The significance of strike-slip faulting in the basement of the Zagros fold and thrust belt

Lateral offsets in the pattern of seismicity along the Zagros fold and thru st belt indicate : basement ave active deep-seated strike-dip that transver se faults segmenting the Arabian faults. The dominant NW-SE trending featur es of the belt have undergone repeated horizontal displacements along these transverse faults. These reactivated basement faults, which are inherited front the Pan-African construction phase, controlled both deposition of the Phanerozoic cover before Tertiary-Recent deformation of the Zagros and pro bably the entrapment of hydrocarbons on the NE margin of Arabia and in the Zagros area. We have used observations of faulting recognized on Landsat sa tellite images, in conjunction with the spatial distribution of earthquakes and their focal mechanism solutions, to infer a tectonic model for the Zag ros basement. Deformation in the NW Zagros appears to be concentrated on basement thrusts and a few widley-spaced north-south trending strike-slip faults which sepa rate major structural segments. In the SE Zagros, two main structural domai ns can be distinguished. A domain of NNW-trending right-lateral faults in t he northern part of the SE Zagros implies that fault-bounded blocks are lik ely to have rotated anticlockwise about vertical axes relative to both Arab ia and Central Iran. In contrast, the predominance of NNE-trending left-lat eral faults in the southern part of the SE Zagros implies that fault-bounde d blocks may have rotated clockwise about vertical axes. We propose a tecto nic model in which crustal blocks bounded by strike-slip faults in a zone o f simple shear rotate about vertical axes relative to both Arabia and Centr al Iran. The presence of domains of strike-slip and thrust faulting in the Zagros basement suggest that some of the convergence between Arabia and Cen tral Iran is accommodated by rotation and possible lateral movement of crus t along the belt by strike-slip faults, as well as by obvious crustal short ening and thickening along thrust faults.