TECTONICS
Year:2018 | Volume:2 | Issue:6|Papers Count:7

Granitoied pluton of Borujerd and metamorphic rocks are cut by many acidic and basic dykes in the east and northeast of Borujerd city. Acidic dykes trends are different and intruded in different times. Acidic dykes involved aplitic and pegmatite dykes and show two main trends, NE-SW and NW-SE and intruded in quartz diorite, granite-granodiorite and hornfelsic rocks. Basic dykes are the youngest activity of magma in this area and only intruded in NE-SW trend in granite-granodiorite rocks. Many of aplitic and pegmatite dykes are deformed and show folding. According to evidence and trends of these dykes, they intruded poly stages in this area. Deformation caused mylonitic fabric in granitoied body and many of aplitic dykes. Deformation evidence show that acidic dykes formed in progressive deformation regime. Basic dykes formed in extension fractures that caused by pressure resulting continental collision of Arabian and Iranian microplats normal to the collision zone.

Paleostress analysis using fault-slip data and trajectory of dykes in the Salafchegan area, west of Qom Province, has improved our knowledge on tectonic regime changes in the late Cenozoic in this portion of Oroumiyeh-Dokhtar magmatic belt. Stress trajectories drawn on the base of dykes show two direction of maximum principal stress along N-S and NE-SW. although fault-slip data analysis of 150 slickensides by MIM method proved the change of stress regime from Miocene to Pliocene in the study area. Additionally, the faulted and sheared anticline of Kharab-Sarahroud is an asymmetric Z-shape fold that cut by NE-SW left lateral strike slip faults. According to right-lateral transpression is was the active tectonic setting in the Oroumiyeh-Dokhtar belt from Miocene to present. The study area is laid between two main faults including Indes right-lateral strike slip fault to the north and Khorheh-Kahak thrust system to the south. Due to contribution of Oligocene-Miocene rock units, folding of Kharab-Sarahroud anticline has occurred in Miocene and perhaps Pliocene; when the first stress regime was active. Then by clockwise rotation stress axes, the fold was sheared and rotated to find Z-shape geometry. Finally NE-SW left-lateral faults cut the fold in Quaternary.

The purpose of zoning the risk of earthquakes and landslides is to divide the earth’ s surface into separate zones based on the actual degree of occurrence of these hazards. In this research first map of landslides distribution in Bagheran Mountain was prepared by aerial photos, geological maps and field surveys. Then effective factors in both earthquake and landslide occurrence are identified, their class density and binary comparison were calculated, effective parameters will prioritize, then determine fuzzy membership degree of parameters by fuzzy logic and finally combined together. Zoning studies suggest that seismic Is acceleration factor has the highest weight in the occurrence of earthquakes in the region. After a combination of landslide and earthquake maps combination was showed respectively16, 35, 20, 19 and 10% of the area are at very high-risk class, high, medium, low and very low.

The Saqqez area, situated in NW of Sanandaj-Sirjan metamorphic zone, was affected by several deformation stages which exhibit as forming of different faulting stages in Ductile to Brittle environments. The development of faults plays an import role in establishment of structural framework and deformation of this area. In this research, the outcropped rock units and main lineaments were extracted by using of remote sensing and GIS techniques. Then, the main and minor faults were defined and measured (their characteristics) in field surveys. The results of Kinematic and Geometrical analysis show that three stages of faulting were happened. The arrangement of faulting primacy is: the first stage faulting (with N130-140 trend) has deformations in ductile circumstance (in western part). Then, this stage was cut by second order of faulting (N60-70) in ductile to ductile-brittle condition. Finally, all of faulting were ruptured and offset by third order faults with N10-20 trend in brittle condition. These three stages of faulting formed the curve-shape of structures and rock unit patterns.

Analysis of seismic sections perpendicular to the fold axis and draw the circles surrounding on this profiles indicate the more bending in forelimb due to the more uplift in sedimentary units in effect the compression performance and thrust faults that caused fractures development and density in the southwest limb. Increasing loss of drilling mud in the forelimb anticline wells is associated with development of tensile and longitudinal fracturs related to increase in shortening and anticline uplift, thrust faults propagation and create the duplex structures in near there wells. The maximum and minimum in-situ stresses directions in well No. 2 located in the medial part of anticline are respectively N50 and N140 which are dependent on the Zagros neogene folding. Tensile-indused fractures or maximum in-situ stress direction was inclined in the eastern part of anticline and showing N30E direction. Borehole Breakout or minimum in-situ stress direction is perpendicular to tensile frauture and has N120 orientation. In the southwest part of this anticline, UGC Map is showing that contours of similar thicknesses are inclined and respect to the adjacent anticline was sinistrally displaced. Very high drilling mud losses in well NO. 4 located in fold southeast plange is due to the location of this well in minimum distance to strike slip fault trace between two anticlines and due to concentrated stresses resulting from dual intraction the northeast fault lineament releated from folding and operation the sinstral fault after the zagros neogene folding.

The purpose of this study is to analyze the accumulation and distribution of stress across fault planes using an analytical model based on the reflection of the detector spectrum on the roughness of the fault surfaces during the failure. Fault Modeling is based on asperities making half-spaces separated from each other. This model considers mechanical interaction between contact points and, therefore, can provide a physical explanation of how to redistribute stress at fail time at a locked fault plane. For a boundary condition, a certain displacement, normal and shear forces are calculated at contact points and compared to the failure criterion. If one or more locked surfaces of the fault do not work, the stresses are recalculated. The stress redistribution that is caused by the failure may cause other locked surfaces to fail. This process continues to achieve a stable state or complete failure of entire fault plane for analysis with detector spectrum. The distribution of stresses as well as the onset and progress of failures depend on the contact geometry and roughness.

Mahneshan area located in northwestern part of Zanjan Province contains highly diverse morphologic units. This morphologic diversity is mainly due to climate factors, tectonic movements, high rate of erosion and lithologic characteristics. Wind erosion is one of the most important factors creating wonderful geologic features such as some specific erosion landforms in this region. This study is concentrated on active tectonics of Mahneshan, analyzing structural and morphotectonic characteristics of the region accompanied by field investigations. Ductile layers of Upper Red Formation have key role in regional kinematic deformation. Mahneshan and Angouran thrust faults are major NW trending active faults in this area. Active faults are mapped in satellite images. Field investigations represent that dominant regional tectonic activities have been active coeval with rock unit sedimentation in Pliocene-Quaternary. Arabia-Eurasia convergence is involved in active faulting along NW trending major thrust faults in the study area.