GEOSCIENCES
Year:2005 | Volume:14 | Issue:55|Papers Count:16

The present study covers the area between longitudes 51°E to 52.5°E. The Central Alborz is an arcuate fold- and thrust belt towards Central Iran. By means of inversion of 181 striated fault planes and related striations the stress evolution from Eocene (rock formation) up to young Quaternary units, (alluvium) cropping out in northern part of Tehran city was studied. The good condition of outcrops in the northern part of Tehran city allowed us to conduct the majority of measurements in alluvium of Plio-Pleistocene (A-Formation) and early Quaternary (B-Formation). The obtained results in Plio-Pleistocene unit up to Holocene show three distinct stress directions. It changes from NW-, N-S- to NE-directed S1in a clockwise manner. Each of this stress state is associated with two tectonic regimes namely compressive and strike-slip.Using the cross cutting relations of individual fault planes in A and B-Formations and differentiation of events, the ages of stress changes were determined.The south flank of Central Alborz indicates a regional NW-SW-directed compression that lasted during the Eocene to Plio- Pleistocene. The NW-SE-directed stress was responsible for forming of faults and related folds with E-W orientation. This event was followed by a strike-slip that we interpret as being coeval with sedimentation of B-Formation. The stress tensor deduced on Mosha fault (Holocene in age) is compatible with focal mechanisms obtained in this region. It shows a NE-SW directed stress associated with a strike-slip regime. By differentiation of the youngest event (NE-SW-directed SI) and oldest event (NW-SE-directed S1) it remains the N-S directed S1, which could have prevailed during late Quaternary (C-Formation). Each of the three mentioned events is associated with compressive and strike -slip regime.  

Inversion of gravity data is one of the most interesting numerical tools for obtaining 3-D images of geological structure. In this study, modeling of gravity anomalies is performed by new linear modeling Method (Compact Inversion). The principle used is to minimize the volume of causative body which is equivalent to maximizing its compactness. The anomalous density distribution is obtained using an iterative technique which is numerically stable and rapidly convergent. The principle can also be adapted to include modeling of gravity anomalies by single density sources. The treatment of noise in data fits naturally into formulations of the inversion procedure. The method is illustrated by inversion of noise-free data and noisy data. The practical effectiveness of these methods is demonstrated by inversion of synthetic and real example. The real data is acquired over chromite ore in Hormozgan province of Iran. The results obtained are compared with existing outcrop and available superficial drilling.

The sequence of sedimentary rocks of after syncline (35 Km west of Semnan) be longs to Karadj, Semnan and Kond formations. Celestite occurs at the lower part of the Kond formation. The Kond formation itself is mainly made of gypsum, limestone and sandy limestone deposited in an evaporitic environment. Based on the type of fossils found in the limestones of the Kond formation, the age of this sequence is attributed to upper Eocene. The formation was formed during a slow and fluctuating subsidence in an evaporitic shallow basin. The layered, rhythmic and elongated lenticular celestite crystals are positioned parallel to the general bedding of the sequence and formed at early principal diagenetic stage. Two forms of celestite crystals are distinguished: a) long automorphic, to xenomorphic, slabs, and b) elongated lenticular gypsum pseudomorphs. The act of silicification, at late diagenetic stages, affected the celestite bearing layers more than other layers. Based on the shape and arrangement of celestite in the evaporitic sequence the genesis of major portion is believed to be digenetic; while a small portion has been probably formed synsedimentarily by saturation of strontium ions in solutions of evaporitic environment. It seems that strontium sulphate (celestite) was formed due to the abundant gypsum in shallow evaporitic environment. Furthermore; celestite could have been formed due to the migration of strontium ions from lower layers (Semnan and Karadj formations) or by transport of the ions by meteoric fluids. Relatively high strontium ion content of the Semnan and Karadj formations suggests a high probability of ion supply to form celestite from these formations.

A biostratigraphic study of calcareous nannofossils trom Kalat Formation of Kopeh-dagh basin has allowed the recognition of the calcareous biozones ofsissingh (1977) CC2S (Upper Maetrichtian) & CC26 (most Upper Maetrichtian) from Chahchaheh and Khesht village and, CC2S (Upper Maastrichian) from entrance of Kalat city.

