نشریه علوم زمین
پیاپی 59 (بهار 1385)

The oil of Asmari reservoirs in three oilfields in the southern Dezful Embayment comprising Parsi, Pazanan and Rag-e safid oilfields were investigated. Preliminary analyses consisting removal of asphaltene and fraction separation (saturate, aromatic, resin and asphaltene) were conducted on selected samples by column chromatography. Results indicate the dominance of saturate components in the studied oils of Parsi and Pazanan oilfields, while aromatic components dominate in the studied oil of Rag-e safid oilfield. Subsequently, normal alkanes and isoprenoids were evaluated by Gas Chromatography (GC), revealing a reducing environment of deposition for the source sediment. Ratio of Pri/nC17 and Phy/nC18 indicate a high thermal maturity unaffected by biodegradation processes. The ratios also indicate that the Asmari oils of the studied oilfields were generated from type II organic matter deposited in a marine environment. Evaluating C27, C28 and C29 stranes and hopanes carried out by Gas Chromatography-Mass Spectrometry (GC-MS). The most important result is that the studied oils have shown Oleanane biomarker in their hopanograms, hence proposing their source rock to be deposited in the Late Cretaceous or younger than it (Pabdeh formation). The Carbon Preference Index (CPI) of around one, high percentage of Ts and Tm hopanes and absence of moretane biomarker, all indicate the high thermal maturity of the studied oils. It can be concluded that the oilfields in south part of Dezful Embayment have similar origin, depositional environment and hence have an identical oil family.

The Mahneshan sheet area lies in Zanjan Province in the northwest of Iran. From the morphotectonic point of view, it is generally zoned in a number of parallel northwest – southeast trending mountain ranges and their intervening valley plains. From the northeast to southwest, the subzones are as follows: - The Andabad - Moshampa basin of thick sequence of Lower Oligocene detrital sediments and hummocky Neogene red-green beds of shallow and evaporating environments (subzone No.1). - The Habash - Moghanlu mountains of longitudinal imbricate subzone resulted from the stacking of many thrust sheets verging to northeast and subsequently exposed the Precambrian (only Kahar FM.) and Phanerozoic rock units (subzone No.2).- The Duzkand - Mahneshan- Yengejeh plain of relatively steppe characters diagonally placed across the sheet area (subzone No.3).- The Ebrahimabad - Inche-Almalu mountain that on the northwest side formed exclusively by Precambrian high- grade metamorphic rock-units and few outcrops of Kahar formation. (Subzone No.4). - The Dandi - Anguran plain of QPl fluvial - colluvial sediments dissected intensely by affluence (subzone No.5).The lithostratigraphic settings and petrological characteristics of rock sequences in two main upland subzones (No.2 & No.4) reflect two sedimentary rift basins and platform regimes for their initial protolith creations.The initial sediments and related volcanic rocks in subzone No. 4 have been intensely transformed by metamorphism to produce gneisses, amphibolites, green schists and marbles, whereas in subzone No. 2 slates, phyllites and semischists developed. It should be noted that the geothermal gradient and metamorphic intensity from rift basin (subzone No. 4) towards platform environment (subzone No. 2) are gradually decreased. Furthermore, ultrametamorphism had occurred and generated the anatectic S-type granitoids throughout the rift basin (subzone No. 4).Some of these anatectic granitoids (such as Moghanlu graintoid) were emplaced as powerful diapiric intrusives very later than their magmatic crystallization and produced brecciated halos instead of metamorphic aureoles around the granitoid masses. Such brecciated halos play the role of suitable channel ways for hydrothermal ore-fluid migrations and development of pervasive alterations alongside the related ore-mineralization. For example, potassic, moderate to advanced argillic alterations and their associated epithermal Sb-mineralization around the Moghanlu S-type granitoid are described in text.

