During the Late Cretaceous, the base of the Graz Paleozoic was affected by late orogenic extension, causing advective heat flow and fluid migration. The extensional detachment separated ultramylonitic carbonates of low-grade metamorphism (Grenzmarmor) from the underlying crystalline units. Fluid alteration and fluid-flow during the Cretaceous tectono-metamorphic events within the Grenzmarmor, Gschwendt and Schöckl Nappe was characterized in several cross sections at different locations (Krenhof, Oswaldgraben, Almgraben, Schöckel, and Fischbach) along the tectonic margins of the Graz Paleozoic by stable isotope gecochemistry, by crush-leach analysis of fluid inclusions as well as calcite-dolomite-geothermometry of marble. The measured δ18O and δ13C values within marble and rauhwacke show a significant covariation, reflecting a systematic change in the oxygen and carbon isotopic composition of the carbonates due to fluid alteration. The intensity of fluid alteration depends significantly on the tectonic position and the prevailing temperature and pressure conditions during deformation. The isotopic composition is altered in settings influenced by retrogression during exhumation of deeply buried rocks (Fischbach, Schöckel), whereas locations related to strike-slip-detachment (Oswaldgraben, Almgraben) are altered in lower intensities. Calculated alteration-temperatures for Oswaldgraben are in the range of 300°C, Fischbach shows lower temperatures conditions during alteration (≈200°C). The location of Krenhof, which is influenced by normal faulting, shows isotopic alteration similar to Fischbach and Schöckel. Late-stage mineralisations of the Graz Paleozoic (Au-Apy Strasseck; Hg Tallack and Marxenkogel; Pb-Zn Arzberg) show indications for Cretaceous oreforming fluid flow. The stable isotope data of host rocks and veins suggest a relation to fluid alteration of the Raasberg-Formation in Fischbach and Schöckel. Hence, a correlation between Late Cretaceous extension, mineralisation and fluid alteration of the southern and eastern margin of the Graz Paleozoic is assumed.