Geopersia
Volume:3 Issue: 2, Summer- Autumn 2013

The Chadegan metamorphic complex is a WNW-ESE- trending antiformal structure located in Sanandaj-Sirjan structural zone, Iran. The inner core of the structure is made of orthogneiss, containing eclogitic lenses. Schists and marbles lie structurally above the orthogneiss and crop out in the external limbs of the antiformal dome. Two main deformational episodes have been documented in the schists and marbles. The first episode (D1 phase) produced S1 foliation, whereas the second episode (D2 phase) produced a penetrative S2 axial plane foliation, F2 folds, and a mylonitic fabric. Relicts of a high-pressure metamorphic mineral assemblage (M1) (phengite+ garnet + sodic-calcic amphibole) have been documented along S1 foliation. A later amphibolite-facies metamorphism (M2) occurred during D2 deformation phase. P-T estimates for M1 stage give an average pressure of 1.6 GPa and an average temperature of 550 °C, whereas M2 stage has been constrained at P = 0.34 – 0.48 GPa and T = 508 - 575 °C. 1 deformation phase and the associated highpressure metamorphic assemblage (M1 stage), documented in the Chadegan complex, were formed during the subduction stage, while the D2 deformation phase and M2 metamorphic blastesis were recorded during the exhumation stage; probably they occurred before the end of Cretaceous.

Tourmaline can be found as an accessory mineral in a variety of rocks including leucogranite, pegmatite, quartz veins, and metamorphic country rocks in Hajiabad-Dehgah area in SE of Boroujerd city. Tourmaline in pegmatites is coarse-grained, subhedral to euhedral, and displays strong to moderate pleochroic blue rimmed by olive green. In contrast, tourmalines from leucogranite, quartz-veins, and hornfels schist are very fine- to medium-grained, mainly subhedral to euhedral and in some cases zoned. They are strongly pleochroic with generally bluish green to brownish olive colors. The replacement of some feldspar grains by tourmaline forming skeletal texture is also common in leucogranite. The tourmaline in pegmatite is Fe-rich schorl (Fe/Fe + Mg = 0. –0.95), whereas those in leucogranite, quartz veins and hornfels schist are of schorl-dravite composition (Fe/(Fe +Mg) = 0.31–0.61). Tourmalines in all these rock types are aluminous, alkali-rich, with Na being the dominant alkali element present, and they have small amounts of X-site vacancy. However, the distinct dissimilarity is the Zn contents of pegmatite schorl tourmaline (on average 0.02 apfu), which are noticeably lower than those of tourmalines of schorl-dravite composition (on average 0.13 apfu). The dominant variability in composition of the studied tourmalines seems to be controlled mainly by the alkali-deficient AlOMg-1(OH)-1 and proton-deficient □AlNa-1Mg-1 exchange substitutions. Tourmaline grains from pegmatite have the chemical features of tourmalines from Li-poor granitoids and associated pegmatites and aplites, whereas those from leucogranite, quartz-veins and hornfels schist possess the chemical characteristics of tourmalines from Ca-poor metapelites, metapsammites, and quartz-tourmaline rocks.

Salt crystallization is one of the most important weathering agents and may limit the durability of building stones. Salt crystallization induces stresses inside the pores of stones. Consequently, stone durability is closely related to its physical properties and strength. The purpose of this study was to propose a statistical model for estimating stone durability against salt crystallization considering both the physical properties and strength of the stones -utilizing multiple regression. For this purpose, 14 samples of building stones were selected and their mineralogical characteristic, physical properties, and strength (density, porosity, water absorption, uniaxial compressive strength, and Brazilian tensile strength) were determined. Then, the salt crystallization test at a sodium sulfate solution of up to 20 cycles was carried out, and the Dry Weight Loss (DWL) of samples was measured. The durability of each sample was assessed by the percentage of weight loss after the salt crystallization test. The relationships between stone durability and the physical properties and strength of the stones- using simple and multiple regression analyses- were investigated. Moreover, statistical models for estimating stone durability were proposed. These models show that stone durability can be estimated accurately by considering both the physical properties and strength characteristics.

Generally, alluvial basins of arid and semiarid zones are the places with excessive groundwater withdrawal, and also they have a high potential for land subsidence. Excessive groundwater withdrawals have caused severe land subsidence in Tehran, Iran. At present, the maximum land subsidence rate is 36 cm/year, covering an area of nearly 530 km2. In the 2000s, as a result of economic and population growth, the area of groundwater withdrawals expanded to both the west and the east. Over the past 28 years, groundwater level has decreased 11.65 m. As a result, the impacts of land subsidence, such as major drop in groundwater level, damage and tilting of buildings and civil structures, and rupture of well casings, have increased in the southwest of Tehran. In accordance with the field and laboratory data, we have constructed a new conceptual model for alluvial basin recognition of the study area. This model describes various hydro-geological units according to their physical properties. Based on this model, a multi-layered aquifer system in southwest plain of Tehran includes three aquifer units and three aquitard units.

