نشریه علوم زمین
پیاپی 75 (بهار 1389)

The Khanjar Pb- Ag (Zn) deposit is one of the stratabound deposits of Cretaceous age in Central Iran. The ore bodies may be grouped into two main geometric types: 1) Lenses of ore bodies congruent with bedding, 2) Ores as open space filling or with brecciate fabric due to faulting. Both types occur in limestone unit (k2b).Three ore bearing facies have been distinguished in the Khanjar area: 1) Siliceous limestone facies; galena, sphalerite and pyrite are the main ore minerals. Minor amounts of chalcopyrite are also visible. 2) Mullusca, Echinoderm wackstone facies with galena and sphalerite. 3) Rudist limestone facies with large amount of galena. As with other stratabound and stratiform Pb- Zn deposits, the main ore minerals are simple and few in number. In addition, galena, sphalerite and pyrite, some tetrahedrite, barite and minor amounts of copper minerals are observed. Pyrite often with framboidal texture and sphalerite with spheroidal texture form always part of paragenesis. Fluid inclusion investigations on saddle dolomite located in fractures with galena and sphalerite demonstrated the homogenization temperature of 145-230 centigrade and salinity of 17.5-23% NaCl equivalent.Geometry of ore bodies, occurrence of ore horizons in certain sedimentary facies, ore textures and structures, depositional environment (Lagoonal), paragenetic sequence of minerals and fluid inclusion data, all suggest that Khanjar Pb- Ag(Zn) deposit is an MVT deposit.

The stratigraphic section of Esfeh is located at 15 km north-east of Shahreza and 65 km south of Esfahan. The aim of this study is to consider the lithostratigraphy, biostratigraphy and how to settle the Permian-Triassic boundary, also the geochronology of them. The biostratigraphic study of this section indicates the existence of index Fusulinidae with the high quality of other places. for instance:Verbeekina verbeeki, Sumatrina annae, Afghanella schenki, Yangchienia iniqua, Eoparafusulina Shengi. In this study the geochronological change of member 3 of the Surmagh Formation with attention to index fossils attributed from Guadalupian to Early Julfian and also the lithoiogical alterations to exist in deposits of the Hambast Formation equivalent to Esfeh section, the Shahreza formation propose is necessary.

Estimate of moment rate is comparatively reckoned as a new method for dealing with tectonic activities rate in different regions and it prepares the way for putting together different methods. In fact, moment rate states rate of energy which exists in deformation system. There are three different approaches to state moment rate that each one express tectonic motion and movement of a region from a particular view. These three approaches consist of: geodetic (surveying), seismic and geology methods. Geodetic method which is determined on the basis of gained strain rate tensor from geodetic data, shows deformation rate (including seismic and aseismic) that is happening in the region at this moment in time. Moment rate which has gained on the basis of historical and instrumental catalogues, shows the total released seismic energy during quake events which are available in earthquake of region and geologic moment rate which gained with geometric parameters of faults, reveals potential of the faults in releasing stored elastic energy in. Geodetic moment rate, seismic moment rate (on the basis of historical and instrumental earthquake data) and geologic moment rate are estimated for Central Alborz region. The most moment rate in the study area belongs to geodetic approach (8.83×1019 Nm/yr) and then geologic moment rate (0.12×1019 Nm/yr) and finally the least quantity belongs to seismic moment rate (0.022×1019- 0.046×1019 Nm/yr). Considering, distribution of earthquake epicenters, the most seismic energy is released in the south parts of Central Alborz and considering high geodetic and geologic moment rates in north parts, it seems, north parts of Central Alborz have higher seismic potential.

In order to study the fossil contents of the Abderaz Formation for biostratigraphical purposes the 300 meters thick section was sampled at type section. The sequence is mainly made up of grey shales and marls with two units of chalky limestone in upper part. The lower contact of the formation with Aitamir Formation is disconform while the upper contact with Abtalkh is continuous. Fifty six species belonging to 16 genera were identified and four biozones were differentiated. These are: Helvetoglobotruncana helvetica (Sigal) total range Zone, 2-Marginotruncana sigali - Dicarinella primitiva (Premoli Silva and Sliter) Partial range Zone, 3- Dicarinella concavata (Sigal) interval Zone and 4-Dicarinella asymetrica (Postuma) total range Zone. Based on, these an age of Turonian-early Campanian is quoted to the formation. Also it was shown that Helvetoglobotruncana helvetica, the index species for middle Turonian exists at the base of the formation while, in the samples immediately below this belonging to Aitamir Formation Rotalipora appenninica, the index for middel cenomanian was recorded. Therefore, lack of index species for late Cenomanian- early Turonian shows a gap spanning this period between the Aitamir and Abderaz Formations. This could be a result of sub Hersinian orogeny.

