Andrzej Konon

Gaw-Khuni Basin: An active stepover structure in the Sanandaj-Sirjan zone, Iran

The Gaw-Khuni Basin is located in the central part of the Sanandaj-Sirjan zone, on the northeastern margin of the Zagros orogen. This basin is one of the continuous zones of Sanandaj-Sirjan zone basins that is filled by Pliocene–Holocene sediments. The Gaw-Khuni Basin is surrounded by an en echelon to parallel arrangement of active faults in dextral strike-slip fault zones that indicate a right-step dilational stepover structure. The boundary faults of this basin are the Eastern and Western Gaw-Khuni, Ramsheh, and Nain-Dehshir faults. Earthquake distribution determined along the faults, dissection and displacement of Holocene sediments, and also the development of pull-apart basins filled with Holocene deposits along the faults confirm that these faults are active. The Gaw-Khuni stepover was formed during transtensional movements produced between two dextral strike-slip faults (Nain-Dehshir and Ramsheh). Also, the Gaw-Khuni pull-apart basin and the Eastern and Western Gaw-Khuni faults developed in a releasing step between the faults and grew in two directions during the time of their formation.

Formation of intracontinental basins in the opposite corners of the Tabas block as coeval structures controlled by transpressional faulting, Iran

The interaction of strike-slip faults in their restraining junctions allowed for the coeval formation of the Tabas and Abdoughi Basins and led to their inversion during the late Cenozoic. The intracontinental basins filled with Neogene and Quaternary deposits were controlled by large-scale dextral transpression along major faults that bounded the Tabas block, which is a part of the Central Iranian block. The anastomosing strike-slip fault pattern facilitated the development of both basins in opposite corners of the Tabas block. The subsided areas were formed as a result of interaction between the restraining junctions of strike-slip faults and thrusts. Flexural loading caused by the uplifted series of thrust sheets resulted in the depression of the opposite fault slabs, which permitted deposition of Neogene sediments. Deformation according to the “bookshelf” mechanism can be considered as a consequence of accommodation of the shortening of the area north of the Main Zagros thrust and externally imposed shearing along the Great Kavir (Doruneh) fault during the collision of the Arabian and Eurasian plates. Related processes of transpression and counterclockwise rotation of the tectonic blocks included in the Central Iranian block favored the interaction of strike-slip faults. The change of far-field stress and continuous transpression caused inversion of the basins and formation of Neogene folds in the northern and southern corners of the Tabas block. The geomorphic features observed along these strike-slip faults and on the thrust surfaces bounding the folds display their recent activity, consistent with present-day seismicity and geodetic measurements within the Central Iranian block.