K. Mohammadiha; M. Sabzehie; M. Ghahraei pour; A. Kosari Torbehbar
Abstract
Located in the NW Iran, in Sanadaj-Sirjan metamorphic belt, the studied area mainly comprises of metamorphic and varied acidic-basic igneous originated rocks. Basic metamorphic rocks have been chemically controlled by two main metamorphic processes including metasomatism and dynamic deformation. Amphibole ...
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Located in the NW Iran, in Sanadaj-Sirjan metamorphic belt, the studied area mainly comprises of metamorphic and varied acidic-basic igneous originated rocks. Basic metamorphic rocks have been chemically controlled by two main metamorphic processes including metasomatism and dynamic deformation. Amphibole and plagioclase are of the most significant minerals occurring in the rocks. Here we represent the chemical variations of those metamorphic minerals in relation to their host rocks and prograde metamorphism. Mineral chemistry analyses of amphibole minerals reveal an increase in Al2O3, TiO2 and a decrease in MgO, MnO during mylonitization of gabbroic rocks. Affected by metasomatism, the Al2O3 and Na2O contents of amphiboles have been also increased. CaO content of plagioclase has declined; in contrast, Al2O3 and Na2O have raised during mylonitization and metasomatism processes. These variations are overally ruled by chemical composition of the intruded pluton, pressure-temperature condition, oxygen fugacity and occurrence of equilibrant phases. Increasing Al and Na brings about tschermakite substitution in the deformed amphiboles and edinite substitution in the metasomatized rocks respectively.
R. Kohansal; S. Zolfaghari; M. Ghahraie - Pour
Abstract
The study area is a small part of the Sabzevar structural zone and confined between Semnan and Khorasan provinces. The oldest sedimentary rocks of this region are Middle Jurassic in age with horizons of calc-alkaline rhyolitic- rhyodacitic lavas in between. First appearance of alkaline basaltic lavas, ...
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The study area is a small part of the Sabzevar structural zone and confined between Semnan and Khorasan provinces. The oldest sedimentary rocks of this region are Middle Jurassic in age with horizons of calc-alkaline rhyolitic- rhyodacitic lavas in between. First appearance of alkaline basaltic lavas, intruded by diabasic dikes in this region appeared along with Early Cretaceous limestone. Late Cretaceous rocks include voluminous calc-alkaline rhyodacitic- rhyolitic and trachyandesitic composition as lavas and dikes, and basaltic dikes with abundant pinkish-cream plagic limestone. This has been overlaid by Paleocene rocks. Harker element variation diagrams indicate contamination and differentiation of basic magma, from a depleted mantel, which is also confirmed with spider diagrams. Tectonomagmatic signatures of Middle Jurassic and Upper Cretaceous volcanic rocks are similar to volcanic arc and syn-collisional magmas which have formed by tectonic movements of Middle Cimmerian and Laramid. Furthermore Austrian orogeny has led to development of Lower Cretaceous basic volcanic rocks within continental plate that are demonstrated in binary and ternary trace element diagrams. The Late Cretaceous-Early Tertiary Laramid orogeny leads to closure of the Neo-Tethys basin by folding and uplifting of the study area. Just in the Marri area lack of intrusive rocks pertaining to mature ophiolitic assemblage, presence of volcano-sedimentary rocks in the upper part of this succession from one side, and abundance of pressure and strike-slip faults with similar mechanism of Doruneh fault from other side, suggest an old suture zone and fast closure of this part of Doruneh- Kashmar trough, and development of colored melange in this area.