GEOSCIENCES
Year:2005 | Volume:14 | Issue:56|Papers Count:16

Aqdarreh intrusi body with an area of 30 km2 is located in 34 km north of Takab, northwest of Iran. This batholith is situated in Central Iran, cutting Paleozoic rocks. Radiometric age of Aqdarreh batholith by K-Ar method is 48.38 m.a., corresponding to Eocene magmatism.Aqdarreh intrusive body consists of tonalite, granodiorite, alkali feldspar granite and monzogranite in which the main mafic mineral is biotite. Further more, there is not any enclave in these rocks.Study of the investigated samples shows that Aqdarreh intrusive rocks have two different generations. Part of the collected samples belongs to I-type granite (calc-alkaline) and others represent the A-type granite (alkaline). It seems that this process is created by the contaminaton of alkaline magma by crustal materials.Geochemistry of the rare earth elements shows that the tectonic setting of the body is compatible with Post Orogenic Granitoids (POG).

Kalut basin (northeastern Ardakan, central Iran) has been formed during Laramian orogeny in the early Paleocene. Because of its moving basement a great thickness of Tertiary sediments (more than 3800 meters in the center of the basin) were deposit. The deposits show a continental facies and only some beds of middle Eocene show a shallow marine environment. This folded basin is characterized by some open synclines with terrigenous core (in Miocene age) and close to tight anticlines with salt core (in lower Eocene age). In the central kalut basin, salt bodies missing link (intrusive salt plugs) and with same trend of b-axis of anticlines and/or with the same strike of pre-existing fault planes. Toward west and east margins of the basin, where the thickness of salt stratum decrease, they are replaced by salt domes (without any intrusion, in the normal sequences) gradually. In the westernmost of the basin any rising salt bodies has disappeared and low relief structures have remained. A remarkable feature is similarity of trends of diapiric anticlines and low relief structures and it seems that some of the diapirs occur in place of pre-existing salt high relief structures. Certainly the rise of the salt bodies here depends on primary relief of these structures.

Estimation of strong ground motion attenuation relations is one of the important problems in earthquake risk analysis and more interesting research subjects in earthquake seismology. In this study, the attenuation relations of horizontal and vertical peak acceleration in East of Iran (one of the active seismotectonic province of Iran) are investigated. Fukushima & Tanaka (1990) model and two steps analysis methods are used in this research. The constant parameters of model are determined for three different soil types using 128 records of 54 earthquakes with magnitude and acceleration values larger than 4.5 and 0.015 g respectively.

Garab manganese deposit is located at a distance of 185 km, northwest of Tehran (32 km, northeast of Taleghn town) in Central Alborz zone. The Eocene and Oligo-Miocene volcano-sedimentary rocks have a considerable extent in the study area that are restricted to a NW-SE trending belt.With respect to host rock, texture, structure and position in stratigraphic column, manganese mineralizationoccurs in three horizons in Oligo-Miocene volcano-sedimentary sequence:Stratiform manganese hosted by red lithic tuff (main horizon of Garab manganese- horizon I). Lenticular manganese hosted by tuffic limestone (Garab mine district -horizon 11). Laminated and disseminated manganese hosted by reddish-brown lithic tuff (Dehdar horizon- horizon 11). Mineralization occurs in stratiform-lenticular orebodies stretching out for about 25 km and showimg massive, banded, laminated, disseminated, coloform, botryoidal and open space filling textures. The ore paragenesis consists predominantly of psylomelane, braunite, pyrolusite, cryptomelane and hausmannite. Fluid inclusion studies reveal that homogenization temperatures range between 180 to 190°C and salinity changes from 18.6 to 23.4 %wt NaCl equivalent.Garab deposit, in comparison with different types of volcano- sedimentary manganese deposits shows broad similarities with the Cuban-type deposits such as tectonic, geological environment, host and associated rock types, geometry, textures, structure and mineralogy.Based on geometry, texture, structure, host rock, ore forming environment, geochemistry and fluid incluion, manganese mineralization in Oligo-Miocene volcano-sedimentary sequence occurs in continental rifling environment and is attributed to volcano-sedimentary activities.

