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In the northern Tyrrhenian Sea, late Miocene \ud intrusions (Monte Capanne pluton and\ud Porto Azzurro pluton) were emplaced at\ud upper crustal levels (<0.2 GPa) in the thrust\ud systems of Elba Island. The emplacement\ud of intrusive rocks is currently explained\ud in the context of late Miocene extensional\ud tec tonics. New detailed structural data\ud collected along a continuous natural cross\ud section through the contact aureole of the\ud Porto Azzurro pluton (eastern Elba) where\ud strain localization has occurred within two\ud west-dipping decameter-scale carbonate\ud shear zones, namely the Calanchiole and\ud Felciaio shear zones, are reported here.\ud These shear zones, characterized by a lithological\ud difference with calcite and dolomite\ud marbles dominant in the Calanchiole and\ud Felciaio shear zones, respectively, exhibit\ud a similar rheological behavior . They represent\ud two weakened layers in which westdipping\ud mylonitic foliation, sheath folds,\ud boudinage structures, and upright folds\ud developed within the contact aureole .\ud Moreover, in correspondence with the\ud Felciaio shear zone, the inversion of metamorphic\ud facies occurs. Meso- and microstructural\ud data give evidence that most of\ud the deformation and displacement in the\ud shear zones was coeval with contact metamorphism\ud and developed under metamorphic\ud conditions retrograde from pyroxene\ud hornfels to hornblende-hornfels facies.\ud Geometric and kinematic features indicate\ud that both shear zones correspond to ductile\ud thrusts, which led to internal stacking of the\ud contact aureole . Therefore, at Elba Island,\ud emplacement of intrusive rocks coeval with\ud late Miocene crustal shortening gives a new\ud perspective on relations between tectonics\ud and magmatism in the northern Apennines

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The Northern Apennines (NA) orogenic wedge formed during Oligocene‐Miocene convergence and westward subduction of Adria beneath the European Plate. Extension ensued in the Mid‐Late Miocene in response to Adria roll‐back, causing opening of the back‐arc Northern Tyrrhenian Sea. Whether extension continues uninterrupted since the Mid‐Late Miocene or it was punctuated by short‐lived compressional events, remains, however, uncertain. We used the K‐Ar method to date a set of brittle‐ductile and brittle deformation zones from the Island of Elba to contribute to this debate. We dated the low‐angle Zuccale Fault (ZF), the Capo Norsi‐Monte Arco Thrust (CN‐MAT), and the Calanchiole Shear Zone (CSZ). The CN‐MAT and CSZ are moderately west dipping, top‐to‐the‐east thrusts in the immediate footwall of the ZF. The CSZ slipped 6.14 ± 0.64 Ma (<0.1 μm fraction) and the CN‐MAT 4.90 ± 0.27 Ma ago (<0.4 μm fraction). The ZF, although cutting the two other faults, yielded an older age of 7.58 ± 0.11 Ma (<0.1 μm fraction). The ZF gouge, however, contains an illitic detrital contaminant from the Paleozoic age flysch deformed in its hanging wall and the age thus is a maximum faulting age. Removal of ~1% of a 300‐Ma‐old contaminant brings the ZF faulting age to <4.90 Ma. Our results provide the first direct dating of brittle deformation in the Apennines, constraining Late Miocene‐Early Pliocene regional compression. They call for a refinement of current NA geodynamic models in the framework of the Northern Tyrrhenian Sea extension.