The origin and tectonomagmatic setting of Taleghan Tertiary volcanic rocks

Alborz Tertiary magmatic activity is mainly attributed to the subduction of Neo-Tethyan oceanic slab; however, the details, such as the source of magmas, are poorly understood. In this resaerch, on the basis of major and trace element geochemistry of Tertiary volcanic rocks from Taleghan, the mantle source characteristics of the volcanic rocks are investigated and a tectonomagmatic model is proposed. Tertiary volcanism in the Taleghan area, as a part of central-western Alborz magmatism, embrace a sequence of mainly basic volcanic rocks that are overlain the Karaj Formation subunits. The Tertiary volcanic sequence in the Taleghan is, from bottom to the top, as follows; 1-basalt-analcime bearing basalt unit, 2 tephrite unit and 3- olivine basalt-trachy basalt unit. The first two units demonstrate the geochemical characteristics of active continental margin volcanics derived from an enriched lithospheric mantle while olivine basalt-trachy basalt unit show the geochemical characteristics of intraplate volcanics derived from asthenospheric plumes. The coincidence of lithosphereic and asthenospheric mantle sources in petrogenesis of Taleghan volcanic rocks is the likely consequence of a postorogenic extensional (relaxation) geodynamic.