GEOCHEMICAL AND PETROLOGICAL CHARACTERISTICS OF LATE TRIASSIC BASIC VOLCANIC ROCKS FROM THE KOCALI COMPLEX; SE TURKEY: IMPLICATIONS FOR THE TRIASSIC EVOLUTION OF SOUTHERN TETHYS

Abstract

The Kocali Complex in SE Anatolia is mainly composed of tectonically imbricated slices of pelagic rock suits (pelagic limestones; cherts; etc); platform carbonates; clastics; serpentinites and basic volcanics. It can be subdivided into four main parts as the Tarasa Unit; the Konak Unit; the Cilo Limestones and the Kale Ophiolite. In this paper; geochemical characteristics of basic volcanic rocks associated with pelagic sediments (radiolarian cherts; pelagic limestones; etc) have been studied along four stratigraphical sections (the Tarasa; the Bulam-2; the Korun-1 and the Korun-2) in the Konak and the Tarasa Units. The age of the volcanic sequences have been assigned to Late Triassic (middle Carnian to Rhaetian) based on the radiolarian data from the associated pelagic rock units. Geochemical data indicates the presence of two different types of Late Triassic volcanic rock groups characterized by E-MORB-type (Group-1 volcanites from the Tarasa Unit formed by mixing of OIB and MORB-type melts) and OIB-type (Group-2 volcanites from the Konak Unit) mantle sources. None of the samples from the Kocali Complex has characteristics of N-MORB type mantle source and was affected by crustal contamination. Based on these data; it can be suggested that all these volcanic rocks formed in a marginal oceanic basin away from the ocean ridge. The presence of Radiolaria and Bivalvia-bearing pelagic limestones and cherts associated to the basic volcanic rocks in the Kocali Complex also emphasize that they all formed in deep marine basin. Geochemical characteristics of Late Triassic volcanics in the Kocali Complex have great similarities and well-correlative to the coeval volcanics previously studied in the Southern Tethyan Belt (e.g. the Baer-Bassit region in NW Syria; the Mamonia Complex in SW Cyprus and the Antalya Nappes in SW Turkey). Taking into the consideration of the geochemical data obtained from Late Triassic basic volcanics in the Kocali Complex and geochemical characteristics of the coeval volcanics in the adjacent units in the Southern Tethyan Belt; it can be suggested that rifting age of the Southern Tethyan Oceanic Basin in SE Anatolia is probably earlier than early Late Triassic (middle Carnian time).