M. Mohajjel; A. Cholgoly
Abstract
Abundant normal faults were locally developed in Pliocene-Quaternary detritus and pyroclastic sediments of Sahand volcano in southeast Tabriz. Well exposed normal faults are synthetic and antithetic, horst and graben and half graben structure systems, drag folds and roll-over anticlines were produced ...
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Abundant normal faults were locally developed in Pliocene-Quaternary detritus and pyroclastic sediments of Sahand volcano in southeast Tabriz. Well exposed normal faults are synthetic and antithetic, horst and graben and half graben structure systems, drag folds and roll-over anticlines were produced by normal faults. The average strike of these faults changes from dominant N-S in east to ENE- WSW in west. Dip of the fault planes changes due to layer competency and rotated older normal faults and layers were cut by later normal faults. In some cases vertical gashes were produced along fault planes and filled by the sediments of upper strata due to extension. Oversteps and bends also occur along normal faults in cross-section. Field investigations indicate that the syn-depositional extension occurred in Pliocene- Quaternary. Style and growth of normal faults in local distinct area in southeast Tabriz indicate that they were possibly produced by local extension (releasing zone) in relation with dextral strike-slip displacement of North Tabriz Fault.
R. Nadri; M. mohajjel; A. Bahroudi
Abstract
The NNW-SSE striking Bidhand strike-slip fault system cut and displaced the Cenozoic volcanic and sedimentary rocks of the Urumieh-Dokhtar magmatic arc in south Qom. Structural evidences show that at least 16 km horizontal displacement in the Eocene volcanics has been caused due to dextral strike-slip ...
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The NNW-SSE striking Bidhand strike-slip fault system cut and displaced the Cenozoic volcanic and sedimentary rocks of the Urumieh-Dokhtar magmatic arc in south Qom. Structural evidences show that at least 16 km horizontal displacement in the Eocene volcanics has been caused due to dextral strike-slip movement along this fault. The compressional and extensional terminations were developed at the western block and not observed at the eastern one. The reverse and thrust faults associated with the drag folds were generated in the northwestern compressional termination and gabbroic sills were intruded in the southwestern extensional termination. Younger syenitic and granitic intrusive (Miocene) were intruded in the vacant space of the northern compressional termination and releasing zones along the central straight segments of the Bidhand fault. Gabbroic sills in the extensional termination at the south-western area of the Bidhand fault were folded and thrusted towards northeast due to the later deformational events.
M. R. Moshrefi far; A. Alavi; M. Mohajjel
Abstract
In this research, separation of paleostress phases in the central part of Dehshir fault is investigated based on the study of heterogeneous fault-slip data and their related slickenside lineations. These data are measured from the Certaceous (Taft limestone), ...
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In this research, separation of paleostress phases in the central part of Dehshir fault is investigated based on the study of heterogeneous fault-slip data and their related slickenside lineations. These data are measured from the Certaceous (Taft limestone), early Eocene (Kerman conglomerate) and Eocene (Volcanics) formations. The main criteria used here to identify sense of fault-slip are stratiographic separation, accretionary mineral steps, Riedel shears and tension gash. The existing faults in the region of investigated often show two NE and NW trend in which the latter is usually dominant. Based on the study of heterogeneous fault-slip data and their related slickenside lineations and using the multiple inverse method, at least two phases are expected. These phases show that the axis of maximum principal stress, σ1, is at NE trend and that of minimum principal stress,σ3, is at NW trend. The location of σ3 usually indicates that the strike-slip and reverse strike-slip faults mostly occur in the region. In addition, the shape of the stress ellipsoid is prolate in the region.
Gh. R. Rastgoo Moghaddam; E. Rastad; N. Rashid Nejad Omran; M. Mohajel
Abstract
Zartorosht gold deposit is located in southeastern part of the Sanandaj-Sirjan zone. Rock units exposed in the area include mafic to intermediate volcanic series, metamorphosed volcano-sedimentary rocks and meta-basites intruded by basic to felsic dikes. These late ...
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Zartorosht gold deposit is located in southeastern part of the Sanandaj-Sirjan zone. Rock units exposed in the area include mafic to intermediate volcanic series, metamorphosed volcano-sedimentary rocks and meta-basites intruded by basic to felsic dikes. These late Paleozoic units have been metamorphosed under lower to medium green-schist facies. Due to several phases of intense deformation, rock sequence indicates new fabrics. The intensity and types of deformation are not the same in the area, so that rock units illustrate ductile-brittle to brittle shear zones.