The "environment" is a universal concept. While urban aspects and urban planning often reveal a limited and fixed idea of the concept of the "environment" in our minds, the "environment", is in fact a much wider concept than that (Shumacher, 1967). This article is to emphasize the complexity of the environment and to show how an urban development model for identification, analysis, assessment and planning can be created by applying environmental models in this wider "environmental" context, with the help of GIS and remote sensing for a part of Tehran, the Iranian capital city. The area observed is district 22 in north-western Tehran, an a region of about 10 000 hectares which is restricted by the Alborz mountain chain in the north, the Kan River in the east, the Tehran-Karaj freeway in the south and the short mountains of Karevansarasangi in the west. Like many cities in other countries, the city of Tehran is experiencing the increasing pressure of improper land use and incorrect land management policies that have exacerbated the problems by disregarding the limitations and potential of land, and its vulnerability and fragility against possible changes. During the last decade the use of GIS and Remote Sensing techniques are increasing (Benaman, 1998) being applied now for identification of natural resources and for the management of urban and environmental projects in major cities of Iran, But the practice of analyzing the development models with the use of GIS in urban development planning is a new experience.

Iran magnesite deposits are mainly discovered in eastern city of Birjand. Afzalabad, Torshak Mohammadi, and Chah khoo Magnesitedeposits were studied with respect to major, trace elements and C-O isotopes. Magnesite is found mainly within ophiolite. They form as vein and lenses. Magnesite mineralization is associated mainly with Nehbandan and Neh fault systems.Nehbandan fault is very steep and also is very deep.North Afzalabad magnesite has the highest Na- content (259-1670 ppm) and this is the result of flysch found in the footwall.South Afzalabad has the lowest Na-content (12 to 275 ppm) because there are no flysch type rocks in the area. Huntite has the highest Na-content ranging from 3046 to 3486 ppm. The lowest Sr found in South Afzalabad (2-8 ppm) and Chah Khoo (0-50101 ppm). The highest Sr content (35-211 ppm) found in Turshak Mohammadi and North-Afzalabad deposits. The highest Mn and Fe found at Chah Khoo and North Afzalabad deposits and the lowest Mn and Fe is associated within Torshak Mohammadi and south Afzalabad deposits. Huntite has the highest Mn and Fe content.C-O isotopic composition of magnesite from Torshak Mohammadi, Afzalabad and Chah Khoo were compared with magnesite deposits associated within Alpine ophiolite belt discovered in Turkey, Greece, Yugoslavia, Austria, and California. The C-O isotopic composition of Alpine ophiolite are δ18O (SMOW) =23- 27%0 , and δ13C (PDB)= -17 to -6% 0  and all of them plot in the same region, but Afzalabad, Torshak Mohammadi and Chah Khoo plot in different field. The δ18O% 0 values of magnesite deposits in Eastern Iran ranging from 31-36 (%0 SMOW) and δ13C ranging is between 1.8 - 8 (%0 PDB). The CO2 had atmospheric origin and the H2O have meteoric origin.

Numerous vertebrates footprints have been found in the Miocene Upper Red Formation sandstone and siltstone layers in the 3 km west of Mushampa village, west Zanjan province. Most of the footprints were preserved as hypichnia, include bird's webbed footprints Culcitapeda tridens and Culcitapeda isp.; tetradactyle footprint Antarctichnus isp. and digitigrad footprints Avipeda isp. A and Avipeda isp.B. Carnivora footprints are Bestiopeda isp. and Credontipes isp. ichnogenuses. It seems that sedimentary environment was a shallow-water pan of a marginal marine environment, and footprints formed on the exposed sediments.

Mass movements are one of the main sources of sediment yield and also increase rill, gully, and badlands erosion. In erosion and sediment yield modeling, in spit of special attention to gully erosion, the role and the effect of mass movement on sediment yield has not been considered. Therefore, evaluation of sediment yield in landslide prone area is much different from the estimate done.In this research relationship between sediment yield and frequency of failure planes have been investigated in central Taleghan basin. The funding can be used to estimate sediment yield in remote areas with no data.Main characteristics of 90 landslides have been investigated in the watershed. On the other hand, sediment yield of the landslide prone sub-basins have been evaluated. The results indicate a coefficient of determination of 0.68 for a bivariat regression model. The results also reveal that 68 percent of sediment yield are due to slope failure in Taleghan watersheds and 33percentare related to the other factors.    

