C’ shear band development in three-phase mineral aggregates (e.g. granitoids)
Comparison of four full-field numerical simulations of shear band development in three phase mineral aggregates, representing a granitoid, deformed by dislocation glide in dextral simple shear up to a shear strain of 20. There are three minerals with different mechanical strength: SP (strong phase in grey, representing feldspar), IP (intermediate phase in white, representing quartz) and WP (weak phase in black, representing mica). The behaviour of the weak phase is anisotropic, in a way that the critical resolved shear stress (CRSS) required to activate glide of dislocations in the basal plane is 10 times lower than that required to activate other slip systems. The intermediate and strong phases behave isotropically and the CRSS required to activate dislocation glide along their slip systems vary (see below). The system goes trough three phases: (1) grain elongation and rotation, (2) S–C fabric development and (3) shear band development and strain partitioning. C’ shear bands form when layers of weak minerals rotate forwards and these structures become inactive when they rotate backwards or shorten and collapse.
45% SP – 45% IP – 5% WP. CRSS for SP and IP are 80x and 40x that of the WP, respectively:
42.5% SP – 42.5% IP – 15% WP. CRSS for SP and IP are 50x and 25x that of the WP, respectively:
35% SP – 35% IP – 30% WP. CRSS for SP and IP are 30x and 15x that of the WP, respectively:
27.5% SP – 27.5% IP – 45% SP. CRSS for SP and IP are 80x and 40x that of the WP, respectively: