JOURNAL OF SCIENCE (UNIVERSITY OF TEHRAN) (JSUT)
Year:2003 | Volume:29 | Issue:1|Papers Count:10

The Gharah-Gol borate deposit, which is located about 80km southwest of Zanjan, northwestern Iran, currently is the only active boron mine in Iran. This deposit is hosted by continental sediments of the Upper Red Formation (URF) with Late Miocene age. The primary ore mineral is hydroboracite and secondary minerals are colemanite, priceite, szaibelyite and ortopinakiolite.The ore body is not stratiform or even stratabound but rather shows cross-cut relations with its clay-marly host rocks. The ore body, with a NE-SW trend, is situated in the fractured core of an anticline as numerous individual lenses of various thicknesses.Two major fault systems, with NE-SW and NW-SE directions are restricting the ore body. The first set of fault systems played important roles by creating conduits for circulation of the ore-bearing fluids and preparing required spaces for ore deposition. Downward percolation of the meteoric waters via fractures and faults and heating due to high geothermal gradient established a thermal convective flow in the area. High boron-bearing tuffs have been leached by groundwater circulations. Upon arrival of these ascending boron-bearing fluids in the open spaces of the clayey-marly facies, due to domination of the reducing conditions, mineralization occurred. During secondary alterations by descending meteoric fluids primary hydroboracite converted to colemanite and priceite.

A part of Alburz Mountains which is located between Damghan plain (in the south) and Gorgan plain (in the north) structurally is as-SE vergence thin skinned fold - thrust belt. Sequential thrusting and related folding has been the most common style of deformation since Late Triassic. Thrust faults with foreland and hinterland dipping duplex geometry show S-SE vergence and are divided in tow category 1) Cimmerides ductile thrust faults which formed during Late Triassic-early Jurassic Cimmerian collision and 2) Alpine brittle-ductile and brittle thrust faults which formed during Alpine compressional movements. Studying of minor structure in thrust sheets reveal that each thrust sheet has been formed during three stages including 1) shortening parallel to bedding, 2) folding, 3) thrusting. Direction of Maximum shortening in this region based on orientation of structures (such as fold and thrusts) has been NNW-SSE since Late Triassic due to Convergence between Iranian microplate and Turan plate during Cimmerian and Alpine orogeny.

Shah-Kuh granitic pluton of eastern Iran, 500 km2, has cut the regional metamorphic rocks of Deh-Salm Complex in southern part and in the clastic rocks of Shemshak Formation in the northern part. The aim of this paper is the study of the southern part of the contact metamorphism aureole of Shah-Kuh granitic pluton.Based on the mineralogical and textural studies, three different metamorphosed zones of sillimanite, andalusite and biotite have been identified outward from the contact. The maximum temperature of the contact metamorphism which has detected in sillimanite zone, estimated approximately 6000C at the pressure of 2 k bar.The crystal size distribution (CSD) on the N" - L and 1n N" - L graph shows that all studied cordierits have the same origin and were formed during a metamorphic event.

In this study the effect of different petrophysical parameters on the velocity of compressional waves has been studied. A coloumn of 70 m height has been selected from the Asmari formation in one of Iranian oil reservoirs. The petrophysical parameters were determined for 150 plug samples. The well logs obtained for desired depths were evaluated and corrected to obtain a correlation between the petrophysical properties and the velocities. The data from petrophysical experiments and well logs were matched.The results show a scattered linear relation between the velocity of compressional waves and porosity values, but the variation of velocity has been formulated as a function of porosity and density. The effect of depth, density, and absolute permeability has also been analyzed.

The Band-e-Golestan drainage basin with a surface area of about 320 km2 is located southwest of Mashhad. This catchment area consists of three subbasins: Mayan, Dehbar and Jaghargh. Rivers in this basin flow toward the northeast and are connecting to Kashafrud River. These rivers are single channel and consequent with the bedload sediments. In many gravel-bed rivers, the grain size changes as exponential toward downstream. Most studies on the cause of downstream fining in the rivers emphasize hydraulic sorting as the dominant fining mechanism. Grain size variations and causes for fining downward were studied at 57 sites. Compositionally, gravels in the study area consists of phyllite, slate and quartzite. Consequently, These sediments are poorly sorted, positively skewed and mainly platykurtic. In the upstream, most of the boulders are phyllites while in the downstream, slate makes up the framework of gravel. The percentage of abrasion in slate is about 25.5 while that of the phyllite is about 28 (Estimated by a Los Angles Machine). Grain size distribution shows a weakly bimodality in the upstreams and becomes strongly bimodal toward downstream. Finally, at the end reach, three modes appeared, two are gravelly and one is sandy. The main factors in downstream fining of grain size in the study area, are: a) the rapid reduction of slope and b) selective transport (Hydraulic Sorting) due to changing of hydraulic condition, controlled by hydrology of drainage basin as well as catchment slope.

