Fault rocks and fault mechanisms(断层和断层机理)-R.H.Sibson.pdf

Fault rocks and fault mechanisms
R. H. SIBSON
SUMMARY
Physical factors likely to affect the genesis of the with the production of mylonite series rocks
various fault rocks--frictional properties, tem- possessing strong tectonite fabrics. In some cases,
perature, effective stress normal to the fault and fault rocks developed by transient seismic fault-
differential stress--are examined in relation to ing can be distinguished from those generated
the energy budget of fault zones, the main by slow aseismic shear. Random-fabric fault
velocity modes of faulting and the type of fault- rocks may form as a result of seismic faulting
ing, whether thrust, wrench, or normal. In a within the ductile shear zones from time to
conceptual model of a major fault zone cutting time, but tend to be obliterated by continued
crystalline quartzo-feldspathic crust, a zone of shearing. Resistance to shear within the fault
elastico-frictional (EF) behaviour generating zone reaches a peak value (greatest for thrusts
random-fabric fault rocks (gouge--ia-- and least for normal faults) around the EF/OP
cataclasite series--pseudotachylyte) overlies a transition level, which for normal geothermal
region where quasi-plastic (QP) processes of gradients and an adequate supply of water,
rock deformation operate in ductile shear zones occurs at depths of lO-15 km.
SINCE LAPWORTH'$ (I885) description of the type mylonite from the Moine
Thrust in NW Scotland, there have been many petrographic descriptions and
classifications of the texturally distinctive rocks found associated with fault zones
(. Waters & Campbell 1935, Hsu 1955, Christie 196o , 1963, Reed 1964, Spry
I969, Higgins 1971 ). These rocks provide a tangible source of information on the
processes which operate in major fault zones, but little has been done to correlate
the various types of fault rock with different deformation environments and modes
of faulting.
In this paper, I discuss t