Multiple ignimbrite eruptions around 15 Ma in the North Pannonian Basin: Volcanology, geochronology, and geochemistry of the Tar-Jató tuffs

We present volcanological, geochronological, and geochemical evidence suggesting that the Miocene Tar-Jató “middle tuffs” in the North Pannonian Basin all belong to the same volcanic system producing multiple silicic explosive eruptions. These eruptions probably originated from a caldera (now buried under the Pannonian Basin) during a period around 15 Ma. Based on Bayesian age modelling of the dated ignimbrite horizons, the recorded eruptive activity lasted for 300–500 kyr between c. 15.3–14.9 Ma. Such prolonged, multi-episodic ignimbrite volcanism is considered unique in the region, as similar eruptive sequences of a single system have not been previously documented. The Tar-Jató eruptions deposited mostly successive ignimbrites with a total preserved thicknesses of up to 200 m. They were fuelled by geochemically nearly homogeneous magma, which nevertheless differs from any other ignimbrite in the Pannonian Basin and thus provides a distinguishable marker horizon. The vertically varying FeO content of the ignimbrites, together with locally interbedded epiclastic layers, is consistent with the extended duration of the volcanism, which probably occurred in three subsequent series, characterized by low, hybrid and high FeO content, respectively. This conclusion contrasts with a single eruption phase proposed earlier and dated at 14.9 Ma; we suggest that this age represents only the youngest eruption series. Trace-element geochemistry shows the southward distribution of this presumably youngest unit, as it correlates with the 14.9 Ma Plaz tuff (Mt. Medvednica, Croatia), located 300 km of the reconstructed source vent. On the other hand, the slightly younger (14.8 Ma) Bidrovec tuff also from Mt. Medvednica correlates with the Tibolddaróc tuff (14.7 Ma) in the North Pannonian Basin. Other definite distal counterparts of the Tar-Jató tuffs remain unknown. Comparative trace-element geochemistry also demonstrates that the Tar-Jató tuffs cannot be correlated with the 15.3–15.4 Ma tuffs widespread across the western–southwestern part of the Pannonian Basin System and the Dinarides (e.g., Kuchyna, Lučane-1, Gacko, and Požeška gora tuffs).