Iranian Journal of Geology
Year:2012 | Volume:6 | Issue:22|Papers Count:7

In order to examine the influence of Sub-Hersinian and Sub-Senonian tectonic phases in the Aghajari Oil Field, three stratigraphic sections were studied around the boundary of Sarvak and Ilam formations in wells No.56, 140 and 82. The existence of biozone No.29 (Wynd, 1965) with Turonian in age at the top of the Sarvak Formation which overlays the biozone No.25 (Wynd, 1965) indicates the continuity of sedimentation from Cenomanian to Turonian. The effect of Sub-Hersinian phase was minor and caused some facies changes in all three wells. In wells Nos.56 and 140, the biozone No.29 (Wynd, 1965) with Turonian in age is overlain by the biozone No.30 (Wynd, 1965) which belongs to the Ilam Formation. This condition represents a gap between Turonian and Santonian at the boundary of the Sarvak and Ilam formations which is the result of the Sub-Senonian phase. In well No.82, the time of this gap is slightly more and continued until the Late Santonian as a result of the Gurpi Formation with Late Santonian in age which has overlain the Sarvak Formation with Turonian in age.

Jirandeh area, in northwest of Qazvin, is a part of western Alborz structural zone that includes extensive outcrops of Middle-Upper Eocene volcanic and pyroclastic rocks (composed of olivine basalt, trachyandesite, andesite and trachyte) and post Eocene intrusions. Field relations in addition to petrographic features and geochemical trends of volcanic rocks on major, minor and trace elements variation diagrams indicate that this rock suite had formed by fractional crystallization of a basic magma. This magma has high-K calcalkaline nature and characteristics of subduction related continental arc magmatism. The mentioned magma has been formed from 12-15% partial melting of an enriched garnetlherzolitic mantle source at 90-110 km depths and was erupted via deep fractures and faults, during Middle-Upper Eocene from the intra-arc extensional basin of western Alborz.

Duplexes in Kamarhaji Mountain have east-west trend. Duplexes are parallel to the Shekarab fault system. Shekarab fault is a reverse fault with sinistral component that is located in the southern parts of the area. It is considered one of the terminal branches of the Nehbandan fault.Based on Geometric-Kinematic analysis, duplexes are of the horsetail structures types which are located of the side view on each other. There are flower structures in the direction perpendicular to the horsetail structures, that had led the central layer of the duplex structures had maximum height. In duplexes of this region, ramps have strike slip mechanism with thrust component. Existingflats are non-horizontal and most of them have thrust mechanism with strike slip component. Due to the mechanism offlat, transfer direction is to the west side. Since the younger ramp is on the hanging wall of the previous ramp (in other words, younger orientation is into hinterland), the formation model for duplexes is break-back model that examined in the laboratory of Experimental Tectonics. According to the results obtained from different trends of shortening on structures, such as folding and duplexes, the paleostress show two-stage of deformation. Position of strain l3 axis in the first stage of deformation, according to analysis of the conjugate joints, is N42, 00, and according to analysis of joints tension is N40, 07 which help axial surface of folding obtained N38, 14. Shortening at this stage of deformation is 41.46 percent. Position of strain l3 axis in the second stage of deformation, according to analysis of the conjugate joints, is N83, 02, and according to analysis of the joints tension is N84, 00 which help to position the duplexes about N90E. At this stage, strike – slip faults have been further developed, shortening at this stage of deformation is 20.30 percent and the amount of slip along theflats is 2640 meters. According to the geometric-kinematic analysis, duplexes formed during deformation at the second stage that is associated with progressive deformation.

