مجید شاه پسندزاده

The Sangan Mining District (SMD) in the north of the Cenozoic magmatic belt of eastern Iran is constituted of predominantly acidic to intermediate volcanic and pyroclastic rocks, intruded by the Eocene granitoids. In the Baghak Fe skarn deposit, these granitoids are composed of pre-mineralization biotite quartz monzonite, biotite syenite to biotite syenogranite, alkali feldspar quartz syenite to alkali feldspar granite and syn-mineralization quartz alkali syenite and quartz syenite. These I type granitoids have a magnesian metaluminous, calcalkaline, high K alkaline to shoshonitic nature. The granitoids show enrichment of LREE/HREE and LILE/HFSE with negative anomalies of Eu,Sr,Ta,Th and Ti, posetive anomalies of U, K, Ba, and Rb together with high La values and Zr/Nb, Nb/Th, Nb/U, and Nb/La ratios which suggest not only their slab-derived mantle source, but also crustal mixing in evolution of the magma. The Sm/Yb versus La/Sm, Sm/Yb versus Sm and Dy/Yb versus La/Yb show derivation of the primary melt from low partial melting (2-5 %) of a garnet-spinel lherzolite at depth of ~66-68 kilometers of the upper mantle, affected by continental crust melts. According to this research, the tectono-magmatic setting of the granitoids is suggested syn- to post-orogenic magmatic arc.

Subduction-related magmas are characterized by enrichment of large ion lithophile elements (LILEs), light rare earth elements (LREEs) and depletion in high field strength elements (HFSEs) (Harangi et al., 2007). These geochemical signatures of magmatic rocks are commonly explained by the addition of hydrous fluids from subducting oceanic lithosphere combined with the flux of melts from subducted sediments to the mantle wedge, lowering the mantle solidus and leading to magma generation (Aydınçakır, 2016). Asthenospheric mantle, subcontinental lithospheric mantle and/or lower crust may be the principal source of these rocks (Eyuboglu et al., 2018). In addition, magma differentiation processes, such as fractional crystallization, crustal contamination, and magma mixing may also play an important role in the genesis of these rocks.This research study presents new petrological and geochemical data from the volcanic rocks with NW–SE trending, which are situated in the northwestern margin of the Central –East Iranian Microcontinent (CEIM) (south-east of Khur, Isfahan Province) which have been formed during the peak activity of Eocene. Study of this typical small volume subduction- related magmatism will be useful in understanding the origin and geological evolution of the Central Iran in Cenozoic.

The petrographic investigations on Eocene volcanic rocks from the SE of Khur area were carried out with an optical microscope (Olympus-BH2) in the petrology Laboratory of the University of Isfahan, Iran. Major and trace element concentrations of samples from whole- rocks were obtained by a combination of inductively coupled plasma mass spectrometry (ICP-MS) and inductively coupled plasma atomic emission spectroscopy (ICP-AES) at the Als Chemex Laboratory of Ireland. The chemical compositions of 4 samples (B865, B866, B867, and B868) were determined by Neutron Activation Analysis (NAA) in the Isfahan Activation Center The detection limit was 0.01% for all major element oxides and 0.01 ppm for rare earth elements. Mineral abbreviations were adopted from Whitney and Evans (2010).

Eocene volcanic rocks with trachy-basalt and trachy-basaltic andesite composition are exposed in the northwestern part of the Central-East Iranian Microcontinent (CEIM) (SE of Khur, Isfahan Province, Central Iran). These rocks which have a dominant northwest-southeast trend crosscut the Cretaceous sedimentary rocks.Petrography and mineral chemistry analyses indicate that the predominant rock-forming minerals of volcanic rocks are olivine, plagioclase, clinopyroxene and orthopyroxene. Phenocrysts set in a fine to medium grained matrix of the same minerals plus sanidine with minor amounts of opaque minerals. Secondary minerals are chlorite and calcite. The most common textures of these rocks are porphyritic, microlitic porphyritic, poikiolitic and glomeroporphyritic. Geochemical analyses of whole rock samples show that these rocks have been enriched in alkalies and large ion lithophile elements (Cs, K, Rb, Sr, Ba,), and have been depleted in high field strength elements (HFSE) (Ta, Nb, Ti). All samples indicate moderate to high fractionation in LREE patterns. These geochemical signatures point out to the subduction-related calc-alkaline nature of these rocks and their similarity to volcanic rocks of continental arcs or convergent margins (Yu et al., 2017). Pb enrichment and low values of Nb/La, Nb/U and Ce/Pb ratios reveal that crustal contamination has played an important role in magma evolution (Srivastava and Singh, 2004; Furman, 2007). The large volume of hydrous fluids coming from the subducted slab rather than sediments have caused enrichment and metasomatism of the subcontinental lithospheric mantle source. The geochemical characteristics of the studied rocks suggest that the parental magma have been derived from partial melting of a metasomatized spinel lherzolite of lithospheric mantle, which was previously modified by dehydration of a subducting slab. The tectonic environment, in which these rocks were formed has probably been a volcanic arc. Subduction of oceanic crust around the Central-East Iranian Microcontinent (CEIM) is the most reasonable mechanism which can be used to explain enrichment in volatiles of the mantle, and the calc-alkaline magmatism of the study area in Eocene times.

