Appendix: Location and description of sampling sites
Hajnáčka diatreme (48°13’5.88”N, 19°57’19.44”E)
Basaltic diatreme in the center of Hajnačka village represents a remnant of a maar-feeding channel. The diatreme is composed of palagonitized tuffaceous breccia penetrated by scoria breccia and a basaltic dyke. Whole rock and isochron K/Ar dating yielded ages between 3.2 and 2.4 Ma, and accordingly the diatreme was affiliated with the 3 rd
volcanic phase ( Vass et al. 2002 ). Apatite was obtained from a 1 m large block of maar wall that was slumped in the feeding channel and later intersected by a basaltic dyke ( Figs. 2a, b ).
Gemerské Dechtáre maar (48°14’6.36”N, 20°1’35.40”E)
Remnants of this newly discovered maar are exposed in a small quarry, ~20

40 m in size,
1.4 km SE from Gemerské Dechtáre village. Zircon and apatite were isolated from a layer of non-coherent, black, fine- to medium-grained lapilli tuffs with blocks of agglutinated tuffaceous breccias ( Fig. 2c ).
Jelšovec maar (48°16’49.79”N, 19°35’28.66”E)
The maar complex, extending over a 1.7

1.5 km area west of Jelšovec village, is hosted by siliciclastic sediments of the Upper Eggenburgian Bukovinka Formation and the Ottnagian
Salgótarján Formation. Marginal parts of the maar are composed of phreato-magmatic pyroclastic rocks – palagonitized tuffs and lapilli tuffs. The central part is filled with a 2-14 m thick sequence of diatomite and smectite-rich diatomaceous clay interlaced with tuffaceous clay and tuffites ( Vass et al. 1998 ). A brecciaed basaltic dyke with upper mantle xenoliths was penetrated in a borehole. According to its position in the NW part of Lučenec Basin, the maar is traditionally affiliated with the Upper Miocene Podrečany Formation. Apatite was isolated from a stratified succession of palagonitized tuffs and lapilli tuffs alternating with wet surge and pyroclastic fall deposits ( Fig. 2d ) in a small abandoned quarry located on an internal slope of the tuff ring.
Pinciná maar (48°21’45.65”N, 19°46’29.96”E)
This small circular maar, 760
 930 m in size, located 1 km northeast of Pinciná village, is famous for its economic alginite reserves ( Vass 1998 ) and occurrence of exotic igneous
(clinopyroxenite, hornblendite, syenite, pincinite) xenoliths (
Huraiová et al. 1996, 2005; Hurai

et al. 1998 ). The maar formed on the paleosurface composed of the Egerian Lučenec
Formation (Szeczeny schlier) and it was later buried beneath a 20-30 m thick layer of limnofluvial deposits of the Poltár Formation ( Vass et al. 2007 ).
Several small quarries and outcrops occur in the outer and inner portions of the tuff cone, composed mostly of palagonitized lapilli tuff with basaltic bombs and up to 1 m large fragments of gabbros, syenites, granitoids and low-grade metamorphic rocks. Maar lake sediments are represented by aleurites and pelites. The central part is filled with a 30-40 m thick alginite complex underlain by clays, tuffitic clays with diatomites, epiclastic volcanogenic sandstone and lapilli tuff. According to its geographic position, the maar was affiliated with the Upper Miocene Podrečany Formation. U-Pb-Th dating of zircon and monazite from syenite xenoliths yielded ages clustering at 5.8±0.1 and 5.4±0.1 Ma ( Hurai et al. 2010 ), i.e. at the Upper Miocene-Pliocene boundary. Zircon grains from the same syenite xenoliths were used also for (U-Th)/He dating in this work.
Hodejov maar
(48°17’51.81”N, 19°59’2.60”E)
This partly eroded maar at the SW margin of Hodejov village evolved during two stages.
The older portion of the tuff cone was destroyed by a violent freatomagmatic eruption followed by Hawaiian- and Surtseyan-type eruptions. Volcanic activity finished with
Strombolian eruptions that produced the uppermost horizon containing basaltic bombs. The lava flow along the southern margin of Hodejov village extends from the volcanic centre
(Buda hill) located 3.8 km SSW from the maar. The lava flow belongs to 4 th or 5 th volcanic phase, according to 1.7±0.2 Ma K/Ar age. The Hodejov maar is affiliated with the 6 th
volcanic phase according to geomorphologic criteria, in spite of a 4.6±0.8 Ma K/Ar age obtained on a basaltic bomb collected from the upper part of the maar ( Vass et al. 2002 ). Apatite and zircon were extracted from a fine-grained lapilli tuff exposed at the base of the SE slope of the maar structure, formed during the second stage.
Fiľakovo – Castle Hill maar (48°16’16.59”N, 19°49’34.25”E)
The maar is represented by a relict tuff ring with ruins of a medieval castle on top. The maar complex succession starts with coarse, unsorted wet surge deposit, sedimented on Lower
Miocene sandstones of the Fiľakovo Formation. Superimposed is the succession with well stratified fine- to coarse-grained palagonitized lapilli tuffs with variable proportions of vesicular basalt and fragments of Miocene sediments. Alternation of finely laminated, massive, unsorted and sorted coarse beds indicates dry surge, wet surge and pyroclastic fall

deposition. The maar is believed to be coeval either with Günz glacial or with the
Günz/Mindel boundary ( Vass et al. 2002 ).
Apatite and zircon were collected from coarse grained wet surge deposits from the base of the tuff ring section exposed in the eastern slope of the Castle hill.