Radiogenic strontium isotopes (87Sr/86Sr) of vein carbonates play a crucial role in the tectono-metamorphic study of fold-and-thrust belts and accretionary wedges and have been used to document fluid sources and fluxes, for example, along major fault zones. Moreover, the 87Sr/86Sr ratios of vein carbonates can trace the diagenetic to metamorphic evolution of pore fluids entrapped in accreted sediments. Here we present 87Sr/86Sr ratios of vein carbonates from the paleo-accretionary complex of the central European Alps (Glarus Alps, Switzerland) that formed during early stages of continental collision. We show that the vein carbonates trace the Sr isotopic evolution of pore fluids from an initial seawater-like signature towards the isotopic composition of the host rock. This relation allows us to constrain the diagenetic to low-grade metamorphic conditions of deformation events, including imbricate thrusting, folding, cleavage development, stratal disruption and tectonic transport of thrust slices, bedding-parallel shearing, and extensional vein-formation. Taken together, the strontium isotope systematics of vein carbonate provides new insights into the prograde to early retrograde tectonic evolution of Alpine accretionary complex and helps to understand aspects that are not sufficiently clear from traditional cross-cutting relationships.