Page 128 - Microtectonics

5.2 · Brittle Fault Rocks 117

Fig. 5.5. Pseudotachylyte in a foliated amphibolite. The foliation is cut by the pseudotachylyte. A main fault vein transects the rock from top
right to lower left. An injection vein occurs at left. Isolated fragments lie in a dark pseudotachylyte matrix. Boundaries between pseudo-
tachylyte and wall rock are sharp. Paine, South Chile. Width of view 14 mm. PPL

Fig. 5.6. Contact of a pseudotachylyte vein (top) and the wall rock (bottom). The boundary is sharp where quartz and feldspar grains (white) are
in contact with the pseudotachylyte matrix, but an embayment exists where a biotite grain (centre) is in contact. This structure is attributed to
preferential corrosion of the biotite crystal by pseudotachylyte melt along an originally straight fracture surface. The biotite grain is strongly
kinked, probably due to brittle deformation preceding pseudotachylyte generation. Vestfold Hills, Antarctica. Width of view 5 mm. PPL