CHARACTERIZATION OF A KARST AQUIFER IN A COMPLEX TECTONIC REGION, SOUTHWESTERN IRAN

摘要

Characterization of karst aquifers is not unique and depends on geological and structural settings, relief, precipitation, and the interactions of these parameters. Therefore, the characterization of a highland karst aquifer in tectonized geological settings is still a challenge, especially in a region with scarce hydrogeological data. In this study, we characterize an inaccessible highland karst aquifer under the severe compressional stresses of two thrust faults, using extensive hydrogeological data by an integrated approach. The Malagha karst aquifer is located in the southern limb of the Malagha Anticline in a tectonized highland zone and is bounded by the Malagha and Qale-Tol thrust faults. Dam construction-related data including hydrochemical data, stable isotopes, water table levels, geological logs, permeabilities, fracture zones from numerous boreholes, and data from three dye tracer tests were used to evaluate the aquifer behavior. The exposed breccia zones and the significant water table differences on both sides of the Qale-Tol thrust fault core confirm the barrier behavior of the fault. The damage zone is highly fractured based on the geological logs, resulting in a relatively uniform water level distribution. The karst water flows through the extensive fracture networks inside the damage zone with no evidence of converging toward any main conduit. The type of flow is most probably diffuse, based on two dye tracer tests, the flat water table, and continuous high permeabilities up to a length of 140 m. The general flow direction is parallel to the fault strike, toward the downstream alluvium bounded between two impermeable formations. This conclusion is based on water balance, geological settings, and delta O-18 and delta H-2 data. Due to the flatness of the water table, such conditions as the mound below the Abolabbas River, bedding plane dips, and fractures and joints may locally control the flow direction. The footprint of the karst water and the rech