نشریه علوم زمین
پیاپی 122 (زمستان 1400)

Mila Formation includes five members in the Tuyeh-Darvar section, west Damghan. Fifth Member of formation comprises alternations of calcareous shale, limestone and green shales. Trace fossils of this member includes Cruziana problematica, Gordia isp., Helminthopsis abeli, Helminthopsis tenuis, Palaeophycus striatus, Planolites beverleyensis, Psammichnites gigas, Scolicia strozzii and Treptichnus pedum. Circulichnis montanus abundant in the upper most layers of the fifth Member and is circular cylindrical ring in shape. Circulichnis is a fodinichnion, that produced by progressive and plasticity behaviors of annelids. It seems that these trace fossils are belong to the mid parts of the turbidite rhythmic sequences and formed in the turbidity conditions of the sedimentary environment.

The Upper Cretaceous succession (UCS) of the north Sanandaj-Sirjan zone consists of five units. The units are 2000 m thick, including shale, sandstone, limestone, intrafomational conglomerate with interbedded basaltic- andesitic lava. This succession is unconformably underlain by Lower Cretaceous and overlain by Paleocene conglomerates. The geochemistry of the samples represents ratios of Al2O3/TiO2 (18-22), La/LuCN (5.43-24.4), La/Sc (0.51-2.53), Th/Sc (0.42-0.68), LREE/HREE (Nd/ErCN > 5), and negative anomalies of Eu/Eu* (0.26-0.89) and Nb/Nb* (0.14-0.82). These characteristics indicate that the samples are immature, first-order sediments, and were eroded from intermediate to acidic arcs in the subduction zone. The volcanic rocks were formed during the intracrustal melting of an altered oceanic slab at high pressures in the garnet-amphibolite facies. The geochemical compositions and vertical lithofacies stacking patterns of the UCS imply that the depositional environment has changed during sedimentation from a trench to trench slope and forearc basins arising from continent-ward migration of the magmatic arc. The activities of Late Cretaceous volcanism resulted in the upwelling of anoxic water, demise of planktonic, and formed pyrite in the deposits. Samples on the Th/Yb-Ta/Yb diagram fall in the ACM and WPVZ fields, indicating tectonic evolution from low-gradient subduction to extensional volcanic conditions.

In the Gezeldash_daghi region, there is a significant outcrop of Miocene volcanic activity with andesitic composition associated with pyroclastic deposits including tuff, breccia and agglomerate. These rocks have porphyry to microporphyry texture with coarse crsytals of pagioclase, and matrix includes plagioclase, hornblende and minor biotite. Zoning, sieve texture in the coarse crystals of these lavas is an indicative of unstable conditions during magma solidification. These lavas have calc-alkaline nature. The geochemical characteristics of Gezeldash_daghi lavas such as LREE enrichment than HREE as well as enrichment of LILE elements with negative Nb, Ti and P anomalies indicate their affilliation to subduction setting. These rocks contain high amounts of SiO2, Sr, Sr / Y and La / Yb, and lower values of Y, MgO, and Yb than classic calc-alkaline volcanic rocks, and may indicate lava adakitic features. Based on the geochemical data, these lavas had formed partial melting of subducted oceanic crust. The depletion of rare earth elements indicates a residue containing garnet and hornblende in the source area.

Based on lithostratigraphy analysis, Cheleken Formation in the studied section of the Gorgan plain, subdivided into lower sandstone and upper mudstone/marl units. Based on petrographic analysis, the sandstone sediments include low textural and compositional maturity litharenite and sublitharenite. Conglomerates are polymictite orthoconglomerate with variables carbonate and chert grains. High percentage of the porosity as vuggy, channels and fractures in the sandstone and conglomerates and even mudstone deposits displays high reservoir potentional for the studied sediments and hence necessitates the exploration studies in the Iranian part of the SCB. Based on the youngest nannofossil species, a late Miocene to middle Pliocene (?) age is defined for the Cheleken Fm. in the studied area. Nannofossils distribution of the studied succession displays the SCB was connected to the Black Sea and Mediterranean Basin in the late Miocene- early Pliocene and the Pleistocene and was isolated in the main part of the Pliocene.

Tirka area is situated in NE Iran as a part of the TCMB which consists of Paleogene sediments and volcanic rock units with a combination of Eocene intermediate to basic rocks. The research aim is to determine the alteration zones using C-N fractal model based on ASTER satellite images. First, the ASTER data was processed using SFF method for determination of iron oxide, propylitic, phyllic, and argillic alteration zones. The C-N fractal model is utilized for the separation of different parts of alteration zones. The results derived via the C-N fractal model showed that the main trend of the alteration zones is in NE-SW direction. Also, based on the C-N log-log plots, there are six geochemical populations for iron oxide alteration, four geochemical populations for argillic and phyllic alterations, and five geochemical populations for propylitic alteration. There is a high intensity of alteration zones commences with 223 for iron oxide, 204 for argillic, 199 for propylitic and phyllic alteration zones. In order to validate the results, field observations and petrographical studies based on thin-polish sections were carried out. These data confirmed the alteration zones obtained by the modeling. the data obtained from the combination methods, were verified by Logratio matrix,

Prediction of groundwater inflow into tunnels during excavation is one of the most important problems of tunneling projects. There are many analytical and empirical methods to predict the amount of groundwater entering the tunnels, which are generally not highly accurate. Permeability and water head are the main affecting parameters in estimation of groundwater inflow in current prediction methods. Due to the complexity of the geological and hydrogeological conditions of hard rock formations, it is necessary to enter other geological factors to estimate groundwater inflow into the tunnel. In this paper, for the first time, Geomorphological Rock Mass Strength (GRMS) classification is used as a criterion for estimating the groundwater entering the tunnel. The obtained data from two tunnels in different geological setting were used to study the effect of rock mass classification parameter on estimation of groundwater entering the tunnel. The results show that for both tunnels, GRMS have a significant correlation with the amounts of groundwater inflow into the tunnels.

