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
Masoumeh Ahangari; Mohssen Moazzen
Abstract
Amphiboles in olivine-bearing hornblende- gabbros from NW of Salmas were crystallized in various textures including oikocryst and interstitial textures in the matrix, outer part of reaction rims around olivine, and at the rim and cleavages of clinopyroxene. On the basis of petrographical and textural ...
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Amphiboles in olivine-bearing hornblende- gabbros from NW of Salmas were crystallized in various textures including oikocryst and interstitial textures in the matrix, outer part of reaction rims around olivine, and at the rim and cleavages of clinopyroxene. On the basis of petrographical and textural studies, amphiboles were formed later than the other minerals in the olivine-bearing hornblende- gabbros. The REE and trace element composition of amphiboles from two different textures including interstitial and matrix amphiboles (group one) and amphiboles after clinopyroxenes (group two), indicate that the studied amphiboles were formed by either crystallization of interstitial melt/fluid or interaction of interstitial melt/fluid with early crystalized minerals such as clinopyroxene and plagioclase. Hence, according to the textural and mineralogical data and trace element composition of amphiboles, olivine-bearing hornblende- gabbros were crystallized at least at two stages. The first stage include fractional crystallization and formation of olivine, clinopyroxene and plagioclase and the second stage was interaction of the relict melt/fluid with early crystalized minerals, specially clinopyroxene and plagioclase and formation of amphibole.