The December 20, 2007 earthquake has occurred three months after the September 16, 2007 earthquake near the Tabriz city in East Azarbaijan province. We have used SH- waves accelerographs data and Brune model to estimate the causative fault plane parameters. The strike, dip and rake have been estimated as 310o, 85o and 170o, respectively. The focal mechanism shows right- lateral strike slip, which is consistent with the North Tabriz Fault. This is the first focal mechanis for the North Tabriz fault based on the strong ground motion data.

The Simin- Darreh Moradbeik shear zone is located in the south of Hamedan city with 5 km width and at least 10 km length. The portion of contact metamorphic rocks, plutonic rocks and migmatits are affected by this shear zone. At least three ductile deformation stages are recognized by folding and foliation of each stages of deformation. All of deformation stages are coaxial and created interference pattern of folding. Field evidence shows tension and shear stress in this area. The shear zone dips to northeast and northwest with normal sense of shear movement. This shear zone deformed locusom of migmatite, boudinage of andalusite porphyroblast and formed granitic mylonite from Khako granite. Distribution of mylonitic foliation poles show refolding of this shear zone at the next deformation stages. According to deformation stages in Hamadan tectonites, possibly this shear zone formed syn to post second deformation (D2)

The only geologic evidence of the neotectonic activity of theTorud region is its seismisity which assumed to be related to the Torud seismogenic fault. This fault has been overlain by the Quaternary alluvium in the major part of its length. Therefore, the study of morphotectonical characteristics of the region gives more evidences about its activity. Calculation of three morphotectonic indices including stream length - gradient (SL) and ratio of valley - floor width to valley height (Vf) of stream channels and mountain front sinuosity (Smf) shows high SL values (425 - 1044) and low Vf (2.68 - 3.34) and Smf (1.05 - 1.44) values and indicate that the region has activity specially at two parts: central part (near the mountain front) and northwestern part (near the main divide of the Torud mountains) and therefore the tectonic activity class of the region can be number 1. The activity of the central part can be due to the movements of the Torud fault. The activity of the northwestern part is the result of the uplift of the region which is related to the at least one fault parallel with the Torud fault that has formed the relic mountain fronts at recent past. The distribution of strain of this activity shows the progressive deformation from north northwest to south southeast and from west to east.

The paper presents a method for evaluating relative active tectonics based on geomorphic indices useful in evaluating morphology and topography. Indices used include: stream length-gradient index (SL), drainage basin asymmetry (Af), hypsometric integral (Hi), ratio of valley-floor width to valley height (Vf), index of drainage basin shape (Bs), and index of mountain front sinuosity (Smf). Results from the analysis are accumulated and expressed as an index of relative active tectonics (Iat), which divided into four classes from relatively low to highest tectonic activity. The study area along the south flank of the central Alborz mountain range in north Iran is an ideal location to test the concept of an index to predict relative tectonic activity on a basis of area rather than a single valley or mountain front. The recent investigations show that neotectonism has played a key role in the geomorphic evolution of this part of the Alborz mountain range. Geomorphic indices indicate the presence of differential uplifting in the geological past. The high class values (low tectonic activity) for Iat mainly occur in the south and southeast of the Karaj drainage basin, while the rest of the study area has classes of Iat suggesting moderate to high tectonic activity. Around the Amirkabir Lake, Iat has the highest value. The distribution of the indices defines areas associated with different mountain fronts and estimates of relative rates of tectonic activity. More than half of the study area is classified into classes 2 or 1 of high to very high tectonic activity in terms of the apparent geomorphic response. In different tectonic environments with greater rates of active tectonics, the values of indices would differ as well as their range in value. The stream network asymmetry (T) was also studied using morphometric measures of Transverse Topographic Symmetry. Analysis of the drainage basin and a number of sub-basins in the study area results in a field of T-vectors that defines anomalous zones of the basin asymmetry. We test the hypothesis that areas with great stream migration are associated with indicatives values of Iat.

Abundant chevron folds were produced in well-bedded red thin layers radiolarites in Kermanshah area. Various fold hinge area structures were produced due to competency contrast and change of thickness in radiolarian shale and thick-bedded limestone intercalation in radiolarite sequence. Different styles of folding exist in massive to thick-bedded limestone and shale where they are inter-bedded with radilarites. Unique thin layers of the radolarite layers were folded in parallel shape but change of folds shape and mechanism were produced where thick bedded limestone or thin layers of radiolarian shale intercalations exist. Fold accommodation faults were generated in cases during folding. Geometry and style of folding indicate that deformation in radiolarites was produced by parallel folding due to buckling mechanism with southwest vergence. Thrust faults were generated during later stages, displacing some parts of the folded radiolarites.

