Basement Faults and Their Relationships to Salt Plugs in the Arabian Platform in Southern Iran Geological setting The ZMR in southern Iran, located on the Iranian side of the Arabian Platform, are one branch of the Alpine-Himalayan orogenic belt. The stratigraphy and sedimentology of the Zagros Thrust and Fold belt have been described by James and Wynd (1965), by Falcon (1974), and Farhoudi (1978).The Phanerozoic column is about 12000 m thick. Paleozoic sedimentation was mainly epicontinental; from Permian to Miocene time it consisted chiefly of carbonates. The Tethys Sea began to subducted under the Iranian Plat in the Late Cretaceous. Cessation (Ross and others, 1973) or slowing of subduction resulted in carbonate sedimentation in Early Cenozoic time (Farhoudi, 1978) as well as the deposition of 400m evaporatic materials in the Miocene. Orogenic movements began in the Middle or upper Miocene when sedimentation became clastic. The opening of the Red Sea intensified folding and uplift, which are still going on. Most of the salt diapirs are located in the southeastern part of Fars Province, especially near Bandar Abbas (Figure 1).The diapir field is bounded by the Oman Line to the east, the Kazerun Fault to the west, and the Main Zagros Thrust to the north. Only a few salt diapirs reach the surface northwest of the Kazerun Fault near the Main Zagros Thrust, they occur in great number in the form of small islands in the Persian Gulf, south of the boundary of the Zagros Folded Belt (Ala, 1974). The presence of numerous salt domes, mainly of the Paleozoic Hormuz Formation, indicates active tectonics of the ZMR. Although salt domes have been reported in many places of the world, e.g. to the north of the Gulf of Mexico in the USA and in the northern part of Germany, most of them are not outcropped and have been detected by geophysical methods. In contrast to them salt domes in the ZMR and in the Persian Gulf are not only high elevated domes, but in many cases the salt is flowing down the flanks as “Salt Glacier”. Some of the salt domes are more than 1000 m higher than the surrounding area, e.g. Kangan salt dome. Some of them have been used as open cast mines. It’s more soluble than limestone and in contrast to the latter; it has plastic behavior and impede the flow of fluids. The Tertiary Gachsaran Formation, consisting mainly of salt, anhydrite and marl layers, acts as one of the best cap rocks of hydrocarbon in the Middle East. The structure of the Zagros Thrust and Fold Belt consists of numerous, mostly northwest trending synclines and Anticlines. Steep flanks on most individual structures face southwest (Falcon, 1969). Dextral displacements have been reported on faults parallel to the Main Zagros Thrust between 33º-35ºN (Tchalenko and Braud, 1974) and on the Kazerun Fault (Falcon, 1974). The near-basement salt and Miocene salt play a major role in the morphology and structure of the Zagros Thrust and Fold Belt. These salts cause disharmonic folding and do not permit sub-salt structures to continue upward. Earthquakes epicenters The distribution of epicenters of the last century and the salt plugs of the area are studied. These earthquake epicenters are gathered tensely in special regions that probably show the development of basement faults in three directions (NW-SE, N-S, NE-SW). Most of these trends are conformed with the ones gained from the study of axis deviation of anticlines and synclines and with the trend of the salt plugs as well as that are shown in figure 2.  Figure 2. Trend of postulate basement faults in the study area |