In this research, using fuzzy logic (gamma) methods, analytic hierarchical analysis (AHP), and based on the weighting of exploratory layers by the opinion of geoscientists, modeling of mineral potential for lead and zinc metals in the Khondab sheet. The geochemical layer related to Pb-Zn metals has been prepared using the singularity index (SI) method, which has high accuracy in detecting weak and hidden anomalies. All exploratory layers and substrates including lithology, geochemistry, the density of lead and zinc deposits and mineral signs, the density of faults and silica and carbonate alterations were weighted using the fuzzy logic (gamma) method and ranged from 0 to 1 and fuzzy layers with gamma value (γ) of 0.95 were combined with each other and prepared the potential maps for Pb-Zn metals in the study area. Then, using the AHP method and forming a suitable matrix for the exploratory layers, the layers were weighed and a potential map of the desired metals was obtained. The results showed that the AHP method identified more anomalies compared to the fuzzy logic (gamma) method and the anomalies obtained from this method show more compliance with the Pb-Zn deposits in these regions.

The Urmieh- Dokhtar magmatic belt (UDMB) lying parallel to the Zagros suture zone is resulted from the subduction of Neotethyan oceanic lithosphere beneath the southern margin of Eurasia. The studied volcanic rocks of the Razan- Avaj area are part of UDMB magmatism. These rocks are composed of olivine-basalts, basalts and occasional trachyandesites with alkaline nature. The interlayered stratigraphic relationships of volcanic horizons with sediments of Qom Formation implies Oligo-Miocene age. Major and trace element contents of volcanics and chemical modeling are indicative of significant role of olivine + clinopyroxene + plagioclase fractional crystallization (35-45%) in melt compositional trend. Bulk rock chemistry of theses rocks displays LREE/HREE enrichment and lack of HFSE negative anomaly similar to oceanic island basalts (OIB). It seems that after Eocene magmatic flare-up with obvious magmatic arc signatures in UDMB, during the Oligo-Miocene the origin of magmas has shifted to a deeper asthenospheric mantle. Probably, after the initial stages of the Arabian-Eurasian plate collision in the Late Eocene-Early Oligocene and the slab roll-back, an upwelling asthenospheric mantle is injected into the mantle wedge and is weakly affected by the subduction material, which is the source of Oligo-Miocene melts.

The Oshvad skarn type deposit was formed during the intrusion of a felsic mass into the Permian and Triassic carbonate rocks and ion exchange occurred between the intrusion mass and these units. In order to determine the properties of the mineralizing fluid in this skarn, several fluid inclusions in quartz and calcite minerals of the mineralization zone were analyzed. The results show that these minerals have two types of fluids inclusion. The first group includes L+V type, low to medium salinity, and with homogenization temperature of 194 to 480°C. The second group includes V+L type, low to moderate salinity, and homogenization temperature of 338 to 448°C. The origin of L+V type fluid inclusions are magmatic-meteoric and metamorphic type and V+L fluid inclusions are metamorphic type. Mixing and dilution of fluids occurred during the mixing of meteoric waters with magmatic-metamorphic fluids. These processes are the main factors of mineralization in this deposit. Fluid inclusions data show that fluid pressure has been 50 to 150 bars during the ore-forming minerals. Also, the fluid temperature has been between 200 to 360°C. The data suggest that the ore minerals have been formed in depth of 650 meters lower than the old water table.

Located at the Arabia-Eurasia collision zone, the E-W trending Bozgoosh Mountain aligned perpendicularly to N-S trending Chehel-Nour Mountain in the northwest of the Iranian Plateau. There is not any thermochronometry study has been performed to determine the initial time of their uplift and exhumation. Our low-temperature Thermochronometry analysis in the apatite U-Th/He (AHe) system in combined with previously unpublished data set at central Bozghush Mountains and structural data show that the onset of the Late Cenozoic uplift and exhumation of the Bozgoosh Mountain (~19-25 Ma) is a bit older than Chehel-Nour - Gaflankuh Mountain (~15 Ma). It seems that deformation of the Bozgoosh Mountains started at with respect to middle Miocene unset time of deformation at Chehl-Nour and Gaflankuh Mountain. Then it can be concluded that these two perpendicular maountain ranges have not been formed in a single phase of partitioned deformation. On the other hand N-S trending Chehel-Nour and Ghaflankuh Mountains have similarly deformedsynchronous with the N-S trending part of the southern Talesh Mountains in its eastern border. Our results have also document that the Bozgoosh and Chehl-Nour mountains intersection is actually a part of Bozgoosh mountain.