conditions that appear to have given rise to Earth’s grasslands. Gran Barranca, Argentina, exposes South America’s longest sequence of Cenozoic vertebrate fossils, c. 42 to 19 Ma, whereas the Rio Gallegos area provides some of the best preservation of mid-Miocene mammals, c. 16-17 Ma. Caroline is currently investigating plant microfossils in more detail, and Rich is further studying faunal evolution. Our group, led by graduate student Robin Trayler, is investigating oxygen and carbon isotope compositions of fossil teeth and bones to understand better the broad climate and vegetation trends that may have given rise to ecological change. High-precision geochronology links these records to marine systems.

Pleistocene ecology and climate

There are lots of Pleistocene fossils around the western US, and we have been studying sites in Wyoming, Idaho and southern Nevada now for several years. In our most recent work, in collaboration with the USGS and San Bernardino County Museum, graduate student Amanda Drewicz is using carbon and oxygen isotope compositions of fossil megaherbivores to investigate atmospheric circulation systems during the Last Glacial Maximum, especially to identify moisture sources. This work has implications for the fate of desert wetlands in a warming future.

Trace element uptake in fossils

I am collaborating with several other researchers to understand chemical alteration during fossilization. I am currently working with former post-doc Celina Suarez (University of Arkansas) to measure trace element profiles in fossil bone of differing ages to understand diffusive uptake in natural systems and link them to crystallographic and isotopic changes. Amanda Drewicz is also conducting trace element uptake experiments on modern and fossil enamel to identify their susceptibility to post-depositional alteration. Analysis of diffusion profiles is in collaboration with Dr. Rick Hervig, at Arizona State University.

Controls on bioapatite isotope geochemistry

Graduate student Robin Trayler has initiated experiments to synthesize bioapatite. We hope to better understand controls on bioapatite major element, trace element, and isotopic compositions. He is also investigating the isotopic implications of how teeth mineralize.