Deciphering the pressure-temperature path in low-grade metamorphic rocks by combining crystal chemistry, thermobarometry and thermodynamic modelling: An example in the Marguareis Massif (Western Ligurian Alps, Italy)

Unveiling the pressure‒temperature path of low-grade metamorphic rocks is challenging because of the occurrence of detrital minerals phases and high-variance mineral assemblages (i.e., chlorite–white mica–quartz). This paper offers an attempt to reconstruct the pressure–temperature history on metapelites from a low-grade metamorphic unit, i.e., the Cabanaira Unit, located in the Marguareis Massif (Western Ligurian Alps, Italy). In order to obtain the most robust result possible, multiequilibrium thermobarometry, forward modelling and crystallochemical indexes measurement are used together to reconstruct a pressure–temperature path, considering strengths and weaknesses of each of these methods. This multidisciplinary approach allowed us to reconstruct the metamorphic evolution of the unit of interest, characterized by a pressure peak achieved under low-temperature conditions (0.85-0.68 GPa and 250-285 °C) followed by decompressional warming (low pressure–high temperature, 0.4-0.6 GPa and 300-335 °C). This pressure‒temperature path is consistent with the tectonic evolution of the investigated area proposed by previous authors, where a geological scenario in which the Cabanaira Unit experienced subduction-related processes was postulated, even if the reasons for warming remain unclear. Multiequilibrium thermobarometry is considered to be the most suitable method to unravel the metamorphic history of low-grade rocks, while forward thermodynamic modelling and the calculation of crystallochemical indexes seem to resolve only some segments of the pressure‒temperature path.