The role of subduction-accretion processes in the tectonic evolution of the Mesozoic Tethys in Serbia

Abstract

Ophiolitic rocks and melange occur in two belts in Serbia; to the northeast (the Vardar zone) and to the southwest (the Dinaride ophiolite belt) of the Drina-Ivanjica belt, which is interpreted as being a microcontinent rifted from Apulia. The Tethys in the Vardar zone has a long and complex Palaeozoic-early Tertiary history that is still poorly understood. Ophiolitic rocks are known to have formed at least in the early Late Jurassic. Some of the extrusives apparently formed in a supra-subduction zone setting, based on immobile element geochemical evidence. The Mesozoic Tethys in the Vardar zone closed, at least partly, by the latest Jurassic. Evidence from the Apulian margin in the southwest, and from the Drina-Ivanjica belt further to the northeast shows that a small Red Sea-type oceanic basin rifted in the Late Permian-Early Triassic, followed by spreading in the mid-Late Triassic to Early Jurassic. Evidence from immobile trace elements shows that these extrusives are of mid-ocean ridge and within-plate type. During the early Late Jurassic, this southerly oceanic strand began to close, creating melange, as a classic subduction/accretion complex. MORB- and seamount-type lavas, channelised micaceous turbidites, rare calciturbidites and large limestone masses (capped by condensed successions) were incorporated in the melange through tectonic processes. Many of these units originated at, or near, the southwestern margin of the Drina-Ivanjica inferred microcontinent. Less deformed debris flows (‘olistostromes’) reflect gravity reworking and/or diapirism with accumulation mainly in perched basins above the subduction zone. Large, overriding harzburgitic ophiolite thrust sheets may have developed in response to incipient spreading above a subduction zone dipping to the southwest. These ophiolites were emplaced northeastwards, complete with metamorphic soles, in response to collision of the trench with the Drina-Ivanjica belt. Southwest-directed sliding of sediments into the foredeep took place prior to suturing in the Tithonian and later transgression by clastic sediments.