Large-volume Permian felsic volcanism in the Tisza Mega-unit (East-Central Europe): Evidence from mineralogy, petrology, geochemistry, and geochronology

Abstract

Permian felsic volcanic rocks are widespread in the Tisza Mega-unit (Carpathian–Pannonian region), covering a relatively large area from southern Transdanubia (Hungary) to the Apuseni Mountains (Romania). The present occurrence and structural position of these Permian volcanic rocks are the result of a complex tectonic evolution (including Alpine nappe stacking and Neogene extension); meanwhile, multiple hydrothermal effects and deformation modified their microtexture and chemical composition. In this study, the same emphasis was given to Permian felsic volcanism as well as the subsequent fluid- and/or deformation-related processes in the Tisza Mega-unit to extend our knowledge in regional issues (e.g., geochronology, stratigraphy, and lithologic correlations) and to investigate if the variably altered volcanic rocks can be used in petrogenetic studies.The zircon U-Pb dating yields ages of ∼270.4–262.9 Ma for the Apuseni samples and ∼268.4–260.2 Ma for those of the Pannonian Basin. Whole-rock geochemistry, considering immobile trace elements, since most of the major element compositions were severely modified by alteration processes, indicates that the studied rocks are dacite to rhyolite. They belong to a voluminous silicic volcanism during the Middle Permian, most probably related to rifts.Petrography, whole-rock geochemistry, and X-ray powder diffraction mineralogy revealed that the predominant alteration of the studied rocks is hydrothermal sericitization, locally superimposed by mylonitization in greenschist to subgreenschist conditions during Alpine orogeny. The K-Ar dating of the separated illite fractions confirms that the ductile deformation acted during the Turonian nappe stacking, as the main Alpine deformation phase in the study area.On a regional scale, the Permian magmatism in the Tisza Mega-unit looks significantly younger than the similar magmatic activity of the stable Europe (∼300–290 Ma).