Faculty Candidate Seminar - Whitney Behr

01/11/2016 - 12:00pm


DATE:  January 11, Monday, 12:00 p.m.  

LOCATION: Hubbs Hall 4500 
SPEAKER:  Whitney Behr Ph.D.
University of Texas Austin

TITLE:  Constraints from Exhumed Rocks on the Strength and Rheology of Continents

A long-standing, unresolved question in geodynamics centers on the magnitude of deviatoric stress in the continental lithosphere— i.e. what is the integrated strength of the crust and upper mantle, and at what depth does the peak strength reside? Stress in the lithosphere is traditionally estimated by extrapolating laboratory-derived flow laws to natural conditions, producing lithospheric strength profiles (also known as ‘Christmas-tree diagrams’); these form the basis for many geodynamic models of processes ranging in scale and rate from regional post seismic relaxation to global mantle convection. The use of these profiles requires some specific assumptions about rock type, grain size, water content, thermal gradient, deformation mechanism, strain rate and degrees of localization— all parameters that are likely to vary by 2-3 orders of magnitude regionally within the earth, and by up to 10 orders of magnitude in the earth relative to the laboratory. Recent technological advances such as electron backscatter diffraction and high resolution elemental mapping, however, have led to a much greater potential for characterizing these parameters in natural systems both methodically and quantitatively for individual regions. Direct measurements of stress, temperature, pressure, and water contents, coupled to grain-scale observations of grain size and deformation mechanisms allows the problem to be inverted such that natural observations feed back to place much needed limits on the extrapolation of laboratory flow laws to Earth. In my talk I will present several examples of how lithospheric strength can be measured using detailed field and microstructural analysis of exhumed crustal and mantle rocks. I’ll also discuss the implications of these observations for lithospheric mechanics and highlight some remaining challenges in this field.

Faculty Host:  Lisa Tauxe (ltauxe@ucsd.edu)
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Hubbs Hall 4500