Traces of Carnian volcanic activity in the Transdanubian Range, Hungary

Abstract

The South Alpine–Dinaridic realm was affected by igneous activity in the Middle Triassic; the marine carbonate platforms and the adjacent basins contain highly variable intrusive-volcanic assemblages. We studied the petrography and determined the zircon U–Pb ages of the Triassic volcanic products in the Transdanubian Range. The geochemical features and thus the geodynamic context of the magmatism are badly known, as the rocks experienced variable chemical alteration. The exact duration of the igneous activity is also poorly constrained, as the geochronological data of the former studies were obtained mostly by the weathering-sensitive K–Ar and Rb–Sr methods and thus some data even being younger than the age of the stratigraphic cover. The presence of andesite dikes and of pebbles and cobbles (< 20 cm) of basalt, andesite, rhyolite and of rhyolitic tuff in the Triassic carbonate platform deposits indicates that within the Transdanubian Range formed a volcanic complex in Triassic. The major mineralogical and geochemical features of the Transdanubian igneous suite are similar to the Triassic formations in the Southern Alps. However, dissimilar zircon composition excludes the immediate relationship of the zircon-bearing silicic formations in the two tectonic units. New U–Pb ages show that the beginning of the volcanic activity is probably coeval with the eruption of the widespread “pietra verde” trachytic tuffs in the Upper Anisian–Ladinian successions, but the majority of the ages are younger than those ash layers. The new age constraints give a bench-mark for the termination of the volcanic activity in Carnian time in the Transdanubian Range.