Microtremor measurement, as one of the well known methods in site effect study and seismic microzonation, is a very convenient, simple, and economic tool to estimate the effect of surface geology on seismic motion. H/V (Nakamura's technique) has received great attention from all over the world with its simplicity together with quick information about dynamic characteristics of ground and structures. In this study, the Nakamura's technique has been used to estimate fundamental frequencies and amplification factors of 40 sites in the southwest of Tehran. Different techniques in Nakamura's method are applied on more than 480 time windows of microtremor measurements. The results at different sites indicate that the variation of resonance (fundamental) frequencies is fast in the SW and W-NW of the study region, whereas in the central and eastern parts this variation is slow. Essentially, the resonance frequencies differ from 1.5-2.5 Hz in eastern and central parts to 3.5-4.5 Hz in SW and W-NW. The estimated amplification factors indicate that the alluvial deposits in the SW of Tehran can amplify the magnitude of earthquakes up to 6 (+/-2) at resonance frequency.

Panj-kuh iron ore deposit is located in 50 km southeast of Damghan. volcanic and pyroclastic rocks of the Eocene with composition of andesite–trachyte are the main host of the ore deposit. Injection of quartz monzonitic intrusion into volcano–sedimentary and volcanic rocks of the Eocene in the center and south of the study area has resulted in skarnization and formation of Panj-kuh iron deposit.Pyroxene, epidote and amphibole are the main silicate minerals and magnetite (and hematite), pyrite, chalchopyrite, malachite and azurite are the ore minerals. Extensive abundances of the sodi–calsic alteration which is defined by presence of albite, scapolite, and Mg-Ca-mafic minerals (diopsid), and constricted potasic alteration with minor distribution which is defined by orthoclase and biotite, major magnetite accompanied with minor pyrite and chalchopyrit, formation of malachite and azurite within the volcanic rocks are the most important features of the area. Also, geochemical investigations show that the intrusive rock samples of Panj Kuh have high MgO, SiO2, Ni, V, Sc and lower contents of K2O and Rb/Sr. The samples plot in the chalk alkaline and alkaline in the AFM and SiO2-(Na2O+K2O) diagrams respectively. They show metalminus and oxidation characteristics. These features are indications of the metasomatic skarn mineralization which formed by metasomatic fluid. Major and trace elements comparison of the Panj-kuh intrusion with other intrusions associated with skarn mineralization of the world, indicate some features of the gold and copper bearing skarns in the Panj-kuh skarn that recommend new exploration projects for the copper and gold in the Panj-kuh district.

Pumping test data in karstic aquifers are usually analyzed using conventional methods originally developed for granular aquifers. Theis (1935) and Cooper-Jacob (1946) straight-line methods are the most common conventional methods applied to karstic aquifers. Some investigators have utilized double porosity based methods for analyzing pumping test data in karstic aquifers. However, this question might be raised that which method is the most appropriate for analyzing pumping test data in karstic aquifers. It seems that the most appropriate methods for almost all pumping test data in karstic aquifers are Theis (1935) and Cooper-Jacob (1946) methods. However, methods based on double porosity theory should be applied for some of pumping test data. In this paper, the most appropriate method for analyzing pumping test data in karstic aquifers is addressed based on a number of pumping test data obtained from different karstic area.

Devonian corals of Bahram Formation in Cheshme Shir area (South of Osbak-kuh) were studied. In the study section, more than 18 species belonging to 10 genera of Rugose corals were identified. The following genera are: Sinodisphyllum, Spinophyllum, Glossophyllum, Acantophyllum, Temnophyllum, Cystihexagonaria, Marisastrum, Hexagonaria, Ceratophyllum and Pseudozaphrentis, which suggest an Upper Givetian-Frasnian age.According to coral morphology, 2 assemblages were distinguished. The first assemblage occurs in the reef areas and is composed of colonial corals forming patch reefs. The second assemblage is composed of dissepimented corals of median size that occurs in shallow water of an open shelf.

