Experimental studies on rheological properties of transition zone minerals

Yale University, New Haven CT

Investigators

Abstract

The rheological properties of transition zone minerals have a strong influence on how mantle convection works. There is clear evidence, from seismic tomography, for intense deformation of deep sinking cold materials in the mantle transition zone. However, intense deformation of cold materials is at odds with the conventional view of temperature sensitivity of rheological properties. The main purpose of this project is to provide a new data set, based on newly developed high-pressure deformation techniques, by which we can solve this paradox. One hypothesis to resolve this paradox is that the phase transformations that occur in the transition zone will make materials weak by grain-size reduction. However, so far there is no quantitative data on the sensitivity of rheological properties of transition zone minerals on grain-size. In this project, the investigator will perform a series of laboratory experiments on wadsleyite (one of the transition zone minerals), using RDA (rotational Drickamer apparatus), to determine the flow laws for grain-size sensitive deformation mechanisms. Samples to be used are synthetic polycrystalline aggregates with controlled grain-size and water content. Specimens will be deformed at constant strain-rates using RDA, and the mechanical data (stress-strain curves) will be obtained in-situ at a synchrotron facility (NSLS at Brookhaven). Deformed samples will be examined ex-situ after the recovery to study the microstructures using a range of techniques including optical microscope, EPMA, SEM (EBSD), FTIR, Raman and TEM. The results will shed light on how mantle convection occurs in Earth and how Earth evolves thermally.