COLLISION-INDUCED MANTLE DYNAMICS AND ITS MAGMATIC FINGERPRINT FOR CENOZOIC VOLCANISM IN THE PERI-ARABIAN REGION

Post-collisional Cenozoic magmatism in the peri-Arabian region evolved in three main pulses in the Eocene, late Miocene-Pliocene and Plio-Quaternary, and progressed from shoshonitic, calc-alkaline to more alkaline compositions towards the south through time. All volcanic sequences show similar trace element and REE patterns, with negative Nb, Ta, Hf, and Zr anomalies, strong enrichment in Rb, Ba, Th, La, and depletion in Ti, Yb, Y, relative to N-MORB, indicating a subduction-metasomatized lithospheric mantle as their melt source. Two coeval but separate collisional events within the Tethyan realm in the early Eocene were responsible for slab detachment and asthenospheric heat input: (1) collision of the Eastern Tauride-South Armenian microcontinent with the Eastern Pontide arc at a north-dipping subduction zone in the Northern Neo-Tethys, and (2) collision of the Arabian plate with the Bitlis-Pütürge and Sanandaj-Sirjan continental blocks at another north-dipping subduction zone in the Southern Neo-Tethys. The resulting partial melting of the subcontinental lithospheric mantle produced hybrid magmas that developed the post-collisional magmatic units in discrete, ~E-W-trending belts, straddling the early Eocene suture zones. The late Miocene through Plio-Quaternary volcanic sequences occupy much of the Turkish-Iranian high plateau, Lesser Caucasus, peri-Caspian area, and Central Iranian Volcanic Belt, and occur as fissure eruptions and stratovolcanic centers mainly along NW-SE-trending transtensional, dextral strike-slip fault systems. Although these volcanic sequences display increased alkalinity in successively younger units, their high La/Nb ratios and LILE enrichment indicate a hint of subduction zone influence in their mantle melt source. This inherited subduction fingerprint in the Plio-Quaternary volcanic units suggests the existence of some mantle lithosphere beneath the modern Turkish-Iranian plateau. Partial melting of an upwelling asthenosphere in the hinterland of the Arabia-Eurasia collision zone contributed a greater enrichment in alkali content of the younger magmas, and it was triggered by delamination of the mantle lithosphere on a regional scale.