Selected Article


Ion probe and fluid inclusion evidences for co-seismic fluid infiltration in a crustal detachment


We have investigated the geochemical pattern of fluid infiltration in the extensional detachment of Tinos Island (Cyclades, Greece). Ion microprobe O-isotope analyses and fluid inclusion studies have been conducted in strain fringes developing around pyrite blasts in the mylonite of the shear zone. Micro-scale traverses in quartz and calcite fibres show that δ18O increases from 17-18 to 20-21‰ in 1 mm towards the blast, drops of 3‰ in ∼200 μm, then rises again in the direction of growth. δ18O variations are interpreted as transient influxes of exotic fluids into the shear zone between periods of closed system buffering by the host rock. Fluid inclusions trapped in the fibres show fluctuating salinities (0-4 wt% NaCl eq.) and densities that reflect drops of the pore pressure from lithostatic (λ=1) to hydrostatic (λ=0.4) values during fringe growth. Isotopic and microthermometric data are consistent with models of seismic pumping developed for compressive shear zones. We therefore suggest that co-seismic pore pressure variations developed suction forces sufficient to drive large-scale fluid migration in the Tinos detachment, as in convergent tectonic settings.