Petrology
M. Sadeghian; S. H. Hosseini; A. Hemmati; S. Shekari
Abstract
Granitoid plutons of SW Mayamey (60 Km east of Shahrood), located at the most northern margin of the central Iran structural zone, have granite composition (in general) and calk alkaline and peralouminous nature. In spite of coverage of these granitoids by Late Triassic – Early Jurassic sedimentary ...
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Granitoid plutons of SW Mayamey (60 Km east of Shahrood), located at the most northern margin of the central Iran structural zone, have granite composition (in general) and calk alkaline and peralouminous nature. In spite of coverage of these granitoids by Late Triassic – Early Jurassic sedimentary rocks, Late Neoproterozoic host gneiss are exposed in limited areas. These granitoids invaded by two series of the Late Neoproterozoic and middle Jurassic diabasic dikes. Although post – Liass, Pre- Dogger, younger than Jurassic and older than Cretaceous ages are considered for these granitoids, but for the first time U–Pb age dating on separated zircons indicates Late Neoproterozoic age (Late Ediacaran) (545±10 Ma) for them and they are a part of very ancient basement rocks of Iran. The studied rocks are similar Band -e-Hezar Chah, Sefid Sang, Delbar, Shotor Kuh, Reza Abad and Do Chah granitoids in age. Mayamey granitoids are resulted from partial melting of metapelites and metagraywackes, and they belong to S-type granioids. SW Mayamey granitoids were generated in a collisional tectonic setting in the Late Neoproterozoic, in relation to closing of intracontinental back arc basin and then metamorphism of the associated rocks from greenschist facies to amphibolite and rarely granulite facies, which finally companied with s-type granitization
M Sadeghian; S Shekari
Abstract
Darreh-Bagh granitoidic pluton in the northwest of Aligoodarz composed of two felsic and mafic parts, with lithological composition range from diorite to quartzdiorite, and granodiorite to leucogranite respectively. Felsic rocks have calc-alkaline and peraluminous affinity and belong to S-type and continental ...
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Darreh-Bagh granitoidic pluton in the northwest of Aligoodarz composed of two felsic and mafic parts, with lithological composition range from diorite to quartzdiorite, and granodiorite to leucogranite respectively. Felsic rocks have calc-alkaline and peraluminous affinity and belong to S-type and continental arc granitoids (CAG). The most significant characterizes of felsic part are as follows: presence of the metapelitic andalusite bearing enclaves, silica (quartz fragments which inherited from quartz vein with metamorphic origin), surmicaceous and metapasamitic enclaves and also andalusitic xenocrysts through out of the felsic part. Mafic rocks have calc-alkaline and metaluminous affinity and belong to I-type and continental arc granitoids (CAG). Based on the field observations, petrographical and geochemical characterictics, penetration of basic-intermediate magmas into late Triassic - lower Jurassic metapelites and metagraywackes caused to rise temperature up to produce a large scale contact metamorphism including andalusite hornfels and sillimanite hornfels. Intersecting the temperature of melting point of metapelites and metagraywackes resulted in producing melts with suitable composition for forming of S – type granitoid plutons. Then, the produced magma ascended to the higher levels in the upper crust and emplaced in it. Granitoid magmas emplacement are associated with low-extent contact metamorphism up to cordierite hornfels facies.
A Aslani; S Shekari
Abstract
The southern Alvand granitoid with an area of 120 km2 is situated at south and southwest of Hamedan city. The porphyry biotite bearing granitoids are the main constitute of the pluton. Biotite is responsible for magnetic behavior of this pluton. The magnetic lineation (L), foliation (F), and anisotropy ...
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The southern Alvand granitoid with an area of 120 km2 is situated at south and southwest of Hamedan city. The porphyry biotite bearing granitoids are the main constitute of the pluton. Biotite is responsible for magnetic behavior of this pluton. The magnetic lineation (L), foliation (F), and anisotropy (P) parameters of oriented samples of 107 stations were measured at environmental and paleomagnetic laboratory based in Geological Survey of Iran, Tehran, Iran. The analysis of these parameters revealed there exist reverse relationship between dipping angle of magnetic lineation and foliation with their numerical magnitude, and magnetic lineation and foliation are accordance with magnetic anisotropy in Alvand granitoid. The above mentioned relationship may resulted due to interaction of different effective forces during ascending and emplacement of magma as well as their ability in ordering magnetic minerals in various positions within the magma. As ordering the magnetic minerals increasing, the numerical magnitude of magnetic lineation and foliation also, increase. The microstructural analysis also showed that most of the observed orientation in enclaves and alkali feldspars of the studied area is due to magma flow. In this study, where ever the numerical magnitude of magnetic lineation was high, the magnetic ellipsoid was prolate and where ever the numerical magnitude of magnetic foliation was high, the magnetic ellipsoid was oblate. The Darreh-Bagh granitoid of northwest of Aligodarz city in Sanandaj- Sirjan zone, shows the same relationships between magnetic parameters and is used as a support in this study.
