مجله یافته های نوین زمین شناسی کاربردی
پیاپی 10 (پاییز و زمستان 1390)

Main goal of this study is to reveal the petrography and origin of dolomites in Shahbazan Formation in the east of Eslamabade- Gharb. An outcrop was sampled in study area and 49 samples were collected. Two types of dolomites were identified, type I with xenotopic texture of clear dolomite crystals, type II with idiotopic texture of filthy (blurry) dolomite crystals. Type I is anhedral to subhedral, very fine-to fine-crystals (5–16 μm crystal size, dolomicrite); type II is subhedral to euhedral, and fine-to medium-crystals (16–62 μm crystal size,dolomicrosparite). According to size and shape we concluded these dolomites formed during early diagenesis, however, type II dolomites were probably recrystallized during later diagenesis and their crystal size are increased up to 220 μm. We suggest these dolomites were formed due to basinward flushing of meteoric fluids during sea-level fall in a humid climatic regime. Mixing of meteoric and marine fluids promoted dolomitization of limestones theShahbazan Formation in mixing zone. Consequently, some porosities were occluded by later calcite precipitation.

Kermanshah ophiolites are a complex and crashed zone. In this zone, gabbro, dolerite and peridotites are the most important unit within the complex ophiolite. Pridotites in the study area are metamorphic type; they are strongly crushed which caused an intense hydrothermal alteration. The resulted secondary minerals include:lizardite, chrysotile, antigorite, chlorite,talc, magnesite, iddingsite and brucite. Mineralogical study on these peridotites indicate a low grade metasomatism (green-schist facies) which were superimposed by amphibolite facies metamorphism. The condition of formation of these minerals and their reactions are discussed in this research.

Abbas Abad area has an old copper mining history; in this area outcrop of volcanosedimentary sequences exist; lithological composition of volcanic parts are generally andesite and trachyandesite and sedimentary parts includes sandstone, limestone, conglomerate and shale. Mineralization in this area has occurred in a broad region (
35 Km2) in volcanic rocks with porphyry to megaporphyry texture. For surveying of arsenic distribution in this area chemical analysis on 52 samples of stream sediments near deposits located in north and northeast part of Abbas Abad (including Damanjala, Madan Bozorg, Asiadiv and Lab-e-Kal deposits) were done. Arsenic distribution, according to broad mineralization and old mining history were stndied. Arsenic distribution map shows the highest concentration of arsenic is in north east of the region; also using arsenic contents of stream sediments, background,threshold and anomaly values of arsenic determind which are 16 ppm, 21 ppm and 33 ppm respectively.

Hoz-e-Soltan playa catchment area 195 km2, depth 25-50 cm, is located 85 km southwest of Tehran. The objective of this research was to determine the paleoclimate and water table fluctuations in Holocene through sedimentary facies studies. In this research, 9 cores (maximum length of 7 meters) were taken from the lake substrate, and then facies investigations, such as sediments’ characteristics, organic matter contents, colors, crystals of evaporative minerals and sedimentary sub-environment were determined. 155 subsamples were prepared from different sedimentary facies, and then granulometric analysis and mineralogy (XRD) were carried out. Results indicated that there are 5 sedimentary subenvironments,including sand flat, mud flat, saline mud flat, salt pan and ephemeral lake in the studied cores. On the basis of granulometry results, 5 sedimentary types were recognized in the subsurface sediments; slight gravel-bearing sandy mud, slight gravel-bearing muddy sand, mud, sandy mud and muddy sand. Sedimentary sub-environments of HS1 and HS2 cores are in relation to saline-mud flat and mud flat environment, respectively. Also, during Holocene lake water table fluctuation were drown and wet and dry period sediments were defined. Result shows that 6 major drought period exist in this region so during the last few thousand years, the lake had wet and dry conditions. Recent climate change and globalwarming doesnt serious effect on more drying of the lake; these wet and dry periods were frequently repeated.

