Petrology
Najla Saki; Ghasem Ghorbani
Abstract
The study area is located in the N Turood, S Shahrood, and NE of Central Iran structural zone. Many basaltic dikes in this area intruded into the Eocene volcanic rocks and they also contain many gabbroic enclaves. Plagioclase (labradorite, bytownite-anorthite), amphibole (calcic, pargasite- magnesiohastingsite), ...
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The study area is located in the N Turood, S Shahrood, and NE of Central Iran structural zone. Many basaltic dikes in this area intruded into the Eocene volcanic rocks and they also contain many gabbroic enclaves. Plagioclase (labradorite, bytownite-anorthite), amphibole (calcic, pargasite- magnesiohastingsite), and pyroxene (calcic, diopside-augite) are the essential minerals of these rocks. With the attention of the minerals chemistry, magma forming of these rocks has mainly subalkaline nature and during their crystallization fugacity of oxygen has been high. Geothermometry of these rocks suggest crystallization equilibrium temperatures are at 1100-1200°C for pyroxenes, and 825-888°C for amphiboles. Geobarometry calculation by using of Altot of amphiboles in host basaltic rocks, basaltic dikes and enclaves estimated between 8.51 to 9.21 kbar (depth of 30 to 33 km), 7.41 to 9.16 kbar (depth of 27 to 33 km) and 6.84 to 7.46 kbar (depth of 25 to 27 km), respectively. The chemical characteristics of studied minerals in differents diagrams show strong compositional similarities and indicate that nature and origin of these rocks are the same and most likely the magmatic reservoir or reservoirs of the studied basaltic rocks were at depths of 33 to 25 km of the lower crust.
Economic Geology
Morteza Delavari; Amir Ali Tabakh Shabani; Samaneh Ghanbari
Abstract
The Oligocene dacitic volcanic rocks display widespread exposures in south of Julfa (eastern Azerbaijan). They generally show porphyritic to hyalo-porphyritic textures with major minerals of plagioclase, amphibole, quartz and biotite. Electron probe micro analyzer (EPMA) data indicates oscillatory zoning ...
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The Oligocene dacitic volcanic rocks display widespread exposures in south of Julfa (eastern Azerbaijan). They generally show porphyritic to hyalo-porphyritic textures with major minerals of plagioclase, amphibole, quartz and biotite. Electron probe micro analyzer (EPMA) data indicates oscillatory zoning and chemical variation of amphiboles (pargasite and edenite). The plagioclase crystals are, chemically, andesine (An= 29-51%) which mostly display oscillatory zoning. Based on geobarometric calculations, plagioclase displays pressures of 5 to 8 kb and amphiboles demonstrate different pressure ranges of 1.5 to 3 and 5 to 9 kb. Moreover, geothermometric calculations of plagioclase and amphibole provide temperatures of 1020-1050 and 850-900 °C, respectively. On the basis of geobarometric results, crystallization and growth of the minerals took place in magmatic chambers of different levels. Some of the amphiboles nucleated in lower continental crust and subsequently grown during magma ascent in middle crust whereas some others crystallized in the upper continental crust. Therefore, existence of minerals of different levels inside the studied rocks could be related to magma mixing in shallow magma chambers.
Petrology
Nargess Shirdashtzadeh; Ghodrat Torabi
Abstract
In this study, some mantle lherzolites of Ashin ophiolite are investigated which contain evidence of a geotectonic/metamorphism during exhumation and obduction of oceanic lithosphere on the continental crust, after closure of Neo-Tethys Ocean. Based on petrography, their primary rock-forming minerals ...
