Tethyan Subduction to Post-Subduction Magmatic Evolution and Pulsed Porphyry Cu-Mo Deposit Emplacement in the Southernmost Lesser Caucasus

The composite Meghri-Ordubad and Bargushat plutons and associated porphyry Cu-Mo deposits of the Zangezur-Ordubad region, southernmost Lesser Caucasus, were emplaced during a long-lasting, stationary Tertiary magmatic evolution. All magmas have a subduction-related signature. Radiogenic isotopes reveal a mantle-dominated magmatism, with the mantle component becoming more predominant with time. Trace element geochemistry indicates progressive thickening of the crust from the Eocene to the Miocene. Eocene calc-alkaline, normal arc (non-adakitic) magmatic activity was related to subduction of the Neotethys beneath Eurasia, and magmatism was dominated by fluid-related enrichment. The Eocenece magmatic stage generated the first pulse of porphyry Cu-Mo deposits. During collision to post-collision evolution, magmatism evolved to shoshonitic during the Oligocene, and talc-alkaline to high-K talc-alkaline and adakitic during the Late Oligocene and Mio-Pliocene. The younger magmatic evolution involved a mantle source metasomatised by a sedimentary component. The second stage of porphyry Cu-Mo deposits is associated to the collision to post collision Oligo-Miocene adakitic magmatism. Increasing mantle contribution with time was favoured by mantle flow through a slab window/tear opened as a consequence of progressive indentation and deformation of the Eurasian margin by the Gondwana-derived South Armenian block during final closure of the Neotethys.