جستجوی مقالات مرتبط با کلیدواژه "feldspar" در نشریات گروه "زمین شناسی"

Masteroon area is located in the northeast of Azna city, in the Sanandaj-Sirjan zone. The rocks units include a relatively uniform sequence of slate and phyllite with a granodiorite intrusive mass that includes pegmatitic complex. The most important minerals include quartz, alkaline feldspar, plagioclase, tourmaline and muscovite. Quartz is high pure and does not have any other elements. EPMA shows the albite-type feldspar with a lesser extent than orthose-type with a less than 550⁰C crystallization temperature. This can be due to the result of below the freezing of the feldspars composition during the cooling of the mass. The available tourmalines are of schorl and alkaline type with a deficiency in the X position, and their numerous and abundant presence, automorphism and absence of chemical zoning, indicate that tourmalines are magmatic. Muscovites are present in two forms: coarse-grained in pegmatites and fine-grained in joints and cracks, and the coarse-grains does not stretch to phengite.

Blue-colored corundum (sapphire) is found in syenitic pegmatites in Alvand igneous complex in the Khako area. From the petrographic point of view, the host rock is composed of feldspar and small amounts of quartz, which includes corundum crystals of transparent to translucent blue color, 1 to 6 cm long, covered with a sheath of mica with a composition of muscovite to phengite. It seems that the core of corundum crystals crystallized in the magmatic stage in equilibrium with mica + aluminosilicate + feldspar ± perthite, and in the next metasomatic stage, corundum crystals grew from the reaction of plagioclase and mica. The chemical composition of the main minerals in pegmatite rocks indicates the magmatic origin of these rocks, which were formed during the magmatic differentiation process. In the continuation of the metasomatic cycle, the geochemical conditions for formation of new corundum crystals and regrowth of primary corundum have been prepared by reducing the silica content (de-silicification) and increasing the Al/Si ratio. These processes during post-magmatic cycles in granite masses, are known as Plumasite processes. The classifications done in pegmatites, based on abundance of rare elements and phosphorus content in feldspar crystals, indicate fertility of these rocks from rare elements. These pegmatites are included in the group rich in lithium and beryllium. Moreover, comparison of the chemical composition of corundum crystals with famous corundum deposits in other parts of the world shows that these rocks have a special similarity with magmatic corundum deposits in connection with synthetic intrusive masses. In addition, these rocks show a composition similar to magmatic deposits created by metasomatic processes.

 The left lateral Doruneh Fault System (DFS), is one of the longest, and most prominent, strike-slip faults in Iran, extending from the eastern border of Iran to the central Dasht-e-Kavir with a curved geometry. DFS is the response of the convergence between the Arabian and Eurasian plates in the regional tectonic map. Regarding to scaling relationships this fault with length of >600 km has the potential to produce earthquakes with magnitudes higher than 7.5. M. It performs an important role in the regional tectonics and is certified to be active by its well-preserved geomorphological features all along its trace. However, despite clear Quaternary activity expressed in the geomorphology, has no record of historical and instrumental earthquakes of magnitudes M ≥ 6, which is in contrast to the neighbouring Dasht-e Bayaz region, which has suffered from many earthquakes recorded both instrumentally and historically. Determining whether the Doruneh fault is capable of generating large-magnitude earthquakes similar to the Dasht-e Bayaz is important due to its risk to close cities and towns. In other word, it is necessary to determine the hazard of this fault in the area. One way to conduct the Earthquake Hazard Assessment is to calculate the slip rate. The slip rate of a seismogenic fault is a crucial parameter for establishing the contribution of the fault to the seismic hazard. one method for calculating the slip rate is measuring the displacement by the fault and dividing it by the period during which this displacement has occurred. Clear scarps in alluvial fans and river terraces can be observed both in satelite imagery and in the field along the entire Doruneh fault length. The geomorphology of the fault contains numerous indications of cumulative left-lateral slip over various scales. By dating and finding the age of these offset geologic features, we can determine the average slip rate. We describe one site where Late Quaternary landforms are displaced by the fault. Two generations of alluvial fan are present on the north of Khalilabad village. There are two parallel east-west fault traces on the fan surfaces at this site, with the two traces separated from each other.

To determine the slip rate two parameters are required: the displacement and the period that has taken that the displacement occur. Optically Stimulated Luminescence (OSL) is one of the best methods for determining sediment age in arid and semi-arid zones such as Iran. OSL enable evaluation of the time that has elapsed since quartz and feldspar, were last exposed to daylight. During exposure to light the luminescence signal within the grains is optically bleached until the signal is zeroed. Once the grains are buried and sealed from daylight, the luminescence signal being induced by naturally occurring radiation and being accumulates again. The time passed since the last daylight exposure is calculated by dividing the dose accumulated in the sample since its last exposure to light by the dose rate.The study site in this research is the eastern alluvial fan near Khalilabad, which is located in the west of Kashmar. Google earth was employed to observe and measure the apparent offset of a riser between eastern and the western fan surface, which appears to be relatively straight both upstream and downstream of the fault. The estimate is that Doruneh fault has displaced the eastern alluvial fan by about 40-60 meters. Two sediment samples were collected from this alluvial fan for luminescence dating. Potassium feldspar was then separated from them. To determine the age of potassium feldspar, two parameters of equivalent dose and annual dose are required. SAR method was used to measure the equivalent dose and analyst program was used to analyze the data. The dose rate was calculated using present-day moisture content, radioisotope concentrations and burial depths.