The Quaternary lamprophyres and related rocks from west Salmas are laid on the floodplain deposits in the border of the Sanandaj-Sirjan and Uromieh-Doukhtar magmatic zones. These rocks are all alkaline and include mostly camptonitic lamprophyres, contaminated lamprophyres, basalt, trachy-basalt, and trachy-andesite. The rocks have been croped out as prismatic and scoria structures with porphyritic and glomeroporphyritic textures. High ratios of Lan/Ybn, Lan/Smn and Smn/Ybn, occurrence of spinel, augite and diopside, alkaline characteristic of all samples, and calculations of partial melting based on the distribution coefficients indicate a melting process about between 1 and 7 percent of a mantle with spinel lherzolite composition. Based on the partition coefficients of elements in different minerals,large ionic lithophile elements (LILE), which are mobile, and lead were mostly controlled by amphibole, biotite, and augitic clinopyroxene, rare earth elements (REEs) by amphibole and clinopyroxene, high field strength elements (HFSE), which are immobile, by amphibole,clinopyroxene and biotite (but not a lot), and first series transition metals of periodic table of elements, depending on which element and rock, by biotite, amphibole, orthopyroxene,olivine, and clinopyroxene during the crystallization of the magma.After ceasing of Neotethys subduction beneath Central Iran, slab break off occurred likely in the remnants of the Neotethys oceanic crust right in the location of the collision zone of Arabian-Eurasian plates. The process occurred at the within plate setting. Arabian oblique tectonic pressure to the Eurasian plate and increasing activity of right-lateral strike-slip faults,which resulted of slab break off the Neotethys remnants, caused thermal doming and decrease of lithostatic pressure in the mantle, and hence, was developed decompression melting in the upper mantle. Occurrence of these processes successively led to the rocks show tectonically within plate characteristic along with interacting of subduction elements. The mantle meltswere erupted along these fault system.

In this research, groundwater quality of Hoz-e-Soltan Lake have been studied for drinking and irrigation uses according to different parameters. This lake with 195km2 catchment area located at 85 km of southwest of Tehran-Qom highway. In order to investigate is groundwater quality characteristics in Hoz-e-Soltan Lake, 34 data from water of well taken in 2008 were selected for processing and interpretation. All data were processed for determination of groundwater quality such as MAR, SSP, RSBC, PI, KR and SAR after editing of data. Base on Piper and Scholler diagram, different groups of water and suitability for drinking and irrigation uses were determined. Results show that Electron Conductivity is equal to 5308.8 μmohs/cm and total dissolve solid is 3446.4 mg/l. The pH value of the aquifer is high indicating an alkaline nature with an average of 8. Total hardness average of samples is equal to 806.8 which shows that the Hoz-e-Soltan groundwater was not suitable. The groundwater type of study area is classified in Na-Cl-SO42- class. Also, base on Na% average equal to 67.1,groundwater resources of the study area belong to the suspicious class.

Erosion is one of the most active processes in surface of the earth. Erosion can cause soil destruction, shortage of groundwater, rangeland degradation, and eventually much damage to agriculture and livestock. Sorhe drainage basin, with an area of 39.4 square kilometers, is located in North Karaj. The study area is mostly formed by sedimentary and pyroclastic rocks. Kahar Formation with the Precambrian age is the most ancient rocks and Quaternary deposits are the youngest rock units in this area. Over 50 percent of the total area belongs to Karaj Formation rock units. Erodibility of rock units are affected by six main factors:geology, climate, tectonics, slope, vegetation cover, and weathering. The most important factors to erosion in this area belong to tectonics and slop. In addition to sedimentology and petrography of rock units, using experimental method of Sediment Yield Potential (SYP), the sensitivity of the formation was calculated in 5 classes. On this basis, Soltanieh formation is the most resistant with low erosion and Quaternary deposits of Qal and Qt are most sensitive rock units to erosion. Sediment yield rate was estimated 889.27 tons per hectare in the year.According to obtained information and using Arc GIS software, erosion type maps,susceptibility of formation to erosion, and finally sediment yield potential map (SYP) were prepared in Sorhe drainage basin.