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 Ocean. Blocks within the ophiolitic mélange on Mt Ivanščica were investigated to determine the petrological and geochemical characteristics of the effusive rocks and to carry out radiolarian dating of the associated pelagic sedimentary rocks. The analysed effusive basic rocks represent chemostratigraphically uniform subalkaline high-Ti massive tholeiitic basalts characterized by an enriched composition typical of incompatible element-enriched mid-ocean ridge basalt (E-MORB). These basalts are compatible with c. 9–11% of partial melting of an enriched mantle source transitional between primitive and depleted MORB-type mantle and were formed in the non-subduction geotectonic setting of E-MORB-type rocks. This reflects an initial succession of oceanic protocrust formation and the onset of ocean spreading. Radiolarians from the chert and shale successions associated with the basalts indicate a Late Anisian–Early Ladinian age of initial ocean floor spreading, which continued into the Langobardian. The 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 reaffirm a 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