JOURNAL OF SCIENCE (UNIVERSITY OF TEHRAN) (JSUT)
Year:2005 | Volume:30 | Issue:2|Papers Count:12

Tourmaline along with quartz is the main mineral in the quartz-tourmaline veins, which cut the granitic massif and the clastic rocks of Shemshak Formation in the northern part of the Shah-Kuh area, Eastern Iran. This mineral is also present in the greisens and some leochocratic microgranities as accessory mineral. A total of 27 point analysis of tourmalines from these rocks have been carried out by the electron microprobe. Accordingly, the tourmalines fall in the Schorl field of the Fe50 Al50-Al-Mg50 diagram. Some of the major elements in the tourmalines, including Fe, Mg, Ca, Al and B, in the northern part of the pluton, could be driven from the sedimentary rocks of Shemshak Formation.The chemical composition of the tourmalines has been compared with tourmalines associated with granite related to Sn and Sn-W hydrothermal mineralization in South Africa, Namibia and New Zeland. The FeO*/(FeO*+MgO) ratio of tourmalines from the veins reduces toward the pluton center. This indicates the proximity of the element-rich fluids, thus, the origin of these elements could be ascribed to the Shemshak Formation.According to the electron microprobe analysis Sn is an important trace element in the tourmaline of the veins. The image analysis shows that Sn is present in this mineral as disseminated or as fine inclusions of cassiterite. Compositions plotting below the Schorl- Dravite line, on the ternary cations plot of Fe50 AI50-AI-Mg50 and Al50 point to substitution of some Al by Fe+3, hence, to relatively more oxidizing conditions. These conditions induce the formation of cassiterite.

A few scattered outcrops of limestones are present south of Mashhad along the Binalood mountains, most of which are observeable in north of Aman-Abad village. Four stratigraphic sections were measured that thickness varies from 30 to 85 meters. They are mainly composed of limestone with a few horizons of siliciclastic rocks, including sandstone and conglomerate. Abundance of Orbitolina in these rocks, especially Iraqia simplex species, indicates that they are Aptian in age. Petrographic studies of 105 thin sections showed that the Cretaceous sediments in the study area consist of four carbonate and two siliciclastic lithofacies. The carbonate rocks were deposited in a shallow carbonate platform of ramp type, including open marine, shoal, lagoon and beach / tidal flat sub-environments. The siliciclastic rocks were deposited in continental, probably, fluvial depositional system. Field and laboratory studies showed that the sediments are composed of two depositional sequences Ds 1 and Ds2 which are bounded by erosional boundaries (SB 1). Each sequence begins with lithofacies which indicates the transgression of the sea and makes shallow parasequences after still standing of the sea. Sea level changes during the Lower Cretaceous in the Binalood region are similar to global changes proposed by other researchers, with differences related to local and regional geological event.

The syenogranitoid body of Almogholagh is located on the north of Asadabad. Despite of being young, it is positioned at collision contact of Zagros subduction zone. It is anomalous compositionally (high K and very high Na). On the basis of this study, it is indicated that the primary magmas were responsible for generating of this plutonic mass, are originated from a subducting oceanic crust under a continental crust at the end of the Laramid Orogeny phase, being emplaced and crystallized within the lower parts of the crust.Later on, and in the presence of F and B fluids it is remelted and enriched of alkalies, particularly in sodium under the pressure of less than 5k bars (water vapour). Since waning slowly upwards pertitic textures were formed. Finally, under the effect of a sudden tectonic event a rapid uprising movement had taken place, which losing its water content were rapidly crystallized and granophyric textures being formed, where finally emplaced at the late Pliocene. Therefore, it is suggested that compositional anomalous of some subduction related igneous bodies of the crust in Iran [e.g. in Almogholagh) were formed as a result of remelting under the presence of F, B bearing active fluids.

