engleski

Evidence of the spreading culmination in the Eastern Tethyan Repno oceanic domain assessed by the petrology and geochemistry of N-MORB extrusive rocks from the Mt. Medvednica ophiolite mélange (NW Croatia)

The Eastern Tethyan Repno oceanic domain (ROD), from the Zagorje-Mid-Transdanubian Shear Zone, borders the Meliata-Maliak and Dinaric-Vardar oceanic realms. The domain lacks ophiolite complexes and oceanic rocks are restricted to four Early Callovian to Late Valanginian ophiolite mélange sectors integrated in the Kalnik Unit. Previous research on ophiolitic rocks from the Kalnik Unit provided a detailed tectonomagmatic evolution of crust formation at different settings from the Late Anisian to the Cretaceous. N-MORB-type crust with peculiar supra-subduction signatures formed on a spreading ridge from the Late Carnian (~225 Ma) to the Late Pliensbachian (~185 Ma), and the first intraoceanic subduction rocks were dated as Late Bathonian (165 Ma). The newly discovered basaltic rocks, in coherent slices with the Latest Bajocian-Early Bathonian (~169 Ma) radiolarin cherts from the Mt. Medvednica ophiolite mélange sector, completed the Late Pliensbachian-Late Bathonian chemostratigraphic gap in the domain. The analysed unfractionated extrusive rocks lack any influence of a subduction related component, [(Nb/La)n = 1.16– 1.34 ; Th/Ta = 0.99–1.05] and are akin to proper N-MORB compositions [(Nd/Lu)N-MORB ~ 1.1 ; (La/Lu)cn = 0.82– 0.92] that were derived from a slightly depleted mantle source [εNd(T=170 Ma) = +6.21 to +6.27 ; (87Sr/86Sr)i = 0.703365 to 0.703511]. The rocks are interpreted as vestiges of the middle oceanic ridge crust formed during the culmination of spreading in the ROD.

petrology ; geochemistry ; N-MORB extrusives ; ophiolite mélange ; Bajocian-Bathonian ; Zagorje-Mid-Transdanubian Zone ; Mt. Medvednica ; Croatia

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