TECTONOSTRATIGRAPHY, STRUCTURAL GEOMETRY AND KINEMATICS OF THE NW IRANIAN PLATEAU MARGIN: INSIGHTS FROM THE TALESH MOUNTAINS, IRAN

摘要

The structural geometry and kinematic variations along curved fold and thrust belts and their interaction with neighboring rigid basement blocks are not well understood. In this study, we present a structural mapping and stratigraphic analysis of the Talesh Mountains, Iran, to document the timing and evolution of this curved orogen due to collision with the South Caspian Block. NE and SW verging oblique slip thrust faults are the main structural features in the northern and southern parts of the mountains. The N-trending central part of the range is connected to the curved ends of the Talesh Mountains by a system of high angle reverse faults with right lateral strike-slip sense of motion. Restored cross sections indicate greater horizontal shortening (25-30%) in the southern parts which gradually decreases toward the center (13-16%), and then increases to the north (22%). A compilation of stratigraphic sections across the region indicates three major phases of regional deformation in the early Oligocene, middle Miocene and early Pliocene. The middle Miocene phase, in good agreement with other data sets across the Iranian Plateau, is the onset time of deformation for the Talesh Mountains. The regional convergence direction has changed during this major phase of deformation in the NW margins of the Iranian Plateau. The observed kinematic variation along the major faults across the Talesh Mountains is likely resulted from a regional change in the shortening direction in middle Miocene. Variations on the measured Late Cenozoic horizontal shortening across the northern, central and southern parts of the Talesh Mountains resulted from their different orientations with respect to the regional convergent direction as well as interaction with the rigid south Caspian block. These results highlight that the orientation and timing of deformation was strongly influenced by the neighboring Caspian block and regional variations in the convergence direction associated with evolution of the Iranian Plateau.