The evolution of the Meliata-Hallstatt ocean and of its southern and northern margin
in the Inner Western Carpathians are described. The main rifting began during the
Pelsonian and the sea-floor spreading ended at the beginning of the Middle Carnian
contemporaneously with the Raibl event. The subduction began in the latest Triassic
and the final closing of the ocean, accompanied by uplift of the adjacent marginal
areas, was dated as basal Oxfordian. Remnants of the oceanic-suboceanic sequence occur
in two tectonic positions: (1) Obducted nappes that contain, mostly as tectonic melanges,
the whole Middle Triassic to Middle Jurassic sequence, including large bodies of dismembered
ophiolites of Ladinian to Early Carnian age. (2) Evaporite melanges at the base of
nappes that are derived from the northern margin of the ocean. These evaporite melanges
consist of Late Permian evaporitic matrix and blocks of a dismembered Ladinian to
Lower Carnian ophiolitic sequence. In the Inner Western Carpathians both the northern
and southern marginal sequences of the Meliata-Hallstatt ocean and the transitions
into the carbonate platforms are present in different nappes. The southern marginal
development is characterized by Middle Carnian distal clastic Raibl Beds and by Middle
Jurassic rhyolithic volcanism, both missing in the northern marginal development.
Because the subduction-related Middle Jurassic volcanism (contemporaneous with the
turbidites in the southern Meliaticum) is restricted to the marginal area south of
the Meliata-Hallstatt ocean, southward-directed subduction is indicated. To the south,
on the adjacent carbonate platform, a Jurassic basin with Aalenian to Bajocian ophiolites
opened. This may be a back-arc basin. In the Eastern Alps only the northern marginal
zone and the adjacent carbonate platform are preserved, but parts of the dismembered
ophiolites in the Haselgebirge may be of Ladinian to Late Carnian age like in evaporitic
melanges in the same tectonic position in the Inner Western Carpathians. The final
closing of the Meliata-Hallstatt ocean is indicated by the abrupt end of the turbiditic
sedimentation in the oceanic suboceanic domain and by uplift in the marginal areas,
where Lower Oxfordian radiolarites are overlain by shallow-water Upper Oxfordian to
Tithonian or Neocomian limestones (Silica Nappe, Hallstatt Nappes). With the evidence
of the final closing of the Meliata-Hallstatt ocean near the Middle/Late Jurassic
boundary, the Cimmerian orogenesis (in the genetic sense of Sengor, 1984, 1985) is
now also proven in the Inner Western Carpathians and in the Eastern Alps. A continuation
of the Meliata-Hallstatt ocean into the Pontide ''Paleotethys'' (= Cimmerian ocean
sensu Kozur, 1990) through the Transylvanian oceanic domain and the Strandzha Unit
is assumed. A connection with the Vardar ocean is impossible, because in the Vardar
Zone no Triassic ophiolites or basic volcanics are present and the ophiolites have
Jurassic age.