Sepidar anticline in southwest of the Zagros, located in a tectonically active area, is delineated by the Sepidar, Sabzpoushan, Khafr and other active faults. This anticline has lost its cover of soft Miocene and Pliocene sediment and is now developed solely in the Asmari resistant limestone. Fractal dimensions of drainage pattern, fractures and earthquake in the Sepidar anticline show different values which varied in the NW-SE direction. Based on these variations, the northwestern parts of the fold have more tectonic activity than the southeastern parts. The transition between these parts correlated with saddle in the fold crest, which has undergone less uplift than the surroundings parts of the fold. Asymmetric forked drainage pattern, sinuosity drainage, and dry valley in the Sepidar flanks are geomorphological evidences of lateral propagation of folds. These geomorphological evidences and Inverse Distance Weighting (IDW) maps of fractal variations demonstrate the Sepidar anticline as a sub-cylindrical fold resulted from linear linkage with a saddle at the location where the two initial folds linked.

The Late Neoproterozoic-Early Cambrian albite-bearing metasomatite, rhyolites and rhyodacites predominantly constitute the host rocks of the Choghart magnetite-apatite deposit in Central Iran. The geologic evidences show three types of albites in the host albite-bearing metasomatite. The performed mineralogical and geochemical investigations display enrichment of REE-Y-Ti-Th in the pink and fleshy red albites, whereas the white albites are barren without any ore mineralization. The concentration of REE-Y-Ti-Th-U bearing minerals along the fractures, the variation of Th/U ratio and result of stable isotopes studies of the calcites syn-paragenesis with the abiltes reveal the involvement of mixed magmatic and high-midium temperature hydrothermal processes play an important role in the ore genesis. The similarity pattern of the REEs and trace elements in different types of abilte-bearing metasomatite and rhyolite manifest the origin of REE-Y-Ti-Th mineralization as the rhyolitic-rhyodacitic magmas, related to a continental/oceanic subduction zone. According to this research, tectono-magmatic setting of the albite-bearing metasomatite in the Choghart deposit is suggested as a Calc-alkaline magmatism, associated with the active continental margin and oceanic island arcs.

The Dehsheikh peridotite massif, as a part of the Esfandagheh ophiolitic mélanges, is located in the south of Baft, Kerman province. Structural analysis of the ophiolitic complexes play an important role in understanding geodynamics of the orogenic belts. In this research, structural elements of the eastern part of the Dehsheikh peridotite massif as well as prevailing deformational patterns of the area and its relation to the Zagros orogenic belt was studied. The chromitite folds, dunitic/pyroxenitic dykes and ductile to brittle shear zones (faults and magnesite veins) constitute the principal structures of this area. Structural evidence indicate two successive tentional/transtentional and dextral transpressional deformational phases. The early D1 deformation took place in a back-arc basin during ascending of the Dehsheikh Peridotite massif. This caused emplacement of the lithospheric mantle in the low crust level, and was accompanied by deformation of the chromitites and intrusion of the dunitic/pyroxenitic dykes. The next D2 right-lateral transpressional deformation with development of the brittle-ductile shear zones accommodated emplacement of this massif in the high pressure-low tempretaure Sanandaj-Sirjan metamorphic zone.

