Boninitic and tholeiitic basaltic lavas and dikes from dispersed Jurassic East Othris ophiolitic units, Greece: petrogenesis and geodynamic implications

Abstract

Pillow lavas, massive lava flows, and sub-volcanic dikes of tholeiitic basaltic composition are found to be members of the Vrinena, Aerino, Eretria, and Velestino dispersed Middle-Upper Jurassic ophiolitic units in East Othris. The Vrinena and Eretria ophiolitic units appear to have been emplaced onto the Pelagonian continental margin during the Upper Jurassic-Lower Cretaceous, whereas the Aerino and Velestino units seem to have been finally emplaced during postPalaeocene times. Geochemically these are divided into two groups: Group I includes subduction-related boninites and low-Ti basalts from the Vrinena and Aerino units, and Group II high-Ti basalts show spreading-type characteristics occurring in the Eretria and Velestino units. Primary magma of the Group I volcanics appears to have been formed after high partial melting degrees (~18%) of a highly depleted harzburgitic mantle source, under relatively high temperatures (mantle potential temperature~1372°C). Petrogenetic modelling also suggests that the primary magma of the Group II volcanics were formed after lower partial melting degrees (~7%) of a moderately depleted mantle source. The petrological and geochemical data from the East Othris dispersed and diversely emplaced ophiolitic units provide evidence of a common intra-oceanic supra-subduction zone (SSZ) origin within the Pindos oceanic strand of the Western Tethys. Specifically, Group I lavas and dikes from Vrinena seem to represent the extrusive part of an almost complete fore-to island-arc ophiolitic sequence. Dikes of Aerino most likely correspond to fore-arc magmatic material that intruded within exhumed serpentinized ultramafic rocks through a subduction channel that developed close to the slab and towards the fore-arc and the accretionary prism. The Group II volcanics either corresponded to a fore-arc magmatic expression, which extruded earlier than Group I volcanics and prior to the establishment of a mature subduction zone, or represent back-arc to island-arc magmatism that was contemporaneous to the fore-arc magmatic activity during rollback subduction. ARTICLE HISTORY

Multiple Rodingitization Stages in Alkaline, Tholeiitic, and Calc-Alkaline Basaltic Dikes Intruding Exhumed Serpentinized Tethyan Mantle from Evia Island, Greece

“…Compositionally similar rocks from adjacent regions have been reported in several ophiolitic occurrences of Central Evia [35], Othris [36], and Koziakas [38]. Gabbroic protoliths also exhibit compositional similarities (i.e., low TiO 2 and comparable SiO 2 contents) with gabbros from the Torbat-e-Heydarieh [39] and Darrehanjir-Mashhad ophiolites in NE Iran [40].…”

“…It also displays a very low Nb/Th ratio (<1.3) clearly pointing to subduction-related setting [34]. Basalts of IAT affinities have been reported in several localities of Evia within the formations of the Pagondas mélange [24,35], whereas compositionally similar island arc tholeiitic subvolcanic rocks have been reported in the adjacent region of East Othris [36]. In the chondritenormalized REE diagram (Figure 4(a)), the preserved protolith displays comparable patterns with the RIATD, especially regarding the relatively immobile MREE and HREE, whereas the LREE were slightly depleted depending on the degree of rodingitization.…”

Post-magmatic processes recorded in bimodal chromitites of the East Chalkidiki meta-ultramafic bodies, Gomati and Nea Roda, Northern Greece

“…These ratios are generally consistent for all chromitite types. The composition of the G1 parental melts is akin to a MORB source (Melcher et al, 1997;Rollinson, 2008;Zaccarini et al, 2011;Chen et al, 2019), while the G2 and NR parental melts demonstrate boninitic affinities (Falloon et al, 2008;Koutsovitis and Magganas, 2016;Chen et al, 2019;Huang et al, 2021).…”

Mantle source heterogeneity in a Neoproterozoic back-arc basin: Geochemical and thermodynamic modeling of the volcanic section of Wadi Ghadir ophiolite, Egypt

“…Geochemical diversity of ophiolitic rocks is commonly attributed to the extent and type of magmatic processes operating in the ascending or residing melts at the different crustal levels. In a supra-subduction zone setting, melts generated by partial melting of different mantle sources also contribute to the heterogeneity of ophiolitic rocks (e.g., Dilek et al, 2008;Metcalf and Shervais, 2015;Koutsovitis and Magganas, 2016;Rogkala et al, 2019;Golich and Vysotskiy, 2020). The magmatic and geochemical evolution of supra-subduction zone (SSZ) and volcanic arc (VA) ophiolites are largely controlled by the mode and nature of mantle melting.…”