The Mianrahan’s ophiolitic complex out crops in the northeast of Kermanshah and along with the Zagros thrust zone. In Mianrahan sheet, these ophiolites are located along the NW-SE and parallel to the Zagros Thrust in...The Mianrahan’s ophiolitic complex out crops in the northeast of Kermanshah and along with the Zagros thrust zone. In Mianrahan sheet, these ophiolites are located along the NW-SE and parallel to the Zagros Thrust in the ground. The rocks of this ophiolite complex consist of peridotite, serpentinites, gabbro, dolerite dykes, basaltic lavas associated with marine sediments containing the cretaceous limestones, siliceous limestones and radiolarites. Stratification of this ophiolitic complex is similar to lithological facies sequence of the oceanic crust. However, in some parts, it could be seen as scattered and melanged in the ground. Petrographic study of Mianrahan’s ophiolitic complex started with the ultramafic sequence and followed by sedimentary rocks.展开更多
Accommodation of continental convergence by crustal thickening and lateral transport is mainly featured as strike-slip faulting along the trends roughly orthogonai to the orientation of plate convergence. This style o...Accommodation of continental convergence by crustal thickening and lateral transport is mainly featured as strike-slip faulting along the trends roughly orthogonai to the orientation of plate convergence. This style of faulting will affect seismicity of the involving areas which can be proved in low seismic zones by determining regional stress pattern using numerical methods. Accordingly, the stress distribution and deformation pattern of the South Sanandaj-Sirjan zone in the northeastern part of the Iranian-Arabian collision zone is investigated here using a three dimen-sional mechanical model. The modeled area is bounded between the Zagros thrust fault on the west and Dehshir-Baft fault in the east. The model is composed of three layers： the upper two layers represent the upper brittle and lower ductile crust of the collided continent and the lowest layer represents the lithospheric mantle. The upper crust behaves as an elastic material while the lower crust is considered as a non-Newtonian viscous fluid layer. The lithospheric mantle is taken as a low-viscosity material which is not allowed to move in any direction relative to the overlying layers. The Zagros thrust fault was treated with two different dip values saying 90° and 45° but Dehshir-Baft fault was modeled as a vertical fault and allowed to have a dextral movement regarding to the existing evidence. The driving mechanism applied to the western side of the model was chosen considering two different approaches including a kinematic approach （the Arabian-Eurasian convergence velocity; 35 mm/yr） and a dynamic approach （an external boundary force equal to 3.55E＋17 N）. The resulted stress field indicates an orogen-parallel component of right lateral shear along the Zagros fault implying a rotational deformation pattern within the modeled region that suggests a stress partitioning in the study area. The pattern also indicates a stress accumulation towards the south which could be a reason for the regional seismic quiescence between the two seismic Zagros thrust and Dehshir-Baft faults. Based on the present modeling results, it seems that high stress localization on the boundary faults can be a support of block structure approach or quasi-rigid blocks deformation within the study area. The resultant patterns of stress and displacement fields are generally totally comparable with plate boundary shear zones and have been proven by field data.展开更多
文摘The Mianrahan’s ophiolitic complex out crops in the northeast of Kermanshah and along with the Zagros thrust zone. In Mianrahan sheet, these ophiolites are located along the NW-SE and parallel to the Zagros Thrust in the ground. The rocks of this ophiolite complex consist of peridotite, serpentinites, gabbro, dolerite dykes, basaltic lavas associated with marine sediments containing the cretaceous limestones, siliceous limestones and radiolarites. Stratification of this ophiolitic complex is similar to lithological facies sequence of the oceanic crust. However, in some parts, it could be seen as scattered and melanged in the ground. Petrographic study of Mianrahan’s ophiolitic complex started with the ultramafic sequence and followed by sedimentary rocks.
文摘Accommodation of continental convergence by crustal thickening and lateral transport is mainly featured as strike-slip faulting along the trends roughly orthogonai to the orientation of plate convergence. This style of faulting will affect seismicity of the involving areas which can be proved in low seismic zones by determining regional stress pattern using numerical methods. Accordingly, the stress distribution and deformation pattern of the South Sanandaj-Sirjan zone in the northeastern part of the Iranian-Arabian collision zone is investigated here using a three dimen-sional mechanical model. The modeled area is bounded between the Zagros thrust fault on the west and Dehshir-Baft fault in the east. The model is composed of three layers： the upper two layers represent the upper brittle and lower ductile crust of the collided continent and the lowest layer represents the lithospheric mantle. The upper crust behaves as an elastic material while the lower crust is considered as a non-Newtonian viscous fluid layer. The lithospheric mantle is taken as a low-viscosity material which is not allowed to move in any direction relative to the overlying layers. The Zagros thrust fault was treated with two different dip values saying 90° and 45° but Dehshir-Baft fault was modeled as a vertical fault and allowed to have a dextral movement regarding to the existing evidence. The driving mechanism applied to the western side of the model was chosen considering two different approaches including a kinematic approach （the Arabian-Eurasian convergence velocity; 35 mm/yr） and a dynamic approach （an external boundary force equal to 3.55E＋17 N）. The resulted stress field indicates an orogen-parallel component of right lateral shear along the Zagros fault implying a rotational deformation pattern within the modeled region that suggests a stress partitioning in the study area. The pattern also indicates a stress accumulation towards the south which could be a reason for the regional seismic quiescence between the two seismic Zagros thrust and Dehshir-Baft faults. Based on the present modeling results, it seems that high stress localization on the boundary faults can be a support of block structure approach or quasi-rigid blocks deformation within the study area. The resultant patterns of stress and displacement fields are generally totally comparable with plate boundary shear zones and have been proven by field data.
