Stratigraphy and Palaeontology
Zahra Khajehjavaran; Gholam Reza Ghadami; Mohammad Poosti; Abbas Moradian; Behrouz Karimi Shahraki
Abstract
Andesites are located in the north of shahr-e-babak , central Iran, Urumieh- Dokhtar belt. The main texture in these rocks is porphyry and their phenocrysts are plagioclase (Andesine to Labradorite), pyroxene (Augite), amphibol (Tschermakite and Magnesiohornblende). These properties are signatures of ...
Read More
Andesites are located in the north of shahr-e-babak , central Iran, Urumieh- Dokhtar belt. The main texture in these rocks is porphyry and their phenocrysts are plagioclase (Andesine to Labradorite), pyroxene (Augite), amphibol (Tschermakite and Magnesiohornblende). These properties are signatures of calc- alkaline series formed in a volcanic arc setting. Based on geochemical studies, the rocks show enrichment in LREE rather than HREE. The lack of significant Eu anomalies in REE pattern indicates oxidation state of magma during crystallization. Based on geochemical studies, the clinopyroxenes are Augite and have been crystallized from magma with almost 10% H2O. Fe3+ values of the clinopyroxenes reveal high oxygen fugacity in the magma. Based on the mineral chemistry data, pressure estimates from the clinopyroxenes in the range of 6-10 Kbr and composition yield the crystalization temperatures that range from 900-1100 OC. Typically, clinopyroxenes occure at calc-alkaline orogenic igneous rocks. The plagioclase composition yield the crystalization temperatures that range from 650-750 OC. According to the present study, the rocks are probably the result of the subduction of the Neo-Tethys oceanic lithosphere below the Sanandaj-Sirjan zone, during the Eocene and in a volcanic arc environment.
Economic Geology
Seyevahid Shahrokhi
Abstract
The chemical composition of chlorite group minerals show that physicochemical condition of crystallization and their formation. The chemical analysis of chlorite from biotite alteration has done based on 30 points of 8 rock samples by electron microprobe. The composition of chlorite samples is located ...
Read More
The chemical composition of chlorite group minerals show that physicochemical condition of crystallization and their formation. The chemical analysis of chlorite from biotite alteration has done based on 30 points of 8 rock samples by electron microprobe. The composition of chlorite samples is located in repidolite- pychnochlorite domain. The mole fraction in the interlayer phase, range from 0.97 to 0.99, indicating a complete lack of smectite layers and purity of chlorite. Calculation of the structural formula of chlorites in Malvak area show that the number of silicon atoms are in the range of 2.64 to 2.91 (apfu) and the sum of the octahedral cations are 6 (apfu). Chlorites of the Malvak area are trioctahedral type. The low titanium content of chlorites, the presence of titanium minerals coexite with chlorite cleavage, and the presence of early biotite crystals are evidence of biotite to chlorite alteration. The mean temperature of chlorites in the Malvak area is 340 ºC, which corresponds to the temperature obtained with the geothermometry of biotite-altered to chlorites. Mesothermal type fluids from the granitoid mass in the study area have been effective in chlorite occurrence. Also, regional metamorphism has played an important role in the chlorite formation.
Ramin Samadi; M. V. Valizadeh; H. Mirnejad; H. Kawabata
Abstract
Metamorphic rocks of Dehnow area mainly consist of gray to black fine-grained schists. Garnet schists are closer to the tonalitic body than the garnet chloritoid schists. There is a thin layer of staurolite and andalusite bearing hornfels between these schists and the Dehnow tonalitic body. Garnet schists ...
Read More
Metamorphic rocks of Dehnow area mainly consist of gray to black fine-grained schists. Garnet schists are closer to the tonalitic body than the garnet chloritoid schists. There is a thin layer of staurolite and andalusite bearing hornfels between these schists and the Dehnow tonalitic body. Garnet schists and garnet chloritoid schists of Dehnow area are mineralogically comprised of quartz, biotite, muscovite, garnet, chlorite, chloritoid, tourmaline and ilmenite. Geothermobarometry results indicate that hornfels (550oC, 4.3 kbar) and garnet chloritoid schist (486-497oC) have formed in lower equilibrium condition in comparison with garnet schist (569oC, 5.3 kbar).