Ordovician-Devonian magmatism in the north of Shahrood: implication for long lived rifting of Paleotethys in eastern Alborz

One of the characteristics of the Ordovician to the Devonian rock units in the north of Shahrood is the presence of high volumes of igneous rocks with basaltic composition as dyke and sill. The greatest volume of these rocks are widespread in Soltan Meydan Basaltic Complex with a thickness of about 1000 m as numerous basaltic lava flows، basaltic agglomerates، tuffs and some sedimentary intercalations which have been formed during the upper Ordovician to the early late Silurian. Active extensional tectonic prevailing on the area and violent detaching in continental lithosphere in this interval time led to sudden decompression on the rising mantle plumes، providing conditions for extensive partial melting and generation of high volumes of basaltic magma. Geochemical evidences show that the produced magmas have transitional to alkaline nature and generated from a rising enriched mantle plume source in an extensional intracontinental rift setting. The nature and tectonic setting of this basaltic magmatism during the lower-middle Paleozoic indicate continuation of long lived extensional movements related to the earlier stages of Paleotethys rifting in the north of Iran.