Ophiolitic mélange with components of the Middle Triassic, Lower and Middle Jurassic radiolarites in the Ozren and Borja-Mahnjača massifs (Central Dinarides, Bosnia and Herzegovina): Impact on Neotethys evolution

Ophiolitic mlanges of the Ozren and Borja-Mahnjaa massifs comprise Middle Triassic, Lower Jurassic, and Middle Jurassic radiolarites. The Middle Triassic radiolarites from clastic components in the mlange of the Ozren ophiolite complex (OOC) predominantly contain the species Annulotriassocampe and Triassocampe species, together with marker species of the Ladinocampe multiperforata Zone, belonging to the Illyrian. These Middle Triassic radiolarites are remnants of the Maliac Ocean, which opened during the Late Anisian. The inferred continuation of the Middle Triassic radiolarian sedimentation to the Early Jurassic is recorded by radiolarites from block-in-matrix in the mlange of the Borja-Mahnjaa ophiolite complex (BMOC). Their Sinemurian-Pliensbachian age is indicated by species of the genera Canoptum, Katroma, Droltus, Lantus, Gorgasium, Charlottea, Bipetis, Paleosaturnalis and Paroanella. Such Lower Jurassic radiolarites were so far unknown from the Dinaric ophiolite complexes. The Middle Jurassic radiolarites cover the pillow basalts of the OOC. Their microfauna indicates the Bathonian-early Callovian age based on the LADs of Mizukidella kamoensis and Hemicyrtocapsa carpathica and FADs of Transhuum brevicostatum, Cinguloturris cf. carpathica, Loopus venustus and Protunuma turbo within the UAZ 6-7 Zone. The Middle Jurassic radiolarites are also interbedded in the pillow lavas of the BMOC. In addition to common species of the UAZ 6-7 Zone (e.g., Transhuum maxwelli, Eucyrtidiellum unumaense, Unuma gordus), they also contain the species Takemuraella veghae and Eoxitus cf. baloghi, which are limited to the Bathonian. Considering the radiolarites from the pillow basalts, the OOC and BMOC are interpreted as the mlanges with the reworked clasts of the Middle Triassic to Lower Jurassic radiolarites, but also with the Middle Jurassic radiolarites. The Middle Triassic radiolarites of the OOC and the Lower Jurassic radiolarites of the BMOC represent rare remnants after the closure of the Middle Triassic to Lower Jurassic Maliac Ocean of the Neotethys. The newly-formed Neotethyan oceanic crust was terminated by the Middle Jurassic radiolarian deposition in an inferred fore-arc/back-arc basin until the Bathonian to early Callovian.