Petrology
Mahsa Jamshidnia; manijeh Asadpour; Masoumeh Ahangari
Abstract
Qushchi gneisses in the north of Urmia city are a part of magmatic-metamorphic complex in NW of Sanandaj-Sirjan zone. Gneiss, with eldsparses and schist, form Precambrian basement of the area. These rocks contain lipidogranoblastic, augen, porphyroblastic and myrmekite textures, and composed of quartz+ ...
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Qushchi gneisses in the north of Urmia city are a part of magmatic-metamorphic complex in NW of Sanandaj-Sirjan zone. Gneiss, with eldsparses and schist, form Precambrian basement of the area. These rocks contain lipidogranoblastic, augen, porphyroblastic and myrmekite textures, and composed of quartz+ alkaline eldspars (orthoclase and microcline perthites) + plagioclase+ biotite± pyroxene, muscovite± amphibole± epidote +zircon+ opaque. Field, petrography and geochemical evidences were used to know the genesis of igneous (ortho) or sedimentary (para) of these gneisses. All the evidences imply an igneous origin (ortho) for the studied gneisses. In fact, the protolith of these gneisses are porphyritic granite to monzonite rocks and has calcareous-alkaline and peraluminous nature. It can be inferred that the protolith of these rocks which formed in the late Neoproterozoic, belong to the calc-alkaline magmas in active continental margins or volcanic arcs (VAG). Further tectonic events have transformed them into gneisses.
Petrology
manijeh Asadpour; Soraya Heuss
Abstract
Acidic patches with alkali-granite nature have been intruded within the mafic rocks of the Qushchi complex (70 Km north of Urmia city). This area is northwestern part of the SSz zone with Precambrian basement. These granits have high amounts of K2O and SiO2 (over 70 wt%). Dating by U-Pb age of zircon ...
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Acidic patches with alkali-granite nature have been intruded within the mafic rocks of the Qushchi complex (70 Km north of Urmia city). This area is northwestern part of the SSz zone with Precambrian basement. These granits have high amounts of K2O and SiO2 (over 70 wt%). Dating by U-Pb age of zircon grains show 303.4 ± 2.2 Ma, indicating late Carboniferous - early Permian magma activity. The presence of older cores in some of zircon grains with age between 400 to 600 Ma, indicate presence of older rocks in the study area. The whole-rock isotopic analysis show negative initial Nd (t) = -1.3 with TDM = 1.61. These data provide evidence for partial melting of crust (with Neoproterozoic- Cambrian age) in early Permian. The 87Sr/86Sr = 0.752348 and εNd = -1.4 of whole rock and Th/U (>0.5) values in zircons show the involvement of more crustal and less mantle components, during the opening of Neo-Tethys Ocean. Due to the same mineralogical and geochemical composition and homogeneity with Qushchi granite, it is inferred that these patches are genetically related to Qushchi granite and are A type granite.
M. Asadpour; S. Heuss
Abstract
The Ghalghachi leucogranite intrussion with approximately 2 Km2 is located in west Urmia Lake and 70 Km north of Urmia city. This intrussion in form of small stock has intruded into Precambrian metamorphic rocks including gneiss, schist and amphibolite. This area is part of the Sanandaj-Sirjan zone in ...
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The Ghalghachi leucogranite intrussion with approximately 2 Km2 is located in west Urmia Lake and 70 Km north of Urmia city. This intrussion in form of small stock has intruded into Precambrian metamorphic rocks including gneiss, schist and amphibolite. This area is part of the Sanandaj-Sirjan zone in northwestern of Iran. This is the first time that age of leucogranite was determined by LA-ICP-MS zircon grains 558.6 ± 3.8 Ma that indicates acidic magmatic activity and the presence of Pan-African basement similar to the central Iran. The presence of older cores in some of zircon grains with age between 900 to 2500 Ma suggest the presence of older rocks in the study area. The rock show negative initial eNd (t) values of -4.3 with TDM 1.61 that are consistent with partial melting of a primary crust (with Paleoprotrozoic age) that was formed during the Neoproterozoic the same as Arabian Shield. The 87Sr/86Sr and εNd of whole rock and Th/U values in zircons show the involvement of more crustal and less mantle components, during the opening of Paleotethys Ocean.