Gold mineralization occurs in ductile-brittle and brittle shear zones. In ductile-brittle shear zones, gold mineralization occurs parallel to the foliation with lenticular geometry along the strike and dip of the foliation. Analysis of samples from silicified parts of this zone indicates 0.5 to 7.95 ppm Au. In these zones, deformation fabrics can be observed as primary mylonitization in marginal and middle parts, and brittle fabrics in central parts. Gold mineralization in brittle type shear zones has occurred mainly along N70W to E-W and southern dipping normal faults. This type of mineralization includes gold-bearing veins and siliceous-sulfidic bands and can be followed in a 1.5 km long zone. Au grade in samples from siliceous-sulfidic zone is 17.2 ppm and sometimes it reaches up to 35.7 ppm. Mineralized rock units in shear zones indicate different types of alteration including chloritization, epidotization, sericitization, carbonatization, argilization, silicification and sulfidization. Siliceous-sulfidic alteration corresponds to ore-bearing zones within the shear zones.
Studies suggested temporal and spatial relation between alteration and deformation. Spatial relation is explained by overlapping alteration and deformation zones. Foliation parallel open spaces (generated during ductile deformation and mineralization processes) and also micro-fractures in porphyroclasts (generated during grain cataclastic flow) have been filled with hydrothermal - stage quartz and pyrite indicating temporal correlation of alteration and deformation. Au grade changes have close relation with deformation and alteration intensity. This relation has been distinguished by analysis of samples taken from trenches and tunnels perpendicular or parallel to general foliation of rock units. High gold content is related to intensely deformed (mylonitic and ultracataclasite) siliceous and sulfidic parts and Au-bearing siliceous-sulfidic parts coinciding with the inner parts of alteration zones.
Ore-mineral assemblages in the area are relatively simple including pyrite, arsenian-pyrite, rarely galena and sphalerite. Based on microscopic studies, Au occurs as free grains and electrum. Also electron-microprobe and electron-microscope analysis indicate that at least some of Au grains are in sulfide minerals lattice. According to these studies, gold has been observed with both pyrite and arsenian-pyrite phases. Ag has also been detected in sulfide minerals lattice and siliceous gangue.
Controlling parameters for mineral concentration in Zartorosht deposit are shear zones (ductile-brittle and brittle) and alteration (silicification and sulfidization). Based on the comparison of Zartorosht main characteristics with orogenic gold deposits, Zartorosht has the most similarities with orogenic gold mineralization; therefore, it is considered to be of this type.
M. Rahgoshay; I. Monsef; H. Shafaii Moghadam; M. Mohajjel
Abstract
Petrofabric, structural and geochemical study of the ultramafic tectonites in the Khoy ophiolitic complex suggest that these tectonites including low-temperature NW-SE shear zones cut the high-temperature to medium-temperature NE-SW mantle flow direction. Microstructures in these tectonites, record a ...
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Petrofabric, structural and geochemical study of the ultramafic tectonites in the Khoy ophiolitic complex suggest that these tectonites including low-temperature NW-SE shear zones cut the high-temperature to medium-temperature NE-SW mantle flow direction. Microstructures in these tectonites, record a fabric transition from oblate porphyroclastic and oblong porphyroclastic textures (related to the high- and medium-T deformations in mantle sections) to mylonitic textures (with low-T deformation in the shear zones). The study of olivine LPO patterns in high- and medium-T deformation samples of mantle shows slip on the (010) [100] high-temperature-low stress and (0kl) [100] moderate-temperature systems (up to 1000o) while olivine LPO patterns in the low-T deformation samples within the shear zones indicate gliding along (001) [100] low-temperature slip system (800-900o). Spinels in these peridotites show high variations in Cr number (10 to 90) and Mg number (50 to 90). Cpxs rich in Cr suggest a low degree of partial melting in these peridotites. The very variable composition of the spinels may be the result of partial melting process and recrystallization of these minerals in the mantle lithosphere during the detachment phase and the development of the shear zones.
SH. Shafiei Bafti; S.A. Alavi; M. Mohajjel
Abstract
Faryab area at the southeastern part of the Sanandaj-Sirjan zone, containing the Paleozoic rocks in the internal part of Zagros Orogen, displays two folding episodes through a progressive deformation event. Axial planes of recumbent F1 folds dip moderately to the north and the ...
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Faryab area at the southeastern part of the Sanandaj-Sirjan zone, containing the Paleozoic rocks in the internal part of Zagros Orogen, displays two folding episodes through a progressive deformation event. Axial planes of recumbent F1 folds dip moderately to the north and the axes also plunge moderately to NW - SW. F1 folds were generated in a flexural-flow condition in whole lithological units. Thrust faults were produced along the overturned limbs of the F1 folds. These thrusts are most abundant in the central domain, the north of Zartorosht Au-index. At the southern edge of the central domain, displacement of large slabs of calcschist with interbedded marble were produced by these thrust faults.
Overturned limbs were cut by ductile shear zones of thrusts and development of green-schist facies in these shear zones implying the medium dips for thrusting. F2 folds were developed by co-axially refolding of F1 that are well exposed in Pasefid, Zartorosht and Zehmakan anticlines. Structural data shows the variation of F2 axis between S45W - N80W directions. Interference patterns of Z on S, M on S and S on S indicate coaxial refolding F1 by F2 (Hook Type).
