morteza delavari; Fatemeh Arab Asadi; Ali Mohammadi
Abstract
Extensive sedimentary- igneous rock associations of Paleozoic age crop out in southwest of Julfa (northwest of Iran). Geochemically, the igneous rocks display various basic to acidic ...
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Extensive sedimentary- igneous rock associations of Paleozoic age crop out in southwest of Julfa (northwest of Iran). Geochemically, the igneous rocks display various basic to acidic compositions. The basic rocks occur as several lava flows intercalated with Devonian siliciclastic units. Also, the acidic igneous rocks consist of rhyolitic lavas and associated pyroclastics (tuffs and ignimbrites). Based on zircon U-Pb dating, the acidic volcanics represent the age of 297±4 Ma (Carboniferous- Permian boundary). The Devonian basic volcanics are chemically sodic alkaline and characterized by fractionated rare earth element (REE) patterns (LaN/YbN=5.2-17). Furthermore, trace element chemistry of Devonian volcanics implies their formation in within-plate and non-subduction zone environment in accord with Devonian magmatism in other parts of Iran (Alborz and Central Iran). On the other hand, the major and trace element chemistry of acidic volcanics suggests their similarity to A (A2)-type granitoids. Therefore, the Permian acidic magmatism is probably related to an anorogenic (post-collisional) tectonic setting which in this case, the effects of the Hercynian orogeny in northwest of Iran could be assumed.
