GEOSCIENCES
Year:2006 | Volume:16 | Issue:61|Papers Count:18

Mafic rocks in NE of Hashtjin area are composed of basalts, spillite, olivine basalts, and esitic basalts, andesites, dacites, pyroclastic rocks and numerous doleritic dikes cutting all these rock units. In this area, basalts have calc-alkaline and within plate affinity. These basalts have high content of LIL, LREE and HFS elements. Titano-magnetite grains in mafic rocks are divided into Ti-rich varieties and less Ti-rich types (rich in Fe+3). Plagioclases show normal zoning and their phenocrysts have high An content compared to the plagioclase microlites. Salite composition and the high content of Al, Fe and Ti are the main characteristics of Pyroxenes. The enrichment of mafic rocks in incompatible elements, calc-alkaline and within plate nature as well as high Al content of basalts, enrichment of pyroxenes in Al, Ti and Fe, could be all an indication to suppose the implication of a continental arc for the genesis of these rocks.

Ahwaz anticline in the front of Zagros folding belt has created one of the giant oil fields of Iran with a production rate of 10 times more than the average world production rate. Due to the importance of fracture density and direction in the carbonate reservoirs, a research project with the support of National Iranian South Oil Company (NISOC) was fulfilled in 2 years. The main objective of this project was the comprehensive structural study and its final goal was application of all available data for comparison of fracture density and direction patterns in surface and subsurface horizons. For certainty, various methods were applied that most of them were initiative. One of the basic methods was axis transmission technique and in addition subsurface data of SVSL seismic profiles and FMS/FMI logs data were compared. Final results of this comparison lead surface and subsurface fractures in Ahwaz anticline have 90% agreement in direction and 75% in density.

The Gole Gohar iron deposit is located at about 55 km southwest of Sirjan and in the eastern edge of the Sanandaj- Sirjan structural zone of Iran. The host rocks of the ore deposit include metamorphosed sedimentary±volcanic rocks of the green schist facies, probably of Upper Proterozoic-Lower Paleozoic age. The most important host rock units include shale, sandstone, gabbroic-basaltic and diabasic sills, diamictite and cherty carbonatic sequences that have been changed to thick carbonate successions in the upper units. The structure of iron ore comprises macro, meso and microbanding of magnetite associated with shale, sandstone and cherty carbonates. The presence of diamictites and phenoclasts in magnetite banding and host rocks indicates an iron ore association similar to the Rapitan banded iron ore. Magnetite banding, granular, banded and massive textures all represent deposition of iron as hydromagnetite. The presence of organic matter (graphite) and microlayers of pyrite indicates variation due to reducing-oxidizing conditions controlled by oxygen fugacity at the time of formation of the iron ore. The sills of basic rocks in the region are of tholeiitic basalt characteristics that represent the process of inactive oceanic rifts at the time of ore formation. The presence of diamictites and dropstones represents glacio-marine deposition associated with vo1canic-exhalative activity. The recharge of seawater into rifting basin reacts with basic intrusives, old metamorphic iron bearing rocks and old banded iron ores, causes leaching and discharging of iron and silica, producing exhalative hydrothermal fluids. The up flow discharge of hydrothermal solutions into the seawater and sedimentary basin, followed by reaction with cold glacial water, causes hydromagnetite deposition within sediments and diamictites. The presence of massive magnetite texture, abundant tourmaline and low content of manganese indicates proximal ore mineralization in the central part of the volcanic-sedimentary activities formed at about 100-250°C.

This paper evaluates the effect of lime on mechanical behavior of improved soil. The soil tested is characterized by liquid limit of 49, plastic limit of 17 and plasticity index of 33. Atterberg limits, unconfined compressive and California Bearing Ratios (CBR) have been performed in the soil sample.In this study, 27 specimens with 3, 6 and 9 percent quick lime and curing period of 28, 56 and 90 days were prepared. The specimens were placed in curing room temperature with 30°C and 60 percent humidity. Compressive tests were performed on 10x10x10 cm samples.Three specimens with 3, 6, 9 percent quick lime was compacted under 10, 25 and 56 blows in five layers. The CBR tests were performed on specimen with curing period of 28, 56 and 90 days. The amount of swelling, water content and dry density were measured during different curing periods. The comparison of CBR and compression test results indicates that 6 percent of quick lime and 56 blows for different curing period yield the best result.

