Adria Microplate Structure and its Geodynamic History Since Early Mesozoic

Despite decades of extensive research, the precise lithospheric architecture and evolutionary trajectory of the Adria microplate, sandwiched between the converging Eurasian and African plates, remain subjects of intense geological debate. Although numerous paleotectonic models have been proposed over the last 100 years, the crustal evolution and dimensions of the Adria remain subjects of significant debate, often yielding conflicting results.

Conducted within the framework of the GeoAdria project, this study addresses existing tectonic uncertainties by integrating crustal-scale balanced and restored cross-sections with numerical lithospheric models. We investigate the structural architecture of the Apennine and Dinaride fold-and-thrust belts and their shared Adriatic foreland. Our numerical modeling results reveal a deep-seated lithospheric structure defined by two distinct lithospheric slabs with opposite dips. We interpret the slab beneath the Apennines as the western Adriatic continental lithosphere, which was originally contiguous with the Ionian Ocean. Conversely, the slab beneath the Dinarides represents the eastern continental margin of Adria, formerly adjacent to the consumed Vardar Ocean. These opposing slabs are interpreted as the products of continental delamination triggered at the end of oceanic subduction.

Quantitative analysis of a 758-km-long transect across southern Adria, indicates a minimum total shortening of 291 km (~28%). Of this total, 148 km (31%) was accommodated within the Southern Apennines, while 143 km (25%) occurred in the Southern Dinarides. Based on these numbers, we conclude that the Adria microplate had a minimum NE-SW width of 1050 km during the Jurassic, and thus between 126 and 621 km narrower than suggested by previous paleogeographic reconstructions.

By assuming basement area preservation, we calculated a restored Jurassic crustal thickness of 23–28 km for the central and eastern Adria domains. This crustal framework facilitated a paleogeography of shallow-water carbonate platforms limited from deep basins steep slopes analogous to the modern Bahamas Carbonate Platform.

In this geodynamic frame, we reconstruct the Adria microplate as an integral part of the African plate prior to the breakup of Pangea (~250 Ma). In this configuration, Adria was situated south of the subducting Paleo-Tethys Ocean, allowing for a direct connection between the shelf-basin systems of Southern Adria and the Pelagian Basin offshore Tunisia. Following the fragmentation of the African margin, Adria drifted toward the NNE, eventually reaching a position near the Eurasian margin as Paleo-Tethys subduction was almost consumed at this paleolatitude. This migration occurred during the Early­–Middle Jurassic, preceding the Middle–Late Jurassic opening of the Ligurian-Tethys Ocean between Iberia-Eurasia and Africa.

This research is funded by the GEOADRIA (PID2022-139943NB-I00) project from the Spanish Government