Introduction
My primary research interests focus on the kinematic evolution of highly extended terrains and the tectonics of exhumed high temperature and (ultra)high-pressure rocks, and I use them to address a wide variety of global geodynamic questions. The various kinematic models for the formation and evolution of these structures have profound implications for geologic processes as far reaching as the formation of sedimentary basins, melt generation, spreading center dynamics, and kinematics of syn- to post-orogenic collapse of overthickened continental crust. Furthermore, deep crustal rocks exhumed in highly extended terrains preserve phase assemblages and fabrics that provide a virtual window into the lower crust, and represent a unique opportunity to investigate questions regarding crust–mantle interactions and lower crustal flow, as well as the timing, metamorphic conditions and kinematics of continental collisions and ultrahigh-pressure tectonics.
Lab Facilities:
Many of the projects my students and I work on require sample preparation in the mineral separation labratory here at Cal Poly. Complete descriptions of our lab facilities and procedures can be viewed here. Image caption: Cathodoluminesence image of zircon illustrating chemical zoning associated with an igneous core and a metamorhpic rim.
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Current Research Projects:
LOWER-CRUSTAL FLOW, LIVERPOOL LAND, EAST GREENLAND
| The Greenland Caledonides formed in the upper, or overriding plate of the Caledonian Orogeny, and present a unique opportunity to study deformation styles in the retro-arc of a continental collision. Our preliminary work in Liverpool Land, has identified amphibolite–eclogite/granulite-facies rocks at three distinct structural levels and orogenic events spanning >40 Myr (EPSL 2010). By correlating the Liverpool Land gneisses with the well-defined tectonostratigraphy farther to the west, this study will provide a first look at orogen-normal patterns in the timing of early Caledonian anatexis and melt generation, and add insight into the relationships between lower-crustal flow and crustal thickening, extension, and exhumation of weak lower–mid crustal material in contractional settings. |
 Kyanite + garnet gneiss saturated by plagioclase-rich melt. Note the deformed and split kyanite crystal immediately above the pencil.
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CORDILLERAN PALEOGEOGRAPHY
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The base of the Cordilleran miogeocline is characterized by thick sequences of Neoproterozoic–Lower Cambrian quartzites and siliciclastic sedimentary rocks. I am using detrital zircon geochronology to determine the provenance of these basins in Eastern Nevada and along the Idaho–Utah border. This data can be used to correlate these rocks with similar rocks from other areas, define discrete basins, and ultimately, reconstruct the paleogeographic and tectonic setting of the region during the Neoproterozoic. Image caption: lost in the piñon pines—sampling the McCoy Creek Group in the Pilot Range, NV. |
Past Research Projects:
NORWEGIAN ULTRAHIGH-PRESSURE EXHUMATION
Pelitic schist with ~15 kbar porphyroblastic phase assemblage cut by ~10 kbar asymmetric shear fabrics associated with displacement along the Nordfjord–Sogn Detachment Zone. |
The Caledonides of western Norway represent one of the largest and perhaps best-exposed ultrahigh-pressure (UHP) terranes in the world. These terranes are thought to have been primarily exhumed along the Nordfjord–Sogn Detachment Zone (NSDZ), a multi-kilometer thick package of normal-sense asymmetric tectonites. Using field work and geologic mapping along the Hornelen segment of the NSDZ in conjunction with (micro)structural geology, thermobarometry and Sm/Nd garnet geochronology, I was able to show that asymmetric deformation along the NSDZ was responsible for the exhumation of UHP rocks from the base of the crust, but not from mantle depths (GSA Bulletin paper). My ongoing work in the Hornelen area focuses on muscovite 40Ar/39Ar thermochronology from the detachment tectonites. |
NEW APPLICATIONS IN LA-MC-ICPMS
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As a post-doc at the University of Arizona AZ LaserChron Center, I was involved in the development of several new geochronologic and geochemical applications for laser ablation multi-collector ICPMS . Projects that I worked on include: the development of small-volume laser ablation for generating U/Pb age maps of complexly zoned zircon (Chemical Geology, 2008), and the calibration of suitable apatite and titanite standards for U/Pb geochronology. Figure caption: Laser pits in zircon used for the small-volume technique: pits ~12 microns in diameter by ~4 microns deep allow sampling of discrete age domains within zircons that display complex zoning associated with the growth of zircon in multiple events. |
KINEMATICS OF DETACHMENT FAULT CORRUGATIONS
| Meter through 10’s-of-km-scale extension parallel folds, or corrugations, have been described associated with normal-sense detachment faults in a variety of tectonic settings including mid ocean ridges, core complexes, and lithospheric-scale shear zones. Of the many competing models for the formation of these enigmatic structures, a series of previously unidentified extension-parallel faults in the Northern Snake Range metamorphic core complex of east-central Nevada (MS Thesis) and simple finite-element modeling of exhumation and muscovite cooling ages in western Norway (AGU poster) suggest that along-strike variations in strain rate may play an important role in the formation of detachment fault corrugations. Ongoing field mapping and structural analysis of second-order folds in the Northern Snake Rage and in the Catalina Mountains of southern Arizona will further test this differential strain rate hypothesis. |
 Second-order fold in quartzite cascading toward the Sacramento Pass Basin and with its axis slightly oblique to the extension direction. Could this be an example of a flow perturbation fold? |
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