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In this study, some mantle lherzolites of Ashin ophiolite are investigated which contain evidence of a geotectonic/metamorphism during exhumation and obduction of oceanic lithosphere on the continental crust, after closure of Neo-Tethys Ocean. Based on petrography, their primary rock-forming minerals are orthopyroxene, clinopyroxene, olivine, and chromian spinel. Mineralogy and geothermobarometry indicate that these 4-phase lherzolites were formed in the lithospheric mantle (at pressures ~ 21.6 to 8.6 kbar) by melt/wall rock reactions (at temperatures ~ 1012-1183 °C). Then, they were emplaced and obducted on the continental crust along the fault zone of this region, and consequently deformed. The first ductile deformation event occurred in the depth of lithosphere and resulted in high-temperature mylonitization at temperatures higher than 600 to 800 °C. Mineralogical features confirm pressure decreasing of this stage by subsolidus reaction of pyroxene and spinel and substitution of plagioclase and olivine. Therefore, petrography and thermobarometry data are indicative of the spinel to plagioclase lherzolite facies for these rocks. Finally, they partially underwent brittle and cataclastic deformation at temperatures below 600°C and lower pressures and depth during exhumation. However, most of plagioclases were replaced by with prehnite, pumpellyite, chlorite, hydrogrossular and xonotlite minerals by further alterations.
F. Rostami; M. Delavari; S. Amini; A. Dolati
Abstract
The Permian volcanic rocks of Central Alborz (northeast of Baladeh- Siahbisheh) crop out between Ruteh and Nesen Formations. The volcanic rocks are predominantly basaltic and plagioclase- phyric. Ferromagnesian minerals such as clinopyroxene and olivine are not modally abundant and sometimes are totally ...
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The Permian volcanic rocks of Central Alborz (northeast of Baladeh- Siahbisheh) crop out between Ruteh and Nesen Formations. The volcanic rocks are predominantly basaltic and plagioclase- phyric. Ferromagnesian minerals such as clinopyroxene and olivine are not modally abundant and sometimes are totally altered. Based on microprobe data, clinopyroxene and plagioclase are diopside (En34.2-36.4 Wo43.1-47.2 Fs14.9-18.1) and labradorite (50<An%<55), respectively. Clinopyroxene and plagioclase geothermobarometric calculations shows the temperature and pressure ranges of 1050 to 1200 °C and 2 contents (4.94- 7.24 wt. %). Clinopyroxene chemical data display that the parent melt was alkaline basalt, generated in a within plate setting. On the basis of our findings it can be stated that, Central Alborz was a continental passive margin in middle- late Permian at south of Paleo-Tethys and its magmatism was likely triggered by late Paleozoic extensional tectonism of northern margin of Gondwana during the early stages of Neo-Tethyan development.
N. Khanmohammadi; A. Khakzad; J. Izadyar
Abstract
Zaker iron deposit is located in the northeast of Zanjan city and is a part of Tarom volcano – plutonic belt in Azarbaijan – West alborze structural zone. The main rocks of the area consist of folded volcanic - volcanoclastic rocks including breccia tuff, lapilli-tuff and andezitic – ...
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Zaker iron deposit is located in the northeast of Zanjan city and is a part of Tarom volcano – plutonic belt in Azarbaijan – West alborze structural zone. The main rocks of the area consist of folded volcanic - volcanoclastic rocks including breccia tuff, lapilli-tuff and andezitic – basaltic lava of Amand member of Karaj formation with Eocene age that folded. Plutonic rocks with probably Oligocene age with various lithology changing from quartzmonzodiorite, quartzmonzonite to quartzsyenite with NW-SE trend were intruded into the volcanic – volcanoclastic rocks. Fe-mineralization occurred in interval of plutons and volcanic - volcanoclastic rocks. The main ore mineral is magnetite – apatite with minor amounts of quartz and calcite. As well as magnetite- apatite mineralization, pyrite with minor amounts of chalcopyrite occurred in sulphide veinlets. The mineralization has been seen in five forms: veinlets of magnetite in form of stock- work, massive magnetite- apatite, banded magnetite- apatite, coarse grained magnetite- apatite veins and sulphide veinlets. Intrusion of ore deposit into host volcanic rocks, are associated with skarn metasomatism that form actinolite, talc, chlorite, phlogopite, quartze, calcite and epidote. Geothermobarometry for the skarn part, indicate that XCO2 is about 0.9, pressure of 2 kbar and the temperature is about 400-500 0C for metamorphic reactions. Detailed studies on textures and structures suggest the source of the iron from Zaker granitoid body and volcanic rocks are host rocks for iron deposit. Mineralography investigations are indicative of magmatic origin and show the best correlation with "Kiruna–type" iron ores.