Search

In this paper we present new data on the Jurassic radiolarian assemblages collected in seven sections of the sedimentary cover of the Mirdita ophiolites in Albania. These ophiolites form an outstanding NNW-SSE trending ophiolitic belt representing the remnants of the Mesozoic Neo-Tethyan oceanic lithosphere in the Mediterranean area. The studied sections were sampled in the sub-ophiolitic mélange of the Western Mirdita ophiolites (Rubik Complex) and in the Eastern Mirdita ophiolitic sequences. In the sub-ophiolitic mélange the oldest ages of radiolarians associated with the basalts are referable to the UAZ 4-5 (late Bajocian to latest Bajocian-early Bathonian) and UAZ 5 (latest Bajocian-early Bathonian). In the radiolarian cherts belonging to the Eastern Mirdita ophiolites similar ages were found: from UAZ 5 (latest Bajocian-early Bathonian) to UAZ 5-7 (latest Bajocian-early Bathonian to late Bathonian-early Callovian). These new biostratigraphic ages are consistent with the tectono-magmatic evolution of the Jurassic Neo-Tethys. In fact, the UAZ 4-5 and UAZ 5 correspond to the very early stages of subduction initiation, whereas the slightly younger UAZ 5 and UAZ 5-7 ages found in the Eastern Mirdita ophiolites could correspond to the subsequent mature stage of the subduction. [ABSTRACT FROM AUTHOR]

This study is focused on slide blocks including oceanic lavas associated with pelagic sediments within the eastern part of the Ankara Mélange. A detailed petrological characterization of the volcanic rocks and a detailed biochronological investigation of the associated radiolarian cherts in eight sections (east of Ankara) was carried out. The volcanic rocks are largely represented by basalts and minor ferrobasalts and trachytes. They show different geochemical affinities and overlapping ages including: (a) Late Jurassic – Early Cretaceous garnet-influenced MORB (middle late Oxfordian to late Kimmeridgian–early Tithonian and early–early late Tithonian; late Valanginian–early Barremian); (b) Early Cretaceous enriched-MORB (middle late Barremian–early early Aptian; Valanginian to middle Aptian–early Albian); (c) Middle Jurassic plume-type MORB (early–middle Bajocian to late Bathonian–early Callovian); (d) Late Jurassic – Early Cretaceous alkaline basalts (middle–late Oxfordian to late Kimmeridgian–early Tithonian; late Valanginian to late Hauterivian). All rock types show a clear garnet signature, as testified to by their high MREE/HREE (middle rare earth element/heavy rare earth element) ratios. The coexistence of chemically different rock types from Middle Jurassic to Early Cretaceous times suggests that they were formed in a mid-ocean ridge setting from partial melting of a highly heterogeneous mantle characterized by the extensive occurrence of OIB-metasomatized portions, which were likely inherited from Triassic mantle plume activity associated with the continental rift and opening of the Neotethys branch. [ABSTRACT FROM AUTHOR]