P. Liaghat-Zadeh; Majid Shahpasandzadeh; M. Honarmand; H. Ahmadi-Pour
Abstract
The Dehsheikh Ultramafic-Mafic Complex (DUMC), as a portion of the Esfandagheh-Faryab ophiolitic melange belt, accommodates several chromitite ore deposits, but their emplacement and relation to the regional structures remain ambiguous due to structural complexities. The Dehsheikh Ultramafic Massif is ...
Read More
The Dehsheikh Ultramafic-Mafic Complex (DUMC), as a portion of the Esfandagheh-Faryab ophiolitic melange belt, accommodates several chromitite ore deposits, but their emplacement and relation to the regional structures remain ambiguous due to structural complexities. The Dehsheikh Ultramafic Massif is composed of harzburgites, dunites, chromitites, pyroxenites, and lherzolites. The chromitite ores, embedded in a dunitic host rock, are concentrated in the central part of the massif in the active Bozorg mine and also abandoned Ajdari and Konar mines. According to the results, the DUMC has experienced three deformational phases of D1-D3. The high-T transtenssional D1 deformation is recognized by injection of the pyroxenitic dykes (Di1), development of the dextral ductile shear zones (Dsz1) and rootless folds (F1) in the dunite-chromitites sequences. These evidences could demonstrate ascending of the Dehsheikh mantle diapir in the upper mantle during the D1 deformation. The D2 dextral transpressional deformation is characterized by formation of the conjugate F1b right-lateral strike slip faults (with reverse component) and F1a thrusts and associated V1 magnesite veins. The D2 structures developed along with emplacement of the DUMC under the prevalent Zagros oblique reverse faulting in the ophiolitic mélange belt. Finally, the D3 was accompanied by conjugate F2a right-lateral strike slip faults (with normal component) and F2b normal faults, associated with development of the V2 magnesite veins under the local transtenssional regime along the Zagros fault. The F1 folds and F1-F2a,b faults structurally controlled deformation and emplacement of the chromitite ore deposits.
A. Shafiei Bafti; M. Shahpasandzadeh
Abstract
According to potential of the intra-continental strike-slip faults for occurrence of large earthquakes, which are also considered as the main elements of active continental deformation, determination of their geometry and kinematics along with recognition of the active segments and temporal structural ...
Read More
According to potential of the intra-continental strike-slip faults for occurrence of large earthquakes, which are also considered as the main elements of active continental deformation, determination of their geometry and kinematics along with recognition of the active segments and temporal structural evolution is necessary. The oblique-slip fault of Ravar with about 137 km length is extending in vicinity of Ravar, north of Kerman. In the north of study area, the fault extends parallel to the Lakar-Kuh fault, but in the south converges toward to the Lakar-Kuh and the Kuh-Banan faults. Upthrusting of the eastern block of the Ravar fault and east-ward thrusting of the Lakar_Kuh fault system constructed a positive flower structure. The motion of the Ravar fault have caused the dextral displacement and an accumulative horizontal displacement of the drainages about 940-970 in the north since Pleistocene. Regarding a minimum horizontal slip-rate of about 0.54 mm/yr, the recurrence time of earthquakes with Mw~ 6.7 would be about 1400 year. In the middle part of the fault, the Reidel fractures of R, R, and P has been well developed and caused a dextral deflection of the Esmail-AbadRiver about 16m. With assumption of characteristic earthquake occurrence, the maximum slip per event could be about 0.75 m, which is consistent with the minimum displacement of the recent gorges. The amount of horizontal dextral displacement of the fault decreases toward to the south, whereas the vertical component of the fault motion increases, so that the Pleistocene deposits show about 10 m difference in elevation across the southern part of the fault. Concerning the trend of meizoseismal zone of 1911/04/18 Ravar earthquake (M~ 5.8, I0~ VIII) and parallelism of trend of the co-seismic surface rupture (N13W) with the southern part of the fault, the Ravar fault could be responsible of this earthquake. In addition, the active cross-faulting of the Dehu, the Dehzanan, the Chatrud, the Pasib, and the Darbid-Khun control the recurrence time and magnitude of the earthquakes in the study area.
M. Shokri; M. Ghorashi; H. Nazari; R. Salamati; M. Talebian; J.-F. Ritz; H. Mohammad khani; M. Shahpasand zadeh
Abstract
The Astaneh fault with a length of more than 75 km is located in NW of Damghan. Morphotectonic investigation along the Astaneh fault and left - lateral displacement in quaternary deposits shows that, Astaneh is an active fault. It is necessary to recognize paleoseismicity of Astaneh fault because, this ...
Read More
The Astaneh fault with a length of more than 75 km is located in NW of Damghan. Morphotectonic investigation along the Astaneh fault and left - lateral displacement in quaternary deposits shows that, Astaneh is an active fault. It is necessary to recognize paleoseismicity of Astaneh fault because, this fault is located in seismic zone of Komes historical earthquake with Ms=7.9 (Ambraseys & Melville, 1982). Many people (more than 45000) were killed in Damghan city in Komes historical earthquake. In this paper, 4-5 paleo events along the Astaneh fault are presented through paleoseismological investigation.