Abstract
In the Blanský les granulite Massif built mainly by felsic calc-alkaline HP–HT Grt + Ky granulite, occur rare small bodies of hyperpotassic (K2O < 7 %, up to c. 14 %, K2O/Na2O = 3.1–9.2 wt. %) granulite with Grt or Px. Characteristic are high concentrations of Cs, Rb, Ba and U at variable enrichments in Zr and Hf; contents some HFSE (Ti, Nb and Ta) are extremely low.
The Sr–Nd isotopic ratios document the derivation from mature crustal sources (Eps337 -5.5; 87Sr/86Sr337 = 0.7109-0.7279). Ap saturation temperatures are high, close to the previously estimated conditions of (re)crystallization for both calc-alkaline and hyperpotassic granulites.
The hyperpotassic granulites are interpreted as Viséan igneous rocks. The parental magma could have originated by low degrees of HP–HT, non-eutectic partial melting.
The low-scale melt was most likely expelled close to the HP–HT metamorphic peak or at early stages of decompression from common Moldanubian calc-alkaline granulites.