Mechanism of development of ptygmatic folds in migmatites and migmatititic schists in Simin area, Hamadan

The ptygmatic folds are intestinal folds that violent bends and twisting in manes can be seen in them. These folds are seen in many of the evolved migmatites and migmatitic schists in Simin area. But they are not present in migmatites evolved from hornfelses. Growing and expanding of ptygmatic folds in migmatites occurs during separation of leucosome and mesosome. This process develops in second process by the active folding boundaries of leucosome and increasing of branches of veins. A sharp rheological differences between folded veins with background is the most important reasons of growth and separation of ptygmatic shapes. Probably development of shear zones, presence of schistosity and the large size of minerals present in evolved migmatites is compatible with development of these folds in the area.