SYN-MIGMATIZATION WAY-UP CRITERIA

Most geopetal (way-up) structures are developed during primary formation or soon after in sedimentary or igneous rocks. In migmatite terrains the possibly anomalous behaviour of rocks in which melt is present has often limited structural synthesis. Geopetal relationships may, however, be recognizable in at least some migmatites. Asymmetries in two structural relationships ('cauliflower structure' and 'vein cluster'), involving neosome veins conformable with the main foliation of layered migmatites, are interpreted as indicating the way-up of these rocks when they were partially molten. Additional examples recognized in the literature suggest that similar structures can be seen in a wide range of geological environments. These prove to be as reliable as sedimentary top and bottom features and suggest that the migmatites containing them were essentially sub-horizontal while being strained and melted.