INTERPRETING THE TECTONICS OF THE ABU JIR FAULT, KARBLA – NAJAF PLATEAU USING MINERALOGICAL AND GEOPHYSICAL DATA

Abstract

The present study is carried out on Abu Jir Fault across the Karbala – Najaf Plateau which is an outstanding fan-shaped geological feature located in the central part of Iraq on the boundary between the stable and unstable shelves. A clear variation of mineralogical composition percentages of quartz, calcite, feldspar, gypsum and gamma ray in both sides of the fault are recorded. The interpretation of magnetic maps; reduction to the pole and depth to basement (RTP and DTB) indicates three depressions, Al-Habbaniya, Al-Razzazah and Bahr Al-Najaf controlled tectonically by a NW – SE basement graben, and the plateau was a part of the subsided area. Gravity field along an ENE – WSW profile across Abu Jir fault indicates an elongated NW – SE positive anomaly of +0.9 mGal whose source is located at a depth of 3 Km, below the plateau, and the uplift is accompanied by faulting. Dibdibba Formation (Pliocene – Pleistocene) in the middle and southern Iraq has been developed in an active basin located along Abu Jir Fault. A large part of this formation is situated on the eastern edge of the Stable Shelf. The western block of the Fault was upthrown after the Pleistocene as a post-depositional tectonic episode forming an elevated area which had since been intensively eroded due to a new tectonism along the Abu Jir Fault. Sharp variations in mineralogy, gamma ray and geophysical parameters have been recorded on both blocks of the fault and are consistent with field evidence and confirm the new tectonics of Abu Jir Fault.