Ordovician (Cenerian) metamorphism in the Western Carpathians: Evidence from EMP monazite dating of polymetamorphosed granitoids in the Veporic unit, Slovakia

Abstract

Late Ediacaran to Cambrian metagranitoids from the northern Veporic unit of the Western Carpathians show imprints of three metamorphic events, which can be assigned to the Cenerian, Variscan, and Alpine orogenies based on electron microprobe dating of monazite. Metamorphic monazites in the metagranitoids are mostly of the Lower to Middle Ordovician age (480–460 Ma). The Ordovician monazite formed in equilibrium with the metamorphic assemblage garnet, biotite, kyanite, ilmenite and quartz at P-T conditions of 6–7 kbar and 550–570 °C, thus providing clear evidence for Cenerian metamorphism in the Western Carpathians. Variscan metamorphism caused minor monazite growth/recrystallization at 364 ± 13 Ma and produced a new mineral assemblage garnet, kyanite, rutile and phengite at P-T conditions of 20–22 kbar and 670–690 °C. The low-grade Alpine metamorphism is recorded by monazite of Cretaceous age (96 ± 23 Ma), but only in orthogneiss of extremely low-Ca composition.The Veporic metagranitoids show incomplete transformation from magmatic stage, still preserving remnants of plagioclase, K-feldspar and high-Ti biotite. This indicates that the metagranitoids remained relatively dry and failed to complete metamorphic reactions due to kinetic factors at fluid-deficient conditions. Nevertheless, the metagranitoids likely underwent significant geochemical changes during their metamorphic evolution including a severe loss of CaO and Na2O.