نشریه علوم زمین خوارزمی
سال ششم شماره 1 (بهار و تابستان 1399)

The Nikuyeh district is located south of the Tarom-Hashtjin metallogenic province in Western Alborz. Oligo-Miocene subvolcanic intrusion and Mid-Eocene volcanic rocks with composition of dacite (hybrid dacite) to andesite are main igneous units associated with Nikuyeh polymetallic epithermal ore mineralization. Subvolcanic igneous phase consists of I type porphyritic monzodiorite to quartz monzonite and quartz syenite (quartz syenite), and have an average alkali (Na2O+K2O) content of 4.62- 9.9 wt%, and K2O/Na2O content of 0.45- 1.66. The chemical compositions of igneous rocks show that belong to meta- alumina series, high–K calc-alkaline to shoshonitic rocks. Sieve-textured and zoning in plagioclase, corrosion and rounded of phenocrysts, presence of quartz xenocrysts, zoning and bimodal composition of clinopyroxene phenocrysts and presence of hybrid dacite and its three different glass compositions show physicochemical disequilibrium and probably magmatic mixing. Spider diagrams show that igneous rocks are enriched in in large ion lithophile elements (LILE) and depleted in Ta, Nb and Ti which these features are typical of the subduction-related magmas. On the other hand, highly LILE/HFSE and LREE/HREE ratios, low content of TiO2 (<1 percent), and high Ba/Ta ratio are subduction magma features. Tectonic setting diagrams show that district volcanic rocks have high–K calc-alkaline, and subvolcanic rocks located in volcanic arc granitoid (VAG).

Deformed rock units in Tutak and Mahirud regions in northern part of Sistan suture zone include ophiolite, igneous and sedimentary rocks. In this research, based on microstructures and by using Rf /Ф and shear strain methods, finite strain and vorticity analyses were carried out on both sections. The estimated values of mean strain ellipsoid shape (K-value) for both A and B sections are 0.67 and 0.78 respectively, which show flattening strain shape on the modified Flinn diagram and reveal a transpressional regime in the study area. The mean kinematic vorticity evaluated amounts for both A and B sections are 0.51 and 0.71 respectively.
Likewise, the relative contributions of the pure shear component with respect to the simple shear component are 66 to 34 percent for section A; whereas both pure and simple shear components for section B are 50 percent. These results confirm pervious study in this area which mentioned the amount of simple shear components decreased to the termination (to the north) of suture zone.

Azadkuh region located in Central Alborz Range and comprises Paleozoic to Cenozoic rock units. The Azadkoh Fault in the north and the TF4 Fault in the south bounded the region. This study aimed to investigate structural events in the region as a part of central Alborz since Cretaceous. Investigation of structural evidence shows several geological events in Cenozoic at this part of Central Alborz range. Cretaceous volcanic overlay the Triasic-Jurasic Shemshak Formation as angular unconformity. In addition, the Paleocene Fajan conglomerate as angular unconformity overlay the Cretaceous volcanic or older rocks. The presence of Cretaceous rocks and the Karaj Formation within the Eocene basin bounding faults in which syn-sedimentary faults developed demonstrate that the faults formed as normal kinematic acting as the basin bounding faults. Several evidence including high dip angle of the Azadkuh Fault, development of the TF3 Fault as the Azadkuh Fault backthrust in the fault hanging wall, thrust of the younger Cretaceous rocks over the older Triassic-Jurassic rocks, and formation of a pop-up structure in between the Azadkuh and TF3 faults might reflect the inverted normal nature for the faults. During Plio-Quaternary SW-ward movement of the Khazar Block with respect to Central Iran causes transpression tectonics in the region resulted in development of strike-slip faults and related structures that cross-cut the Azadkuh region inverted basin bounding faults.

The Elika Formation forms the major part of the Triassic carbonate sediments in the Alborz basin. In this study, diagenetic processes and geochemical properties of this formation in Shahmirzad section with a thickness of 746 meters in the southern part of central Alborz were studied. Cementation, micritization, neomorphism, dissolution, compaction, dolomitization, dedolomitization, fracturing, hematitization, pyritization and silicification affected the carbonate sediments of the Elika Formation in the study area. Based on petrographic studies (grain size and fabric), five different dolomite types including dolomicrites, dolomicrosparites, dolosparites, dolomite cement and saddle dolomite are recognized in the Elika Formation. All dolomite types are formed during very early to late diagenetic processese. Dolomicrite (dolomite type1) is Sabka type dolomite and this is attributed to Sabka model. Dolomite type2 and 3 are probably formed by mixing-zone model and dolomite type 4 and 5 can be related to burial type model. Diagenetic processes occurred in three digenetic environments of marine, meteoric and burial. Elemental and isotopic analysis of studied rocks represented the effect of meteoric and burial diagenesis in a semi-closed diagenetic system. Aragonite is the original mineral in the studied carbonates of the Elika Formation.

