Iranian Journal of Geology
Year:2009 | Volume:3 | Issue:11|Papers Count:18

Kamari – Dehno Asadolakhan area is located about 25 km SE of Hamadan, NW of Sanandaj- Sirjan zone. Regional and contact metamorphic rocks and deformed pegmatoieds are exposed in this area. Abundant syn-tectonic porphyroblasts were formed in this tectonic region. Four stages of ductile deformation were recognized by different generation of folds and foliations. Fold hinges of the second and third generation are coaxial and plunges to NNW-SSE. Micro folds of the last generation have a minor deflection to the other generations of folds and are plunging both NNE and SSW directions. Since sillimanite is the only growth in the four stage, this stage may have formed under higher temperature comparing to the previous stages. According to temperature relating to each deformation stage numerous porphyroblasts were generated. Interpretation of the time relation of the porphyroblasts and fabrics during these four deformation stages clears the metamorphic conditions in four deformation stages.

The area surroundings the Sanandaj - Dehgolan road, in terms of geological and geomorphologic structure is prone to mass movement occurrences. In the present study, considering the nature of mass movements, the logistic regression model has been used for zoning the probability of mass movement occurrences. Mass movement events were recognized using GIS and satellite image of ETM+ and Ikonos. We have applied layers of slope, aspect, elevation, geology, distance to fault, drainage density, distance to road, as independent variables in the model. After we tested the significance of each independent variable in the model and evaluated the rate of fitting of the model, finally the map on zoning the risk of mass movement occurrences in the study area has been classified in five orders as very low, low, median, high, and very high which in area are up to 34, 22, 17, 9, and 3 km2 respectively.

The NNW-SSE striking Ravand is a strike-slip fault (a segment of Qom-Zefreh fault) extended from southeast of Qom to northwest of Kashan. The Ravand fault is segmented into three parts including the N162 striking southern, the N-S striking central and the N150 trending northern segment. Structural study on this fault show that, dextral strike-slip mechanism is the most recent movement of the Ravand fault and was already as a releasing step over to right in Qom–zefreh fault path that was forming a pull-apart basin because of dextral shear tectonic in this region during convergence between Arabian plate and Iran. This is the reason why the Eocene volcanic deposits exposed in lozenge shaped area surrounded by faults in western part of the Ravand fault.

In the eastern metamorphic complex of Khoy ophiolitic melange, various granitoids have exposed. Petrographic and petrochemical studies indicate that at least two different types of granitoids have occured in this complex. First type is included obduction, peraluminous and S-type granites and has been generated in temperature ranges of 626-760oC. These granitoids are probably produced by partial melting of continental crust after closure stage of Khoy extensional sialic back arc basin and are comparable with peraluminous granites such as Himalaya. The second type is composed of fractionation, mataluminous, I-type granites and has been generated in temperature ranges of 786-884oC. These granitoids are probably coeval with generation of Khoy extensional sialic back arc basin and are comparable with Tethyan ophiolitic plagiogranites. As a result, the first type granitoids probably indicate closing time of Khoy sialic back arc basin and the second type shows the time of generation timing.

In March 9th, 2008, an earthquake with the scale of ML=5.1 occurred in Aryan-Shahr area, about 45 km north of Birjand, east Iran. More than 100 aftershocks were recorded within 8 days after the main shock. Primarily, the Sedeh Fault with N76 trend was a source of this earthquake. But the distribution of aftershock dispersals has been occurred in an ellipsoid district which is not superimposed on Sedeh Fault. The long axis of distribution ellipsoid of aftershocks (N120) is nearly perpendicular to the Sedeh Fault trend.Based on investigation of morphotectonic-neotectonic evidences, aftershock epicenter dispersal and the interpretation of aeromagnetic data reveal the presence of blind fault parallel to long axis of distribution ellipsoid of aftershocks, which has been named Gheysar blind fault.

Volcanic rocks including olivine basalt, basalt, andesite basalt, dacite, trachyandesite and their associated tuffs with the age of Eocene to Plio-Quaternary are exposed east of Qazvin. In order to investigate the kinetic of crystallization of magma, plagioclase crystals, in selected olivine basalt, basalt, andesitic volcanic rocks of Eocene to Plio-Quaternary have been selected. The rocks mainly present porphyritic, glomoroporphyritic and occasionally microlitic textures.In This research, volumetric phase proportion, residence time and nucleation rate for plagioclase crystals in 8 samples estimated by crystal size distribution (CSD) method and results for different samples compared with each other. In general, in spite of compositional and age similarity between samples of different unites, plagioclases present sharp different physical properties. Volumetric phase proportion of this mineral varies from 24.5% in basalt of Plio-Quaternary to 61.25% in basalt of Eocene. Based on the slope of lines in crystal size distribution diagrams, plagioclases have grown in different residence times. Eocene unites present 21 to 55 years and this time for Pli Quaternary unites varies from 22.8 to 30.7 years. Fractional crystallization was the main magmatic process in samples; however, variation of nucleation rate in different rocks with different ages, suggesting the different physical conditions during the crystallization. An extraordinary value for andesitic basalt of Eocene is due to presence of magmatic mingling.

