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Strength and rheological evolution of the lower continental crust

Tildelt: kr 3,4 mill.

The project will study the processes of deformation and the mechanical strength in the lower continental crust. To date, it is unclear whether this part of the crust behaves as a rigid part of the lithosphere or whether it is mechanically much weaker than the upper mantle so that deformation may be localized in the lower crust. As many earthquakes occur in this part of the crust, it is of great importance to understand the deformation processes in the lower crust because the information about the deformat ion processes is the prerequisite for understanding mid- to lower crustal earthquakes. The working hypothesis is that the strength of the lower crust is critically dependent on its H2O-content. If dry, the lower crust is likely to be strong, whereas weake ning may be induced by H2O infiltration. The H2O infiltration may take place along initially brittle zones, which in most cases will be the location of seismic deformation. After fluid infiltration, rock properties change. The deformation processes in suc h zones are likely to change, too, so that they may become weak zones where deformation can be localized. We will carry out rock deformation experiments at similar pressure and temperature conditions as those of the shear zones of the lower crust. The nat ural and experimental microstructures will be compared to natural ones in order to identify the dominant processes and to obtain quantitative information on the deformation properties. In particular, the reaction and grain boundary migration structures of the experimentally deformed samples of feldspar will be studied in detail and compared to natural examples

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FRINATEK-Fri prosj.st. mat.,naturv.,tek