Estimation of flow stresses in mylonitic quartzites of parts of Singhbhum shear zone,Bihar, eastern India

Recrystallized grain size was measured from quartzite mylonite specimens collected from parts of Singhbhum shear zone in eastern India. The specimens were collected along five traverses (Mushabani, Pathargora, Surda, Rakha and Jadugoda) across the elongation of the shear zone. The sheared quartzites range from protomylonite through mylonite to ultramylonite. The microstructural studies of the specimens reflect that dynamic recrystallization was the main deformation process. Estimation of flow stresses were derived from these specimens using empirical equations relating to flow stress and recrystallized grain size. The calculated stresses range from 12–28 MPa (Mercieret al 1977), 23–49 MPa (Twiss 1977), 20–68 MPa (Christie and Ord 1980), considering all the traverses. The results show that these values can only be used semiquantitatively.