Neotectonic vertical motions based on syn-volcanic palaeosurfaces and geochronological data: inferences for crustal and mantle processes (Pannonian Basin, Central Europe)

Rate and timing of neotectonic vertical motions represent an ongoing research topic in inverted sedimentary basins. This presentation offers new data concerning the uplift history of the western part of the Miocene Pannonian Basin system, (Central Europe) which is bordering the Alpine orogenic belt. After the syn-rift phase of ~21–15Ma, the area underwent the post-rift phase which involved differential subsidence reaching several kilometres in basin centres. Parallel to post-rift subsidence process, the basin inversion started during the Late Miocene and resulted in differential uplift, fluvial and aeolian denudation, and river incision.

The late post-rift and the early neotectonic phases were accompanied by extensive basalt volcanism, resulting in the activity of two distinct phreatomagmatic monogenetic volcanic fields, the Bakony-Balaton Highland and Little Hungarian Plain Volcanic Fields (BBHVF and LHPVF) through the Late Miocene to earliest Quaternary (7.96–2.61 Ma). The volcanic fields comprise diverse volcanic landforms, including shield volcanoes, maar diatremes, volcanic plugs and erosional remnants of scoria and spatter cones.

Detailed analysis of volcanic facies was used to reconstruct the topographic position of the syn-volcanic palaeosurface upon which the volcanoes developed. Using the previously published ages of the volcanic rocks and the palaeo-elevations of the volcanic surfaces, averaged uplift rates were derived for all observation points. In addition, previously published exposure age data and geomorphological data were used to constrain the uplift rates.

The reconstructed palaeosurfaces and the calculated rock uplift rates show spatial and temporal variations from ~20 to ~100 m/Ma. Before ~3.5 Ma the two volcanic fields showed opposite differential vertical motions having been positive in the eastern basin margin (Transdanubian Range) and negative in the neighbouring basin centre (Kisalföld/Danube Basin); variations were due to differential post-rift subsidence and the onset of minor neotectonic uplift. After ~3.5 Ma all the studied areas underwent uplift, but the south-western part of the volcanic fields exhibits larger uplift values than the north-eastern one triggering a regional drainage pattern reorganisation. Moving west from the volcanic areas, toward the foothills of the Alps, the uplift rates increased even more and approximating values obtained in the Alpine orogenic belt.

This variable differential vertical motion history points to the interplay of complex governing processes. These could involve the intraplate compressional stress related to neotectonic basin inversion, lower-crustal flow of the weakened crust, and more importantly, mantle processes at depth. This latter could involve lithospheric folding, mantle convection-induced development of a dynamic topography, and the eventual effect of secondary plumes. In addition, uplift could be coupled with surface processes like variable unloading by denudation and loading by sedimentation in the axial and marginal parts of the area, respectively.

The research was supported by the Hungarian National Research, Development and Innovation Office, project 134873 and the HUN-REN Research Grant Hungary project RGH531001.