The area of study is located in the north of Khoy and north west Iran and mainly consists of gneiss, gneissic amphibolites, mylonitic gabbro, diorite mylonitic and mylonitic granite affected by the shear zone form brittle – ductile and ductile deformation. Structural and microstructural study display reverse and strike slip shear zone. Three generations of deformation have been identified in KMC (D1-D3). The D1/D2 deformation is defined by isoclinals folds and S1 and S2 foliations indicate NE-SW (σ1) regional shortening that the deformation condition is ductile. The sense of movement of this generation is dextral. Folds belonging to D3 are generally open to tight asymmetrical and overprint the mylonite foliation. The brittle deformation condition at K-feldspar porphyroclasts and the ductile deformation condition at QR porphyroclasts also indicate a dextral sense of shear that indicates NW-SE (σ1) regional shortening. The deformation condition is near the brittle-ductile transition. Dextral transpression associated with D2/D3 is responsible for the formation of the shear zone. Both D1/D2 and D3 have a dextral sense of movement, and are interpreted as a continuous progressive deformation. From the tectonics point of view, the area demonstrates inclined dextral transpression. The reason for this particular tectonic regime is oblique collision of Arabian platform with west Alborz-Azerbaijan block. The resulting stress was resolved into orthogonal, compressional and shear components. The compressional stress has caused the folding and thrusting whereas the shear stress produced the dextral strike-slip component of Khoy shear zone (KSZ).

Ophiolitic mélange of south Dehshir is a slice of Nain-Baft ophiolitic belt. Blocks of metamorphic rocks that consist of amphibolite, banded Px-Ep amphibolite, Grt-Px amphibolite, Grt-Am gneiss and Grt-Ep hornblendite are cropped out along with crustal and mantle sequence of ophiolites from south Dehshir. Thermoberometry results of three samples of Grt-Px amphibolite, Grt-Am gneiss and Grt-Ep hornblendite are compatible and indicating an average temperature and pressure of 664°C and 8.8 kb, respectively. PT conditions of metamorphic rocks of south Dehshir ophiolitic mélange are in accordance with the conditions of those from the other worldwide ophiolitic sutures. Intimate spatial relation between investigated metamorphic rocks and adjoining ophiolites, PT conditions of metamorphism and whole rock chemistry indicate that these rocks representing oceanic lithosphere of suprasubduction zone and have derived from sole metamorphism event in the subduction initiation setting.

The Alborz Mountain range is formed by collision between the Central Iran, in south, and Eurasia plates, in north, since Late Triassic. Facies studies of sedimentary rocks as well as geochemistry of volcanic rocks of Paleozoic formations on the Alborz and Central Iran indicate sedimentation in rift system and shelf and epicontinental shelf in passive margin of Gondwana. This study represents direction and paleostress analysis of the eastern part of Alborz based on geometry and kinematics of faults for the Cambrian, Ordovician and Devonian Periods. Since many tectonic events occur after the Paleozoic Era in the Alborz Mountain range so just growth faults, active during sedimentation, which were not reactivated by later events were used for paleostress analysis. In total 19 stations, including 297 fault data are measured north of Damghan-Shahrud area. The data were rotated to the first position based on fold axes, and FSA software (Fault Slip Analysis) was applied to calculate orientations of principal stress directions. All of the measurement stations show a proximal North-South extension in Cambrian-Devonian Periods.

Remote sensing techniques allow scientists to study many parameters and features of the Earth’s surface such as geologic units, hydrothermal alterations, landslide, geologic structures, etc. It is possible to study every geologic parameter using single or multi dataset. Spectral features of the Earth’s surface are mainly used to investigate rock units, while rock textures are important parameters which are investigated using RADAR Images. In this paper it was tried to find out a way to improve geologic mapping based on multi-spectral and RADAR data fusion. A part of Kerman Copper Belt (KCB) was selected to evaluate the efficiency of ASTER, ETM+ and ALOS data fusion using two methods (layer stacking and PCA and IHS transform). Two polarized ALOS images were integrated to a new layer (with more information) using resultant vector method and injected to multi-spectral dataset. Results of both methods confirmed the ability of multi-spectral and RADAR data fusion to improve the detection of faults, dykes, hydrothermal alterations and geologic units discrimination in comparison with the multi-spectral data alone.

