This project investigates driving forces and material behavior associated with continental subduction and ultra high-pressure metamorphism through an integration of numerical modeling of continental subduction and structural/petrological evolution of the material caught in the collision. The natural ultra high-pressure and high-pressure assemblages of the Western Gneiss of Norway provide rheological, geometric and geochronological information for the modeling, while the active obliquely convergent plate boundary of central New Zealand serves as a modern analog of a collision-subduction transition. Continental subduction zones represent regions where the crust-mantle interaction changes from nearly horizontal to dominantly vertical, accentuating the competing influences of body and viscous forces in the evolution of continents. Consequently, these zones contain a wealth of information on the basic driving forces and material behavior that control continental tectonics. The ultra high-pressure nappes of western Norway represent one of the few terrains that have traversed the viscera of continental subduction and escaped complete mineralogical overprinting and structural dismemberment of later events. Consequently, they can provide fundamental information on depth and temperature attained during collision, transient rheological behavior of crustal material where the motion in the mantle is transmitted to the crust, and on the spatial trajectories of material through a collisional orogen. These features identify the basic constraints required for coherent mechanical modeling of the collisional process.
The geodynamic models of oblique convergence, conditioned by these observations, provide orogen-wide velocity and strain rates and identify the characteristic length scales of strain partitioning within oblique subduction. Kinematic descriptions at a scale that overlap with field structural observations are being developed that relate the large scale dynamic model to observations made at the level of an outcrop. The research group is integrating these data sets into a three-dimensional dynamic and kinematic model of continental subduction capable of describing particle histories as a function of mechanical, metamorphic and thermal evolution. Because the researchers solve simultaneously for thermal as well as material flow patterns, pressure- temperature and time history of material throughout the subduction process can be tracked. This will provide model particle histories for comparison with the natural petrology.
