Migration of Late Miocene to Quaternary alkaline magmatism at the Alpine-Pannonian transition area: Significance for deformation rates and decoupling of lithospheric levels

Within-plate migration of alkaline basaltic centers is generally related to translation of the lithosphere with a hot spot above a largely stationary mantle plume. Here, we report, for the first time, a hitherto unrecognized migration of small-sized Late Miocene to Early Quaternary alkali-basaltic volcanic centers at the transition from Eastern Alps to the Pannonian Basin. The volcanic centers migrated along the South Burgenland High in a regular sequence over a 95 km distance from NNE to SSW between 11 Ma and 1.7 Ma. The basaltic magmatism was also associated with thinning of the crust and lithosphere and an increase of the thermal gradient as previous studies testify. In detail, three stages of migration are recognized as follows: (i) Stage 1 with a 55 km SSW-toward shift of volcanism between 11 and 5 Ma; (ii) Stage 2 with a 35 km-WSW shift and enlargement of the distribution of volcanic centers between ca. 5 and 3.5 Ma; and (iii) Stage 3 with a S-directed shift of ca. 25 km between 3.5 and 1.7 Ma. We propose that this pattern and mechanism of migration of the volcanic centers along the South Burgenland High resulted from thermally induced progressive thinning of the lithosphere over a mantle plume underneath the ALCAPA block, which was moving from SSW to the NNE between 11 and 1.7 Ma, interrupted by a marked eastward shift between 5 and 3.5 Ma (Stage 2). The Stage 1 shift of alkali-basaltic volcanism can be also observed in the Little Hungarian Plain and South Slovakia volcanic fields, here rotated in a sinistral wrench corridor, and the Stage 2 in the Balaton-Bakony of the Pannonian Basin (north of Lake Balaton). The migration of volcanic centers correlates with orientation and timing of regional shortening phases and inversion of the Alpine-Carpathian-Pannonian system although the overall amount of shortening remains uncertain. The convergence of the Alpine-Carpathian-Pannonian-Dinaric system is driven by the northward motion of the Adriatic microplate. Previous balancing of the shortening of Eastern Alps resulted in an approximately constant convergence rate of ca. 10 mm/yr since 20 Ma ago although the system changed to overall compression since ca. 6 Ma and lower shortening rates can be expected. Interestingly, the reasonable estimated migration rates of volcanic centers are all in a similar order of magnitude between 6.5 and 13.8 mm/yr as the mentioned 10 mm/yr. This is nearly an order of magnitude larger than present-day rates of 1 – 2 mm/yr with E to NE-directed motion, but similar to the global hotspot-fixed reference frame, which implies a ca. northeast-directed motion of >10 mm/yr. Although this could represent an explanation of observed migration of volcanic centers, we exclude it because of the short tracks (maximum 95 km) and small volumes of volcanic products implying rather local plumes in the upper mantle.

Acknowledgements: This work has been supported by the Austrian Science Fund (FWF), grant no. M-1343.