Late Paleozoic-Mesozoic tectonics of the Dinarides revisited: Implications from 40Ar/39Ar dating of detrital white micas

摘要

Detrital white mica has been dated by the single-grain 40Ar/39Ar technique from three distinct stratigraphic levels and tectonic settings within the Dinarides in order to monitor the geodynamic evolution of this segment of Alpine orogen, which is located near the transition of Variscan to Pan-African continental crust. Detrital micas of a Pennsylvanian foreland basin suggest erosion of medium to deep crustal levels of the Variscan orogen. The 40Ar/39Ar ages indicate almost no preservation of older, pre-Variscan crust, except for a low proportion of late Pan-African ages. These data are in accordance with previous findings from the Variscan belt that suggest that the whole upper level of Variscan crust had been nearly entirely eroded prior to molasse deposition. Variscan micas also dominate in graywackes of the Middle to Late Jurassic trench-filling deposits exposed within the Dinaric ophiolite belt, indicating a nearby Variscan continent. No mica from a Mesozoic metamorphic accretionary complex has been detected. By contrast, the Upper Cretaceous Vardar Flysch postdates the emplacement of the Dinaric ophiolite belt as part of the Dinaric-Carpathian metamorphic orogenic wedge, and likely represents a collapse basin postdating Early to early Late Cretaceous nappe stacking. The studied micas comprise a dominant Variscan group and a subordinate Early Cretaceous group from the eroding metamorphic orogenic wedge.