Pre-shortening reconstruction of the adria microplate: Balanced and restored cross-sections through the Southern Apennines–Dinarides (Central Mediterranean Sea)

The Adria plate and/or microplate has accommodated the differential eastward motion of Africa, Europe-Iberia, since the Jurassic times, and the subsequent convergence between Africa and Eurasia from Middle Cretaceous onwards. Its complex tectonic deformation, responsible of the development of the opposing Apennines and Dinarides thin- and thick-skinned fold and thrust belts, remains poorly constrained, fueling an ongoing debate on the original position of Adria, its pre-compressional continental width, and crustal structure. Here we tackle these uncertainties by analyzing and integrating published structural cross-sections, subsurface data and 2D lithospheric numerical models to build a 758 km long regional balanced and restored cross-sections along a SW-NE transect through the Southern Apennines and Southern Dinarides. Employing the line length method for the sedimentary cover and assuming the preservation of the pre-Triassic continental crustal area, we reconstruct the pre-compressional continental width of Adria. The unfolding of the sedimentary cover along the SW-NE cross-section results in an undeformed continental Adria microplate width of approximately 1050 km, slightly under previous estimations (1175 to 1670 km). The minimum total shortening results in 291 km: 148 km across the Southern Apennines and 143 km across the Southern Dinarides. We then calculate the Adria microplate continental crustal thickness during Middle-Late Jurassic time assuming local isostatic balance, obtaining 23 km for the eastern and central Adria sectors, based on shallow water carbonate sequences. In contrast, the western Adria sector at the Southern Apennines results in a restored pre-Triassic continental crustal thickness of only 7 km, suggesting that the middle and lower crustal layers in this sector may have been partially removed, possibly by mantle delamination during Neogene to Quaternary collisional processes. The results strongly support that the Adria microplate was located to the east of the Pelagian Basin and formed part of the African Plate around the Permian–Triassic boundary interval.