PETROLOGY
Year:2013 | Volume:4 | Issue:13|Papers Count:7

Structural elements of four deformation stages have been recognized in the Hamedan schists. These deformation stages were synchronous with regional and contact metamorphism events. Numerous porphyroblasts have grown in the metamorphic rocks as pre, syn and post deformation stages. Andalusites were generated Pre and syn- D2 due to regional metamorphism in the area. Andalusites were oriented in NW-SE trend and were extended, boudinaged and distances between boudins filled by quartz fibers. Garnets have been initiated pre, syn and post D1, syn and post D2 and syn and post D3 in the metamorphic rocks. Staurolites were grown pre D2 probably syn D1, pre and syn D2 and post D3. Sillimanites are found in the andalusites or as fibrolits that were produced during D4 stage. Cordierites were generated by both regional and contact metamorphism and it is found presyn D2 in regional metamorphic rocks.

Ku-e-Kam Khashak is located in the NE of Isfahan (North of Khur). Basic dykes trending NE-SW and intermediate dykes with NW-SE trend cross cut the Upper Cretaceous sandstone, limestone and marl. The intermediate dykes are much more abundant and widespread in the area. Field studies show that the basic dykes cross-cutting the intermediate dykes, indicating that intermediate dykes are older. Primary minerals of the basic dykes are olivine (chrysolite), clinopyroxene (diopside, augite), plagioclase (labradorite, oligoclase), sanidine, magnetite, orthopyroxene (enstatite), spinel, phlogopite and secondary minerals are zeolite (natrolite and mesolite), chlorite, calcite and serpentine. The intermediate dykes are composed of clinopyroxene (diopside), plagioclase (labradorite), sanidine, mica (biotite and phlogopite), amphibole (magnesio-hastingsite) and magnetite as primary minerals and chlorite and calcite as secondary minerals. Basic dykes have xenocrysts of quartz and xenoliths with pyroxenite and hornfels in composition. Mineral chemistry of clinopyroxenes reveals pressure less than 5 kbars and variable PH2O for the formation of these phases. Thermometry of the micas in intermediate dykes show 732- 747oC, whereas the biotites of basic dykes crystallized 699 to 808oC. Petrography and mineral chemistry of the studied dykes indicate sub- alkaline and calc- alkaline characteristic of the primary magma and their magmatic arc setting.

Statistical measurements of crystal size distributions (CSD) are the new method for studying physical and petrological properties of igneous rocks. With emphasis on this method, the Plio-Quaternary lavas volcanic in the NE- Qorveh city are investigated. The lavas are basaltic in composition and there are pyroxenes with sieve texture, skeletal olivines, quartz with gulf corrosion and gneissic xenoliths. Quantity textures are studied in the CSD method. The rate of nucleation and growth timing of crystals are determined by pyroxene crystals size distributions. Timing of growth of pyroxene crystals between 17-36 years suggesting stability of crystallization conditions during eruption in the area. We used the logarithmic population density vs. crystal size diagrams with processing the software CSD correction. In the basaltic rocks of Qezelje-Kand village magmatic contamination occurred. In other volcanoes, such as the Qare-Bolaq volcano, residence time of magma was short.

The Khut and Panah-Kuh skarn deposit is located at about 50 km northwest of Taft in Yazd province. The analyses of major and REE's by microprobe and LA-ICP-MS show that there are two major types of garnet at Khut and Panah Kuh skarns. The garnets in the Khut skarn range from (Ad74.30Gr24.81- d32.06Gr66.61) to almost pure andradite (Adr>96) in composition whereas all Panh-Kuh skarn garnets are almost pure andradite and isotropic. The REE become commonly enriched in garnets during metasomatic process. On the Fe/Ti versus Al/ (Al+Fe+Mn) diagrams, these rocks suggests that over 50% of hydrothermal fluid phase has been effective in the formation of garnets. Comparison of chondrite- normalized REE patterns garnets exhibit that all garnets have light REE (LREE) enrichment and heavy REE (HREE) depletion, with different Eu anomalies. Fe-enriched garnets are characterized with positive Eu anomaly whereas grandite show negative Eu anomaly. Differences in the magnitude of the anomaly reflect local heterogeneities of the system such as protolith as well as metasomatic fluid. The same abundance pattern of REE in the skarn and garnet suggests that garnet is the most important REE host mineral. Therefore, the study of REE geochemical behavior is benefiial in understanding the evolution of metasomatic fluids.

