Termination of Major Strike-Slip Faults Against Thrust Faults in a Syntaxis, as Interpreted From Landsat Images

Assad Iranpanah

The north to northeast-striking Minab fault (Zendan fault) in western Makran, Iran, is interpreted as an intracontinental transform structure that separates, along its length, the Zagros foldbelt from the Makran active trench-arc system. The 200-km long fault has a right-lateral strike-slip component and is terminated at its northern end by the north-northwest and northwest-striking Zagros main thrust. The Minab transform zone delimits the western margin of the Makran convergence zone where an oceanic part of the Afro-Arabian lithosphere is being subducted beneath the Lut and Afghan microplates. A northern extension of the Minab transform zone terminates at an internal convergence boundary within the Bandar Abbas-Minab syntaxis.

The Minab transform fault consists of a zone of generally north-northwest-trending rhombic conjugate strike-slip faults. The pattern of faulting for the Minab strike-slip fault zone, when traced over the entire area on the Landsat image, shows that areas with rhombic sets of conjugate strike-slip faults are separated by a few areas showing only extensional zones. This is compatible with the traditionally idealized reverse-S pattern for the strike-slip faults reported from the United States Basin and Range province. The mechanical explanation for the rhombic pattern of the fault system is consistent with the same pattern and motion as currently exists in the Makran accretionary belt. The Minab transform fault may define the area of a diapiric ramp in the mantle along which the western akran differential movement originated. The fault reflects stress relief associated with the change of the eastern margin of the Afro-Arabian plate from a convergent to a transform boundary termination.

The Bandar Abbas-Minab syntaxis is a bent mountain belt exhibiting changes in the trend of the fold axes from northeast to east-west and to north-south. The syntaxis is enclosed between a series of en echelon right-lateral strike-slip faults in the west and the Minab transform fault with a right-lateral strike-slip component in the east. The latter separates the Makran ranges from the Zagros foldbelt, and provides an overall interpretation of the Bandar Abbas-Minab syntaxis as an area protruding northward between the two sets of terminal strike-slip faults to the east and west.

The origin of the Bandar Abbas-Minab syntaxis is believed to be related to convergence between the Afro-Arabian plate and the Lut and Afghan microplates. The convergence zone is a well-developed trench-arc gap. The western edge of this trench-arc system has been dragged to the north along the Minab dextral fault zone. This zone, which started developing in the Late Cretaceous-Paleocene, is directly responsible for the development of the Bandar Abbas-Minab syntaxis.

AAPG Search and Discovery Article #91030©1988 AAPG Annual Convention, Houston, Texas, 20-23 March 1988.