EGU2011-4270.pdf

The Pfahl shear zone in the Bavarian Forest, Germany, is a NW-SE trending dextral strike-slip shear zone with multiple events from 327-342 Ma to 247 ± 21 Ma. A 150 km long quartz dyke formed along the main fault zone, indicating an important hydrothermal system. The dyke has a layered structure with different types of quartz, transected by a network of quartz veins. Four stages of quartz crystallization were identified: (1) homogeneous µm-sized quartz with angular wallrock fragments, (2) cm- to dm-large angular fragments in a µm-sized quartz mass, (3) mm- to dm-wide quartz veins roughly parallel to the Pfahl zone, and (4) steep, N-S oriented mm- to dm-thick quartz veins oblique to the Pfahl trend. The evolution of the hydrothermal system involved early quartz formation from supersaturated silica solutions, followed by quartz formation from decreasing saline hydrothermal fluids, brecciation, and later en-echelon veins indicating less overpressured fluids with lower silica content.