The last sedimentation period was determined to be 11000 – 16000 years ago. The slip rate of this part of the fault was estimated to be 2.5-5.5 mm per year by dividing the displacement rate over the displacement period.

The Goushe granitoid Pluton is located southeast of Boroujerd. The study area is composed of granite, granodiorite and the microgranular enclaves located in it with the granodiorite to quartzmonzodiorite combination. The microgranular enclaves presence along with evidence of the presence of the non-equilibrium textures such as dissolved margin and plagioclase zoning, sieve textures, mafic clots, blade biotite, feldspar Poikilitic texture indicate the unstable conditions and imbalance in the crystallization environment that probably has been created due to rapid ascent of magma or magma mixing process. Alkaline feldspar and plagioclase crystals in the Goushe intrusive rocks show zoning structure in terms of composition and texture. Feldspar crystals were analyzed in different units such as granodiorite, monzogranite and microgranular enclaves, which are relatively abundant throughout the granitoid intrusion. The plagioclase chemical composition in granitoid rocks changes in the compositional range of albite (An: 2) at the edge to Andzin (An: 33) in the center and the enclavesn plagioclase composition of in a wider range fluctuates from early oligoclase (An: 11) to mid-andesine (An: 36). The alkaline feldspar composition is determined in granitoid rocks with Or = 94-97 and in the enclave with Or = 69-96. The abundance of trace elements Fe, Sr, Ba and Mg in feldspars show an oscillating and variable pattern. The trace and rare elements oscillation pattern from the center to the margin in the feldspar crystal indicates the effective role of the magmatic mixing phenomenon in the formation of the Goushe Pluton.

The Tajar feldspar deposit is located at 15 km southwest of Malayer city, 4 km northwest of Samen city, in the Hamedan province and west of Iran. Study area is located in the north part of the Sanandaj-Sirjan geological zone. Detailed exploration activities carried out for determining of geometrical data of mineralized zones. Indeed, according to the morphological and geometrical data of deposit, the rectangular exploration grid was designed and 45 exploratory boreholes (520 meters total depth) were drilled. Furthermore, for determining of shape and dimension of mineral deposit, lithological columns of mineral deposit and host rocks were designed. Then by providing their geological profiles, at first the volumes that enclosed between each section was calculated and eventually the mineral deposits was determined. Detail exploration results show that the Tajar feldspar deposit have 99286 m3 volume and 258145 tons deposit. Tajar feldspar deposit is sodic type and their mineral composition is oligclase to albite.

Kaolin deposits in the Nivasht and Kabudkamar areas are located in ~25 km northwest of Saveh, Central province. Field observations along with petrographic examinations revealed that genetically these deposits are alteration products of igneous rocks such as andesi-basalt, trachy-andesite, and andesitic tuff of upper Eocene age. In this study, the physical, chemical, and mineralogical properties of the kaolin deposits in Nivasht and Kabudkamar were investigated on the basis of industrial applications. Based upon mineralogical data, the principal constituent minerals in both deposits are quartz, kaolinite, halloysite, muscovite-illite, Montmorillonite, pyrophyllite, plagioclase, hematite, goethite, anatase, akermanite, alunite and/ or natroalunite, and talc. Further investigations in the studied areas showed that the kaolinitic clays have mostly firing color within the range of milky white to dark gray. Consideration of parameters such as capability of water absorption, resistance in dry state, firing contraction, low thermal efficiency, and the values of major oxides demonstrated that the kaolins at Nivasht and Kabudkamar possess suitable standard conditions for application in ceramic (for floor and wall) industries, however, their application in other industries requires further processing.

The alkali feldspars and plagioclases in the Kuh-e Dom intrusive rocks show compositionally and microtexturally zoning structure. The feldspar crystals in the various lithologies such as granite- granodiorite samples, diorite- gabbro samples and relatively high frequency microgranular mafic enclaves existing in the acidic intrusion were analyzed using electron microprobe. The results of the microprobe analysis in the acidic, basic- intermediate rocks and enclaves indicated the normal and reverse zoning in the samples. The chemical compositions of plagioclases ranges from albite (An 9.4) in the rim to labradorite (An: 50.6) in the core for acidic rocks, and from andesine (An: 30.5) in the rim to labradorite (An: 56.4) in the core for the basic- intermediate rocks, and from oligoclase (An: 19.8) to labradorite (An: 66.5) in the enclaves. The frequently of rare elements such as Ba, Sr, Fe and Mg in the feldspars show various and oscillatory patterns. The oscillatory pattern of the major and minor elements from core to rim in the feldspar crystals suggests an effective role of magma mixing phenomena in forming of the Kuh-e Dom intrusion.