RESEARCH INTERESTS

My research interests are in metamorphic petrology, structural geology, isotope geochemistry and thermochronology as applied to problems in continental tectonics. In particular, I'm interested in the relation of metamorphism, deformation, and fluid-flow to crustal growth during convergent-margin and collisional orogenesis. I am also interested in applying what we can learn about mountain belt evolution to gaining a better understanding of paleogeographic relationships between cratonic elements in early Earth history, particularly for Rodinia and Gondwana.

I do field-based studies that combine geologic mapping, structural analysis and petrographic study, with analytical approaches involving kinematic interpretation of petrofabrics, quantitative mineral analysis, geothermobarometry, thermochronology and isotope geochemistry. I address the timing and rates of orogenic processes mainly by 40Ar/39Ar and U-Pb thermochronology, and I use isotopic systems such as Lu-Hf and Sm-Nd to help constrain crustal growth. I also use stable-isotope geochemistry and mineralogy to address questions of fluid interactions with solid phases during metamorphism. Integration of these techniques allows us to constrain the sequences of events, crustal conditions, rock displacements, and the role of fluids associated with tectonic processes.

I have worked in a variety of tectonic settings, including crustal extension, subduction, rifting, and collision, particularly in the Cordilleran and Rocky Mountain regions of North America, and the Transantarctic Mountains of Antarctica. In these areas I have studied the structural and petrologic evolution of convergent plate margins (Klamath Mountains, California), Proterozoic and Archean crustal evolution (Antarctica), the structural evolution of metamorphic core complexes (Mojave Desert of California and Arizona, and Omineca belt of eastern Washington), the effects of fluids, deformation, and rock composition on mineral stability (Proterozoic belts of northern New Mexico and Colorado), strain partitioning during continental-margin transpression (Ross Orogen, Antarctica), and the use of mineral chronometers to trace sediment transport and denudation rates (Ross Orogen, Antarctica).

Most of my work in recent years has addressed the tectonic evolution of the Ross orogenic belt in Antarctica, which spans a very interesting time in Earth history between about 1 billion to 500 million years ago. Relationships in the Ross belt are helping us to better understand the tectonic changes that took place during the transformation from the Rodinia supercontinent to Gondwanaland, as well as the relations between Antarctica, Australia, and North America. I started working in the metamorphic basement to the Ross Orogen in order to understand its role in evolution of the East Antarctic shield. Recently we have been working on the supracrustal successions in order to track the sedimentary response to tectonism and changing provenance through time. Together, addressing both the mid-crustal and supracrustal elements gives us a better picture of the orogen as a whole. Using detrital minerals in the cover succession, for example, we can better tie the two together and address the denudation rates associated with magmatism, tectonic uplift and erosion.

Other directions involve ‘peeking’ underneath the ice cap of Antarctica to better understand crustal evolution of the East Antarctic shield. Two very productive approaches are use of airborne geophysical surveys (mainly magnetics and gravity) and sampling of glacial deposits as proxies of the ice-covered areas that have been eroded from the interior.

The ultimate goal is to sample rocks directly from beneath the ice sheets of Antarctica. I am co-PI on an NSF-funded project to develop a new mobile drilling platform that we plan to deploy in East Antarctica from McMurdo Station and South Pole. The Rapid Access Ice Drill (RAID) will penetrate the Antarctic ice sheets in order to core through deep ice, the glacial bed, and into bedrock below. This new technology will provide a critical first look at the interface between major ice caps and their subglacial geology. Currently in development, RAID is a mobile drilling system capable of making several long boreholes in a single field season in Antarctica. RAID is interdisciplinary and will allow access to polar paleoclimate records in ice >1 million years old, direct observation at the base of the ice sheets, and recovery of rock cores from the ice-covered East Antarctic craton. Near the bottom of the ice sheet, we will use a wireline bottom-hole assembly to take cores of ice, the glacial bed, and bedrock below. Once complete, boreholes will be kept open with a stabilizing fluid, capped, and made available for future down-hole measurement of thermal gradient, heat flow, ice chronology, and ice deformation. RAID will also sample for extremophile microorganisms. RAID is designed to penetrate up to 3,300 meters of ice and take sample cores in less than 200 hours. Its rapid turn-around will allow us to complete a borehole in about 10 days before moving to the next drilling site. RAID is unique because it can provide fast borehole access through thick ice; take short ice cores for paleoclimate study; sample the glacial bed to determine ice-flow conditions; take cores of subglacial bedrock for age dating and crustal history; and create boreholes for use as an observatory in the ice sheets. Together, the rapid drilling capability and mobility of the drilling system, along with ice-penetrating imaging methods, will provide a unique 3D picture of the interior Antarctic ice sheets. The RAID equipment is currently in Antarctic undergoing field tests near McMurdo Station. Stay tuned!