Delta-Type Porphyroclast Tails

Thin section of mylonite from ductile shear zones in NW Vietnam. The feldspar porphyroclasts have delta-type tails that indicate counterclockwise rotation as a result of top to the left sense of shear. Image from website: http://www.ipgp.jussieu.fr/~lacassin/WebTecto/rech/tectorecherche/Extrusion/Frolling.html