فصلنامه زمین شناسی ایران
پیاپی 16 (زمستان 1389)

Durability Index، which is closely related to mechanical properties of rocks، is an important engineering parameter to assess deterioration of the rock against chemical and physical weathering factors. In this study، 14 building stone samples were selected and their petrography، physical properties (including density، specific gravity، porosity، water absorption) and mechanical properties (including uniaxial compressive strength، Brazilian tensile strength، point load strength index، punch strength index، aggregate impact value، and P wave velocity) were investigated. Also، Durability Index Test were performed up to 15 cycles and its correlation in 2، 5، 10، and 15 cycles versus mechanical properties - to perform two-variable regression analysis - was investigated. Results suggested that there is a linear relationship (R = 0. 55 to 0. 91) between durability index (Id15) and mechanical properties. Moreover، by increasing wetting and drying cycle numbers، correlation coefficient between durability incrensing and mechanical properties increased. With respect to results of regression analysis، useing of second-cycle conventional Durability Index Test did not present real durability and for more accurate assessment of the rocks durability، it is necessary to perform the test with more cycles.

Parsi Oil Field is located about 130 km southeast of Ahwaz in the Dezful Embayment. Petrographic studies and Scanning Electron Microscope (SEM) analyses of cutting samples of cap rock of the Asmari reservoir indicate that this member of Gachsaran Formation (Cap rock) consists of anhydrites، marls، halites، a few thin beds of limestone and a bituminous shale layer. Cap rock constituents show a wide variety of textures which can be used in reconstruction of depositional environment and diagentic processes. Sulfate and halite facies alternation along with characteristic textures such as nodular، spherolitic، hopper and dissolution surfaces indicate that the cap rock of the Asmari reservoir has been deposited in salt pan sabkha – lagoon system under warm and dry climatic conditions and periodic feeding. Subsequently، transgression results the marls and carbonates to be deposited in lagoon environment. Then with a regression phase and increase in evaporation، the salt pan developed which resulted deposition of evaporatic sediments. Correlation of various beds in the oil field expresses uniform depositional conditions during sedimentation.

Two distinct collision events have occurred between Arabia and Central Iran plates، during closing of the Neo-Tethys. Structural sections along the collision zone in northwest Iran show characteristics of collision structure. The first collision occurred during obduction of the oceanic components of the Neo-Tethys over the Arabian passive margin during the Late Cretaceous. Deformation along the Arabian passive margin in radiolarite and the high Zagros zones was the result of this event. The high Zagros frontal thrust fault is the maximum limit of this collision tectonic event. The obducted oceanic components، including the ophiolites in this region، unconformably are overlain by Oligocene-Miocene sediments. By the last continent-continent collision event during Late Miocene، the hinterland of the orogen was transported over the collided zone and deformation occurred by rejuvenation of the existing thrust faults in previously collided zone and the Zagros foreland basin was formed (Zagros fold-thrust belt).

The study area is located in northwest of Iran، in the western Alborz-Azerbaijan structural zone. Based on petrography and geochemical studies، the Quaternary basic volcanic rocks of the study area have alkali-olivine basalt and trachy basalt composition and alkalinesubalkaline nature. According to tectonic diagrams، the samples are plotted within-plate continental basalts field. The Quaternary volcanic centers are situated within pull-apart basin structures and are controlled by active faults. The average Ce/Pb and Nb/U ratios of the studied basalts are lower than the value، for average oceanic basalts (OIB and MORB). These ratios are close to the average values of sub-continental lithospheric mantle. According to geochemical characteristics of trace elements and REE patterns، all the analyzed basalt samples have LREE enrichment chondrite-normalized REE patterns، suggesting that they may have been generated by different partial melting degrees (Ahar 3-4%، Maku 1 - 15% and Sarab 5-15%) of a sub-continemtal lithospheric mantle source.

