Variscan vs. Alpine tectonothermal evolution of the Southern Carpathian orogen: constraints from 40Ar/ 39Ar ages

Abstract

40Ar/ 39Ar hornblende and muscovite ages indicate that basement units exposed within all major Alpine nappes of the Southern Carpathian orogen were penetratively deformed and metamorphosed during `late' Variscan (Carboniferous) tectonothermal events. Subsequent exhumation resulted in cooling from ca. 500°C (hornblende K–Ar retention temperature) to ca. 375°C (muscovite K–Ar retention temperature) between ca. 320 and 295 Ma. Late Variscan exhumation of middle crustal levels is interpreted to have resulted from intracontinental contraction and regional uplift subsequent to Variscan continental collision between Gondwana-derived tectonic elements (e.g., Africa) and Laurussia. Muscovite ages within mylonite zones suggest that late Variscan shear zones were probably associated with a regional shear system that developed along the southern margins of Laurussia. Alpine metamorphic effects within the Southern Carpathians are generally nonpenetrative, and are only significant within narrow zones of retrogression that are interpreted to have formed during initial attenuation of Variscan crust associated with formation of the Jurassic Severin rift.