Mantle transition zone analysis using P-to-S receiver functions in the Alpine–Carpathian–Dinarides region: impact of plumes and slabs

SUMMARY This study investigates the mantle transition zone (MTZ) beneath Central and Eastern Europe using a 3-D Common Conversion Point migration of P-to-S receiver functions derived from a dense regional seismic network. The analysis focuses on the major seismic discontinuities at ~410, ~520 and ~660 km depth to assess their depth variations, continuity and implications for past and ongoing geodynamic processes. Our results reveal significant spatial variations in the thickness and topography of the MTZ. In the Western Alps and central Pannonian Basin, the MTZ is thickened up to ~280 km, deviating from the global average of ~250 km. This thickening is attributed to the presence of stagnant slab material in the transition zone, suggesting a long-lasting influence of past subduction, particularly of the Adria Plate and Vrancea slab. In the Carpathians and Dinarides, the 410 km discontinuity is uplifted to depths as shallow as ~400 km, while the 660 km discontinuity reaches depths of ~670–680 km in regions affected by subducted lithosphere, further supporting the presence of cold slab remnants. Additionally, the 520 km discontinuity—often intermittent or absent in global studies—is clearly imaged in many parts of the region, and found at variable depths ranging between ~510 and ~540 km. These depth anomalies suggest the presence of compositional heterogeneities and thermal variations within the MTZ, possibly linked to subducted oceanic crust or recycled lithospheric material. Evidence for mantle upwellings is also observed, particularly beneath the Pannonian Basin, where low-velocity anomalies near the 410 km discontinuity are consistent with small-scale plumes or thermal anomalies. These may be associated with post-subduction processes or intraplate volcanism. Importantly, the Alpine slab itself is not clearly detected in the transition zone, indicating that it may have already sunk below the MTZ or is not well-coupled to the upper mantle structure imaged by receiver functions. By providing new constraints on the structure of the upper mantle and its transition zone, this study refines existing models of regional tectonic evolution. Our findings emphasize the interplay between surface tectonics and deep mantle dynamics and demonstrate that the observed MTZ features preserve a strong geodynamic imprint of both past subduction and intraplate processes across the Alpine–Carpathian–Pannonian–Dinarides region.