Open AccessLocalized ductile shear below the seismogenic zone: Structural analysis of an exhumed strike‐slip fault, Austrian Alps
Author(s) -
Cole Joshua,
Hacker Bradley,
Ratschbacher Lothar,
Dolan James,
Seward Gareth,
Frost Erik,
Frank Wolfgang
Publication year - 2007
Publication title -
journal of geophysical research: solid earth
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.67
H-Index - 298
eISSN - 2156-2202
pISSN - 0148-0227
DOI - 10.1029/2007jb004975
Subject(s) - geology , shear zone , mylonite , muscovite , shear (geology) , seismology , dislocation creep , petrology , quartz , dislocation , tectonics , composite material , materials science , paleontology
The Miocene Salzachtal‐Ennstal‐Mariazell‐Puchberg (SEMP) strike‐slip fault in Austria allows study of the internal structure of a fault zone from the near surface to ∼30 km depth. As it enters the Tauern Window along the Rinderkarsee shear zone, the SEMP fault passes from a dominantly brittle to a dominantly ductile structure. The shear zone consists of three 1‐ to 100‐m‐wide zones of brittle‐ductile and ductile deformation separated by 500‐m‐wide zones of less deformed rocks. The southern shear zone is mylonitic, with ductile amphibole and plagioclase; weak crystal preferred orientations imply that the main deformation mechanism was dislocation‐accommodated grain boundary sliding. The northern and central shear zones are characterized by discrete millimeter‐wide shear zones with ductile quartz, muscovite, and biotite and brittle feldspar. Shear zone nucleation at the grain scale involved dislocation creep and the transformation of plagioclase to muscovite; strain then localized in muscovite‐rich grain boundary shear zones that linked to form throughgoing shear zones.