Paleoichnological study of 46 footprints of vertebrates in the Chahk and region (North of Birjand) shows that they belong to Pantodonts and Dinocerata, which are two orders of extinct herbivores. The most famous genera are Coryphodonts from order Pantodonts and Uintatheres and Tithanotheres from order Dinocerata that lived from the Late Paleocene to the Eocene time.Stratigraphic and petrographic studies show that this region is mainly composed of silisiclastic and carbonate sediments as well as volcaniclastic sediments including 3 facies and 8 subfacies. Footprints are mostly observed in lime mud sediments that are deposited in shoreline condition.

In structural studies, usage of appropriate statistical methods renders practical analysis of abundant data Eigenvalue and eigenvector method is one of the approaches that provides better interpretation of data in structural studies. In addition to describing the method and citing examples from lattice preferred orientation of olivine and amphibole, a chart for comparison of folding forms and K and C values are introduced in this study.

The Qom-Zefreh fault system has almost 220 km length cutting the Urumieh-Dokhtar magmatic belt in central part of Iran. According to orientation and mechanisms, it could be divided in three segments of northwest, central and southeast. Geometry and orientation of reverse faults, and folds in the Qom-Zefreh fault system and shear kinematic indicatores including Natanz slice, reflect a strike-slip displacement to the Qom-Zefreh fault. En-echelon form of the fault segments and dextral displacemenrt esulted in a positive flower structure in two districts of south Kashan and south Ardestan. In comparison, two depressions of north Kashan depression in northwest against the south Zefreh-Gavkhoni depression in the southeast locate at the extension areas of this strike-slip fault system. Lenticular intrusive bodies including Vash granite, reflects local extension along some segments of this strike-slip fault system. The Qom-Zefreh fault is evaluated as one of the basement faults of central Iran which was reactivated by the convergent tectonics of the Neo- Tethys. Obvious displacement of most recent alluvial fans along the Qom-Zefreh fault implies high potential to seismological activity.

In this research a DSS (Decision Support System) is presented for selection of a suitable method for landslide stabilization. The goal of the system is to propose the optimal landslide stabilization method. For this purpose, the main landslide stabilization methods, their limitations, and advantages were reviewed using several references and Iran's landslide databank. Algorithms and final model were written, using a kind of DSS called ALES (Automated Land Evaluation System). The model developed in such a way that user can identify the most appropriate landslide characteristics. To verify the model, Barikan landslide characteristics were imported to the system. Surface and subsurface drainage was introduced as appropriate control alternatives for this landslide. These methods show good agreement with the results presented after detailed field investigation and analysis.

The Shemshak Formation with a thickness of 2080 meters is well-exposed in NE of Jajarm city. In this study, palynolomorphs are identified for the first time and 50 terrestrial palynomorh taxa were identified, in which 29 species of spore allocated to 21 genera and 17 species of pollen to 13 genera. On the basis of stratigraphic distribution of palynomorphs three biozones were recognized and based on the above mentioned biozones the Rhaetian -Lower Bajocian age is suggested for the Shemshak Formation in Jajarm area.

Mining sector has central role in global market. There is a close competition in international market and a high risk is involved in the mining operations. This encourages the investors and researchers to develop methods for evaluating the investment opportunities and prioritization criteria. The objective of this research is economic and strategic ranking of mineral commodities from the operating mines in Iran. 19 mineral commodities are ranked using Taxonomy Numerical Ranking methodology. In this study different indices applied for the evaluation of investment opportunities in the mining industries. Some of these factors are: the Value Added (VA) of mining industries in GDP, VA of mining exports, profitability, market size, investment potential.

