Positive inversion tectonics in foreland fold-and-thrust belts: A reappraisal of the Umbria–Marche Northern Apennines (Central Italy) by integrating geological and geophysical data

Unraveling the tectonic style in the outer zones of fold-and-thrust belts is generally puzzling because the basement–cover relationships are often hidden in the subsurface as in the outer Northern Apennines of Italy. This study aims to reconstruct the deep setting of the Northern Apennine foreland thrust belt by integrating surface structural–geological and subsurface seismic reflection profile and well data, corroborated by a gravity–magnetic modeling. A remarkable mountain ridge, the Umbria–Marche Apennine Ridge (UMAR), which corresponds to a prominent area of structural and topographic elevation, characterizes the morphology of the Northern Apennines. This mountain ridge is constituted by Meso-Cenozoic carbonates involved in Neogene compressive structures and is surrounded by wide exposures of foredeep deposits. The basement–cover relationships are poorly constrained and both thin- and thick-skinned tectonic styles have been applied. The interpretation of subsurface data allowed recognizing a thick pre-Jurassic sedimentary sequence filling a late Paleozoic(?)–Triassic symmetric fault-bounded extensional basin, lying directly below the UMAR. This deep-rooted basin underwent positive inversion during the Neogene compression and thrust–fold development. The reconstructed thick-skinned inversion tectonic model is consistent with both the modest amount of shortening and the remarkable structural elevation of the UMAR. The outcomes of this study reveal that prominent mountain ridges occurring in foreland thrust belts are most likely related to the deep-rooted basement-involved positive inversion of pre-existing extensional basins.