Geophysical-petrological model for bidirectional mantle delamination of the Adria microplate beneath the northern Apennines and Dinarides orogenic systems

This study presents a geophysical-geochemical integrated model of the thermochemical structure of the lithosphere and uppermost mantle along a transect from the Northern Tyrrhenian Sea to the Pannonian Basin, crossing the northern Apennines, the Adriatic Sea, and the Dinarides fold-thrust belt. The objectives are to image crustal thickness variations and characterize the different mantle domains. In addition, we evaluate the topographic response of opposed subductions along this transect and discuss their implications in the evolution of the region. Results show a more complex structure and slightly higher average crustal density of Adria compared to Tisza microplate. Below the Tyrrhenian Sea and Western Apennines, Moho lays at <25 km depth while along the Eastern Apennines it is as deep as 55 km. The modeled lithosphere-asthenosphere boundary (LAB) below the Tyrrhenian Sea and Pannonian Basin is flat lying at similar to 75 and 90 km, respectively. Below the External Apennines and Dinarides the LAB deepens to 150 km, slightly shallowing toward the Adriatic foreland basin at 125 km depth. Our results are consistent with the presence of two mantle wedges, resulting from the rollback of the Ligurian-Tethys and Vardar-NeoTethys oceanic slabs followed by continental mantle delamination of the eastern and western distal margins of Adria. These two opposed slabs beneath the Apennines and Dinarides are modeled as two thermal sublithospheric anomalies of -200 degrees C. Most of the elevation along the profile is under thermal isostasy and departures can be explained by regional isostasy with an elastic thickness between 10 and 20 km.Plain Language Summary This study integrates a wide range of geological and geophysical observations (e.g., elevation, gravity, geoid, seismic tomography) to investigate the density and temperature variations down to 400 km along a transect that extends from the Tyrrhenian Sea and northern Apennines in Italy to the Dinarides and Pannonian Basin in southern Europe. The main objectives are to study the present-day structure and composition of the lithosphere and uppermost mantle, and to evaluate the resulting topography, and finally to discuss their implications in the tectonic evolution of the region. Our results show that the crust and the base of the lithosphere vary significantly in the study region, lying shallow below the basins to much deeper underneath the mountain belts where topography is higher. We also observe two cold and dense zones sitting in the distal margins of the Adria microplate, beneath the northern Apennines and Dinarides, that are interpreted as two opposed subducting slabs that have largely controlled the geodynamic evolution of the study region in the last 30 My.