We develop a model for pore-fluid entrapment during metamorphism of rock layers characterized by contrasting permeability. Asymmetrical vein structures are interpreted as accumulations of pore fluids trapped beneath impermeable layers. We test the model by examining the geometry and mineral assemblages of different generations of veins in layered metagabbros from the French-Italian Western Alps. From this case study, we argue for (1) the structural importance of gravity-driven pore-fluid flow within a permeable, potentially deforming rock during its exhumation (successive eclogite, blueschist and greenschist facies metamorphism in the reference metagabbros) and (2) right-side-up succession of the metamorphic sequence studied.

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