Experimentally deformed feldspar aggregates
Figure caption
36
TA shortened 52% at 1100°C, 10-5/sec, and 1200 MPa; regime 1 dislocation creep.
TA shortened 52% at 1100°C, 10-5/sec,1200 MPa. This sample was deformed in the lower temperature dislocation creep regime (regime 1 of Hirth & Tullis, 1992). The temperature is not high enough to activate dislocation climb and thus grain boundary migration recrystallization serves as the recovery process. Original grains undergo relatively little and very inhomogeneous strain; they develop strong patchy undulatory extinction and sharp deformation bands or even several grain-scale faults, which together with the original grain boundaries develop zones of extremely fine (d~1 µm) recrystallized grains along them. The recrystallized grains are initially strain-free and thus significantly weaker than the larger work-hardened original grains, and thus strain is preferentially partitioned into the recrystallized zones. This photo shows that original grains have been separated into several smaller lozenge-shaped grains, and there are thin zones of extremely fine recrystallized grains along all of the original and the new grain boundaries. The sample had a relatively high yield strength, followed by strain weakening which began when an interconnected network of recrystallized grains developed. Compare the microstructure of this sample with that shown in photo #35, which was produced by cataclastic flow. (W561)