فهرست مطالب قاسم حیدرزاده

Geomorphic evidence along the Siah kuh fault (North of Jajarm) shows this fault has been active during Quaternary. Faulted Quaternary deposits, deflected and offset streams and bisected alluvial fans are among such evidence. These together with fault scarps in Neogene and Quaternary strata reveal young left-lateral motions on the Siah kuh fault as a part of the Shahrud fault system. However, there are Paleozoic and Mesozoic Formations juxtaposed with Neogene and Quaternary deposits along the fault. Some of these old units have cropped out in northeastern termination and bends along the fault, while others are observed where there is not a bend. Therefore, thrust faulting must have brought them to the surface. Aeromagnetic maps show that Siah kuh fault coincides with an aeromagnetic lineament. Consequently, the geomorphic features suggest only the youngest slips on the fault. Therefore, the Siah Kuh has been a thrust fault whose kinematics change and initiation of left-lateral motions resulted from changes in stress regimes and a regional reorganization during Quaternary.

The ~100km-long NE-SW Cheshmeh nay fault zone is located in Alborz-Allah Dagh Mountains. This fault zone is composed of several faults with dips between 40 to 85° toward NW or SE. The Cheshmeh nay fault zone belongs to the Shahrud fault system and has a left-lateral motion. Geomorphic evidence such as deflected streams، bisected alluvial fans and cut Quaternary deposits shows that this fault zone has been active during Quaternary. Exposure of Paleozoic and Mesozoic formations over or in contact with younger units as well as abundant thrust fault planes present in the fault zone indicate that there seems to have been a thrust faulting along the fault zone sometime during its evolution. In addition، the Cheshmeh nay fault zone coincides with the F-431 aeromagnetic lineament، indicating that the fault zone is supposed to be an old basement fault. Making part of the boundary between the Alborz and Kopeh Dagh basins، this fault zone was a basin-bounding normal fault zone which changed the kinematics into a thrust fault zone. This kinematics change resulted likely from the Iran Block moving toward the Turan and Kopeh Dagh regions and/or in Late Cretaceous. Following the regional reorganization in the Arabia-Eurasia collision zone between 3-7 Ma and/or in Quaternary، the Cheshmeh nay fault zone became a fault zone with a dominant left-lateral movement.

The Kopet Dagh (KD) mountain belt in the northeast of Iran contains a sequence of Jurassic-Pliocene folded sedimentary rocks which unconformably covers deformed sedimentary and pyroclastic units of Triassic age and older one. In order to understand a part of tectonic history and the orientation of deforming stress fields, brittle structures were collected and analyzed by Right Dihedra methods. The results show that the KD basin was formed in a NW-SE extensional regime during the Early and Middle Jurassic. Although there is some evidence of compression along the same axis during the Late Kimmerian phase (Late Jurassic – Early Cretaceous), it seems that the Cretaceous layers were folded by a NE-SW compression during the Paleocene. Afterward, the compression stress field has re-oriented to N-S direction and generated the present day strike-slip system following the Miocene.