One of the basic discussions in geosciences is construction of different tectonic zoning maps. In conventional tectonic zoning, not only the great amounts of subjective judgment are involved but also accurate interpretation of high-dimensional data is so difficult and out of human capability. To alleviate these deficiencies, quantitative scientific methods in data mining domain can be applied as an effective and useful tool to construct the new numerical maps in geosciences. In this paper self-organizing map (SOM) neural network that is one of the common methods in data mining has been applied for numerical tectonic zoning of Iran. SOM is an unsupervised artificial neural network particularly adept at pattern recognition and clustering of high-dimensional data. Visualization of high-dimensional data in two-dimensional topological-preserving feature map is another specific capability of SOM that represent both homogeneity within and similarity between clusters. Although there are some similarities between SOM's numerical maps constructed here and the conventional maps but SOM method is more powerful for identification and interpretation of different zones than conventional methods. Utilizing SOM method enables us not only to evaluate the degree of homogeneity in each zone, but also to separate regions zone that experience similar geological evolutionary despite of their geographical locations. For instance Lut and Gavkhuni zones show more homogeneity than Makran and Azerbayejan zones also Kopeh-Dagh and Zagros are located at different regions, they have similar features. The results obtained here represent separation between Makran from East Iranian Ranges and Western Azerbaijan from Alborz Ranges, too. It is important to recognize that the SOM's results are based purely on the geophysical, geological and seismic features presented previously. So correspondences and differences between the SOM's zones and a given zone based on conventional method must receive careful thought.

The Dalichai Formation and its ammonite fauna is studied for the first time in the Parvar area, Central Alborz. At Parvar the Dalichai Formation, with a thickness of about 70 m, consist of an alternation of grayish silty marls, marlstones, marly limestone and limestone and is subdivided into 5 members. A rich ammonite fauna (407 specimens) have been collected from the member 4 and 5, comprising the following families: Phylloceratidae, Lytoceratidae, Oppeliidae, Haploceratidae, Sphaeroceratidae, Parkinsoniidae, Morphoceratidae and Perisphinctidae. These indicate a Late Bajocian and Bathonian age. Member five consists of greenish to reddish, nodular and flaggy limestones and is a typical condensed horizon.

In this study, in order to evaluate the geochemical characterization of Kangan Formation in well B in South Pars Gas Field, geochemical analysis (including preliminary and complementary analysis such as Rock-Eval Pyrolysis, extraction of organic matter (EOM), bitumen fractionation, Gas chromatography and Gas chromatography-Mass Spectrometry) were carried out on core samples. Geochemical results reveal that these samples have kerogen type III and II, indicating a marine organic matter with a little terrestrial input. The organic matter of these samples was derived from source rock(s), with clastic-carbonate lithology which deposited under anoxic to subanoxic conditions. In addition, the above samples exhibt poor to moderate genetic potential with kerogen maturity at the beginning of oil generation (late diagenesis to early catagsnesis). Also, based on column chromatography, the above samples are mainly composed of paraffinic-naphthenic and paraffinic hydrocarbons. A negligible amount of hydrocarbons seems to have been generated locally from Kangan Formation.

Olang Coal Mines in the Ghareh Chai watershed are located 100-130 km far from Gorgan and 20 km to the south of Ramian. In this research, the environmental impacts of these mines in this region including impacts on soil and water resources, slope instability and river bed erosion have been investigated. To evaluate the effects of mine drainage and surface pollutants, 34 water samples were collected in two different seasons, spring and summer. The samples were collected from mine drains and upstream and downstream of the junction points of such drains with streams, and subjected to analysis for chemical constituents. The results have shown that mine drainage has increased salinity and organic content of natural streams, but it has not significantly affected the concentration of heavy metals and other constituents. The most polluted samples are those located close to the dumps. This suggests that improper disposal of mine dumps, which are extensive in the area, is the main cause of soil and water pollution. Therefore, proper sealing of such dumps and optimum management of mine drainage is needed to minimize the negative impacts of coal mining. To evaluate the slope instability and land sliding associated with mining activities, first of all, the position of all land slides were located and mapped. The causes of each landslide were then identified. The analysis shows that land sliding is more common in the mining areas, and human activity together with natural causes such as geology, climate and hydrology play important roles in the occurrence of landslides.

