Tectonics
Mohammad Amir Alimi
Abstract
This paper presents the results of a field study aiming to describe and to interpret origin of the vein network in the south of Birjand. Adjacent to Birjand ophiolite in eastern Iran, the Paleocene-Eocene flysch facies was deposited in the Birjand foreland area concomitant with the Alpine orogeny (Laramide). ...
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This paper presents the results of a field study aiming to describe and to interpret origin of the vein network in the south of Birjand. Adjacent to Birjand ophiolite in eastern Iran, the Paleocene-Eocene flysch facies was deposited in the Birjand foreland area concomitant with the Alpine orogeny (Laramide). The sandstone unit of this facies contain two orthogonal sets of quartzite veins. The N310-340 striking veins (set 1) are arranged parallel to the Bagheran Kuh range front and perpendicular to the vein set 2 (N215-240). The paleostress reconstruction in the Paleocene-Eocene shows that the regional compression direction N240 is perpendicular to the Bagheran Kuh range front. Structurally, to create orthogonal veins, σ1 should be perpendicular to the layering and σ2 and σ3 should be horizontal. This situation was created in the middle Eocene-Oligocene. The post-collision extensions of this period caused a decrease in regional pressure in the region. As a resault, the maximum principal stress (σ1), was changed to a vertical state and intermediate stress (σ2) was parallel to the orogenic pressure. In these conditions, orthogonal tensile openings (state I) were formed as a result of the local inversion of stress and fluid pressure in the flysch facies.
Economic Geology
Fatemeh Esmaeili; Fardin mousivand; Mahmoud Sadeghian; Seyed Mehran Heidari
Abstract
Miandasht copper deposit is located in 110 km east of Shahrood, 24km north west of Abbasabad, and in the Cenozoic volcanic belt of north of Central Iran zone. The major rock units of the study area have Eocene age and include submarine flows (andesite, basalt, and trachyandesit), pyroclastic (tuff breccia ...
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Miandasht copper deposit is located in 110 km east of Shahrood, 24km north west of Abbasabad, and in the Cenozoic volcanic belt of north of Central Iran zone. The major rock units of the study area have Eocene age and include submarine flows (andesite, basalt, and trachyandesit), pyroclastic (tuff breccia and agglomerate) and sedimentary complex (Nomullitic limestone, tuffacous limestone, shale, sandstone and conglomerate). Mineralization in the Miandasht copper deposit occurred as parallel to layering of the host rocks (tuff breccia and agglomerate), and also along with cross- cutting faults of the host rocks in form of stratabound and epigenetic ores. The main ore textures include vein- veinlets, open space filling, disseminated and replacement. The Ores contain primary pyrite, chalcopyrite, chalcocite, bornit, and secondary covellite, chalcocite, malachite, hematite and limonite. The most important wall rock alterations accompanied with mineralization are carbonatic- silicic, sericitic, argillic, and chloritic, and that the amound of carbonatization and silicification increases with closing to mineralization zones. According to geochemical studies, tectonic setting of the deposit was extensional environment formed in a continental margin volcanic arc. Based on essential characteristics of the copper mineralization such as tectonic setting, host rocks, mineralogy, and type of alterations, the Miandasht copper deposit shows many similarities with Manto- type deposits, dominantly formed during orogeny, folding and faulting of the host sequence. It should be mentiond that some charachteristic features of the Miandasht copper deposit including development of argillic alteration, and lack of extensive zeolitic alteration, distinguishes it from other copper deposits in the region including Abbasabad deposit.
Tectonics
MohammadAmir Alimi
Abstract
The Bahlgerd shear zone in the northern margin of Bagheran Mountain is separated Eocene flysch from the Cretaceous ophiolite sequence and Quaternary sediments by southern Birjand and Bahlgerd faults. In the deformation evaluation , sigmoidal array arrays located in sandstone units have been used as strain ...
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The Bahlgerd shear zone in the northern margin of Bagheran Mountain is separated Eocene flysch from the Cretaceous ophiolite sequence and Quaternary sediments by southern Birjand and Bahlgerd faults. In the deformation evaluation , sigmoidal array arrays located in sandstone units have been used as strain markers. Based on the geometry of these arrays, the mathematical equations and R-θ' diagrams of the strain parameters were estimated. The mean values of shear strain (γ), volume change (∆) and convergence across the zone (K) are 0.45, -0.26 and 0.85, respectively. The plotting strain ellipses on the logarithmic Flinn diagram are in the field of flattening, which indicates the simultaneous simple shear and compaction in the region and show a volume reduction of up to 30%. Also, in the Bahlgerd shear zone, the value of θ'> 45 ° and cleavages are created in the direction perpendicular to the opening of the veins, which conforms to the characteristics of the compactional simple shear model. The horizontal strain parameters in the transpression model have similar values the compactional simple shear model. Based on the calculated convergence parameter (0.39), Behlgard shear zone is in the category of slightly convergence zones in which the amount of shortening
R. Arfania
Abstract
The study area, located in 40 km southeast of Eghlid town, is a metamorphozed terrain situated between the Eghlid fault and the Zagros Main Thrust and is a part of the southeastern Sanandaj-Sirjan Zone. The area consists of the highly deformed rocks which have been emerging clearly in dextral ...
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The study area, located in 40 km southeast of Eghlid town, is a metamorphozed terrain situated between the Eghlid fault and the Zagros Main Thrust and is a part of the southeastern Sanandaj-Sirjan Zone. The area consists of the highly deformed rocks which have been emerging clearly in dextral shear zones. Mesoscopic scale analysis carried out for determining the paleostress directions and deformation history of the area. Thus mesoscopic faults, joints and veins were measured and analyzed based on the field measurements and statistical methods. Then fitting structural models were presented for each of them. Furthermore, formation ages of the structures were considered based on relative time scale. According to the results, it can be concluded that two different deformation phases were effective in formation of the analyzed structures.