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

Dehsheikh ultramafic-mafic complex is located in the Esfandagheh ophiolitic mélanges belt of Kerman province. The Dehsheikh complex comprises harzburgite, lherzolite, dunite, chromitite, pyroxenite and layered gabbros. The presence of abundant chromite ore deposits has made this complex important. The complex constitutes part of the Neotethys oceanic lithosphere deformed during upwelling from the upper mantle and later emplacement in the upper levels of the Sanandaj-Sirjan continental crust. Microstructural analysis of this complex reveals three deformation mechanisms including intracrystal plasticity, diffusive mass transfer and cataclasis. The microstructures of deformation twins, wavy extinctions, kink bands, exsolution lamellas, dynamic recrystallizations, microboudins, pull-apart microfractures, mineral stretching and elongation, mineral lineations and shear band cleavages formed due to the intracrystal plasticity deformation mechanism. The diffusive mass transfer deformation mechanism was associated with development of indenting, truncating and inter-penetrating grain contacts and micro-veins. The cataclasis deformation mechanism was accommodated by development of micro-fractures and micro-faults. This microstructural study also manifested different generations of olivines, pyroxenes and spinels under upper mantle to crustal conditions.

Determination of inter-seismic deformations such as fault slip-rate can usually be achieved by using geodetic observations, earthquake geology and paleo-seismology, as well as mechanical, empirical and numerical modeling. In these models, combination of the fault seismic parameters and the GPS data can help estimate the fault slip-rate, the elastic thickness of the lithosphere, the earthquakes recurrence time, the relaxation time of the asthenosphere, the elapsed time of earthquake and the locking depth of the fault. In this study, we utilize the geodetic data of the North Tabriz Fault (NTF) by using random Bootstrap sampling and conducting numerical modeling by code writing in the R and MATLAB softwares. In this concern, the fault slip-rate and elastic layer thickness are estimated to be ~4-6.5±1 mm/yr and ~5-25 km, respectively, for the NW segment of the NTF. Similarly, model results for the SE segment of the fault indicate a slip-rate of ~3.5-5.5±1 mm/yr and elastic layer thickness of ~8-16 km. For the NW segment of the NTF, the asthenosphere relaxation time, earthquake recurrence time and elapsed time are estimated to be ~160-185 years, ~650-950 years and ~200-1400 years, respectively. Model results for the SE segments of the NTF indicate an asthenosphere relaxation time of ~220-340 years, an earthquake recurrence time of ~750-1050 years and an elapsed time of ~200-1500 years, respectively. The results are well consistent with the other paleoseismological and geological results.

Structural data the Kuh-Banan oblique-slip fault system show that this active fault controls the structural architecture of the Tikdar-Goorchoieh area, north of Kerman. The Kuh Banan fault system is consisted of three fault branches with mean trend of N70E in the north of the Tikdar - Goorchoieh village. These fault branches with a dip of 50-70 toward the northwest and slip rake of 50-80 N indicate the prevalent reverse with right-lateral strike-slip motion of the fault. The main strand of Kuh-Banan fault system with a northwest-southeast strike is reported between the Dehsu rock series and Shemshak Formation as the fault branches with a northeast-southwest trend are situated between the Hojedk Formation and Neogene alluviual deposits and Quatrnery sediments. In this area, the Dehsu rock series (Late Neo-Proterozoic-Lower Cambrian) is composed of dolostone and evaporitic rocks which thrusted over the sandstones, shales and limestones of the Hojdak Formation (Jurassic). According to the structural evolution of the Kuh-Banan fault system in the study area, the first fault branch (F3) with three fault slip motion in the northeast-southwest direction has developed between the Shemshak Formation and Dehsu rock series in north of Tikdar. The later fault branches of F1, F2, and F4 with the same trend have propagated the main fault and developed between the Dehsu rock series with the Hodjek, Shemshak and Dahu (equivalent of Lalun) Formations.

Dorouneh Fault is located in the north of Central Iran Microplate with left-lateral strike-slip mechanism and plays an important role in the formation of Iran plateau's morphology. Dorouneh fault, with bend geometry and 900 km length, extends from Hyrmand River in the Afghanistan border to Anarak area in the Central Iran. Dorouneh Fault terminates in the Jandaq area as sub-parallel branches. Towards west, general trend of Dorouneh Fault System changes from northeast-southwest to north-south in the north of Talmessi Mine. Fault branches are observed as left-lateral strike-slip faults with normal dip-slip component in the Jandaq-Talmessi area that is introduced as a trailing extensional imbricate fan. But, considering slip sense inversion along Dorouneh Fault, the main mechanism for formation of western termination before slip sense inversion is a trailing compressional imbricate fan.

