Middle Miocene volcanic flare up preceding and synchronous with the Langhian/Serravallian sea-level decline in the North Pannonian Basin: Insights from ⁴⁰Ar/³⁹Ar dating, geo-seismic analysis and 3D visualization of the subterranean Kralova stratovolcano

The Pannonian Basin System originated from the collision of the African and European tectonic plates, followed by the Miocene extensional collapse that led to the development of a back-arc basins. Accurate dating is essential to comprehend the tectono-volcanic evolution of the region, particularly in the under-studied Danube Basin. Single-grain Ar-40/Ar-39 dating has revealed that volcanic activity in the Danube Basin commenced around 14.1 million years ago, aligning with previous biostratigraphic and radioisotope data from nearby volcanic fields. The initial Middle Miocene pyroclastic deposits were generated by intermediate high K calc-alkaline magmas, contributing significantly to the deposition of thick layers of fine vitric tuffs. The timing and chemistry of the volcanism are consistent with the Badenian rift phase in the Middle Miocene within the Carpathian-Pannonian region, suggesting an intraplate back-arc volcanic environment. Three-dimensional imaging has exposed the buried Kralova stratovolcano, revealing its impressive scale with a thickness between 2620 and 5000 m and a base diameter of 18-30 km. Such dimensions place it among the ranks of the world's largest stratovolcanoes, indicating its substantial impact on the evolution of the Carpathian-Pannonian area. The complex formation history of the stratovolcano points to multiple phases of growth. Furthermore, the basin controlling Mojmirovce-Raba fault's intersection with the stratovolcano implies that fault activity was subsequent to the volcanic activity, being younger than 14.1 million years. Regional age data consistently indicates that volcanic activity in the Danube Basin reached its zenith just prior to and during the lower/upper Badenian sea-level fall (Langhian/Serravallian). K-metasomatism is unique to the stratovolcanic structures and is not observed in the wider regional setting. This study supports the notion of an intricate, interconnected subterranean intrusive system within the stratovolcano, underscoring the complex interplay between geological structures and volcanic processes.