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Exhumation history of the Mid-Bosnian Schist Mts., Central Dinarides

Palaeozoic metamorphic complex of Mid-Bosnian Schist Mountains (MBSM) is situated within the central part of the Dinarides. It is composed of Ordovitian (?) to Lower Permian metamorphics (Fig 1). The degree of metamorphism is decreeing southwardly, whereas the ages of the metamorphism decreasing northwardly. Northernmost parts of MBSM (Busovača unit) is metamorphosed during Eocene time under pressure of 5 Kbar and temperature of 400° C, based on phengite and chlorite geothermometry, within two discrete pulses: prograde stage at 45–42 Ma, and a retrograde stage with peak temperature conditions at 39–35 Ma. Central part of the MBSM (Vranica unit) is characterized by low ductile strain and Paleocene metamorphic overprint at 63 Ma. Two feldspar geothermometry from perthite micophenicrystst population within Vranica metarhyolite gave average temperature of 460°C whereas Ti in low-Fe biotite from metarhyolite matrix gave average temperature of 515°C. Both temperatures are below rhyolite hydrous solidus (i.e. post effusion) and indicate either deuteric metasomatism or maximum peak metamorphism of the Paleocene event. Southernmost part of the MBSM (Bradina unit) show only Variscan metamorphic event (305-285 Ma). overprinted by a Late-Permian to Early Triassic (245 Ma) thermal overprint, interpreted to record a crustal extension.

exhumation; oligocene; Mid-Bosnian schist Mts.; Ar-Ar geochronology; EMPA

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