Mixed mode of deformation and processes along the Tellaro Detachment (Northern Apennines, Italy)

In the inner Northern Apennines (Lerici and La Spezia inland) the exhumed Tellaro detachment fault system is exposed. It can be traced in an area larger than 20 Km² and well observable in continuous kilometer-long coast exposures (Storti, 1995; Clemenzi et al., 2015). The major low-angle fault zone is marked by decameter-thick, carbonate-rich, cataclasites and gouges (“Calcare Cavernoso Fm.”) overlying a footwall of cataclastically deformed low-grade quarzites, phyllites and metaconglomerates (Ladinian-Carnian Verrucano Fm.) belonging to the Tuscan Metamorphic units (Molli et al., 2018). In the hanging wall, synthetic and antithetic splay faults affect the originally ~6 Km-thick Tuscan Nappe succession, thinned to less than 0.6 Km.

Detailed structural data collected at the meso- and microscale, combined with Raman spectroscopy, fluid-inclusion analysis, and mineralogical studies, allowed us to constraints deformation processes and fault activity in a temperature range of 260-120 °C at mid-shallow crustal depth (10-5 Km). Observable deformation structures in the footwall fault rocks provide evidence supporting mixed deformation mode and mechanisms, with intermitted cataclastic flow and unstable brittle slip (aseismic-to-seismic) during the fault activity.