Early Carboniferous successive I/S granite magmatism recorded in the Malá Fatra Mountains by LA-ICP-MS zircon dating (Western Carpathians)

Abstract

In situ U–Pb zircon dating by the ICP-MS technique from tonalite located in the southern margin of the Kriváňska Malá Fatra granite massif records a Concordant age of 353 ± 3 Ma for zircon cores, 342 ± 3 Ma for their rims but the zircons from granodiorite on the northern margin of the massif show only coeval Concordant age of 342 ± 3 Ma from both cores and rims. The obtained ages establish successive Tournaisian and Visean magmatic events in the Variscan Malá Fatra crystalline basement and an intimate relationships between two Early Carboniferous intrusions. The Th/U ratio from zircon cores of Tournaisian tonalite shows a magmatic value of 1.0, whereas the ratio with value of 0.2 from zircon rims most likely represent the thermal imprint from emanated hydrothermal fluids from identified Visean granodiorite intrusion with similar Th/U zircon ratio of 0.4. The short time span of about 11 Ma for the origin of these two granitoid intrusive phases in the Malá Fatra Mountains advocates a relatively rapid Variscan convergence from a probably terminated Tournaisian arc magmatic regime to Visean collisional setting.