In active tectonic regions, topographic features represent ways to quantitatively charactrize the interactions between tectonics and surface processes, providing a basis for modeling landscape evolution. This study examines the tectonic geomorphology of Northern Misho Fault (Northwest of Iran), focusing on the general topographic metrics (SL، Smf، Vf، Fmf، Fd and Eu), drainage patterns (AF and Bs), and river longitudinal profiles. The drainage pattern, topographic analysis and geomorphic properties express the tectonic influence on streams, competing to integrate the northern slope of Misho-Dagh drainage. As a result, oblique and right lateral movements of the northern Misho fault are more than uplift movements, at least in the Late Pleistocene and Holocene. This movement in the western Misho is more than that in eastern Misho. Longitudinal profiles of rivers indicate that present landscape of study area, in addition to the northern Misho fault effects, influenced by secondary faults especially in the eastern Misho, so that the morphometric indices such as Vf has been affected by this secondary faults, too. The northern slope of Misho-Dagh represents a landscape adjusting itself to the modern active tectonic setting.

Tree root, as a reinforcing agent, may improve the stability of soil slopes by two mechanisms: a decrease in the developed shear stress via distribution of applied loads within a larger area, an increase in the mobilized shear resistance via its tensile strength. The latter, in addition to mechanical properties of root, is a function of diameter, number, orientation and deflection angle of the roots with respect to the potential slip surface. Coppin & Richard analytical model was used to asses to what extend willow tree roots can improve the stability factor of a planar slip surface. The required data were provided by a series of in-situ tests in Taleghan region using a large scale field shear stress test apparatus. Tests were run in a natural deposit with and without willow root to measure cohesion and internal friction angle of soil under different root density. At the end of the tests, the diameter and angle at which the roots were deviated and cut were measured in the sheared zone. Experimental results were used in the model for different water levels, revealing that for a 45 degree planar slip surface and a root density of 5 to 26 percent the safety factor rises between 0.5 to 36 percent.

Investigations on Hutk section prove the age of Middle Frasnian to Early Famennian for this section. Three genera and eighteen species have been obtained. Index species such as P. zinaidae and I. vitabilis show the age of Middle to Late Frasnian (hassi – linguiformis Zone) for the lower part of the section. Some of the Famennian index species such as P. semicostatus, I. cornutus, I. iowaensis iowaensis and Pel. inclinatus reveal the age of Early Famennian (triangularis – Late crepida Zone).The new age ranges for some species have been determined in this paper. The earliest presence of I. iowaensis seems to be in Middle Frasnian and the range of P. alatus extends to Early Famennian. The oldest specimens of P. communis can be observed at the base of Hutk section by the age of Middle Frasnian.

This paper presents a study of focal mechanism of earthquakes and stress indicators for Iranian plateau and surrounding regions. All recorded earthquakes with magnitude of 4.5 and higher, occurred from 1964 to 2000, have been studied. The seismological data were taken from the International Seismological Centre (ISC) bulletin and Earthquake Data Report (EDR). More than 400 events of all earthquakes have been evaluated as good quality. Among them, 224 earthquakes are located in the Iranian plateau. Based on P-wave first arrival polarities, focal mechanisms, orientation of the principle stress axes (P and T), nodal planes, and their corresponding errors in cases where more than one solution may fit the data, have been determined. Reliability of the fault plane solutions has been evaluated by the values of the errors of P and T-axes orientations (less than 15), the minimum number of polarities (N>=30), and the score (S>=0.75). The average number of polarities for 224 earthquakes in Iranian plateau is 88. The fault plane solutions indicate that the strike-slip and oblique faulting movements characterize the majority of the earthquake focal mechanisms. 66 percent of the solutions correspond to strike-slip or oblique-slip with a strong strike-slip component faulting, while only about 18 percent of the solutions correspond to the mechanism of dip-slip faulting. Dip-slip movements are mostly reverse. This is markedly in effect of the Arabia-Eurasia convergence by strike-slip and reverses faulting in seismotectonics of Iran. The Frohlich triangle diagrams for Zagros, Alborz, the east of Iran and Makran zones were presented. There are two main alignments of the maximum compressional stress in each zone: NE-SW and NW-SE. The NE-SW direction is compatible with the main regional tectonic stress, whereas, the NW-SE direction seems to be associated with local tectonic movements. The focal mechanisms obtained in this study are in general agreement with those of Centroid Moment Tensor (CMT) solutions reported by Harvard. However, the epicenters given by CMT method are generally misplaced by tens of kilometers from the locations reported by ISC or EDR. As reported by Dziewonski et al. (1981), such a discrepancy is well expected because the location of epicenters in the Harvard CMT corresponds to the centroid of seismic moment release, rather than to the point of rupture nucleation.

