Upper Cretaceous Yüksekova Complex (Type Area), Easternmost Türkiye: Formation and Emplacement of a Proximal Back-Arc Segment of a Tethyan Intra-Oceanic Arc

Abstract

We provide the first comprehensive information and interpretation of the type area of the regionally important Upper Cretaceous oceanic arc, known as the Yüksekova Complex. Here, the arc's development is investigated using field observations, igneous and sedimentary petrography, micropaleontology of planktic foraminifera, x-ray diffraction of fine-grained sediments, igneous and sedimentary geochemistry, structural relations, and regional comparisons. The complex in its type area is a folded and faulted but otherwise intact succession of massive lavas, pillow lavas, and fragmental pyroclastic and epiclastic rocks, interbedded with volcaniclastic and bioclastic turbidites, volcanogenic mudrocks (hemipelagites), Maastrichtian Globotruncana-bearing pelagic carbonates, and sparse felsic airfall tuffs. Intrusive rocks are mainly localized multiple granitic-aplitic dikes, minor basic- to intermediate-composition dikes, and small gabbroic bodies. Geochemical evidence indicates two lava trends, the first tholeiitic to calc-alkaline; i.e., basaltic-andesitic-felsic, and the second alkaline (OIB) with minor but variable subduction influence. Mainly basic- to intermediate-composition detritus was derived from associated basaltic-andesitic volcanics, whereas generally more felsic-composition sediments, which include shallow-water bioclasts, were derived from a contemporaneous, evolved arc volcano and an associated carbonate platform (now not exposed). Comparisons with the Yüksekova Complex farther west (Kovancılar–Elazığ–Maden areas), and with both modern and ancient oceanic arc settings (e.g., W Pacific; Himalayas), suggest that the Yüksekova Complex (type area) represents the proximal segment of a back-arc rift. The alkaline lavas could represent extrusion of deep-sourced, enriched magma along a crustal rupture, or simply be a consequence of mantle heterogeneity. The Yüksekova Complex underwent compressional deformation and low-grade metamorphism related to latest Cretaceous and Eocene emplacement, followed by final, Early Miocene emplacement onto the Arabian continental margin to the south during advanced continental collision. The Yüksekova oceanic arc restores to a Mesozoic ocean basin in southeast Anatolia (Berit ocean), between the Mesozoic Malatya–Keban platform to the north and the Pütürge and Bitlis continental units to the south (and eastward potential extensions).