For neutral and overlapping fault steps, there is a contractional linking damage zone between the fault segments. The orientations of the local s 1 (the maximum compressive stress) and s 3 (the minimum compressive stress) directions strongly depend on the structural position within the transpression zone. The numerical results indicate that at the onset of deformation, displacement vectors are oblique to the regional compression direction (20e90). Three representative fault segment interactions are modelled: underlapping, neutral, and overlapping. These observations may prove useful in understanding mechanisms for fault-controlled enhanced/reduced permeability and fluid pathways.Two-dimensional finite-element modelling of elastic Newtonian rheology is used to compute stress distribution and strain localization patterns in a transpression zone between two pre-existing right-stepping, left-lateral strike-slip fault segments. Two distinct, time-sequential processes are shown to operate during the fault propagation: (1) typical millimetre- to centimetre-spaced solution surfaces form in the distal tip zone of the advancing fault plane (2) as the tip advances, the fault plane breaks through the cleavage as minor shear displacements reactivate some of these nascent surfaces. Cleavage nucleates as solution planes at the front of the advancing fault as the result of stress concentration in this region. A model for the development of the Mattinata Fault is proposed in which the cleavage surfaces are interpreted as fault-propagation deformations. Geometrical and kinematic relationships exist between the fault and the associated cleavage planes, thus: (1) cleavage–fault intersection lines lie parallel to the fault and the sheared cleavage rotational axes and (2) the cleavage–fault angle is almost constantly equal to 40°.
The cleavage consists of sub-parallel solution surfaces, which are often reactivated as sheared solution planes. Typical cleavage development is restricted within the 200–300-m wide fault zone, which is bounded by virtually unfractured wall rocks. Comparison of the Kuh-e-Hori transpression zone, between the Esmail-abad and West Neh left-stepping right-lateral strike-slip fault segments in SE Iran, with the modelling results shows strong similarities with the neutral step configuration.ĭisjunctive, spaced solution cleavage in carbonate rocks is genetically associated with the propagation of the left-lateral, strike-slip Mattinata Fault in the Gargano Promontory, Italy. The modelled mean stress pattern shows a similar pattern to that of the contractional steps, and decrease and increase in underlapping and overlapping fault steps, respectively. A lozenge-(for under-lapping steps), rhomboidal-(for neutral steps), and sigmoidal-shaped (for overlapping steps) trans-pression zone developed between the two segments. Interaction between the two fault segments perturbs the stress field and reflects the heterogeneous nature of deformation. These flow patterns are related to friction effects and different shear deformation, from pure shear outside of the fault steps toward simple shear along the fault segments.
For overlapping faults, the s 1 trajectories within the transpression zone deflects significantly forming a sigmoidal pattern, which is created by two rotational flow patterns close to the fault tips.
Two-dimensional finite-element modelling of elastic Newtonian rheology is used to compute stress distribution and strain localization patterns in a transpression zone between two pre-existing right-stepping, left-lateral strike-slip fault segments.
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