K.
Hessami*+, H. A. Koyi* and C. J. Talbot*
*Hans
Ramberg Tectonic Laboratory, Institute of Earth Sciences, Uppsala University,
Villavägen 16, SE-752 36 Uppsala, Sweden.
+
author for correspondence. email: khaled.hessami@geo.uu.se
Lateral offsets
in the pattern of seismicity along the Zagros fold and thrust belt indicate
that transverse faults segmenting the Arabian basement are active deep-seated
strike-slip faults. The dominant NW-SE trending features of the belt have undergone
repeated horizontal displacements along these transverse faults. These reactivated
basement faults, which are inherited from the Pan-African construction phase,
controlled both deposition of the Phanerozoic cover before Tertiary-Recent deformation
of the Zagros and probably the entrapment of hydrocarbons on the NE margin of
Arabia and in the Zagros area. We have used observations of faulting recognized
on Landsat satellite images, in conjunction with the spatial distribution of
earthquakes and their focal mechanism solutions, to infer a tectonic model for
the Zagros basement.
Deformation in
the NW Zagros appears to be concentrated on basement thrusts and a few widely-spaced
north-south trending strike-slip faults which separate major structural segments.
In the SE Zagros, two main structural domains can be distinguished. A domain
of NNW-trending right-lateral faults in the northern part of the SE Zagros implies
that fault-bounded blocks are likely to have rotated anticlockwise about vertical
axes relative to both Arabia and Central Iran. In contrast, the predominance
of NNE-trending left-lateral faults in the southern part of the SE Zagros implies
that fault-bounded blocks may have rotated clockwise about vertical axes. We
propose a tectonic model in which crustal blocks bounded by strike-slip faults
in a zone of simple shear rotate about vertical axes relative to both Arabia
and Central Iran. The presence of domains of strike-slip and thrust faulting
in the Zagros basement suggest that some of the convergence between Arabia and
Central Iran is accommodated by rotation and possible lateral movement of crust
along the belt by strike-slip faults, as well as by obvious crustal shortening
and thickening along thrust faults.