Petrological evolution of Karlıova-Varto volcanism (Eastern Turkey). Magma genesis in a transtensional triple-junction tectonic setting

A diffuse and voluminous (>1400 km3) Miocene-Quaternary volcanic activity developed around the KarlıovaTriple Junctionin East Anatolia as a consequence of collisional tectonics among Anatolia, Arabia andEurasiacontinental plates. The volcanic rocks of this region are grouped into three phases of activity: 1) Early Phase (Solhanvolcanism; ~7.3–4.4 Ma), with emplacement ofalkali basaltto trachytelava flowsand pyroclastic successions; 2) Middle Phase (Turnadağ and Vartovolcanism; ~3.6–2.6 Ma), mostly with products with the same compositional range plus minordacitesandrhyolites, and 3) Late Phase (Özenç volcanism; ~2.6–0.5 Ma), with emplacement of alkali basaltic, hawaiitic and mugearitic lavas and dykes. Primitive Mantle-normalized patterns of the three rock groups share an enrichedLILEand depleted HFSE contents, with overall positive spikes of Pb and mildly fractionated LREE/HREE trends showing more similar affinity to global subducting sediments rather than tomagmasemplaced in mid-plate settings (i.e., OIB). Initial Srisotopic ratiosof the least evolved compositions range from values lower than BSE (87Sr/86Sri = 0.7041) to radiogenic compositions (87Sr/86Sri = 0.7050). They reflect either FC-like processes, with87Sr/86Sriup to 0.7064, or closed systemfractional crystallization, with87Sr/86Sri = 0.7046–0.7049. Initial Nd are higher than ChUR estimate for the most and the least evolved compositions (143Nd/144Ndi = 0.51267–0.51280), indicating provenance from isotopically depleted sources. Leadisotopic ratiosare characterized by a remarkable homogeneous206Pb/204Pb (18.95–19.04), with207Pb/204Pb (15.65–15.72) and208Pb/204Pb (38.87–39.21) slightly above the Northern Hemisphere Reference Line, pointing towards the EMII end-member. Geochemical modelling for the least evolved volcanic units indicate the likely generation from an amphibole-bearing spinel-lherzolitic source. P-T calculations for partial melting calculations gave lithospheric pressures for initialmagma generation(0.8–1.3 GPa). Possible cause of melting might be related to passive upwelling ofasthenosphereas a response to the local extension linked to the development of North Anatolian and East Anatolian Fault Zones. Anyhow, volcanic units from the KTJ display only limited geochemical signatures of garnet-bearing sources, or any HIMU-OIB like characteristics, as instead observed in the other portions of the Eastern Anatolia. The long-lasting complextectonic evolutionof the Eastern Anatolia is responsible for the large geochemical variability of the magmatic products. However, the general characteristics of KTJ volcanic rocks are mainly dominated by subduction-related signatures, with most of the primary magma characteristics having been heavily masked by fractionation and crustal assimilation processes.