New evidence on the timing of southern Neotethys closure from geochronology and geochemistry of Harmanlı region ophiolite (southeastern Anatolia) and Late Cretaceous granitic rocks: Neotethys closure, ophiolite evolution and granitic magmatism in SE Anatolia

Abstract

The felsic–intermediate intrusions of the Harmanlı region are situated in proximity to the Tauride thrust front in southeastern Turkey. The region containing intrusive and ophiolitic rocks plays a crucial role in understanding the magmatic framework of Late Cretaceous felsic–intermediate igneous rocks in the Adıyaman region of southeastern Anatolia. The geological evolution of southeastern Anatolia during the Late Cretaceous is unravelled through integrated field observations, whole-rock geochemical, petrographic analyses, U–Pb zircon geochronology, and mineral chemistry of granitic rocks that intrude the Harmanlı region ophiolite. The intrusions consist of tonalite, granodiorite, and in places granite, with a subvolcanic phase represented by granophyre, aplite, and granite porphyry. Mafic rocks including gabbro and diorite are also present with microdiorite and diabase in the subvolcanic phase. The new, high-precision LA–ICP–MS U–Pb zircon data provides crystallization ages for the mafic rocks of the Harmanlı ophiolite (gabbro) ranging from 83.8 to 81.7Ma, while the felsic intrusives (granodiorite) have yielded crystallization ages ranging from 80.8 to 79.5Ma. Geochemical data indicate calc-alkaline, I-type magmatism characteristic of a subduction zone environment, consistent with the northward-dipping subduction of the southern Neotethys beneath the Tauride platform. The magmatic arc environment is characterised by the presence of oceanridge granite-normalised multi-element patterns, tectonomagmatic discrimination, and the biotite geochemistry of the intruded rocks. The mafic rocks of Harmanlı region ophiolite exhibit distinct characteristics, including i) depletion in Nb, ii) enrichment in LILEs (Ce, Rb, K, and Th) and iii) a nearly horizontal pattern of HFSEs (high field strength elements) compared to N-MORB. The results suggest that the magmatism occurred during the Late Cretaceous (Campanian), with the intrusions forming at moderate to shallow crustal depths.