Dynamic recrystallization mechanisms and vorticity estimation of the Terrane Boundary Shear Zone (Lakhna shear zone): Implications on dynamics of juxtaposition of the Eastern Ghats Mobile Belt with the Bastar Craton, NW Odisha

Abstract

The Terrane Boundary Shear Zones provide important information regarding tectonics of juxtaposition between different terranes. In this paper, we have studied the Lakhna shear zone, between the Eastern Ghats Mobile Belt and the Bastar Craton. Detailed structural study, sampling and strain analysis through measurement of size and orientation of dynamically recrystallized quartz grains indicate: (i) the Lakhna shear zone is developed on granitic protolith of the Bastar Craton, (ii) mylonites are quartzofeldspathic in composition, marked by SE dipping mylonitic foliation and down dip stretching lineation defined by biotite and quartz grains, (iii) S-C fabric and rotated porphyroclasts indicate a NW vergence thrust kinematics, (iv) recrystallization of quartz grains occurred by climb-assisted dislocation creep through BLG near craton boundary, SGR in the central part of the shear zone, GBM towards the Eastern Ghats margin, (v) temperature of deformation increases towards mobile belt (380–560°C) that suggests thrusting of granulitic hot slab over cold craton and (vi) Wm estimates of 0.9 suggest simple shear deformation. The juxtaposition between the EGMB and the Bastar Craton occurred by simple shear thrusting when the granulitic slab was hot enough to create a difference in temperature and mechanism of dynamic recrystallization across the shear zone.