This greenschist metamorphic grade is seen as a late (Meso-Alpine) overprint, most researchers think the whole Sesia zone or at least part of it has been in eclogite or blueschist conditions during Paleogene subduction. Because clear evidence for high pressure metamorphism is restricted to the internal zone, it is not clear whether the other two zones have also subducted to great depth.
The greenschist metamorphic grade is considered a late (Meso-Alpine) overlay; most researchers think that the entire Sesia zone or at least part of it was in eclogite or blueschist conditions during Paleogene subduction. Given that evidence for high-pressure metamorphism is confined to the core zone, it remains uncertain whether the other two zones have also descended to great depths.