Abstract The core of the Zuccale low-angle normal fault contains a distinctive fault-rock zonation that developed during exhumation, composed of a diversity of fault rocks derived from lithologically heterogeneous wall rocks. Field and microstructural analyses indicate that deformation mechanisms active within the fault core, including brittle fracture, dissolution–precipitation creep and crystal-plasticity, were active broadly contemporaneously. Initially, deformation was accommodated within frictionally weak and inherently stable talc-phyllonites. Although the talc-phyllonites can account for slip at low angles, grain-scale weakening effects were limited by changes over time to the structure of the fault core, resulting from interactions with subsidiary footwall faults. Ultimately, the talc-phyllonites were dismembered into a series of isolated lenses incapable of transmitting grain-scale weakening up to the fault scale. Following this, deformation was accommodated within well-connected units of dolomite-, quartz- and calcite-bearing cataclasite, fault breccia, and foliated fault gouge. Deformation progressively migrated through this latter sequence as a result of precipitation-hardening due to the widespread growth of dolomite. The complexity of fault-zone structure, combined with changes to fault-rock distribution over time, may have resulted in fundamental changes in fault-slip behaviour, an important point to consider given the recent spectrum of slip mechanisms identified along many tectonic faults.

Abstract During the past 18 Ma extensional tectonism has migrated from the Tyrrhenian sea eastward into the Northern Apennines of Italy. The extension is due in part to lowangle east-dipping normal faults, that are now exhumed in the Tyrrhenian islands and Tuscany, while additional extension is still occurring in the Apennine chain (Umbria region, c. 200 km eastward). This tectonic framework is an example where active extensional processes affecting the Umbria region can be studied in exhumed faults that are no longer active. Here a comparison between the Zuccale Fault (ZF), cropping out in the Isle of Elba, and the Altotiberina Fault (ATF), revealed by geophysical data, seismology and seismic profiles crossing the Umbria region, provide insights into the processes affecting low-angle normal fault development and evolution. Recorded microseismicity suggests that the ATF is presently active under a vertical σ 1 . Structural analysis of the ZF depict a comparable scenario with fluid involvement during the activity. The comparison of these two structures suggests movements with fluid involvement along gently dipping planes under a vertical σ 1 , implying that these faults are mechanically weak.