Quaternary syn-collision magmatism from the Iran/Turkey borderlands

Quaternary basaltic and andesitic lavas from the NW Iran/eastern Turkey border area are related to the active Arabia–Eurasia collision. The lavas occur within the Turkish–Iranian plateau, which ceased crustal thickening before the establishment of a number of volcanic centres within Iran and eastern Turkey, beginning at ~ 10 Ma. Models for generating syn-collision magmatism in eastern Anatolia have invoked slab-break-off beneath the thick crust and thin mantle lithosphere of the Cenozoic East Anatolia Accretionary Complex and/or partial loss of the lower lithosphere. Here we report geochemical and Sm–Nd/Rb–Sr data from a ~ 200 km long, N–S traverse that samples volcanic flows in NW Iran, many of which originate from centres in Turkey such as Ararat and Tendürek. Samples are transitional alkali/tholeiitic basalts and andesites. Ararat samples have lower Nb, lower large ion lithophile element (LILE) concentrations with 143Nd/144Nd ~ 0.51290. Other, volumetrically smaller, centres have higher Nb, higher LILE, with 143Nd/144Nd ~ 0.51265. Abundances of LILE and Nb increase from north to south. The presumed degree of partial melting increases in the opposite direction, away from the Arabia–Eurasia suture. Melting is inferred to have taken place in the spinel lherzolite field, largely from a continental lithosphere source influenced by Mesozoic and early Cenozoic Neo-Tethyan subduction, but a separate source with long-term enrichment is needed to explain the high Nb, lower 143Nd/144Nd compositions.