Petrology and geochemistry of basic rocks of the Piranshahr Ophiolitic complex in Zagros belt (NW Iran), compared with the similar rocks from Iraqi Zagros ophiolitic complex
Subject Areas :Keywords: Basic rocks Zagros ophiolite belt , Supra-subduction Iran Iraq,
Abstract :
The Piranshahr ophiolitic complex is located in NW Iran and in the north west of Piranshahr town. Tectonically, the NW Piranshahr ophiolitic complex is severely mingled and the boundary of different units in this complex is indistinguishable. Piranshahr ophiolite includes ultramafic, mafic, sedimentary and metamorphic rocks. Basic rocks with basalt and diabase compositions are exposed in several parts of the region. In this paper, whole rocks geochemistry and petrogenesis of basic rocks were studied in the Piramshahr ophiolite (in the Mashkan and Gerdikavalan areas) and were compared with the geochemistry of basic rocks located in the west of Mawat ophiolite in Iraq (in the Hasanbag, Walash and Neopurdan regions). Composition of basic rocks of Mashkan area in Piranshahr ophiolite and Hasanbag area in Iraq ophiolite is calc-alkaline in nature and depleted with respect to MREE, HREE,Zr, Hf, Y, Ti elements and enriched in Rb, Cs, Ba, U, Th, Pb, LREE elements with negative Ta, Nb anomalies. These geochemical features show that the source of magma was generated in the supra-subduction zone tectonic settings. Composition of basic rocks of Gerdikavalan area in Piranshahr ophiolite and similar rocks in the Walash-Neopurdan areas in Iraq ophiolite represent tholeiitic nature. Tholeiitic nature in these areas show both MORB and volcanic arc affinity. It seems that the tholeiitic magma was probably generated in the lithospheric extension over on subduction zone and these features conform asupra-subduction setting for basic rocks in Piranshahr ophiolite and similar rocks in western continuation of Iraq ophiolitic complex.
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