On the basis of data from the study of structure and earthquake of Ab-e-garm – Avaj fault block, that is in the northern boundary of Central Iran zone, a dominant trend of NW – SE has been deduced. Trends of Ab-e-garm fault zone (N145) in the north and Avaj fault zone (N136) in the south are changed by hidden NE – SW faults (such as Ab-e-garm – Avaj hidden fault). This process is accompanied by the appearance of hot springs, gypsum, etc. Thus, these faults have produced shear zone and the R1 and R2 fault zones have contributed to the zone. On the basis of structural evidence and the distribution of focal instrumental data of the post – seismics, as well as instrumental Harvard data, the continuation of Boein Zahra earthquake fault to the west, with N102 direction, is the main responsible for Changooreh main earthquake, confirming the shear zone model. Remote sensing study indicates that oblique compressional stress with N – NE direction to the lithospheric plates, has caused the mobility of Ab-e-garm - Avaj shear zone faults in a convergent shear structural model. In this zone, the R1 and R2 faults have been gradually activated to the east and extended to Kuh-e-Jarou.

The Lower Cambrian Lalun Formation includes the lower Sandstone, middle Shale and upper Top Quartzite units. The contact of the Shale unit with that of the Sandstone unit is unconformable grading upward to Top Quartzite unit. Two bioherm horizons are present near the base of the shale unit. The Shale unit represents deposition in an estuary environment. The Top Quartzite of the Lalun Formation records deposition in a shoreface depositional setting. Facies and depositional environment of the Hawke Bay Quartzite of the Appalachian Mountains and the Zabriskie Quartzite of California are similar to the Top Quartzite of the Lalun Formation. The upper contact of the Hawke Bay and Zabriskie Quartzites is a regional unconformity signifying the Lower and Middle Cambrian boundary. These deposits, as well as, the Top Quartzite are correlated to similar deposits in Turkey, Oman, China, southwest Europe and south of Australia. They are unconformably overlain by Middle Cambrian rocks, too. Therefore, the unconformity of the top of the Top Quartzite unit is interregional, coinciding with the Lower and Middle Cambrian boundary.Two biostromal and biohermal thrombolite horizons present near the base of Member 1 (2 meters above the boundary) indicating the onset of Middle Cambrian transgression. This event resulted in the formation of the transgressive Mila succession (Members 1-3). Therefore, the Top Quartzite of the Lalun Formation does not belong to the Mila succession and cannot be considered as its Base Quartzite unit, as some geologists have previously suggested.The contact between the Shale and Top Quartzite units is gradational and the two units are bounded by two erosional unconformities. Therefore, the Top Quartzite cannot be considered as a separate lithostratigraphic unit.

