The early history of the Neotethys archived in the ophiolitic mélange of northwestern Croatia

Abstract

Ophiolite exposures in NW Croatia have been attributed to the Western Vardar Ophiolitic Unit and interpreted as derived from the Meliata-Maliac-Vardar branch of the Neotethys. Blocks within the ophiolitic mélange on Mt. Ivanščica were investigated for petrological and geochemical characteristics of effusive rocks and radiolarian dating of associated pelagic sedimentary rocks. Analysed effusive basic rocks represent chemographically uniform sub-alkaline high-Ti massive tholeiitic basalts characterized by an enriched composition typical of E-MORB. These basalts are compatible with approximately 9 to 11% of partial melting of an enriched mantle source transitional between primitive and depleted MORB-type mantle and are formed in the non-subduction geotectonic setting of E-MORB-type. This reflects an initial succession of oceanic protocrust formation and the onset of ocean spreading. Radiolarians from chert and shale succession associated with basalts indicate a Late Anisian to Early Ladinian age of the initial ocean floor spreading, which continued into the Langobardian. Obtained data are correlative with reported blocks interpreted as remnants of the Triassic Neotethys crust from the ophiolitic mélange of the Western Vardar Ophiolitic Unit and further reaffirm common origin from a single ocean basin located east of the Adria microplate. Thematic collection: This article is part of the Ophiolites, melanges and blueschists collection available at: https://www.lyellcollection.org/topic/collections/ophiolites-melanges-and-blueschists