Central Alborz region have already affected by several strong structural tectonic events. There are some different ideas about its latest activities. This study utilities multiple inversion method for paleostress phase separation and structural analysis in the Baijan Fault zone (northeast of Damavand volcano). The latest activity of the Baijan fault system on Damavand's Lava، have printed by slickenside on the fault planes، so the results of analyses is reasonable to recognize and analyze of fault function and extend the results to the recent structural activities. The method enables us to determine position of the principal paleostress axes and the geometrical shape of the stress ellipsoid for reconstruction of paleostress regime dominating the tectonic events by solving reduced stress tensors. Field data were rotated to reach the four effective parameters δ1، δ2، δ3، ϕ. Four groups were separated among the original data sets. The geometrical shape of stress ellipsoid (ϕ) of 0. 2 has been repeated in three of separated groups. In the separated field with ϕ=0. 2، δ2 is sub vertical. This analysis indicates that strike-slip component of the youngest activity of Baijan Fault was more pronounced than the recorded reverse component.

Bed river may reflect the influences of erosion، tectonics and climate change. A factor which has the most important role in these changes is، the effects of tectonic and base level of estuary. In this study، the role of base level changes in the pattern of the channel bed rivers of Polrood، Shafarood and Karganrood around the Sefidrood Delta has been studied. The aim of this research is that the river beds of the Caspian coastline near the estuary are deep cutting. Purpose is at this paper the role of factors on base level changes and geomorphologic changes of the river beds. Digital topographic maps، aerial photos and geological maps re among physical tools of this research. Detailed field work to obtain the sections and longitudinal profile of river bed by recording their locations using GPS were. Data in GIS environment and AutoCAD software are processed. Also، the pattern of river channel based on the findings and Theoretical principles of classification and finally، the interplay of the Caspian Sea water level fluctuations and tectonic effects Alborz combined with other data and analysis has been. The results show that short-term changes in water level of the Caspian Sea near the mouth rivers (up to 5 km from the shoreline) have been affected. This impact in east of Sefidrood that the Knick is closer to the beach and coastal plain is wider than the West and northwest، is more. On the other hand، the Alborz uplifting against South Caspian Plate subsidence has been effected the drainages and about 10 km distance after leaving the mountains caused deep drainages in this area.

Tertiary volcanism in the Taleghan area is marked by a thick sequence of alkali basaltic volcanics that is followed by tephritic volcanics. Trace elements geochemistry of these volcanics indicates a postorogenic extensional geodynamic، possibly due to the continental collision following the subduction of the Arabian and the Iranian plates. This study suggests derivation of both volcanics from a single parental magma. Trace element modeling suggests derivation of this parental magma by 15% partial melting of a spinel–lherzolite source at the depth of 60 to 65 Km. The trace element systematic، along with petrographic evidence، suggests that 45 to 50 % fractional crystallization controlled the alkali basalt evolutionary paths. The fractionating phases and their proportions are: clinopyroxene (45%) + olivine (25%) + plagioclase (25%) + magnetite (5%). Tephritic magma can be produced by about 65% fractional crystallization of the same mineral assemblages together with crustal contamination by amphibolites facies country rocks. Assimilation-fractional crystallization (AFC) modeling reveals significant but variable degrees of crustal contamination in the evolution of the magma to product tephritic rocks with a range of r values (assimilation rate/crystallization rate) from 0. 15 to 0. 45.

In order to improved management of conjunctive operation from down- stream water resources of Shahrchay Dam، Urmia city، system dynamics model (Vensim software) is designed. So، the first effective parameters on the oscillation of surface and ground water as well as interaction between demand and supply of domestic، industrial and agricultural water from both surface and ground water resources have been identified in this area. Then، these parameters and their interactions were coded in dynamic system software. After calibration of model، in order to make correct decisions for integrated resources management، different scenarios such as improved irrigation efficiency، performance of urban waste¬water and demand management were carried out according to the circumstances that may arise in the future in the area. Consequences of model performance for the next four years shows that providing total needs of domestic and industrial water from reservoir dam (if other conditions within the status go to remain); is not correct management in the area، because the reduction of domestic water wells exploitation will increase، water storage volume in the aquifer dramatically. In this case، the range of areas that aeration zone thickness is less need to throw down water table project will be developed. Also، performing waste¬water collection system in Urmia city، regardless of the amount of correct allocation of surface water for domestic and industry; volume of water supplied in the aquifer will be reduced. Therefore، with allocation of agricultural water and green spaces from the treated waste¬water instead of well water will prevent from aquifer supply decrease and salt water influx.