In this article, we studied the dynamic fracture process of Bam earthquake. In two presented models stress heterogeneity on the fault plain was modeled as barrier or asperity and friction included as slip-weakening relationship. Results of models were constrained by near field ground motion recorded in Bam station. In the first model, fracture starts form a weak asperity which waves surround the neighbor barrier and break it down. In the second model, another asperity is included in southern part of the fault. Breaking barrier releases two fracture fronts traveling in two different regimes. One of them travels faster than shear waves and goes to the intersonic velocity. The other front travels with 0.74 shear wave velocity and makes the largest pulse of the record. Both models predict the slip rate successfully, but the second model is more consistent with the real data.

It is about 30 years that Helicopter electromagnetic (HEM) surveys are being used for rapid mineral and ground water exploration, environmental investigations and also geological mapping in extensive areas. Despite this, one of the most important problems in using obtained data from the surveys is accurate interpretation of the data. Otherwise, there will be no beneficial results while spending high costs. Thus the interpretation of the data is as old as the surveys. Several experts have tried to improve the interpretation of HEM data and they have achieved great successes. Almost the results of all these surveys are presented as resistivity (or conductivity)-depth sections. To reach this target, the first step is to solve the electromagnetic induction integral equation. As solving this integral is not possible using analytical methods, several numerical methods such as Laplace transformation, Hankel transformation and Jacobi-Matrix methods have been suggested for the solution of the integral, and different approaches have been presented with each method by various authorities. One of the most important solution methods is fast Hankel transformation. In this paper, it is attempted to use this method for finally obtaining resistivity-depth sections. For solving the induction equation by this method, we need the kernel function of the integral and weighting coefficients that replace the Bessel function in the integral. For this, first we use the Guptasarma-Singh method. Then results of this method are corrected and evaluated. Then, these results will be analyzed and tested with two synthetic models in addition to presenting the results of inverse modeling. Finally, by adding new parameter named α0 to induction equation, we will clearly see an improvement in the results of inverse modeling. Meanwhile, the problem of singularity that occurs at high frequencies is almost removed.

Nannofossils and foraminifera planktonic have been short range stratigraphy and spread vast geographical because of that two fossils groups can be used for subdividing biostratigraphy. According to this, and due to the lack of any correlational paleontological study, the nannofossils of Gurpi Formation have been investigated in north of Gachsaran. This formation has been formed of marl. As a result of this study and based on the obtained nannofossils and foraminifera planktonic, the studied section is Late Santonian to Late Maastrichtian in age, that corresponding to CC16-CC26 Zones (Sissingh, 1977) and Dicarinella asymetrica- Globotruncanita elevata Zone to Abathomphalus mayaroensis Zone (James & wind, 1985).

A new method is developed using modification of Anbalagan method (1992) for slide hazard zonation in coastal desert area. A region in the south of Iran is studied using the method, and the result is compared with the result of zonation using Anbalagan method. This comparison shows that the use of new method can provide better results for slide hazard zonation in coastal desert area in the middle scales.

Chah Salar granitoidic pluton is located in the N of Chah-Salar village, SW of Neishabour, in the northern margin of structural Central Iran zone. This pluton intruded in Sabzevar ophiolitic Zone and based on the field observations, petrographical and geochemical classification diagrams, its lithological composition composed of diorite, quartzdiorite, granodiorite and alkali feldspar granite. Alkali feldspar granites as a much fractionated end-members of this rock association are intruded in this pluton in the form of dikes or apophyse shapes. Granitic pegmatites and their associated quartzolites are the most differentiated end-member of this rock association. Their subvolcanic equivalents such as pyroxene-bearing andesite, andesite, trachyandesite and dacite cut this pluton in the forms of dikes or domes. The studied rocks show variety of textures including granular, myrmekitic, graphic, porphyritic, microlitic porphyry and pilotaxitic. Except alkali feldspar granites which are highly fractionated, the other lithological compositions, on the variations diagrams of major, trace and rare earth elements versus SiO2 or differentiation index show continuous compositional variations. This pluton has calc-alkaline and metaluminous nature and belongs to I-type granitoids. Also tectonic setting discrimination diagrams indicate that the Chah Salar granitoidic pluton belongs to volcanic arc granitoids (VAG) and island arc granitoids (IAG). Detailed investigations of field geology, petrography and geochemical characteristics indicate that magma-forming of this pluton is resulted from partial melting of subducted oceanic slab (metabasite) or metasomatized mantle wedge and then evolved by fractional crystallization, magma contamination or magma mixing.

