Tectonic significance of the geochemistry and petrology of ophiolites in southeast Anatolia, Turkey

Abstract

The southeast Anatolian ophiolites form discontinuous linear belts of oceanic fragments immediately north of the Bitlis-Zagros suture, which marks a continental collision zone between the Arabian platform to the south and the Taurides to the north. The Late Cretaceous ophiolites in the southeast Anatolia are represented by the Kizildag in the Hatay area, the Goksun and the Berit to the north of Kahramanmaras, Ispendere in the Malatya area and Komurhan-Guleman in the Elazig area. The Goksun, Berit, Ispendere. Komurhan and Guleman ophiolites were attached to the base of the Tauride platform (i.e. the Malatya-Keban) along its northern active margin and intruded by the I-type calc-alkaline granitoids of Late Cretaceous age. In contrast, the Kizildag (Hatay) ophiolite was thrust over the Arabian passive margin in the south. The cumulate rocks in the ophiolites are represented by dunite, wehrlite, lherzolite, olivine clinopyroxenite, olivine gabbronorite, olivine gabbro, gabbronorite and gabbro. Highly magnesian olivines (Fo(88) (to 74)) and pyroxenes (Mg#(95 to 60)) as well as highly calcic plagioclases (An(95 to 68)) from the cumulate rocks differ from oceanic equivalents, which mainly formed from a MOR basaltic melt. The order of crystallization in mineral phases, whole rock and mineral chemistry data from the cumulates suggest that the primary magma is compositionaly similar to that observed in modern island arc tholeiitic sequences. The volcanic and subvolcanic rocks exhibit tholeiitic compositions. Chondrite normalized REE, N-MORB normalized multi-element patterns and tectonic discrimination diagrams suggest the existence of two main types of parental basic magmas in the crustal rocks of the SE Anatolian ophiolites. These are (i) IAT series that characterize the Kizildag, Goksun, Ispendere, Komurhan and Guleman ophiolites and (ii) Low-Ti boninitic series known only in the Kizildag ophiolite. The geochemistry of the crustal rocks suggests that they formed in a suprasubduction zone tectonic setting, including arc-forearc environments in the southern Neotethys. These well-preserved plutonic oceanic crustal remnants mainly exhibit an intact ophiolite pseudostratigraphy and are overlain by a volcanic-sedimentary unit made up of alternations of basic to acidic extrusive rocks, debris flows, volcaniclastic sandstones and pelagic limestones, interpreted as a tholeiitic ensimatic island arc assemblage built on the suprasubduction zone type crust. The metamorphism of some of the ophiolites (i.e. Berit) in the SE Anatolia might be related to later stages of intraoceanic subduction during the evolution of the southern Neotethys. (C) 2008 Elsevier B.V. All rights reserved