Complexity of geothermal systems in wedge-top basins: Insights from a 3D geological model of the Tertiary Piedmont Basin, NW Italy

Foreland and wedge-top basins host geothermal systems, in which the nature and architecture of reservoir units, heat sources, and fluid circulation result from a complex tectonic evolution. However, the relationship between tectonics and local geological processes (e.g., sediment dispersal and fracturing), is often not obvious in wedge-top basins, hindering the exploration of their geothermal resources. To investigate the multiscale tectonic-geothermal relationship, we focus our study on the Tertiary Piedmont Basin (TPB), a wedge-top basin formed on the Alps-Apennines junction (northwest Italy). The geometry and thermal structure of the region arise from the interaction between the Alps and Apennines, including processes such as slab break-off, mantle upwelling, and orogenic collapse. The basin fill is up to 6 km-thick and characterized by several unconformity-bounded clastic units, encompassing shelf to deep-water depositional settings. Their spatial arrangement reflect major depocenter shifts and structural regime transitions. The presence of several thermal springs, local high geothermal gradients (>80 °C/Km), and moderately high surface heat flux suggest a deep groundwater circulation, most likely within the highly fractured Alpine basement rocks. We present a conceptual basin-scale 3D model of the reservoir and overlying sealing sedimentary cover, implemented through the analyses and integration of different geological/geophysical data (e.g., seismic reflection lines, structural and petrophysical data), along with a synthesis of the main tectonic events that affected the basin. This model helps unravel possible heating mechanisms and circulation of the geothermal waters in the TPB and the applied workflow can be used on analogue basins to estimate their geothermal potential