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Donna L. Whitney, Principal Investigator

Mechanical Controls on Deformation of the Lithosphere and Asthenosphere at Tectonic Plate Boundaries

This research is using numerical modeling efforts on problems of mechanical interaction of two or three phases of contrasting viscosity. Using both ansys and adeli, a FLAC-like code written by Jean Chery in Montpellier, these researchers are running two-dimensional and three-dimensional finite element models as a simplified means of approaching several geodynamic problems at a range of scales. Both main studies are highly cross disciplinary, using thermal-mechanical numerical modeling as a unifying tool for data from a variety of sources. One project focuses on processes at mid-ocean ridge spreading centers and the other on continental lithosphere. They are analogous in many physical respects but are constrained by very different kinds of data.

Initial work involves the two-phase system of (stronger, elastic plastic) chromite and (weaker viscous) olivine, deforming at high temperature and pressure conditions of the mantle beneath mid-ocean ridges. The stress loaded into chromite by the flow of olivine during deformation can be measured from microfabric studies and serves as a stress gauge. The numerical models are used to simulate these gradients, in order to constrain unmeasurable quantities such as strain rate and minimum melt pressure. The problem of melt phases interacting with olivine and chromite is being looked at in order to understand weakening instabilities and the strain localization process. This work is being done in collaboration with the Mineral Physics Laboratory of Professor David Kohlstedt at the University of Minnesota. Studying these simple systems help understand the mechanisms of melt migration in the mantle and its influence on the geometry of asthenospheric flow beneath mid-ocean ridges.

A second focus concerns the mechanical properties of the lower crust and the degree to which layers in the lithosphere are coupled during deformation along plate margins. It is widely hypothesized that the mechanisms by which crustal rocks are deformed and brought to the earth's surface are linked to the behavior of the upper mantle and lower crust. By evaluating the magnitude and rate of exhumation of rocks exposed along collisional zones, constraints can be placed on coupling between layers in the upper lithosphere. A multidisciplinary approach, applying metamorphic petrology, structural geology, and thermochronology, is being used to characterize and quantify the magnitude and rate of exhumation of rocks now exposed along ancient and modern plate boundaries. Numerical modeling using ansys allows for a more accurate interpretation of field data and allows constraints to be placed on how various degrees of layer coupling within the lithosphere are manifested in the deforming upper crust. Results from this study will significantly add to the understanding of how continental-scale deformation at convergent plate margins is controlled by the variation of rock properties in the lithosphere.

This information is available in alternative formats upon request by individuals with disabilities. Please send email to alt-format@msi.umn.edu or call 612-624-0528.

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