Middle Jurassic strata are well developed at west of shahroud (SE Alborz). In the investigated area two sections at kuh-e Parikhanand kuh-e Tepal have been studied in detail. The Oalichai Formation has a maximum thickness of 235 m consisting of an alternation of bluish-grey limestones and marls, being subdivided into 8 members. The lower boundary with the siliciclastics of the underlying shemshak Formation is sharp and discontinuous, whereas the upper boundary to the light and cliff-forming carbonates of the Lar Formation is rather inconspicuous and transitional .The Oalichai Formation in both sections is fossiliferous. Summing up 1985 fossil specimens were collected, among which the ammonites with 1749 specimens clearly predominate. The fossil-content is mainly concentrated within few meters of red and nodular limestone in the upper part of the section. Based on the ammonite fauna the age of the Oalichai Formation in the investigated area ranges from Upper Bajocian to lower Oxfordian. Pleobigeographically the fauna shows close relationship to western Europe and sub-mediterranean region. This indicates a pale geographic position of the area at the northern Tethys during the Middle Jurassic. The depositional environment ranges from deeper shelve to deeper open marine.

Geochemical characteristics and petrography of the acidic volcanic rocks from the South of Danesfahan indicate that these rocks are products of different petrogenetic processes. Magmatic differentiation through fractional crystallization has played the main role in the evolution of majority of acidic rocks. These rocks include the rhyolites with the following features: 1) porphyritictexture, 2) negative anomaly of Eu, and 3) decreasing LILE and increasing REE contents with increasing silica. A few of acidic rocks from the study area show characteristics implying their generation through partial melting of the upper crustalrocks. These include the rhyolites with the following features: 1) vitrophyric or perlitic texture, 2) lack of negative anomaly of Eu, and 3) the highest LILE/REE and LREE/HREE ratios amongst the acidic volcanic rocks.

Generally, determination of suitable block size, is one of the most essential factor for optimum and economic excavation. In mining ornamental stones by diamond wire it must be such that it does not cause any problems with regard to excavation sequences, be safe and also reduce the costs. This paper presents the results of an investigation which was carried out in Laybid ornamental stone mine. The aim of this research, was to determine the optimum block size with regard to geological and geotechnical conditions and machinary used in this mine. The method has a general trend which can then be applied to any mine with similar excavation method by considering the special conditions of that mine. The optimum block size is determined by calculating operation costs such as excavation, cutting, etc. These calculations were carried out for various block sizes and various graphs plotted. In this mine the optimum block size was determined to be 6x4.5x8 meters for length, width and height of the block respectively. The increase in block dimentions and suitable block dimentions with regard to the main block is an important factor for cost reduction. This procedure will be acceptable up to a point where excavation costs decrease greatly and also no technical problems occur.

Nickel and cadmium compounds are important impurities in zinc electrolyte. In the electrolytic production of zinc, these impuritiesmust be removed from the zinc- bearing solution prior to electrolysis. At the Isfahan Zinc Smelting Factory, nickel and cadmium have been precipitated by sufficient amount of zinc powder and copper sulfate at 50-70°C. The resulting precipitatewas known as nickel and cadmium filter cake and contains 30% Cd, 22.7 Zn, 3.2 Ni and 1.95 Cu. A sample of filter cake was first identified by XRD analysis and microscopic studies. The major XRD peak was matched to Braunite (3Mn2O3 . MnSiO3) and to probable existing of Cd5Ni, Cd2SO4 (OH)2 , (Zn,Cu) SO4(OH) and synthetic CdS. Microscopic studies proved the existence of sulfate phases, native copper and metalic zinc. Nickel sulfate (NiSO4 7H2O) was also observed in the thin section.Leaching results showed that 10% of filter cake was soluble in water, in which 10, 16 and 18 percent of total nickel, zinc and cadmium were dissolved in water, respectively.Results obtained from different methods showed that nickel was present as NiS and cadmium existed in the oxide form. Finally leaching process was carried out with sulfuric acid at different conditions. The effect of temperature, acid concentration, reaction time and pulp density were investigated and the results indicated that about 93% of nickel and cadmium were extracted under the following conditions: T=60°C, t=1.5-2 hr, C=20% , Pulp density (S:L)=60 g/l.

