REACTIVATION OF PRESSURE SOLUTION SEAMS BY A STRIKE-SLIP FAULT

Older structures can be reactivated by movement on younger faults.This work investigates how that reactivation may enhance increased permeability and/or porosity of fluids. The structures, formed by reactivation of regional pressure solution seams [ strike 60-70] by slip on an adjacent left-lateral fault, were mapped [traced directly] at the Les Matelles outcrop [ Petit and Mattauer 1995 ] in the Languedoc region of France. The regional seams all get reactivated as left-lateral, strike-slip faults. Seams away from the fault have classic stylolite features and are anti-mode 1 [Fletcher and Pollard 1981], whereas the reactivated seams all have calcite in left-lateral jogs. There is a mappable gradient of displacement away from the fault. New seams and some veins formed at previous tips of the early seams and along their length as 'winged' and horse-tail' structures. Some link across to adjacent early seams, but some do not. The new seams in turn then get reactivated in right-lateral slip, but visibly, only those oriented between 115-140 degrees. Those at the higher angles [135-140] have more calcite in right-stepping jogs, suggesting a higher fluid connectivity at this time. Winged seams and veins form at the tips of these new seams, curving into parallelism with the oldest set. The local stress field that created the earliest seams rotated clockwise to drive left-lateral motion on the seams during active slip on the main fault. The stress then back rotated [ anti-clockwise ] towards the original direction, creating a right-lateral sense of shear on the optimally oriented segments of the newly-created seams. The perturbation opens the network for enhanced calcite deposition only during the time of active movement on the larger fault.