Petrology of the Paleogene shoshonitic volcanism in north Sarab area, NW Iran: Geochemical, Ar-Ar dating and Sr-Nd-Pb isotopic constraints

Abstract

This study reports the earliest presumably known collisional magmatism of the NW Iran–eastern Turkey–Caucasus region from the north of Sarab city in East Azarbaijan province, NW Iran. Volcanic rocks of the area comprise alternating lava flows of mainly alkalibasalt, andesite, trachyandesite, dacite and pyroclastics (tuff and ignimbrite) affiliated with high-K calk-alkaline to shoshonitic magmatic series. Ar–Ar geochronology of the glass, matrix and plagioclase laths revealed crystallization time restricted to Late Eocene to Early Oligocene (34.90–30.69 Ma) which is coincident with the onset of the Arabian-Eurasian continental collision. Geochemical data show LREE enrichment compared with HREE and Nb and Ti depletion, indicating that they are subduction related. The Sr-Nd-Pb isotopic data reflect the incorporation of oceanic sediment into the magma source. We suggest that the volcanic rocks were generated from a metasomatised subcontinental lithospheric mantle source through 5 to 10 vol% partial melting in an extensional back arc basin by the Neotethys slab roll-back under the Iranian plateau.

Keywords

• Volcanic rocks
• Shoshonitic arc magmatism
• Isotope geochemistry
• Sarab
• Alborz
• Iran