Travertine-bearing hot springs of Ab-e Ask are located at the far northeast margin of city of Tehran and at the eastern side of Damavand Volcano. Fissure-ridge and vein-type travertine are the main deposit types of these springs. Due to tectonic activities, fault zones and fracture systems were formed and provided migration paths for CO2-bearing hydrothermal fluids. Fissure-ridge and vein-type travertine that formed in these zones and systems are resulted from the intense degassing of CO2. Microscopic studies and XRD analyses showed that the fissure-ridge travertine is made from nearly pure calcite with some amounts of quartz mineral. This is also supported with SEM and microscopic studies that photosynthetic microorganisms such as blue-green algae and diatoms have an important role in the formation of travertine. Internal pressure of CO2-bearing hydrothermal fluids resulted in the formation of hydraulic fractures in these rocks. XRD analyses and petrographic studies are also resulted in the recognition of elongated blocky type calcite and other forms of calcite, pyrite, gypsum and a rather few amount of rancieite mineral. Based on stable isotope analyses (including d13C and d18O values), two different origins are recognized for these travertines: fissure-ridge type travertines are related to the de-carbonation of limestone and vein-type ones are related to the magmatic-de-carbonation origin. A considerable enrichment in d13C values is attributed to the de-carbonation of limestone, algal activities and rapid degassing of hot springs.

In the north of Dehgolan in Uromieh-Dokhtar zone, volcanic rocks of Miocene age are exposed. Composition of the rocks is mainly intermediate to acidic and rarely basic. Porphyric texture is dominated. Rhyodacitic lahar and ash are main units in the area. Plagioclase and hornblende are main phonocrystes and quartz, alkali feldspar and biotite are also present. Matrix is mainly silicic glass. The ash unit is characterized by its abundant xenoliths with low density because of high degree of porosity. After petrography and geochemical studies, pozzolanic activity of ash unit was investigated by thermogravimetry (STA) method. Pozzolanic activity for Dehgolan acidic ash is 49.36 percent which present thefirst order stand in classification of activity. Chemically, mole ratio values of Dehgolan samples (Al2O3/ (CaO+Na2O+K2O) per Al2O3/ (K2O+Na2O) are in good agreement with known pozzolans in Iran and other countries.

Since the spectrum behavior of rocks is similar, preparing of geological maps by using of multi-spectral images could be difficult. In this study, the Support Vector Machine (SVM) is used as one of the image classification methods, which has flexibility for individual conditions. The kernels of SVM are performed by Maximum Likelihood (MLC) and Neural Network Classification (NNC) methods in order to produce geological maps and training samples of hand and laboratory samples, as well. The results show that the SVM method has highest precision (83.42%) in all three kernels in comparison with other two methods. Furthermore, this method can reach the 100% precision if uses only 50% of training samples, while in other methods (i.e. MLC and NNC) can not reach the 100% Precision Comparing of results that gained from Jefferis-Matusita method with those from SVM indicate that this method is much more operative than other ones for low discriminative data, and then its efficiency is high for producing geological maps.

Groundwater is the main source of drinking water in Iran and nitrate contamination in groundwater is one of the most common pollution that threats public health. There are some sources for nitrate in groundwater. Nitrate may be originates from chemical fertilizers, animal and manure waste and organic material in the soil. Identifying of the nitrate origin is the most important stage in planning and implementing projects to prevent, reduce and control of the pollution. This study aimed to assess nitrate contamination of groundwater and identify sources of nitrate in the Dezful - Andimeshk plain. Water samples were taken from groundwater wells (102 samples), river (3 samples) and manmade drain (7 samples) in study area to analyze the common cations and anions. The parameters such as pH, temperature, dissolved oxygen and electrical conductivity were measured in the field. Among these samples, 26 samples were selected to measure the oxygen and nitrogen isotope ratios of the nitrate molecules. Result shows that nitrate concentration in north and north-west of the study area is higher than maximum admissible level for drinking water. Concentration of the nitrate from the north to south in the study area decreases. Based on the isotopic analysis, the main source of the nitrate in Dezful-Andimeshk aquifer is chemical fertilizers. However, there are some locations, in urban and rural areas, where nitrate from manure sources is mixed with the nitrate originated from fertilizers. d15N shows positive relation to water depth so that increases with groundwater wells depth. Because of groundwater nitrate denitritification by bacteria, the enrichment of 15N and 18O from the north to the south of the study area are increased.