Missing lawsonite and aragonite found: P–T and fluid composition in meta-marls from the Combin Zone (Western Alps)

Abstract We report the first findings of several occurrences lawsonite and metamorphic aragonite in meta-sediments from Combin Zone (Piemonte–Liguria ocean, Western Alps), where early blueschist-facies episode is poorly documented. New field data (thermodynamic modelling Raman spectroscopy on carbonaceous material) are used to elucidate P–T evolution fluid composition investigate growth breakdown reactions. Two tectonometamorphic units have been identified within with distinct geometry, lithological content P – T conditions. In higher grade unit, occurs as inclusions titanite. Lawsonite garnet were stable at peak conditions (~ 16–17 kbar 460–480 °C) very low X (CO 2 ) values. systematically pseudomorphed, but preserves hourglass zoning or internal fabric associated prograde ductile deformation. The lower unit 8 ± 1 ~ 370–400 discontinuously exposed along western base continental Dent Blanche nappe records similar those recorded by nappe. A discontinuity is, therefore, documented between largest part one hand, other hand. discovery allows a better understanding large-scale structure Alps.