Fossil rifted margins, whereby originally extended continental crust is subsequently stacked in orogenic belts, provide the opportunity to track rift‐related tectonics across different crustal levels. In this study, the tectonothermal evolution of the fossil Adriatic continental margin, sampled in the Italian Southern Alps, is investigated combining new (U‐Th)/He zircon (ZHe) thermochronology from upper crustal rocks with existing data from the originally underlying lower crust, to shed light on the processes responsible for rift localization in the Alpine Tethys system. The Adriatic microplate records a protracted rift evolution, whereby distributed upper crustal stretching at 245–190 Ma was followed by rift localization along its future western edge, culminating in mantle exhumation at 165–160 Ma. A progressive westward younging of ZHe ages, from 280–240 Ma in the Lombardian Basin to 215–200 Ma near the Sostegno and Fenera Basins, indicates that anomalously high thermal gradients were established in the Late Triassic in the area where rifting later localized. The inferred episodic heating was contemporaneous with protracted fluid flow, minor magmatism, and ductile shearing within the originally underlying lower crust. Subsequent normal faulting was initiated post‐185 Ma, as constrained by exhumation‐related ZHe ages in detrital zircons from a syntectonic sandstone. The spatial distribution of the detected heating‐cooling cycle suggests that rift localization along the western edge of the Adriatic Plate was probably favored by a crustal‐scale thermal anomaly, established at 215–210 Ma, followed by thermal decay by 200–190 Ma. Subsequent crust‐wide extension, starting at 185–180 Ma, led to excision of continental crust and mantle exhumation.

We analyze the tectono‐sedimentary and thermochronometric constraints of the Tertiary Piedmont Basin (TPB) and its adjoining orogen, the Ligurian Alps, providing new insights on the basin evolution in response to a changing geodynamic setting. The geometry of the post‐metamorphic faults of the Ligurian belt as well as the fault network that controlled the Oligo–Miocene TPB deposition has been characterized through a detailed structural analysis. Three main faulting stages have been distinguished and dated thanks to the relationships among faults and basin stratigraphy and thermochronometric data. The first stage (F1, Rupelian–Early Chattian) is related to the development of extensional NNW‐directed faults, which controlled the exhumation of the orogen and the deposition of nearshore clastics. During the Late Chattian, the basin drowning is marked by mudstones and turbidites, which deposition was influenced by the second faulting stage (F2). This phase was mainly characterized by NE‐ to ENE‐striking faults developed within a transtensional zone. Since the Miocene, the whole area was dominated by transpressive tectonics. The sedimentation was represented by a condensed succession followed by a very thick, turbiditic complex. At the regional scale, this succession of events reflects the major geodynamic reorganization in the central Mediterranean region during the Oligo–Miocene times, induced by the late‐collisional processes of the Alps, by the eastward migration of the Apennines subduction and by the opening of extensional basins (i. e., the Liguro–Provençal Ocean).

The Alpine Tethys rifted margins were generated by a Mesozoic polyphase magma‐poor rifting leading to the opening of the Piedmont‐Ligurian “Ocean.” This latter developed through different phases of rifting that terminated with the exhumation of subcontinental mantle along an extensional detachment system. At the onset of simple shear detachment faulting, two margin types were generated: an upper and a lower plate corresponding to the hanging wall and footwall of the final detachment system, respectively. The two margin architectures were markedly different and characterized by a specific asymmetry. In this study the detailed analysis of the Adriatic margin, exposed in the Serie dei Laghi, Ivrea‐Verbano, and Canavese Zone, enabled to recognize the diagnostic elements of an upper plate rifted margin. This thesis contrasts with the classic interpretation of the Southalpine units, previously compared with the adjacent fossil margin preserved in the Austroalpine nappes and considered as part of a lower plate. The proposed scenario suggests the segmentation and flip of the Alpine rifting system along strike and the passage from a lower to an upper plate. Following this interpretation, the European and Southern Adria margins are coevally developed upper plate margins, respectively resting NE and SW of a major transform zone that accommodates a flip in the polarity of the rift system. This new explanation has important implications for the study of the pre‐Alpine rift‐related structures, for the comprehension of their role during the reactivation of the margin and for the paleogeographic evolution of the Alpine orogen.