Surface wave amplitudes from explosion sources show less variation for a given event than body wave amplitudes, so it is natural to expect that yield estimation derived from surface waves will be more accurate than yield estimation derived from body waves. However yield estimation from surface waves is complicated by the presence of tectonic strain release, which acts like one or more earthquake sources superimposed on the explosion. Explosions on an island or near a mountain slope can exhibit anomalous surface waves similar to those, caused by tectonic strain release. One of the methods in estimating the yield of nuclear explosions is to determine a relationship between the magnitude and the yield of an explosion. The kind of magnitude employed has an important role in this regard.In this paper, vertical component of long period seismograms at SRO, Mashhad from explosions occurred in Semipalatinsk Test Site (STS, east of Kazakhstan) are considered. First, by using the relationships of IASPEI and Rezapour and Pearce (1998), we determined surface wave magnitude (MS) which is defined as the logarithm of the amplitude plus a distance. correction. Then we derived a relation for Ms versus yield for a data set which includes 15 long period seismograms recorded at SRO Mashhad station from STS nuclear explosions. Furthermore, by digitizing the vertical component of seismograms and transforming them to the frequency domain, the mean amplitude of records at frequency ranges of 0.04 - 0.06 Hz were calculated. Then, surface wave magnitudes in. the frequency domain (Msf) and their corresponding yield-magnitude relationship were obtained. By comparing correlation coefficients of these two yield-magnitude relationships, following relationship Ms = 1.079 log(Y) + 1.714, was chosen for estimating the yield of STS nuclear explosion from seismograms of SRO.

Igneous rocks, a part of a dismembered ophiolitic complex, cropping out in the south of Amlash, are mostly composed of basaltic lavas, doleritic dikes, gabbroic and pyroxenitic intrusions. Clinopyroxenes in these rocks are generally augite and diopside, which belong to calcic pyroxene category. Distribution of Si and Al in clinopyroxene composition demonstrates these minerals are high Al pyroxenes. All si cations with some Al cations enter into tetrahedral sites and the rest of Al occupies the octahedral sites. The distributions of Al at tetra-and octahedral sites may suggest that the clinopyroxenes crystallized at low pressure in a water bearing magma. The content of Fe+ 3 in the pyroxene composition is the direct result of higher 02 fugacity in magma chamber. The temperature of magma crystallization is evaluated from clinopyroxene composition between 900-1100°C.

Dezful Embayment constitutes a part of Zagros Basin and is one of the most prolific oil regions of the world. In this basin, continues sedimentation during geological past was interrupted by short periods of hiatus. Formations assigned to Oligocene and younger strata are Asmari, Gachsaran, Razak, Mishan, Aghajari and Bakhtiari. These formations constitute a pile of huge sediments with varied lithology and thickness. These features and their distribution patterns make them remarkably distinct from the older underlying sediments and have had considerable impact on petroleum system which is directly linked to the assessment of petroleum source rocks.In this study, drill hole data from 13 wells were used for burial history reconstruction and thermal modeling considering the effect of Oligocene and younger sediments on Kazhdumi source rock (Albian). Their impact on generation and migration of hydrocarbon to different oil fields haven been studied. The overlying sediments have played an important role on accumulation of hydrocarbon in candidate reservoirs and their entrapment through cap rocks and overburden assisted by concurrent trap formation.Therefore, in thermal mode ling, the above piles of sediments including effective source rocks and non-source sediments have to given particular attention and studied in detail.

The Biostratigraphical significance and geographical distribution of nine genera of Late Devonian (Famennian) Rhynchonellid in the Central Iran and Alborz such as: Eoparaphorhynchus, Pampoecilorhynchus, Stanaulacorhynchus, Centrorhynchus, Leptocaryorhynchus, Gastrodetoechia, Megalopterorhynchus, Araratella and Paurogastroderhynchus were studied. Three species: Eoparaphorhynchus maclareni, Pampoecilorhynchus arianus and Stenaulacorhynchus cheshmehshirensis are index brachiopoda of Early Famennian. Also Leptocaryorhynchus jamensis is introduced as a index species of Middle Famennian in the Central Iran and Alborz. The species such as: Centrorhynchus turanica; Megalopterorhynchus chanakchiensis, Araratella dichotomians dichotomians, Araratella dichotomians assimulata, Paurogastroderhynchus nalivkini, Paurogastroderhynchus bikniensis are index fossils of Late Famennian.Consequently, these brachiopods are very useful index fossils for precise biozonation Iranian Famennian sediments because they have wide geographical distribution and are short ranged.