The meta-sedimentary and granitoid rocks of the Soresat metamorphic complex (SMC) occur along the northern margin of the Sanandaj-Sirjan zone in NW Iran. Field and petrographic studies indicate that the protoliths of the meta-sediments were shale, siltstone and gray wake with carbonate, arkosics and stone and pyroclastic intercalations. Porphyroblasts of and alusite, sillimanite (fibrolite), staurolite and cordierite are common in the meta-sedimentary rocks that were rich in clay minerals.Four different deformational events are recorded in SMC (D1-D4).01 and D2 events are recorded by F1 and F2 foldsand S1 and S2 foliations, which indicate NNE-SSW regional shortening. The 01 fabric has been largely over-printed during D2 and only relics of S1 foliation survive either in S2 microlithons, or as inclusion trails within inter-tectonic porphyroblasts of andalusite and staurolite. The prominent, regional penetrative foliation (S2) generally parallels bedding planes (S0) within meta-sedimentary rocks. S2 is axial planar to an isoclinal overturned fold of regional scale that was generated by D2. No foliation was recognised for D3. Inclined D3 folds refold the overturned D2 structure. D3 resulted from NNW-SSE horizontal shortening. D4 event is recorded by normal faulting, which, together with erosion, exposed the Soresat metamorphic complex.

Karaj Formation crops out in a very large area in Central Alborz. This formation is middle Eocene in age and mainly formed of green-tuffites and marine shales. According to field observation, this formation consists of heterogeneous assemblage of tuff, tuffite, various sedimentary rocks and some type of lava.Field data on depositional environment of Karaj volcaniclastic sequence indicate that some parts of this thick sequence in study area were mainly formed in a deep to semi-deep environment. Vertical and horizontal variations of facies and sedimentary structures such as graded bedding, slumping, convolute bedding, flute cast and... indicate that turbidity currents and mass flows have an essential role in the genesis of some parts of the Karaj Formation, being responsible for transporting of shallow depth (shelf) pyroclastic products.Submarine channels which filled by massive sediments and olistolites (F facies) are associated with upward thinning and fining sequences on their tops. Main part of shales of the Karaj Formation were formed as pelagic and hemipellagic shales (G facies), in northern parts of the study area. Upward thinning and thickening sequence, and also complete or incomplete Bouma sequences (A-E facies) are abundant in Karaj Formation. Collected data shows that Karaj Formation depositional environment is submarine fan. Data related to paleocurrent directions shows a south to northward one.

Source characteristics of the 2004 Baladeh-Kojur destructive earthquake is obtained by inverting far field waveform data. The information from field investigation and aftershock activity are considered as supplementary data to constrain the source parameters. The source characteristics of main shock are explained in terms of at least three major subevents. Rupture initiated in epicentral area with the first subevent and mainly extended toward west in a unilateral manner. The major slip took place during the first 10 seconds and it is concluded that the directivity played main role for producing extensive intensity in the epicentral region. The source mechanism obtained in this study is predominantly thrust and is in agreement with the mechanism of other earthquakes as well as the orientation of tectonic forces in this region. The total seismic moment is calculated to be M0=4.1×1018 Nm and the total moment magnitude is Mw = 6.3. The source duration of largest subevent is about 7 seconds and its related rupture extension is about 20 km. The calculated maximum dislocation is about 120 cm and the estimated maximum stress drop is about 25 bar. The distribution of strong ground motion indicates two high acceleration areas in epicentral area and toward the west. This indicates that the main shock possibly has a multiple source nature or the media has amplified the ground motion in western part of the epicentral region. This fact should be clarified by more detailed field studies in future. Macroseismic evidence and recorded accelerograms in Baladeh region indicate that the ground strong motion was intense during the main shock. Although Central Alborz had been seismicly active in historical times, there was no evidence that earthquakes as severe as this one had occurred in the vicinity of Baladeh-Kojour region during at least the past 100 years. From the engineering point of view, Baladeh-Kojour earthquake provided ground-motion characteristics of a strong event in the affected area and should be considered as the controlling event for the design of structures with high safety requirements.