It was widely recognized that quantitative pressure-temperaturetime (P-T-t) paths extracted from metamorphic units portray the thermo-mechanical evolutions of orogens (e.g. England and England & Thompson, 1984;England & Richardson, 1977). The latter are usually reconstructed by means of the P-T conditions of highgrade units. However, the reconstruction of P-T paths, especially high-pressure metamorphism, in low-to very low-grade metamorphic rocks, is of paramount importance to better understand the geodynamic evolution of orogens. Indeed, under low-temperature condition reaction, kinetics is sluggish and consequently chemical equilibrium is rarely achieved at the whole-rock scale impeding to unambiguously constrain P-T conditions of metamorphism (Frey & Robinson, 1999;Lanari & Engi, 2017). It is all the more difficult to determine P-T conditions in meta-sediments in which detrital minerals remain as relict phases, so making the so-called reactive rock composition (Lanari & Engi, 2017 and reference therein), to be taken into account in order to model the chemical equilibrium, still questionable. This is the case of the very low-grade Marguareis Unit (Briançonnais Domain), a European fragment of continental crust (Decarlis et al., 2013), located at the boundary between Maritime and Ligurian Alps. This unit was involved in the Alpine collision since middle Eocene age (Seno et al., 2005). The deformation history of the Marguareis Unit has been deeply investigated (Brizio et al., 1983;Sanità et al., 2021), whereas the reconstruction of metamorphic conditions remains partly unconstrained and interpreted as the result of very shallow tectonic events (anchizone, Messiga et al., 1981).