The photograph shows ductile–brittle shear fractures affecting banded and foliated quartzites (Rabassers quartzites), interlayered in a sequence attributed to Upper Proterozoic. The whole sequence was subjected to polyphase deformation and metamorphism during the Variscan. D3 dextral NW–SE shearing caused simultaneous folding and stretching of the preexisting banding. Ductile folding contrasts with shear bands and microfaults arising from a brittle–ductile extension. The ramp-flat-like geometry of the fault caused displacement gradients in the layers producing the reverse drag folds. PhotoID148
The photograph shows ductile–brittle shear fractures affecting banded and foliated quartzites (Rabassers quartzites), interlayered in a sequence attributed to Upper Proterozoic. The whole sequence was subjected to polyphase deformation and metamorphism during the Variscan. D3 dextral NW–SE shearing caused simultaneous folding and stretching of the preexisting banding. Ductile folding contrasts with shear bands and microfaults arising from a brittle–ductile extension. The ramp-flat-like geometry of the fault caused displacement gradients in the layers producing the reverse drag folds. PhotoID148
Photograph: Jordi Carreras/Elena Druguet
Reference: Carreras and Druguet, in press. Photograph of the Month. Journal of Structural Geology