The Sar-Faryab bauxite deposit is located in 250 km east of Ahvaz city in Kohgeloye and Bovair-Ahmad Province, Iran. Structurally the deposit is located in the Zagros Simply Fold Mountain Belt and was formed between the Ilam and Sarvak Formations. The bauxite horizon in this deposit consists of marly limestone, argillite, oolitic-Pisolitic, yellow, red and white bauxite. This study uses the geochemistry of immobile elements (Al, Ti, Zr and Y) to trace the precursor rock of the bauxite deposit and to calculate the mass changes that took place during weathering and bauxitization. The result indicates that Ssi, Ca, Mg, K, Na elements are depleted and elements are enriched during the weathering and bauxitization. Geochemical data show that argillaceous debris in the Sarvak limestone can be the source of the Sar-Faryab bauxite deposit.

In this paper we used orthogonal basis functions and expansion coefficients for inverse modeling of magnetic data. The basis functions chosen are normalized eigenvectors of second derivation of the objective function (Hessian matrix) calculate for an initial model. Limited number of basis vectors obtained in this way defines a new subspace in model parameters space. A new objective function is defined in term of these new parameters and minimized in subspace of original space. As in geophysical inverse problems we need to inverse matrixes that are functions data and geometry of data and model parameters. The matrix inversion in new subspace of the original space will be better conditions due to less dimensionality in the inversion. Since the most significant eigenvectors corresponding the largest eigen values in Singular Value Decomposition (SVD) of matrixes. Others eigenvectors have less influence in fitting data or lead inversion procedures to local minima. With apply subspace method inversion will be fast and stable against the noise. The efficiency of the method is tested with synthetic and real magnetic data (acquired from Moghan area, north-west of Iran). The results proved fast convergence and stability of inversion against the noise.

Sargelu Formation is deeply buried and has limited distribution in Dezful Embayment (limited to the northern part), hence, investigation of petroleum potential of this formation has attracted many petroleum geologists. In this study, hydrocarbon potential of Sargelu Formation in Northern Dezful Embayment is evaluated geochemically. For this purpose 34 drill cuttings from well numbers, 309, 310, 312 and 316 in Masjid-i-Soleiman (MIS) oilfield were selected, and geochemical analyses such as Rock-Eval VI pyrolysis and PY-GC were performed. The results reveal that the formation has "Very Good" hydrocarbon potential because of its high amounts of Total Organic Carbon (TOC). Results were plotted on Van-Krevelen as well as on HI vs. Tmax diagrams, and demonstrated mixed Kerogen Type III and IV due to low HI caused by higher thermal maturity, in well numbers 309, 310 and 312. However, the prominent Kerogen type was determined to be of mixed Kerogen type II and III. In all, the organic matter in well No. 316 has a better Kerogen type (mixed type II and III). All the Samples plotted on Smith Diagram have more than 0.1 S1/TOC ratios and capable of generating hydrocarbon. The Pr/nC17 vs. Ph/nC18 ratio demonstrates marine environment for Sargelu Formation. Pyro and thermograms reveal that normal alkanes are dominated in C15 - C20 range, while heavy normal alkanes are missing due to its high thermal maturity. In all it can be concluded that Sargelu Formation in MIS oilfield, due to its paleoenvironment as well as burial depth exclusively has a good quality of organic matter with adequate maturity at the end of oil window and hence is gas-prone.

Piles of maps from different sources with varying scales and formats and different styles and absence of a proper solution for integrating vast amount of information has resulted in a complexity for preparing mineral potential map. Using GIS not only organizes the information related to mineral exploration but also has the ability to produce and integrate information layers in different models with more precision and speed and supports spatial decision makings. In this article mineral potential map of Now Chun copper prospect has been produced for determination of drilling points. Used layers in this study include rock type, structure, alteration, mineralization indicators, anomaly zone of chargeability and apparent resistivity and metal factor, anomaly of copper and molybdenum and Cu-Mo additive indexes. After information preparation, Factor maps were weighted and integrated in the inference network. Integration use of Fuzzy logic and index overlay operators in inference network can eliminate defects in other models and provide more flexible integration of factor maps. Regarding to produce mineral potential map, mineral potential zones of porphyry copper were located in north-east parts of studied area. Eventually, the degree of correlation between mineral potential map and those operated exploration boreholes have been estimated for two different classes, 63.16 % and 64.52 %. Comparison between the high potential points indicated by our mineral potential maps with those previous drilled boreholes reveals about 26% discorrelation. It means that if such present study had been done before any drilling operation, it could have saved 200,000$ just for drilling expenditure.