Subsurface structure and tectonic evolution of an intermontane basin at the hinterland-foreland transition: Insights from the tectonically active Mugello Basin (Northern Apennines, Italy)

This is the authors' abstract. We don't add key points for this paper.

The main drainage divide of the Italian Northern Apennines marks the transition between hinterland of the belt experiencing post-orogenic extension and the foreland that is still undergoing orogenic accretion. While Neogene extension migrated northeastward forming several intermontane basins, the influence of crustal shortening on their evolution remains debated. The Quaternary Mugello Basin, located where the tectonic shift from compression to extension occurred relatively recently, is a key site for this debate. Due to limited geological and geophysical data, three competing structural models exist: (1) a half-graben with occasional compressional pulses; (2) a purely extensional synform evolving into an asymmetric graben; (3) a compressional basin only recently affected by extensional faulting. To determine which model is most likely, we integrated geological field observations, borehole data, fluvial morphometry, and seismic microtremor acquisitions collected along five transects. Our results reveal a synform-shaped top substratum with a depocenter located in the central part of the basin, effectively ruling out the half-graben hypothesis. However, field observations, basin geometry and disequilibrium of the river network along the northeastern margin suggest the presence of normal faults along this margin. Our integrated approach allowed us to propose a model for the tectonic evolution of the Mugello Basin under a continuous extensional regime implying fault-propagation folding mechanisms to explain the basin geometry and stratigraphic architecture of the syn -rift units. These findings provide critical constraints on the seismotectonic framework of the Mugello Basin and the broader regional transition from syn-orogenic compression to post-orogenic extension.