Variscan S-type granitoids in the Tisza Mega-unit (Carpathian–Pannonian region): petrology, geochronology, geotectonic implications, and correlation

Two-mica leucogranites and/or granodiorites, often affected by various degrees of post-emplacement deformation and/or metamorphism (i.e., sheared granites, metagranites or orthogneisses), occur in several parts of the Tisza Mega-unit (Carpathian–Pannonian region), including the Apuseni Mts. (Romania), the Papuk Mt. (Croatia), and basement highs of the Pannonian Basin (Battonya–Pusztaföldvár and Algyő–Ferencszállás areas, SE Hungary). Despite the similar petrological characteristics (e.g., mineralogical composition, texture), these formations have not been compared to each other yet for correlational purposes and the scarce geochemical and almost completely lacking geochronological records also demanded further petrological investigations and datings.

Petrographically, granitoids from all the studied areas (SW Apuseni Mts., Papuk Mt. and the previously mentioned basement highs) proved to be similar, medium to coarse-grained monzogranites or granodiorites, containing quartz, plagioclase, K-feldspar, biotite, and muscovite. In some quarries or rarely in drill cores aplites and pegmatites were also found. As accessory components most commonly apatite, zircon, monazite, and xenotime, occasionally garnet were identified. As secondary phases sericite, albite, chlorite, epidote, kaolinite, and calcite appear frequently. Whole-rock geochemistry revealed that despite the various post-magmatic alterations (deformation/metamorphism/fluid effects etc.), the majority of the granitoids preserved their primary major and trace element compositions. All of them proved to be subalkaline, peraluminous, alkali-calcic or calc-alkalic with basically magnesian and S-type (rarely S/I-type) character. Major and trace element distributions, chondrite-normalized REE patterns (with slight negative Eu anomalies) and other relatively immobile trace element (HFSEs) concentrations showed significant similarities among the studied samples suggesting their common origin and local correlation possibilities within the Tisza Mega-unit. Interestingly, samples from the Papuk Mt. geochemically differ from the others as well as the aplites and pegmatites associated with the Codru granitoids (Apuseni Mts.). The former might represent a different source and igneous episode; however, the geochemical distinction of the latter (with more pronounced negative Eu anomaly and lower concentrations in REEs and HFSEs) is rather odd. Trace element-based discrimination diagrams (e.g., Yb vs. Ta, Yb+Ta vs. Rb) suggested that most of the studied rocks are volcanic-arc granites and only a few of them (basically aplites and pegmatites) are syn-collisional despite their typical S-type mineralogy (e.g., muscovite, monazite, garnet) that unequivocally referred to continental crustal sources.

Considering another means of geotectonic discrimination (e.g., Sr/Y and La/Yb ratios) and the ascertainment of Broska et al. (2022) in case of Western Carpathians granitoids, it is feasible that the studied granites bear the geochemical signature of a slab break-off, being crust- and mantle-derived, too, while shallower level melts (aplites and pegmatites) represent purely crustal sources in the Variscan orogeny. The latter corresponds to the calculated zircon saturation temperatures, as well (granites: 740–780 °C, aplites/pegmatites: 580–600 °C).

Preliminary datings (Battonya granitoids, SE Hungary) suggested that the main zircon crystallization period occurred in the Early Carboniferous (356 Ma) that fits well into the regional geological framework of the European Variscides.

This study was financed by NRDIF (K131690).

Broska, I., Janák, M., Svojtka, M., Yi, K., Konečný, P., Kubiš, M., Kurylo, S., Hrdlička, M., Maraszewska, M. (2022). Lithos 412–413:106589