This thesis reports the findings of multi-approach studies on major upper crustal fault gouge zones In the Internal Zone of the Betlc Cordilleras, southern Spain, and experimental work designed to attempt to simulate the features observed In natural fault zones.
In the Betlc Zone’s Alpujarrlde Complex four phases of deformation were recognised. Major third phase brittle extenslonal faults cross-cut and thin second phase thrusts (Adra J Murtas) emplaced on more ductile shears zones. Gouge kinematic Indicators Indicate hanglngwall slip on the extenslonal faults to the northwest, equal to the emplacement direction of the thrusts. Cumulative slip on the gouge zones Is estimated to have been 4.6-5.5km.
Intra-fault material In the extensional faults Is phy I I I te-der I ved gouge, comminuted largely by fracture-accommodated grain boundary sliding. Shearing of phyIloslIIcate dominated gouge develops mesostructures which have competing work hardening and work softening effects. Work hardening effects Include:(a) the antithetic rotation (continuous deformation) of shear planes (discontinuous deformation) particles and host rock slivers to generate fabrics antl-clockwise of the fault zone boundaries In dextral shear and, (b) the deactivation of shears. Work softening Is achieved by the propagation of new shear surfaces, shear linkage and shear reactivation. The phyllfte gouges show deform- utlon spreading rather than progressive localisation, which may arise from work hardening during gouge flow. Displacement shifting away from work hardened zones leads to the strain modIfloat Ion of mechanically softer protogouges and/or failure and slip at the gouge-host rock Interface. Structures on the Interface resemble those on recent selsmlcally active faults.
Gouge particle comminution resulted In bulk and single mineral particle size distributions (psd's) which vary from coarse skews via scale Invariance to fine skews. Two dimensional fractal dimensions calculated for scale Invariant psd's (D=2.3+/-0.02 for all particles, and D=2.33+/-0.34 for quartz particles only: 2mm-0.001mm range) cannot derive by uniform or non-uniform length reduction models. For the scale Invariant distributions no upper limit was found, but lower limit deviation occurred at 20mlcrons. Effects Including enhanced cracking along grain boundaries, or from quartz-mica compliance differences under load, the dispersion of trail-derived particles, or Impingement suppression may explain lower limit deviation.
Comparison of experimentally deformed quartz and quartz-kaolInlte synthetic gouges showed that the effect of adding kaolInlte Is to reduce the quartz comminution rate. Increase the range of s+rains across which transient particle size scale Invariance persists, and to enhance work hardening. In mica rich gouges, the hardening rate Increases as particle size decreases, and c°incldes with the maximum rate of mica comminution, the most homogenous deformation In shear 2°nes, and the maximum proportion of back-rotated particles.