Fault rocks and fault mechanisms

Abstract

Physical factors likely to affect the genesis of the various fault rocks—frictional properties, temperature, effective stress normal to the fault and differential stress—are examined in relation to the energy budget of fault zones, the main velocity modes of faulting and the type of faulting, whether thrust, wrench, or normal. In a conceptual model of a major fault zone cutting crystalline quartzo-feldspathic crust, a zone of elastico-frictional (EF) behaviour generating random-fabric fault rocks (gouge—breccia—cataclasite series—pseudotachylyte) overlies a region where quasi-plastic (QP) processes of rock deformation operate in ductile shear zones with the production of mylonite series rocks possessing strong tectonite fabrics. In some cases, fault rocks developed by transient seismic faulting can be distinguished from those generated by slow aseismic shear. Random-fabric fault rocks may form as a result of seismic faulting within the ductile shear zones from time to time, but tend to be obliterated by continued shearing. Resistance to shear within the fault zone reaches a peak value (greatest for thrusts and least for normal faults) around the EF/QP transition level, which for normal geothermal gradients and an adequate supply of water, occurs at depths of 10–15 km.

Petrogenesis and U-Pb and Sm-Nd geochronology of the Taquaral granite: record of an orosirian continental magmatic arc in the region of Corumba - MS

“…The software Open Stereo was used for structural data analysis (Grohmann et al 2011) and the shear zone rocks were classified according to Sibson (1977).…”

“…Pegmatite pockets up to 4 m thick are observed. In the mylonitic portion of this facies, stretched and rotated alkali feldspar porphyroclasts occur in a fine-to medium-grained quartz-feldspathic groundmass which is classified as mylonite (Sibson 1977), based on the relationship between porphyroclasts and groundmass.…”

Different styles of faulting deformation along the Dead Sea Transform and possible consequences for the recurrence of major earthquakes

“…The Arava fault is represented by fault breccias (limestones with more than 30% of visible fragments; Sibson 1977) and fractured rocks, which are developed on either side of the fault. However, clay gouges and cataclasites were not observed.…”

Crush zone structure in a compressional step:

“…T 10 2 D P L P 10 2 L Scholz, 2002 T D P L P 2 Segall and Pollard, 1980;Richard et al, 1995;Okubo and Schultz, 2006;Sibson, 1986a, 2003114 10 495 515 200810Woodcock and Fischer, 1986, 1999 ; Kanamori, 1981, Otsuki and Dilov, 2005Richard et al, 1995McClay andBonora, 2001 Davis et al, 1999;Okubo and Schultz, 2006 1982, 1982bKanaori et al, 1985, 1982a, c Satake et al, 1984Ui et al, 1988, 1983, 1998GPS Ito and Wada, 2002Hirahara et al, 2003;Goto et al, 2005;Mizuno et al, 2005Mizuno et al, 70 , 1998, 2003, 1983Takagi et al, 2005Takagi et al, 1988 Sibson, 1977;, 1996, Higgins, 1971Wise et al, 1984;Schmid and Handy, 1991;Braathen et al, 2004Braathen et al, 1996 fault brec- …”