Original paper

U-Pb zircon isotopic evidence for mid-Devonian migmatite formation in the Gory Sowie domain of the Bohemian Massif, Sudeten Mountains, SW Poland

Aftalion, M.; Bowes, D.R.


U-Pb isotopic data for 5 measured fractions of zircon from a homophonous granitoid-looking plagioclase-quartz-biotite diatexite in the Góry Sowie domain of SW Poland scatter about a projection of the chord (LI 369 ± 15Ma; UI 1750 ± 270Ma) for a gneiss elsewhere in the domain and their distribution is consistent with an age of metamorphism-migmatization generally corresponding to c. 380Ma concordant U-Pb monazite ages from the diatexite. A 0.65-1.2 Ga range of 207Pb/ 206Pb apparent ages is interpreted as the result of the presence of varying proportions of a hybrid population of Precambrian xenocrystic zircon in the different fractions and as supporting the derivation of the migmatite from a sedimentary protolith. The mid-Devonian episode of tectonothermal (and igneous) activity has coeval counterparts in some Czech and German domains of the Bohemian Massif and is significant in evolution of the Hercynian orogen. Arguments are presented against previous interpretations of the metamorphism-migmatization having taken place in Ordovician times.