Pages: 245 - 256
Authors: PETER IVAN
Abstract: Relics of the oceanic crust of the Triassic-Jurassic Meliata Ocean are preserved as dismembered incomplete ophiolite sequences only in several small lithostratigraphic units mostly in the Inner Western Carpathians. The current data on these remnants with special emphasis on volcanic rocks are summarized in the present paper. Mafic volcanic rocks representing relics of the Meliata oceanic crust differ from each other by the following characteristics: (1) preservation of magmatic textures and structures, (2) geochemical type, (3) metamorphic evolution, (4) related sedimentary rocks and (5) recent tectonic position. On the basis of these differences, three groups of metabasalts related to the former oceanic floor can be discerned: (1) HP/LT metamorphosed basalts and dolerites with scarce gabbro as slices and small blocks in the Borka Nappe, (2) mostly LP/LT metamorphosed basalts and dolerites occurring as olistoliths in melange in the Jaklovce, Meliata, Bódva Valley Ophiolite and Darnó Hill Formations, and (3) recycled, almost complete ophiolite magmatic rocks forming clasts in the Upper Cretaceous Gosau-type conglomerate from Dobsinska Ladova Jaskyna village. The distribution of relatively immobile trace elements (REE, HFSE) in metabasalts indicates their formation in the back-arc setting. In the initial stage of opening of the Meliata Ocean, the arc-like and back-arc basin basalts, erupted in the environment of carbonate or pelitic sediments, were generated. The evolved stage is characterized by generation of basalts close to the N-MORB type in association with abyssal sediments. Basalts close to E-MORB are assumed to be a melting product of an enriched mantle source probably locally present beneath the spreading basin. Closure of this ocean in the Middle Jurassic time was related to the subduction and formation of the accretionary prism. Mostly the relics of the marginal parts of the former oceanic basin were subducted and consequently exhumed, whereas the relics of central parts were preserved in the accretionary prism. The original location of the Meliata Ocean suture is not known. The present-day tectonic position of the oceanic crust relics in the Inner Western Carpathians is extremely complex as a consequence of the repeated nappe forming activity, erosion and plate kinematics. It seems likely that these relics represent a western continuation of the Hellenide-Dinaride ophiolites displaced by microplate motions in the Miocene.
Keywords: Western Carpathians, Meliata Ocean, geodynamics, back-arc basin, oceanic crustDownload PDF document Show Text Version