The host rocks of the Esfordi deposit consist of rhyolitic tuff lower Camrianand rhyolite along with dolomites of the Rizu series which are widely affected by sodic-calcic hydrothermal alteration in the north and the east. Typical mineral assemblage in the alteration zone is amphibole, albite, hematite, calcite and chlorite based on petrographic studies. The amphiboles in the Na-Ca alteration zone are within the calcic amphibole group with edenite and actinolite compositions. The average (Na+K)A content of the edenite and actinolite is 0.67 and 0.11 respectively. Chemically, edenite in comparison with actinolite is enriched in TiO2 (0.93), Al2O3 (11.34), FeO (13.55), Na2O (2.09) and Cl (1.05). Whole rock analysis reveal appreciable enrichment of FeOt, MgO, CaO, Na2O, P2O5 and Y2O3 in the Na-Ca altered rocks relative to unaltered host rocks. The calcite and quartz veins crosscut the Na-Ca altered rocks. The Na-Ca altered rocks and calcite veins d18O values (relative to SMOW) vary between 10.5 to 12 ‰ and between 14.1 to 18.1 ‰ respectively, while their d13C values (relative to PDB) vary from -3.8 to -4.2 ‰ and -5.5 to -6.3 ‰ correspondingly. On the basis of O and C isotopic data on the host rocks, Na-Ca alteration occurred at 300-400oC and the calcite veins formed at temperatures lower than 300oC. According to available data, alteration is interpreted to develop by mixing of meteoric waters with magmatic fluids in Esfordi mine.

Gandom Berian area is a basaltic messa composed of dark flows covering about 480 km2 of the western part of Lut desert in the northeast of Kerman. In this area, the fault system follows a north-south trend and, basaltic lavas have flowed along this trend. It seems that in Gandom Berian area, the activity of Nayband fault has created a tensional tectonic regime leading to the creation of open fractures in the crust which have conducted the flow of magma to the surface. Comparing maps of the lineation index factor of Nayband fault and also the related maps to situation of volcanic cones admit the role of fault in formation of Gandom Berian basaltic magma. The presence of coarse euhedral olivine crystals along with coarse crystals of clinopyroxenes and the absence of magmatic quartz, all reveal a fast deep ascending magma through fractures system and deep faults. The deep fracturing of Nayband fault has prevented the mixing of magma with crustal contamination. The high La/Nb value (with average 1.7) along with low ratio of Ce/Pb and Pb/Nd indicate low mixing of magma in the studied area. Also, none scattering compatible element plots show negligible magma mixing. Uniformity in crystal size distribution (CSD) plots and its constant slope indicate the low impact of physical processes such as magma mixing in basaltic magma which effects the crystallization of plagioclase microlites during its ascent to the surface. The main cause of steepness in CSD is the rapid quenching of basaltic magma during upwelling which leads to plagioclase fine microliths. The presence of olivine and clinopyroxene phenocrysts indicates that in the primary magma, crystallization had occurred before ascent and eruption. Based on Dy/Yb versus La/Yb plot the Gandom Beryian basalts were formed by 8 to 10% partial melting of a garnet-lehrzolite parental rock. In general, lower partial melting of upper mantle (less than 10%) leads to the creation of alkaline basaltic magma. On the other hand, Gandom Beryian basaltic magma has characteristics similar to a high magnesium parental magma with low degree of evolution.

The basic and rarely intermediate dyke swarms have been injected into one of the tonalitic bodies in the southwest of Soltan Abad. Amphibole is the main constituent of the most samples and variable modal abundance of epidote, plagioclase and white mica are observed. Chemical characteristics of amphiboles indicate their magmatic origin and compositional indicators along with barometry calculations point to their crystallization at high depths. Whole rock geochemical characteristics of dykes signifying basaltic composition with tholeiitic affinity. Their spider diagrams and rare earth elements patterns are compatible with amphibole accumulation and their generation in the subduction zone. On the basis of field evidences such as intimate spatial relation between dyke and the host tonalitic-trondhjemitic body and the paucity of amphibole in the intrusion bodies of the study area, the prevalence of hornblendite as cumulate in the orogenic belts and phase equilibria of water-bearing basalts a hypothesis of amphibole fractionation from an intermediate adakitic melt produced by subducted oceanic crust partial melting and the formation of amphibole-riched cumulate and felsic tonalitic-trondhjemitic melt. Magmatic origin of amphibole and its crystallization at relatively high depth, whole rock geochemical characteristics of dykes like low contents of SiO2 and upward convex of middle rare earth elements in the spider diagrams and furthermore according to the considerable contents of SiO2 and very prominent adakitic characteristics of host tonalite also support this phenomenon.