In order to study the biostratigraphy of the Upper Cretaceous deposits in north of Lut block, one stratigraphic section in Bahabad south-west Bajestan area was selected and sampled. The thickness of the Upper Cretaceous deposits in this section is 152.48 meters and based on lithological changes it is divided into five rock units: clastics rocks, gypsiferous marl, lower limestone, marl and upper limestone. The lower boundary due to lack of outcrop is not recognizable and the upper boundary underlies the recent erosional deposits. In biostratigraphic studies with the exception of two basal rock units that have no fossils in the other three rock units: lower limestone, marl and upper limestone 53 genera and 47 species of benthic foraminifera were recognized and two biozones identified as follows:Biozone 2: Rotorbinella campaniola- Pararotalia tuberculifera- Pseudocyclammina massiliensis assemblage zone Biozone 1: Rotorbinella mesogeensis- Pararotalia boixae- Dicyclina sampoi assemblage zone. According to the determined biozones and fossils associations the age of four basal rock units are Cenomanian and upper limestone unit is Santonian- Early Campanian. A sedimentary gap is visible during Turonian- Coniacian between marl and upper limestone rock units in this section.

Pelitic schists containing high-pressure mineral assemblage were found from the Sanandaj-Sirjan metamorphic belt in northwest of Nahavand city in western Iran. Textural observation as well as chemical analyses of minerals shows that pelitic schists of the Nahavand area recorded two metamorphic stages. The earlier stage (M1) is testified by relicts of pyroxene, glaucophane and phengite inclusions in core of albitic plagioclase and winchite and phengite cores in chemically zoned amphibole and white mica, respectively. While the second stage (M2) is documented by tremolite, chlorite and muscovite in the main schistosity and in the pressure shadow of albitic plagioclase blasts. P-T estimation of M1 and M2 metamorphic stage by using calibrated thermobarometers and Thermocalc software revealed an average pressure and temperature of 15.5 kbar and 575 ◦C for the M1 stage, whereas the M2 stage has been constrained at P= 4.5 kbar and T= 600 ◦C. The obtained P-T pattern show a clockwise path in which the high-pressure metamorphic stage of M1 continued by the retrograde low-pressure metamorphic stage of M2. This P-T path could be formed during subduction of Neo-Tethys oceanic plate under Iranian plateau.

The study subvolcanic intrusion, comprising syenodiorite, monzonite and quartz-monzonite, is cropped out in Talkh-rud valley located in the northeast of Damavand volcano flank. This sub-volcanic intrusion possesses porphyritic texture and consists of plagioclase, alkali feldspar, phelogopite, amphibole, clinopyroxene, apatite and titanomagnetite. Evidences of disequilibrium such as zoning and sieve textures in plagioclase and opacity of phlogopite crystals could be due to variations in water vapor pressure during magma ascent. The intrusion is geochemically metaluminous, alkaline and shoshonitic and tectonically plots in the realm of within plate volcanics. Normalized to the chondrite and primary mantle multi elemental spider diagrams show enrichment of LREE and LILE and depletion of HREE and HFSE such as Ti, Nb. Comparison of these rocks with their extrusive counterparts, i.e., trachy-andesites and trachytes of Damavand shows no significant difference between the geochemistry and mineralogy.

Joint roughness coefficient (JRC) is one of the most important properties of discontinuities to determine the amount of shear strength in Barton- Bandis (1982) failure criterion. One of the weaknesses of this parameter is its high dependence on personal judgment in adapting the joint profile to the standard sections of Barton and Choubey (1977). Various methods have been devised to solve this problem, the aim of the paper is a simple formula based on fractal dimension. In this study, two relationships based on fractal dimension by box counting and correlation dimension methods are presented for estimating the joint roughness coefficient. Also, the value of JRC using them is estimated for 192 rock joint profiles and compared with other JRC determination relationships. Accordingly, in these equations, sharing of the asperity amplitude to profile length ratio, in addition to the fractal dimension parameter, increases the accuracy and wider range for calculating the Joint roughness coefficient than single-parameter relations.