Mishan Formation (Middle Miocene) is the middle part of Fars Group. To determine its facies, sedimentary environments and sequence stratigraphy, this formation has been studied in three sections in the west of Fars and one section in the east of Boushehr.Mishan Formation consists of carbonate and siliciclastic facies deposited in a Carbonate Rimmed Shelf. Two sequences with both type 1 and type 2 sequence boundaries were recognized with in the deposits that are in accordance with a part of Tejas mega sequence (TB2). The age of this formation is referred to the second epoch of Middle Miocene (Serravallian).

In this research durability of rocks used in rubble mound breakwaters has been studied. As a part of this research, twelve casestudies have been conducted on twelve breakwaters located on the northern coast of Persian Gulf in Bushehr Province (between Naay Band estuary in Assaluyeh Port to Bushehr Port). Moreover, to conduct extensive site investigations, some samples were collected from different cross-sections of breakwaters. In each case, standard quality-control tests were carried out onsamples and test results compared with different authentic standards. Furthermore, thin sections of each sample were prepared and classified by petrographical microscope. In addition, actual and natural properties of the samples were examined with respect to environmental conditions. Type 1 and 2 sequence boundary, Tejas mega sequence, TB2, Serravallian.

Over 300 small and large dikes are exposed in Moradloo district, covering an area of about 140 km2 in the north of Meshkin Shahr (NW of Iran). They dominantly oriented in NNE-SSW strike and intruded into the Lower Eocene volcanic breccias. Previoustudies showed that the rocks were Pyroxene and esite and tephrite, regardless of geochemistry and geodynamics. Our petrographic studies indicate that there are at least 6 different petrological groups and magma mixing and contamination have played role in their formation. Geochemical diagrams not only emphasize the fractional crystallization as a principal process of magma evolution but also indicate their potassic and shoshonitic characteristics and generation by the low degree partial melting of LlLE enriched source or metasomatized mantle materials. Finally discrimination diagrams show continental, post-collisional and islandarc settings for their emplacement. Analyzing all data obtained shows that the petrogenesis and geodynamics of the dikes are accompanied with complex model in which the partial melting of metasomatized mantle wedge, the melting of ancient subducted oceanic crust, the interpenetrating of tectonic regime and finally the fractionation and evolution of parent magma in chambers or conduits have had significant roles.

Microtremors were recorded on 38 locations within the Kerman city urban area in order to develop a basis for preliminary seis-mic microzonation studies. A site on exposed bedrocks, east of the city, was also measured to evaluate the spectral characteristics of sources of micro tremors. All recordings were done using portable 3-component digital seismograph with 96dB dynamic range, capable of recording microseisms induced by natural and artificial sources, and high-gain short-period (1-sec) seismometers.Measurement was carried out during night-time to ensure quality recoding and reduced unwanted environmental noises.Extensive numerical processing and analysis were performed to obtain reliable power density spectra. Transfer function of the alluvial plain at measurement points was estimated by reducing the effect of the sources of tremors from calculated spectra. Nakamura technique was applied to eliminate the effect of ambient seismic sources. Results are presented in terms of a zonation map of dominant periods for the alluvial basin.The spatial distribution of dominant periods indicates a complex underground structure beneath the city. On average, the dominant periods increase from east to west and from north to south. The results are constrained by the location of few late cretaceous outcrops, east of the city. Further detailed subsurface geotechnical and geophysical investigations are required to draw a light on the geological structures beneath the city.

Diversification of trace fossils is due to the animal activity in the sedimentary environments. In addition to the variety of the behavior of animals, the mode of preservation of trace fossils leads to diversification of ichnofossils. Trichophycus pedum ichnospecies which is an index trace fossil of basal Lower Cambrian in Global Stratotype Section (GSS), has been recognized for the first time from the uppermost lower shale member of Soltanieh Formation and has been systematically studied. These studies suggest that the type of preservation of Trichophycus pedum led to polymorphism of this taxon, which in turn arises from the ethologically controlling factors and physical structures of sedimentary environments. Polymorphism of these ichnofossils leads to the introduction of the new sty le of preservation and sedimentary environments.

