⁴⁰Ar/³⁹Ar hornblende dating of a microgranodiorite dyke: implications for early Permian extension in the Moldanubian Zone of the Bohemian Massif

Abstract

Laser fusion ⁴⁰Ar/³⁹Ar ages of titanian pargasite from a microgranodiorite dyke swarm in the southern Bohemian Massif effectively date the early Permian (late Autunian) emplacement of dykes into a cool Moldanubian crust. This intrusion represents the youngest magmatic phase recorded in this part of the Moldanubian Zone. Strontium and neodymium isotopic ratios of microgranodiorites point to magma derivation from re-melting the lower crustal rocks with a possible component of upper mantle composition. Spatial and temporal association of the dykes with movements on a major N–S (NNE–SSW) tectonic discontinuity (Blanice–Kaplice–Rödl fault zone) suggests that their emplacement corresponds to the maximum age of fault movements associated with the E/W-oriented extension in this part of the Bohemian Massif.