جستجوی مقالات مرتبط با کلیدواژه « نابر » در نشریات گروه « زمین شناسی »

The Nabar area that is a part of the Urumieh- Dokhtar volcano- plutonic belt is located in the south of Kashan. Research works such as Emami (Emami, 1993) and Abbasi (Abbasi, 2012) have been done about the geology of this area.
Rock units in the study area contain middle- upper Eocene intermediate to acidic lavas and pyroclastic rocks, green marl, shale and sandy marls of Oligo- Miocene, limestones of Qom formation, intrusive granitoids with Oligo- Miocene age and quaternary travertine and recent alluvium (Emami, 1993). The volcanic and sub volcanic rocks of this area are composed of andesite, trachyandesite, dacite, rhyolite and porphyric pyroxene diorite along with pyroclastic rocks.
In order to achieve the aims of this work, at first field surveying and sampling were done. Then, thin and polished thin sections were prepared. Some of the samples were selected for microprobe analysis and clinopyroxene minerals were analyzed by using JEOL- JXA-8800 analyzer with a voltage of 20 Kv and a current of 12 nA in the Kanazava University of Japan and Cameca-Sx100 analyzer with a voltage of 15 Kv and a current of 15 nA in the Iranian mineral processing research center, Karaj.
On the basis of petrographic investigations, porphyritic, porphyroid, fluidal, amygdaloidal and porphyry with microlitic groundmass are common textures of these rocks. Also plagioclase, clinopyroxene, amphibole, biotite, sanidine and quartz are essential minerals, opaque, zircon and apatite as accessory minerals are observed in the studied rocks. Clinopyroxenes are observed with corona texture that resulted during the uralitization process. On the basis of minerals’ chemistry, pyroxenes are Fe- Mg- Ca type in composition (Morimoto et al., 1988). These clinopyroxenes are augite. Investigations indicate that mineral composition of clinopyroxene can be effectively used to evaluation the P-T conditions during crystallization. Previous research works have proposed several methods such as Soesoo (Soesoo, 1997) and Putrika (Putrika, 2008). Thermobarometric studies of clinopyroxenes reveal that Nabar rocks were formed at temperatures of 900 -1200 ˚C and the pressure of 2-5 kbar. According to the Aoki and Shiba (Aoki and Shiba, 1973) and Helz (Helz, 1973) approaches, the pyroxenes of the studied rocks are in a range of low to medium pressure that shows crystallization of clinopyroxenes during ascending of magma in different depths. Also according to Helz (Helz, 1973), the water vapor content in the crystallization of clinopyroxenes is more than 10 percent. Using AlIV versus AlIV 2Ti Cr diagram which depends on the amount of ferric iron in pyroxenes, we can get oxygen fugacity. Based on this diagram, the pyroxenes which crystalized at high oxygen fugacity, has been situated above the line of Fe3. Furthermore, Cameron and Papike (Cameron and Papike, 1981) have mentioned to the distances of the samples from the Fe3 line and noted that further distances of the samples from this line are indicating more oxygen fugacities in their geological setting. On the basis of this diagram samples were located above the line of Fe3橷 these rocks are formed in high oxygen fugacities. Pyroxene composition depends on the chemical composition and tectonic setting of the host lava which can be used widely to determine tectonic setting of the rocks. On the basis of approaches of Le Bas (Le Bas, 1962) and Sun and Bertrand (Sun and Bertrand, 1991), the chemical composition of clinopyroxenes shows that the studied rocks are related to calc-alkaline series and orogenic settings.
On the basis of mineral chemistry, pyroxenes are Fe-Mg-Ca type in composition. These clinopyroxenes are augite. Thermometric studies of clinopyroxenes reveal that Nabar rocks are formed at temperatures of 900-1200 ˚C. According to the distribution of aluminum in clinopyroxenes, these minerals were formed at 2-5 k bar pressure and water vapor content of more than 10 percent. Therefore, pyroxenes of the Nabar rocks are in a range of low to medium pressure that shows crystallization of clinopyroxenes during ascending of magma in different depths. Moreover, the volcanic rocks in Nabar were formed in high oxygen fugacity. The chemical composition of clinopyroxenes reveals that these rocks are related to calc-alkaline series and orogenic settings.

The studied area is located in the east of Nabar village and southwest of Kashan¡ a part of the Urumieh – Dokhtar magmatic arc. The volcanic rocks belonging to Eocene age¡ are composed of pyroxene andesites¡ andesites¡ dacites and rhyolites. Porphyritic¡ glomeroporphyric¡ microlitic¡ and sieved textures are the most common textures of these rocks. Plagioclase¡ clinopyroxene and amphibole are the predominant minerals in the pyroxene andesites and andesites¡ whereas dacites and rhyolites are characterized by the presence of plagioclase¡ amphibole¡ quartz¡ biotite¡ and K-feldspar. Inequilibrium textures including embayed plagioclases and quartz with rounded margins¡ and oscillatory zoning in the plagioclases¡ sieved texture¡ and dusty rims are evidences of magma mixing. The enrichment in LREE and LILE and the HREE and HFSE depletion in the chondrite and primitive mantle normalized diagrams point to calc-alkaline nature of the rocks studied and they are related to volcanic arcs setting. High ratio of La/Nb (2-4.36) and negative Ti and Nb anomalies in spider diagrams can support crustal contamination hypotheses of these rocks. Also¡ low ratio of Nb/La (0.23-0.5) and high ratio of Sr/Ce (8.4-19) indicate contamination of parental magma with crustal materials. The rocks studied are formed from magma which is derived from enriched-mantle with 1-5 percent partial melting of spinel-lehrzolite.

The east Nabar volcanic rocks with Eocene age are located in the southwest of Kashan and Uromieh-Dokhtar magmatic belt. These rocks are composed of basaltic andesite، andesite، dacite and rhyolite. Plagioclase، amphibole، clinopyroxene، biotite and quartz are the essential minerals of these rocks. Very few apatites are observed in some plagioclases. Epidote، calcite، chlorite، sphene and opaque are secondary minerals. Porphyritic، glomeroporphyric، microlitic and poikilitic textures are common textures in these rocks. On the base of microprobe analyses the composition of plagioclase ranges from oligoclase to labradorite، the clinopyroxenes are diopside and the amphiboles are magnesio-hornblende and tremolite. The chemistry of clinopyroxenes show that these rocks belong to sub-alkaline series and volcanic arcs. On the base of barometry of clinopyroxenes، the study rocks formed in medium to low pressure during their ascending. The volume of water in the crystallization environment of clinopyroxenes was high and the rocks studied formed in high oxygen fugacity. The thermometry of clinopyroxenes reveals the temperature of 975 oC for their crystallization. The amphiboles thermobarometry shows the pressure of 2. 97 kbar and the temperature of 700-750 oC.

The Nabar plutonic rocks is located in the northwest of Isfahan and in the Urumieh-Dokhtar magmatic belt. Based on the petrologic studies, the Nabar complex is composed of gabbro, gabbro-diorite, diorite, quartz diorite, tonalite and quartz monzonite. Mineral chemistry shows that pyroxenes are Na-poor in composition and are classified as clinopyroxenes and orthopyroxenes which are diopside and hypersthene. The composition of these minerals can be correlated to pyroxenes of calc-alkaline series. The composition of amphiboles plot in two groups of Fe-Mg-Mn amphiboles and calcic amphiboles. The plagioclase compositions are variable from oligoclase to bytownite in the analysed samples. Using Al barometry in hornblend, pressures of about 2 Kbar are estimated for the intrusive body.