The study area with coordination of 54° 30¢ to 54° 39> E and 35° 18> to 35° 21> N is located in Moalleman area, in the south west of Torud Quadrangle. In the structural-sedimentary zoning, this area belongs to depression parts. In the north part of the areae, equivalent of the Karaj Formation crops out from Sosanvar village to the south of Gandi kaolinite deposit. This formation is composed litho logically of shale, mar1, sandstone, limestone, dolostone, radiolarite, tuffite, zeolite, and bentonite with the age of Lutetian (Middle Eocene). This paper has been focused on the types, composition, and environment of bentonite and zeolite layers of So sanvar bentonite and Gandi zeolite formation.Accordingto these investigations the bentonites and zeolites have been formed from acidic volcanic glass (ryolitic and dacitic) andtheir magmatic series is alkaline.Conversion of glass to bentonite and zeolite has occurred under diagenetic conditions in shallow sea water (e.g. lagoon). In diageneticconditions, the bentonites have absorbed magnesium and calcium and zeolites absorbed sodium and potassium. The clay form of this Wyoming-type bentonite is smectite (bedellite) and zeolites are Na-clinoptilolite type.

Porosity and permeability are two important characteristics of a hydrocarbon reservoir. The core measurements are usually used for these two parameter determination. This method is not only very expensive but also coring in many wells is not performable.Another method for this target is using of empirical equations. Any of these methods are associated with many problems; In addition, statistical methods will have some problems due to input data obtained from well logs. Artificial neural network is a new method, recently used in oil industry for prediction of petrophysical properties.This study is performed on Asmari Formation in Gachsaran oil field located in south of Iran. For porosity estimation two nets are used. One of these nets has 3 input parameters (density, sonic and neutron logs) and another has 10 input parameters (neutron, gamma, density, sonic, ILD, ILS, water saturation and spatial coordinate). Correlation coefficient between these nets predicted porosities and core porosities for generalization were 0.914 and 0.938 respectively and from multiple linear regression equation a 0.658 correlation coefficient is obtained. For permeability prediction two networks; one have six input parameters(density, sonic, gamma, ILD, ILS and porosity that obtained from porosity net with ten input parameters) and another with eleven input parameters (neutron, gamma, density, sonic, ILD, ILS, water saturation, spatial coordinate and porosity from porosity net with ten input parameters) and multiple linear regression equation are 0.851, 0.858 and 0.617 correlation coefficients are obtained respectively.

Chabahar Bay is located along the coast of the Oman sea in Sistan province in southeast of Iran. This area is a part of coastal Makranzone (one of the geological zones of Iran) that had undergone sea level changes along the Late Quaternary. Multiple sedimentary sequences and several pale shorelines were formed due to these processes. In this investigation, 21 pale shorelines were recognized by using GIS analysis. In the borehole at the north of Chabahar Bay, 14 layers were discovered that could be related to Late Quaternary sedimentary sequences and correlated to glacial and interglacial periods. All layers of bore hole were analyzed for grain size, sedimentary structures and fossil contents. Four radiocarbon measurements have been made on the lowest and uppermost marine layers of bore hole and on C7 and C21 of paleoshorelines. The lowest layer of bore hole has 17,600 14C yr B.P, related to Cataglacial or Flanderian transgression, outcropped at 15 m height and 5,300 m distance to present shoreline.Sedimentary sequences have shown 4 transgressions and retrogressions occurred from Cataglacial to the present. On the other hand, from 4,690±40 yr RP, 20 pale shorelines have been formed, which the duration of each may be about 230 years.

Bon-Dono Gneisses are exposed in the core of Tutak anticline, 200 km NE of Shiraz. Tutak metamorphic complex or the Host rock of the segneisses is part of Sanandaj-Sirjan Metamorphic Belt Field. Studies have shown that: (l) the age of protoplast of Tutak complex is Upper to Lower Paleozoic. It is comprised of various micaschists, amphibolites, marbles and green schist. They are metamorphosed in a pre-Upper Jurassic metamorphic event. (2) Tutak complex had been invaded later by a granitic body.Previous regional metamorphic rocks had been subjected to a contact metamorphism resulted from this intrusive magma. (3) This granitic body had been subjected to mylonitization in a shear zone and converted to the so-called Bon-Dono Gneiss. Field, petrographic and geochemical studies all indicate magmatic nature of original protolith of so- called Bon-Dono gneisses.