In this research, effects of different parameters on elastic wave velocities were assessed for eight carbonate rock specimens and different theories applied to laboratory data. Ultrasonic measurements were made on the samples in both dry and saturated states. Pore pressure of fluid (kerosene) was kept constant at 5MPa and the range of effective pressures was from 5MPa to 60 MPa. Central wave frequency of P-wave was I MHz and that of S-wave 0.6 MHz. All the experiments were carried out in room temperature. The results show that by saturating the samples, P-wave velocities will increase but S-wave velocities show negligible changes. An increase in effective pressure causes the velocities to rise in both dry and saturated states, though the rate of P-wave velocity increase is more than that of S-wave. Results also show that wave velocities will increase by increasing the density or decreasing the porosity.We applied Gassmann and Biot theories to the laboratory data. The results showed that these theories were in agreement with the results of ultrasonic measurements. Gassmann deviation was between -3% and +1%. Biot dispersion for P- and S- wave velocities was less than 0.3 and 0.5 percent, respectively. We also concluded that wyllie's time average equation did not show a good agreement with the laboratory data.

In this paper, a new "smallest" Chimaeroid egg capsule, Chimaerotheca farsensis n.sp. and its characteristics are described.This butterfly-likeegg capsule of chimaeriod fishes consists of three parts: embryo case in central portion, Membrane and Tail.This is the first report of Triassic fishes from Iran.

Laniz structural sub-zone, located between Ahar-Maygoon faults in north and Imamzad-e-Davood fault in south, is one of the structural sub-zones in the south of Central Alborz range. In this paper, an intial model is presented on structural evolution of the Laniz sub-zone as one of the south Central Alborz range sub-zones. This model is based on geometry, kinematics, and strain analysis of the structures. The model can also be used as a reference frame to interpret structural evolution of the south Central Alborz range. Field mapping accompanied by structural interpretation of the study area shows that thrust faults with minor strike component that dip towards north and south, are the main structures that control deformation in the sub-zone. The geometry of these thrust faults is similar to the geometry of Pop-up structures in which the older rocks are exposed and well developed in all structural sub-zones of the range. Hanging wall anti forms and footwall synforms accompany all these thrust faults. These folds are asymmetric and their geometric and kinematic analysis show that they were developed by propagation of thrust faults. Therefore, they were classified as fault propagation folds. These thrust faults were disrupted and translated by almost north-south trending transverse faults with greater strike slip component. Furthermore, these faults that also caused passive rotation of the thrust-related folds are interpreted as the result of interaction between Alborz range arid Caspian Sea oceanic floor basin in Late Tertiary. This caused compressional and thrust tectonics to be substituted by transpressional tectonic regim in the south Central Alborz range. The very low values of measured strain on samples along the fault zones indicate that this tectonic regim is of the thin-skinned one.

Frasnian deposits are very widespread in Iran (Central Iran and Alborz Range) and brachiopoda (specially Rhynchonellida) are considered as their index fossils. The genera: Cyphoterorhynchus, Ripidiorhynchus, Paropamisorhynchus, Coeloterorhynchus, Lateralatirostrum and Ladogilina are Frasnian Rhynchonellid of Iran, that their geographic and stratigraphic distribution was studied, and their biozonations were based on the Brice (1977) in Afghanistan. Two genera: Ripidiorhynchus and Cyphoterorhynchus have more species as well as wide distribution. Hence they have more biostratigraphicl importance than other genera. Also the Coeloterorhynchus genus has shorter age extent (Late Frasnian) than other genera.Consequently, the Rhynchonellida have very biostratigraphical applications in Iran and even in the Word, because of their extensive geographic distribution and short age extent.

In this research, two-dimensional analysis is applied to surrounding underground excavations that behave in nonlinear elasto-plastic manner. A computer program (FEP: Finite Element Program) was developed based on finite element method. The main output of applying the FEP is the calculation of the value of stress and strain in elasto-plastic conditions. The principles of FEM in stress analysis are first described, then the principles of solid mechanics explained, and consequently the final formulas of finite element analysis are derived. Main formulas of plasticity are defined and then combined with elastic formulas to acquire the FEM elas to-plastic formulas. The details of subroutines can be found after the theoretical discussion. Finally, the ability of software was examined by execution of the FEP with theoretical and practical examples. A good agreements observed when the FEP is compared with other program (Ansys) and empirical methods. Criteria definition of rock mechanics is the main advantage of the FEP with respect to other softwares.