engleski

Tectonothermal history of the basement rocks within NW Dinarides: new 40Ar/39Ar ages and synthesis

Very low-grade and low-grade metamorphosed basement rocks from distinct inliers of the Africa-derived northwestern Dinarides (Medvednica Mts. and Sana-Una Paleozoic unit, respectively) have been studied with the multi-grain step-heating 40Ar/39Ar technique in order to compare and reveal their tectonothermal history. 40Ar/39Ar ages from detrital white mica of the very low-grade basement rocks of the Sana-Una Paleozoic gave a Variscan age of ~335 Ma. The new age is in agreement with 40Ar/39Ar ages from the very low-grade basement exposed at Petrova and Trgovska Gora of the NW Dinarides (Borojević-Šoštarić et al., 2009). Within low-grade metamorphic basement rocks from the Medvednica Mts., we found no Variscan ages. White mica from phyllitic basement rocks of the Medvednica Mts. give predominantly Early Alpine ages ranging between 135 and 122 Ma and younger Alpine ages of ~80 Ma. The Early Alpine ages of 135 and 122 Ma are interpreted to date the onset of ductile nappe stacking predating the formation of Gosau-type collapse basins. The late Early Alpine event of ~80 Ma can be traced in the entire Cretaceous-aged orogen of the Circum-Pannonian region and is synchronous with subsidence of the Gosau-type basins and opening and closure of the neighboring Sava-Vardar zone.

Cretaceous overprint; Variscan; Dinarides; basement; nappe stacking

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