Alireza SHIRZADI¹, Seyed Jamal SHEYKHZAKARIYAYI¹, Abbas ASIABANHA REZAYI², Mohsen NASRABADY² & Chris HARRIS^3
1Islamic Azad University, Science and Research branch, Tehran, Iran.e-mail: alirezashirzadi@yahoo.com
¹Islamic Azad University, Science and Research branch, Tehran, Iran.e-mail: sheikhzakariaee@srbiau.ac.ir
²Department of Geology, Faculty of Science, imam khomeyni international university, Ghazvin, Iran.e-mail: asiabanha@tmu.ac.ir
²Department of Geology, Faculty of Science, imam khomeyni international university, Ghazvin, Iran.e-mail: nasrabadi@tmu.ac.ir
³Department of Geological Sciences, University of Cape Town, Rondebosch 7701, South Africa.e-mail: chris.harris@uct.ac.za

MINERALOGICAL CONSTRAINTS ON THE PETROGENESIS OF SUBVOLCANIC INTRUSIONS IN SABZEVAR OPHIOLITE (NE IRAN)

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The Upper Cretaceous Sabzevar Ophiolite, with an approximate area of 2000km², is located as a 200 km-long EW band, in the NE of Iran. According to previous work, three magmatic non-ophiolitic series are distinguished inspatial relation to this ophiolite of which the Oligo-Pliocene ADR subvolcanic rocks have been restudied in the current work with the aid of new petrographical and geochemical data. The studied rocks are distributed, as small or large dikes or domiform and coniform outcrops from the east to the west of the ophiolite. The magmatic series cover a rather extensive silica range from basaltic andesite to rhyolite (53-74 wt.%). The whole rock major element compositions define a medium K calc-alkaline subductionsuite. The rocks represent evolved melts from primitive parent. Garnet crystals in rhyolite yielded δ¹⁸O value of +5.9‰, which is consistent with the derivation of the rocks from mantle-derived parental magmas with a probable restricted source contamination from subducted materials and/or slight contamination with the crust. Amphibole-plagioclase pair geothermobarometric determination indicated magmatic temperatures and pressure of mineral equilibration in the range of 549-1073°C and 2.8-10.2 kb respectively. The main mechanism of differentiation was likely fractional crystallization.