In order to study the crust in Azarbaijan area, 2654 earthquakes data recorded in 8 stations of Azarbaijan network, during 3.5 years, are processed. 42 earthquakes of the recorded data occurred in this area. By making 42 profiles, including one source and two stations, P-wave travel times are calculated. Then by choosing an initial three-layer model, Depth and velocity parameters of each layer are optimized. The results of optimization are used for contour map plots of velocity and depth variations. Velocity discontinuities and sudden variation in depth, observed on the maps, are related to the faults in the area. Velocity variations with depth were 3.5-7.5km/s and depth variations of first and second interface respect to the surface were 4.5-6km and 18-22km respectively.

Eleven marine palynomorph species including nine dinoflagellata cyst species belonging eight genera and two acritarch species belonging to one genus were recognized from Shemshak Formation at Ozon Mountain. According to their stratigraphic distribution, two biozones, Nannoceratopsis spiculata Biozone and Valensiella ovulum Biozone were erected. Based on the stratigraphic range of dinoflagellata cyst species an age of Toarcian-Early Bajocian is suggested for the upper part of the formation.

Estimation of shear wave velocity (Vs) in seismic studies of hydrocarbon reservoirs is very important. In this study, Vs is estimated in one of the hydrocarbon carbonate reservoir in an oilfields at southwest of Iran. For 32 core plugs bulk density, grain density, porosity, permeability, compressional and shear wave velocities were measured. Elastic wave velocity measurement conducted in both dry and saturated samples under reservoir condition. Detailed petrographical studies carried out for all samples. Petrophysical parameters such as volume of shale and porosity were determined from corrected gamma ray log (CGR) and neutron and density logs respectively.Shear wave velocity has been estimated as a function of compressional wave velocity, obtained from sonic log, lithology, porosity, volume of shale and formation pressure.By comparison between estimated Vs, calculated by different relationships for carbonate rocks, with laboratory results, it is concluded that equations of Castagna & Greenberg (1992) and Castagna (1993) give good results.In this study, improved new equations are also presented for estimation of Vs from Vp as follow:Vs=0.5243 Vp+ 0.0451                               Linear model (R2=0.84)Vs=-0.1068 Vp2+1.5106 Vp - 2.2008           Square model (R2=0.85)In order to improve the above relationships, we verified sensitivity of these velocities to some parameters including: lithofacies, porosity type, volume of shale, depositional environments and the amount of porosity.

The study area is located in the NNE of Tehran, at Fasham area (west of Zaigun Village) in the central Alborz Mountain. Barut Formation, with a total thickness of 270 m, composed of coloured shale, very fine sandstones, siltstones and over 30 interbeded calcareous and dolomitic rocks. The age of Barut Formation is probably Precambrian. The carbonate sequence of Barut Formation consist mainly of stromatolitic rocks with stratiform, laterally link hemispheroid (LLH) and stacked hemispheroid (SH) shapes.Based on petrographic (size and fabric), elements and isotopic studies, four dolomite types were recognized. Variation in dolomite types is mainly related to early to late diagenetic processes leading to changes in composition of dolomitizing fluids. Geochemical studies also indicate that medium to coarse grain dolomites formed in shallow to deep burial setting under reducing conditions. Sea water was the major source of Mg for early diagenetic dolomite (type 1), while Mg for late diagenetic dolomites (type 2, 3, 4) were sourced by shale pressing processes. Decrease in MgO % from 37 to 84 % in montmorillonite and chlorite, support that source of Mg for dolomitization in burial setting was mainly provided by leaching of Mg from Mg - bearing clay minerals. Calculation of organic matter in carbonate samples indicates that the amount of organic matter in dolomites are three times more than limestones. As dolomitization processes increased by increasing organic matter contents, part of dolomitization in Barut Formation can be related to availability of organic matter.Palaeo temperature calculation (based on δw of -3± 1 and heaviest δ18O value of -5.05%) indicate that early diagenetic dolomite formed in seawater ranging in temperature between 42 - 50°c

Thirty samples were examined to document the nannofossil assemblage and determine the biostratigraphic zonation. Samples were taken from a borehole drilled at Sisseton (NE South Dakota). 92 species of nannofossil were determined and photographed. Biostratigraphic study of calcareous nannofossils allowed recognition of Late Early Campanian to Early Late Campanian age for the studied section.