Petrology
Mohammad Saadat; Robab Hajialioghli; Mohssen Moazzen
Abstract
The Qotur metamorphic complex in west of Khoy is consist of various metamorphic rocks including of metabasites, metapelitic and meta-calcareous rocks and serpentinites. The metagabbros form main outcropping rocks in the area. Plagioclase and pyroxene are the main porphyroclasts of metagabbros. Epidote, ...
Read More
The Qotur metamorphic complex in west of Khoy is consist of various metamorphic rocks including of metabasites, metapelitic and meta-calcareous rocks and serpentinites. The metagabbros form main outcropping rocks in the area. Plagioclase and pyroxene are the main porphyroclasts of metagabbros. Epidote, tremolite/actinolite, calcite and chlorite are formed during low grade metamorphism of these rocks. Based on geochemistry results, protolite compositions of the investigated rocks are plotted on the gabbroic field of the classification diagram. They have calc-alkaline magmatic series. Considering the discrimination tectonic diagrams the Qotur metagabbroic rocks have been formed at the island arc tectonic setting. On the basis of U-Pb zircon geochronological data, the rocks are formed at 162.6±7.6 Ma corresponds to the late Jurassic (Oxfordian). On the basis of results obtained from isotopic dating and geochemical data of the Qotur metagabbros, we suppose that they formed related to the sialic back arc basin of Neotethys, Jurrasic Island arc rocks of Sevan-Akera zone corresponds to the North branch of Neotethys oceanic suture and/or in continuation of the Piranshahr and Serow ophiolites as a Zagros-Bitlis Zone. However perecise results will be need to tectonic works and more geochemical and isotopic data from variety of metamorphic and igneous rocks.
M. R. Rezapour; V. Simmonds; M. Moazzen; R. Hajialioghli
Abstract
The Qohrud granitoid body of Miocene age is located 40 km SW Kashan, ranging in composition from granite through granodiorite to tonalite. Hydrothermal activities following the magma intrusion have brought about formation of various coarse automorphic and colored quartz crystals within the fractures ...
Read More
The Qohrud granitoid body of Miocene age is located 40 km SW Kashan, ranging in composition from granite through granodiorite to tonalite. Hydrothermal activities following the magma intrusion have brought about formation of various coarse automorphic and colored quartz crystals within the fractures and cavities of different lithologies. The quartz crystal varieties include transparent, semi-transparent, pale green, yellow and black crystals, as well as those with smoky and reddish brown roots and also crystals containing tiny acicular rutile inclusions. Mineral chemistry, as well as fluid and solid inclusion studies on the colored and automorphic quartz crystals indicate that various physical and chemical factors, such as temperature, pressure, magma and host rock compositions, hydrothermal fluids and the associated alterations, as well as pH and Eh were involved in the formation of these automorphic colored crystals. The solid inclusions within these automorphic quartz crystals might have formed in two ways: 1) introduction of the necessary elements for the formation of quartz and the solid inclusions by the fluids and then, entrapment of these inclusions within the growth layers of quartz crystals; 2) direct introduction of very fine mineral particles within the growth layers of quartz, leading to occurrence of various colored crystals. Smoky crystals can be formed by the replacement of Si by Al and also by the presence of U and Th within them. The reddish color of quartz crystals was recognized as the result of the presence of fine rutile needles. Automorphic black-colored quartz crystals are formed at oxidant and almost high pH conditions by initial precipitation of magnetite and then, manganese oxides at the outermost growth layers. The green quartz crystals have been resulted from chloritic and epidotic alterations within the host and neighboring rocks.