The N-S strike-slip Mangharak fault zone is located in Zagros simply folded belt, and continuous from about Shiraz to south of Dehram for about 140 km. Various large salt plugs such as Jahani, Firuzabad, Gach in the middle part of Mangharak fault zone ,and small salt plug in Kaylag thrust pierce the cover layers. Existence of salt plugs in this area indicates the presence of viscous basal decollement layers at depth, which may cause variation in structural style above and below the decollement. Spatial distribution of decollement layers are analyzed through experimental analogue modeling method.As a result when cohesion coefficient between basement rocks and sedimentary sequence is high, tapper angle of the thrust and fold belt is high and width of deformation is narrow. Existence of Hormoz salt Formation has decreased the cohesion coefficient between basement and cover sequence. Consequently, in the studied area the tapper angle of deformed belt is variable and closely related to the spatial distribution of the decollement layers. In the west of Mangharak fault zone, cohesion coefficient and tapper angle are high, width of deformed zone is low, however in the east of Mangharak fault zone, cohesion coefficient and tapper angle are low, and width of deformed zone is high.

Palynological and foraminiferal contents of 30 samples taken systematically from Gurpi Formation at its type section were studiedin order to determine water-level fluctuations and the general trend of water-level during the depositional course of the formation. Statistical studies on foraminiferal contents of the samples show that the planktonic to benthonic ratio (P/B) and diversity decrease while benthonic foraminifera with larger size and epicontinental sea fauna (ESF) and shallow water fauna (SWF) increase in general towards the upper parts of the formation.On the other hand dinoflagellate cyst abundance and diversity show an increasing trend which looks like a contradiction at the first glance. To describe this apparent controversy and determine the water level trend, changes in composition of palynomorphs and the organic matter preservation state (lability factor) was studied. Statistical studies show that in the lower parts of the section the lability is low and the ratio of structure-less organic matter (SOM) to marine palynomorph is high. This indicates a low state of preservation of organic matter for the lower portion. In the upper parts lability is high while the ratio of SOM to marine palynomorph is low which indicate a better state of preservation for the upper parts.Statistical studies on the Gonyaulacoid dinocysts which are eurytopic forms and indices for open marine, inner neritic and outer neritic environments confirm the results gained from the foraminiferal studies. Combining all these data and comparing them with the well-known Tyson palynofacies analysis diagrams confirm a relatively deep basinal condition for the lower part and a relatively shallower and proximal shelf environmental condition for the upper part of the Gurpi Formation.

The Qeshm earthquake in 27 November 2005 with magnitude ML=5.6; mb=6.2 occurred in Qeshm Island in the Persian Gulf and the main shock recorded in 11 strong motion acceleration building house research center (BHRC).In the study, the strong motion records are used to obtain an estimate of source parameters, high frequency attenuation and spectral decay parameter for 6 stations from 11 stations that is good S/N rate.The source parameters are obtained by fitting the data by a dislocation source model combined with an exponential model for the attenuation. The source parameter estimated is as follow:M0=1.13*1025 ±5*1024 dyn-cm, r=6.3±1.17 Km, Du=26±1.4 cm Ds=21±1.2 bar, Td = 4.3 secAnd estimated moment magnitude (Mw= 5.95±0.17) agree well with values obtained previously from Harvard University by CMT method. -1rif The high frequency attenuation obtained using from amplitude spectral method that can be written as A (f,r) = G(r).e -prf/ab that here G(r) is geometrical spreading.Estimates of path averaged crustal shear wave quality factors give results in the range between 60 - 367, and mean of spectral decay parameters for two horizontal components in the ranges between 0.08 - 0.12 sec.

The immense amount of geotechnical data, stored as paper files, is normally hard to handle. In recent years the electronic storage of these data has become more popular. As the storage of geotechnical data in a national level is not feasible in a single database, a decentralized system of electronically handling of geotechnical data is designed for Iran. In this system, the data is stored by different organizations and companies and a virtual center is responsible for leading the users to the proper data. In this respect, first a proper geotechnical data dictionary were defined and then a data model was designed for these data. Although the design and construction of a virtual data centre is more complicated but it can search large amount of data and give much better results in a shorter time. The Geotechnical Databank of Iran is under construction in the National Geosciences Database of Iran.

Many statistical tools are useful in developing qualitative insights into a wide variety of natural phenomena; many others can be used to develop quantitative answers to specific questions.Unfortunately most classical statistical methods make no use of the spatial information in the earth science data. A large number of useful or potentially useful multivariate techniques are available, e.g., kriging, moving average, factor analysis, cluster analysis, and fourrier filtering as well as an increasingly large number of them are being applied in geologic and geochemica1 investigations. Yakla is a typical and important oil and gas region in north Tarim basin in China. Therefore, a lot of exploration work has been already carried out in this area. Samples collected from the area were analyzed for their hydrocarbon mass tractions and multivariate techniques combined with other data helped the authors to identify the hydrocarbon anomaly in Yakela.