In geophysical inverse problems with increasing number of data and model parameters or increasing level of data errors (noise), we have many problems about model instability and inversion of bad condition matrixes. Progressive methods can be use for achieving desire convergence and precision in mentioned systems base on real geological reality.Most geophysical inverse problems can be solved by minimizing a misfit function between observed data and theoretical estimations. In inverse problems studying model stability and independence of model parameters can be done by Error analysis and resolution matrix. Other important factors for evaluating inverse methods are rate of convergence, running time of computer codes and number of iterations. This paper had focused on Marquardt-Levenberg (ridge regression) as one of conventional and efficient geophysical inverse method against subspace inversion to invert Magnetic data. In subspace inversion, Spanning original model parameters space to some subspaces can be done in two essential manner respects to physical dimension of model parameters.The efficiency of subspace method is demonstrated by comparing quality of resolution matrixes and error analysis in Marquardt-Levenberg with subspace inversion method. Comparison results show that the subspace method has fast and stable convergence compare to conventional method.

The Asmari Formation is one of the most important rock units as oil-producing reservoirs in the Zagros basin. The type section of the Asmari Formation is located at Tang-e-Gel-e-Tursh approximately 50 km south-west flank of Kuh-e-Asmari Anticline. The Asmari Formation has informally been divided into the Lower, Middle and Upper parts in the Zagros Basin. However, the Asmari Formation at type locality consists only of the Middle and Upper parts at and the lower part is replaced by basinal shale of Pabdeh Formation. The Asmari Formation has a thickness of 631 meters in Katula stratigraphic section at northern flank of Kuh-e- Safid Anticline of Izeh area. This section is one of the most completed outcrops in the Zagros Basin.Based on stratigraphic value of identified well-known microfossils, six biozones were recognized throughout the Asmari Formation as follows: 1. Nummulites intermedius -Nummulites vascus Assemblage Zone (Wynd, 1965)2. Lepidocyclina-Operculina-Ditrupa Assemblage Zone (Wynd, 1965)3. Archaias asmaricus-Archaias hensoni Assemblage Subzone 2b (adams and bourgeois, 1967)4. Elphidum sp.14-Miogypsina Assemblage Subzone 2a (adams and bourgeois, 1967)5. Neoalveolina (Borelis) melo curdica Zone (Wynd, 1965)6. Globigerinoides spp. Acme Zone (Tahmasbi Sarvestani)Therefore, based upon the above-mentioned biozones, the Asmari Formation is assigned to the Early Oligocene-Early Miocene in katula area.As a result the stratigraphic section of Katula is one of the most completed outcrops in Zagros Basin for the Asmai Formation. Therefore, we propose Katula stratigraphic section as reference section for the Asmari Formation.

Mohsen Ebneh Ali Area is located in the southeast of Borujerd, the northwest of Sanandaj-Sirjan zone. The main Lithology of the area includes Mesozoic volcano-sedimentary rocks which metamorphosed in green schist facies. Petrography and Heavy mineral study and non-magnetite fraction’s trace elements analysis used to interpret the source of rocks.The Heavy minerals grains identified are gold, Stibnite, Sulfur, Orpiment, Malachite and Pyrite. The identified heavy metallic minerals are principally affiliated with different alterations and ore-bearing zones.Lithogeochemical exploration studies show two main results: 1- Utilization of minor and trace elements characteristics of samples let to the identification of anomalous spots and study of primary lithogeochemicak aureoles. 2- Development of zoning model for determination of blind gold deposits in the study area. According to the present study, gold anomalous zone associated with Ag, As, Sb, Zn, Cu, and Pb, is in the central part of the mapping area and intersect the trend of metavolcanic rocks.Dominant host rocks of the anomaly are intermediate and mafic metavolcanics with Chloritization, Carbonatization and Silicification and Hematitized wall rock altrations.The results of analysis show that (Au5-Ag74-Sb1471) PPM and (As1%). Calculated correlation coefficient in correlation matrix of elements shows a maximum gold positive correlation with As (+0.81), Ag (+0.73), Cu (+0.68), Pb (+0.64) and Zn (+0.63) and to less amount with Bi, W, Mo.These metallic elements, together with K, Al-enrichment are potential indicators elements for geochemical exploration in the study area, especially when combined with the primary lithogeochemical aureoles pattern. Study of primary aureoles reveals a vertical zoning.The correlation between heavy mineral studies and lithogeochemical exploration and field study show that there is a probability of gold mineralization in the study area.