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Original Article |
1 Hans Ramberg Tectonic Laboratory, Department of Earth Sciences, Uppsala University, Villavagen 16, SE-752 36 Uppsala, Sweden (e-mail: hemin.koyi{at}geo.uu.se)
2 Department of Geology, Tarbiat Moalem University, Mofateh St., 15614, NO. 49, Tehran, Iran
3 Present address: SRK Consulting, Level 6, 44 Market Street, Sydney, NSW 2000, Australia
4 International Institute of Earthquake Engineering and Seismology, PO Box 19395/3913, Tehran, Iran
5 Geologisch–Paläontologisches Institut, Johann Wolfgang Goethe-Universität Frankfurt/Main, Senckenberganlage 32–34, D-60325 Frankfurt/Main, Germany
Analogue models are used to study the mechanical relationship between basement strike-slip faults and salt diapirs. Displacement along a strike-slip fault in 1 g models resulted in extension along pre-existing jogs and the formation of oblique extensional faults, where reactive diapirs were triggered in some models. In the centrifuge models, prescribed cuts, simulating pre-existing structures, were reactivated during simple shear deformation of the models, resulting in formation of pull-apart basins, which were intruded by diapirs. The models show that because of the low ratio of salt to overburden thickness in the Zagros (0.15–0.35), it is unlikely that diapirs have formed solely, if at all, as a result of movement along basement strike-slip faults. Two mechanisms are suggested. First, pre-kinematic thin overburden and continuous movement along a releasing bend in the cover units may have triggered some of the diapirs in the Zagros, which were later downbuilt to their current geometry by additional sedimentation. Second, movement along the strike-slip faults (e.g. the Kazerun and Mangarak faults) induced oblique movement along NW–SE Zagros structures (folds or thrusts) resulting in the formation of pull-apart basins where diapirs were eventually intruded. Fault plane solution of shallow earthquakes supports the second scenario, which is also in agreement with previous interpretations that some of the salt diapirs associated with basement faults are younger than Zagros shortening and young southwestwards.