The Aghdarband .is the only pre-Jurassic basement of the Kopet-Dagh basin exposed in NE Iran. The ophiolithic and igneous rocks of the Kopet-Dagh are exposed in the southwestern part of the study area. This complex divided to three rock units. First unit is ophiolithe melange that contains metaharzburgite, serpentinite and metagabro that are metamorphosed and alterated. Second unit is acid tuffs that forms in the different location at the edge of continental margin (magmatic arc). Third unit is a flysch type metamorphosed sediments that contains sequence of thin bedded shale and sandstone. These rock units are affected by three stage of faulting. First fault series are the thrust faults with northeast dipping. These faults are covered by the Kashafrud Formation (Lower Jurassic). Therefore, they were active during the pre-Jurassic time. In the other words, the subduction in the southern edge of Turan plate produced accretionary prism in trench and these faults were activated during this period. The end of subduction and collision of Iran and Turan plates in latest Triassic time and during Cimmerian Orogeny caused that this complex overriding on the Iran plate margin. Then, erosion of suture complex, including ophiolithic rocks, resulted the deposition of mollase detritic sediments at the base of Kashafrud Formation. Second stage of faulting is related to Paleogene activity where the Kopet-Dagh basin closed. These faults are also dipping toward northeast and displaced all of the sedimentary rock units of the Kopet-Dagh basin. This activity is related to Alpine Orogeny that contemporary closed oceanic basin of Neotethys in the Zagros basin as well as closure of epicontinental sea in the Kopet-Dagh region in the north of Alborz and south of Turan plate. Latest important tectonic activity took place about 5 million years ago after collision of Indian and Asian plates. This collision caused oblique compression and activation of oblique-slip or strike-slip faulting in the study area that is still active today. As a result of these activity, a thin-skinned fold-thrust belt is formed that can be seen in the Aghdarband area.

Measuring over 453 faults with slickenside lineation on 28 Karaj Formation localities in southern part of central Alborz, different methods including: conjugate faults analysis, R% method, fluctuation histogram of and right dihedra model were tested comparatively .On the basis of these methods, the arithmetic mean of the angle of internal friction determined to be 35.75 degrees in the whole study area. In different localities low internal angle coincides with high fracture density, low topographic relief and vice versa. Interception of misfitangle curve with ordinate axis shows astonishingly the same magnitude as the mean angle of rock-mass internal friction

In this study, based on the results obtained from laboratory measurements of compressional and shear wave velocities on 5 sandstone samples from Gadvan formation and 5 limestone samples from Sarvak formation under different confining pressures in both dry and water-saturated states, the effect of both pressure and saturation on velocities have been investigated. The measurements have been performed in Technology Research Center (TRC) of Japan National Oil Corporation. Gassmann's theory is applied to the data to predict the saturated velocities from dry ones and a good agreement was found. The data also demonstrates simple relationships between compressional and shear wave velocities for both sandstone and limestone samples separately. A linear relationship for sandstones and a nonlinear one for limestones.

In this study by analyzing laboratory data in gas-filled rocks, it is shown that the Poisson's ratio (PR) increases with increasing differential pressure. Also in liquid-saturated rocks the relationship is opposite; PR decreases with increasing differential pressure. Thus as sediments pass through the transition zone from load bearing to a suspension, the Poisson's ratio is expected to rise almost exponentially. Therefore, the none-linear portions of these curves at low differential pressure are the most relevant to pore pressure at deeper depths. This result will have a significant impact for deepwater sediments hazards, where pre-stack inversion of P-wave seismic data for Poisson's ratio and diagnostic charts is used as a pressure indicator.

Microbial facies of thrombolite and stromatolite were developed and reached to their maximum diversity after each world wide mass extinctions (biotic recovery time). In study, the Permo- Triassic successions were investigated in Kuhe- Dena and Kuhe-Surmeh areas, in order to obtain the microbial facies development at the P/T boundary in the Zagros Basin. The obtained data indicate different microbial communities in the Lower Kangan strata, where the mass-extinction has happened in the Zagros Basin, consisting of KuheDena and Kuhe-Surmeh successions. . The microbial facies is marked by co-existed organisms such as blue-green algae and small marine metazoans in both studied areas with the same conditions. The thrombolite facies is characterized by clotted fabric or mesoclot microscopic texture in which has been produced by the biogenic interaction during the biotic recovery time, indicating the mass extinction effects at the P/T boundary in the Zagros sedimentary Basin. However, it should be mentioned that the obtained evidence such as microbial facies suggest somehow different mass extinction effects in two the studied areas. On the other hand, the mass extinction phenomena was compared with the Alborz Mountain Ranges, Arabian pennensula, North America and Western Europe at the P/T boundary. This comparison indicates the same microbial facies development after extinction, or biotic recovery time.