This paper presents the criteria and applied methods in the screening of potential sites for the wastewater treatment plant of the Falavarjan district, northwest of Esfahan province. For this the nine parameters that were selected as main criteria, 7 parameters were considered to define the buffer zones in the natural and artificial terrains. At the first stage of the study, unsuitable zones were excluded and the weights of the main and subclasses were calculated using AHP method. Then, each parameter was mapped into a GIS system as an individual data layer. The final susceptibility map, which had been produced by overlapping all data layers, was divided into 4 categories. Then, the three top ranked areas were selected from the very suitable class. In order to locate the site with the minimum effect on the environment, the Leopold Matrix was used. Finally, area 1 was selected, by both TOPSIS and EIA, as the most preferable option for the construction of the wastewater treatment plant.

Bentonite deposits of economic interest are widespread in Tashtab Mountains (Khur), east of Isfahan province, Iran. Several bentonite deposits have been developed in this area as a result of Eocene volcanic alteration. These deposits are classified as Khur bentonite horizon. XRD analyses reveal that alteration products consist of Na-montmorillonite, kaolinite, quartz, calcite, and crystobalite. The studied volcanic rocks predominantly consist of andesite and basalts, which have developed in back arc basin. Field studies demonstrate that there are many active faults that have had a significant role in transporting great volumes of silicic liquids to the surface and precipitated as geode, jasperoid and silicic veins. Alteration of volcanic parent rocks to bentonite is accompanied by gains and losses of some elements. The concentration of major and trace elements displays variable reduction in analogy to the parent rock. Most of the Large Ion Lithophile Elements (LILEs) are markedly depleted; Nb, U, Cr, Ni and V. The aforementioned elements have relatively decreased, whereas Al, Ti and Zr are rather immobile. Cesium is essentially derived from hydrothermal fluids and incorporated in bentonite structure. Both argillic and silicic zones are enriched in Cs. The chondrite –normalized Rare Earth Element (REE) patterns show similar trends in the andesite-basalt as well as bentonite and silicic zone. Slight depletion of REE’s, and in particular heavy REE’s, is observed in the bentonite samples in comparison with the unaltered rocks. Hydrogen and oxygen stable isotope results indicate a meteoric source of fluids responsible for transformation of volcanic rocks into bentonite at a temperature of about 83°C. The hydrothermal fluids have reached the surface by fault system activity, and silicic liquids have escaped frequently in a sedimentary basin, caused probably by Miocene compressive stresses.

Accurate permeability estimation has always been a concern in determining flow units, assigning appropriate capillary pressure and relative permeability curves to reservoir rock types, geological modeling, and dynamic simulation.Acoustic method can be used as an alternative and effective tool for permeability determination. In this study, a four-step approach is proposed for permeability estimation from acoustic data. The steps include estimation of the Stoneley wave slowness from conventional logs using a support vector machine neural network, determination of the Stoneley wave slowness in non-permeable zones, calculation of the Stoneley permeability index, and calculation of the Stoneley-Flow Zone Index (ST-FZI) permeability using the index matching factor (IMF). Finally, a comparison is made between the ST-FZI permeability with those derived from CMR log and core analysis. The results of this study show that acoustic method in conjunction with robust SVM neural network can be considered as an accurate tool for permeability estimation in the mixed clastic-carbonate reservoirs with complex pore type systems.

This study presents the nannostratigraphy and nannofossil events in the lower boundary of Kalat Formation in the East and West of the Kopeh- Dagh basin. The Kalat Formation comprises of coarse grained detritus limestone with subordinate sandstone intercalations. In the current study, six sections have been chosen in the East and West of the basin which are as follow: Dobaradar section, Kalat section, Chahchaheh section, Sheikh section, Qaleh Zoo section and Jozak section. In the Dobaradar section 22 species have been determined, in the Kalat section 25 species, in the Chahchaheh section 32 species, in the Sheikh section 28 species, in the Qaleh Zoo section 20 species, and in the Jozak section 18 species have been determined. The boistratigraphy based on calcareous nannofossils allows the identification of nannofossil standard zones CC25- CC26 in the East, and CC21 and CC26 in the West of the Kopeh- Dagh Basin in all of the sections, indicating that the investigated deposits are Late Maastrichtian – late Late Maastrichtian in age in all sections in the East, and early Late Campanian – late Late Maastrichtian in all sections in the West of the Kopeh- Dagh Basin. The nannofossils response to the Maastrichtian climate evolution is investigated in the lower boundary of Kalat Formation. Warm water indicators (Uniplanarius sissinghii, Micula murus and Micula prinsii) suggest warm surface water conditions in the studied thickness. In the lower boundary of the Kalat Formation, based on Lithraphidites spp. and Watznaueria barnesae, lower fertility conditions with low productivity at the end of the Maastrichtian were suggested.