The study of sulphate reducing bacteria effects (Desulfovibrio genus) has been focused on decreasing of some trace element concentrations in recent sediments of Khorram Abad watershed. The bacterias are a group of anaerobic microorganisms that have evolutionary varieties and frequently found in recent soils and waters. Adaptation of isolated culture of these bacteria has been performed through five successive generations. The rate of lead and selenium consumption in new generations (the fourth and fifth generations) of these bacterias, compared to the primary generations, indicates a sudden increase, as a consequence of purity of new generations (particularly fifth generation) and their culture enrichment. Thus, cultures of new generation are more suitable for decreasing of element's pollution in streambed quaternary sediments of this region and promote the biogeochemical processes. Maximum and minimum absorption rates of metallic trace elements in sediment by Desulfovibrio bacteria refer to chromium and lead respectively. Chromium is very important for bacteria growth and transition of exponential growth phase to constant phase. Lead solubility is low in aqueous systems and has relatively high frequency in stream sediments because of its poor absorption by bacteria. Maximum rate of sediment's transition elements removed by aforementioned bacteria is vanadium. This element participates frequently as an organometal in hydrocarbon compounds and the bacterial metabolic ability for its consumption is relatively high. It is possible to use microbial technique to minimize the sediment pollution related to this element with respect to high concentration of vanadium in quaternary organic shale of final sites of the northwest channels of the area. The maximum concentration of toxic elements is related to silty/clayey deposits of drainage distal zones of study area and microbial activity of mentioned bacteria is highest with regard to lowering of energy in these environments.

The study area, a part of Alborz-Azarbaijan zone, is located in about 20 km east of Heris district, NW Iran. The plutonic rocks are diorite, granodiorite, quartzdiorite and quartz-monzodiorite of the Middle-Upper Eocene, intruded into the Eocene volcanic rocks. Magmatic and hydrothermal fluids derived from the magma altered both plutonic and volcanic rocks. The texture of granitoid rocks are granular, porphyritic nicto granular and the rock - forming minerals are plagioclase, alkali feldspar, quartz, augite, hornblende, zircon and apatite. Petrographical studies show that nonequilibrium textures such as acicular apatites, skeletal hornblendes and abnormal zoning in plagioclases can be regarded as an evidence of mixing of an acid and basic magma. Field, petrological and geochemical investigations show that the granitoids are I-type, high K, calc alkaline, meta-aluminous and belonge to continental arc or post collision arc.

The western Avaj intrusive bodies, composed mainly of gabbroic rocks, have intruded into low grade regional metamorphic rocks of Razan Subzone and formed small and elongated plutons. The gabbroic rocks in the marginal part of intrusions deformed during emplacement and show mylonitic texture. The foliation in the marginal mylonitic gabbro is parallel to the foliation of host metamorphic rocks with NW-SE direction. A narrow low grade metamorphic aureole was formed around these intrusions. Petrologic relationships and the origin of the different intrusive outcrops are demonstrated by petrography and geochemical studies. Geochemical signatures on spider diagram indicate that the role of fractional crystallization on the magma evolution was more important than the contamination or partial melting. Trace element pattern on the spider diagrams suggests an extensional regime for tectonic setting of the gabbroic rocks. Seemingly, these rocks were possibly generated by partial melting of an enriched lithospheric mantle source (EM) in depth of about 50 to 60 kilometers.

The Kopet Dagh (KD) mountain belt in the northeast of Iran contains a sequence of Jurassic-Pliocene folded sedimentary rocks which unconformably covers deformed sedimentary and pyroclastic units of Triassic age and older one. In order to understand a part of tectonic history and the orientation of deforming stress fields, brittle structures were collected and analyzed by Right Dihedra methods. The results show that the KD basin was formed in a NW-SE extensional regime during the Early and Middle Jurassic. Although there is some evidence of compression along the same axis during the Late Kimmerian phase (Late Jurassic – Early Cretaceous), it seems that the Cretaceous layers were folded by a NE-SW compression during the Paleocene. Afterward, the compression stress field has re-oriented to N-S direction and generated the present day strike-slip system following the Miocene.

The major Quaternary faults in Alborz – Central Iran border zone can be classified based on their strikes into three sets: northeast, northwest and east – west. In this paper, we have used a model to evaluate their movement potential that presented by Lee et al. (1997). Their theoretical model is based on the relationship between fault geometrical characteristics and regional tectonic stress field. The results show that the north Semnan and the north Sorkheh fault zones are of the highest movement potential in the area, despite the lack of their seismic records.