A recrystallized grain size piezometer for experimentally deformed feldspar aggregates

A recrystallized grain size piezometer for low-temperature migration recrystallization in feldspar has been experimentally calibrated. Hot-pressed samples of fine-grained albitic feldspar (grain size 1-10 μm) and a natural albitic feldspar aggregate (∼150 μm) were deformed in simple shear and axial compression at a temperature of 900°C and a confining pressure of 1500 MPa. Transmission electron microscopy (TEM) verified that deformation occurred by recrystallization-accommodated dislocation creep. Grain size distributions were measured from scanning electron microscopy (SEM) photographs of polished and etched samples. The results yield a recrystallized grain size piezometer relationship of d=55±5· σ^-0.66±0.07 where d is the geometric mean grain size (μm) and σ the differential stress (MPa). The exponent is higher than that determined in previous studies of other materials for rotation recrystallization and high-temperature migration recrystallization, indicating that different recrystallization mechanisms have distinct recrystallized grain size piezometer relationships.