Seismic cycle in bituminous dolostones (Monte Camicia Thrust, Central Apennines, Italy)

Seismic ruptures often propagate along fault zones cutting km-thick sequences of carbonates (e.g., Wenchuan Mw 7.8, 2008, China; L’Aquila Mw 6.1, 2009, Italy). As a consequence, fault rock assemblages may record the seismic cycle under a wide range of loading conditions, temperatures (up to 1250°C during co-seismic slip), and fluid-rock interactions. The Monte Camicia Thrust in the Italian Central Apennines is exhumed from ∼3 km depth. The footwall rocks are made of bituminous dolostones cut by a network of faults accommodating up to several meters of displacement. Fault slip zones are mm– to cm–thick and bounded by ultra-polished (“mirror-like”) surfaces independently of their displacement. Deformation in the studied slip zones is accommodated by cataclasis and pressure solution in carbonates, and viscous flow in the foliated bitumen. Some of the faults with displacements > 0.10 m have multiple slip zones, separated by “mirror-like” surfaces, and include clasts of foliated bitumen and fragments of older slip zones sealed by calcite precipitation. We conclude that (1) slip zones record post- to inter-seismic (foliated bitumen) and co-seismic (fragments of bitumen) deformation in a fluid-rich environment (calcite precipitation) and (2) mirror-like surfaces formed during all stages of the seismic cycle.