Intracrystalline deformation of garnet, wollastonite and pectolite grains during development of a crenulation cleavage in the sheared skarn

Abstract

This study focuses on a mylonitic skarn at the margins of a harzburgite of the Neyriz mantle diapir, Iran. The studied sample contained garnet porphyroclasts in a wollastonite and pectolite matrix. The microstructures of porphyroclasts and matrix are analyzed using electron backscatter diffraction (EBSD). Detailed analysis of garnet porphyroclast distortions and subgrain boundary trace analysis suggests that (110) 〈110〉 dislocation control intracrystalline deformation of garnet grains. Wollastonite and pectolite crystallographic preferred orientations (CPOs) are dominated by (100) parallel to foliation plane and 〈010〉 parallel to lineation. However, a dominance of low angle misorientation axes parallel to 〈010〉 precludes 〈010〉 dislocations from significant involvement in intracrystalline deformation. Schmid factor analysis also shows this slip system does not have high integrated Schmid factor. These observations suggest that oriented grain growth may be responsible for wollastonite and pectolite CPO development. Schmid factor analysis suggests (001) 〈100〉 and (100) 〈001〉 slip systems in the wollastonite and pectolite were involved in intracrystalline deformation and are linked kinematically to S2 and reactivated S1 planes.