Dorouneh Fault System (DFS) is located along northern border of Central Iran microplate. Its mechanism is left-lateral strike-slip with reverse dip-slip component. Considering curve geometry of DFS, it is divided into three major parts: eastern, middle and western. Middle part extends from Torbat-e-Heidarieh city in the east to Anabad village in the west. It passes through Quaternary loose alluviums. DFS is composed of different segments in this part. Bend and right-lateral en echelon geometry at surface and left-lateral strike-slip movement of DFS cause local transpression that is observed as young folding. Fold core is composed of Neogene marl, sandstone and siltstone and fold limbs are composed of Pleistocene loose gravely sediments. Mentioned folds were formed by two different mechanisms: first, Anticlines that formed in right-step bends of DFS and second, pressure ridges that are limited among parallel branches and overlaps of DFS. Estimation of relative uplift rate along mentioned folds indicates that more earthquakes occur in regions with higher uplift rate.

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.

Dorouneh Fault System، as an active fault in Iranian Plateau، plays an important role in deformation and geomorphology of the region. This fault has caused some earthquakes in the 20th century. Detail study of Dourouneh fault's seismic characteristics indicates that in spite of Dorouneh Fault's high movement in Recent time، number of earthquakes and their magnitude is low that may be resultant of low slip rate، long recurrence interval and occurrence of creep on the fault. On the other hand، there are some witnesses that are indication of earthquake occurrence along Dourouneh fault which are accompanied with surface rupture.

More than 80% of drinking water of highly populated and expanding city of Gorgan, as one of agricultural centers of Iran, is supplied by local groundwater resources (Ziarat, Garmabdasht, and Shast-kola aquifers). Chemical analysis of groundwater samples of Gorgan district indicates two regions of anomalously high concentration of nitrate (Ziarat aquifer) in the urban area. High chloride concentration in water from dug wells corresponds with the anomalous high values of nitrate. Low concentration of nitrate in Shast-kola as well as Garmabdasht aquifers, where main land use is agricultural activities respect to Ziarat aquifer, demonstrates low/no effects of fertilizers on the contamination of groundwater. Determination of NO3/Cl and K/Cl ratios depicts sewage effluents and urban runoff as the main sources of nitrate contamination of the groundwater. Moreover, rapid urbanization and the encroachment of residential development into surrounding forests release considerable nitrate to the underlying shallow aquifers.

Landfill sites could be associated with the environmental impacts of surface and groundwater pollution due to landfill leachate percolation to the hydrological system. Such issues occur due to the unsuitable selection of geological areas as the waste disposal site, characterized without any effective capping and bottom liners. The goal of this research is the investigation of hydro-chemical quality of the groundwater in the vicinity of Gorgan MSW landfill. The result of geochemical study of the groundwater samples in the landfill area indicates that prominent cations and anions concentrations are more than Drinking Water Standards. Although in the south of Gorgan disposal site, the average total concentration of Na+,K+, Mg2+, Cl-, SO42-, PO43-, NO3-, and NH3- are measured 27.80, 2.80, 38.82, 90.20, 141.20, 0.18, 20.37, and 0.02 mg/l respectively in the groundwater wells. But in the nearby Gorgan MSW groundwater wells, the average total concentration of these contaminants are reported 218.8, 7.20, 71.42, 183.30, 200.30, 0.50, 61.90 and 0.17 mg/l respectively. Range of turbidity, E. C., and T.D.S. amounts, along with concentration of Na+, Cl-, SO42- and NO-3 contaminants in the groundwater wells of adjacent of Gorgan MSW is more than groundwater wells in the south of Gorgan disposal site. According to strongly and positive correlation of EC with Na+, K+, Cl-, SO2-4 and TDS of the groundwater, S- SW to N-NE flowing of groundwater, and unsanitary disposal of Gorgan MSW without any effective liner, which lies on the loess deposits (76% slits and 23.5% clays as kaeolinite, illite, and semectite) it could be concluded that the infiltration of landfill leachates have caused the contamination of the ground water.Geohydrochemical facies of groundwater types are determined as Ca2+Na+HCO-3Cl- and Na+HCO-3. Usage of the groundwater resources in the vicinity of landfills area by the residential municipal and rural people, which has a potential impact on public health, requires controlling of the leachate seepage and designing lining systems for preventing contamination of groundwater.