The Eldivan ophiolite and volcanic rocks in the Izmir-Ankara-Erzincan suture zone, northern Turkey: Geochronology, whole-rock geochemical and Nd-Sr-Pb isotope characteristics.

Gabbros and dolerite dikes of the Eldivan ophiolite and basaltic volcanic rocks of the ophiolitic mélange in the central part of the ?zmir-Ankara-Erzincan (IAE) suture zone were investigated for their 40Ar/39Ar age and whole-rock-major-trace element and Sr-Nd-Pb isotope compositions. Based on geological and geochemical characteristics basaltic volcanic rocks in the ophiolitic mélange are subdivided into two groups (Groups I and II) with ocean island basalts or enriched mid-ocean ridge basalt characteristics, respectively. Gabbros and dolerite dikes of the Eldivan ophiolite (Groups III and IV) have instead geochemical compositions indicative of a subduction-related environment. The volcanic rocks of Group I have 87Sr/86Sr(i) between 0.7037 and 0.7044, ?Nd(i)-DM of - 4.5 to - 5.6, and 206Pb/204Pb(i) ranging between 18.35 and 18.75. Group II volcanic rocks have higher 87Sr/86Sr(i) values (0.7049-0.7055), ?Nd(i)-DM ranging between - 5.4 and - 6.0, and 206Pb/204Pb(i) between 18.14 and 18.62. The Nd isotopic signatures and 207Pb/204Pb(i) values of the volcanic rocks of both groups point to a different source with respect to those of the Eldivan ophiolite. The low 206Pb/204Pb(i) values relative to the ophiolitic rocks seem to exclude a significant contribution from a HIMU reservoir, whereas the 207Pb/204Pb(i) values slightly above the NHRL might indicate some contribution from an EM2-type reservoir. Gabbros (Group III) of the Eldivan ophiolite and dolerite dikes (Group IV) cross-cutting the ultramafic part of the ophiolite show 87Sr/86Sr(i) between 0.7038 and 0.7053, ?Nd(i)-DM from - 2 to - 3.6 and 206Pb/204Pb(i) between 18.10 and 18.80. The gabbros yield ca. 150 Ma 40Ar/39Ar amphibole-plateau ages, which, together with the geochemical data, indicate that they were produced above subducted oceanic lithosphere in the IAE ocean domain in Late Jurassic times. Therefore, the Eldivan ophiolite in the IAE suture zone constitutes a link between the Hellenide-Dinaride ophiolite belts to the west and the Armenian-Iranian ophiolites to the east.