Migmatites are mysterious rocks. We still do not know how they formed. Maybe they represent half-completed melting process? But maybe these lighter-colored bands are just molten material (magma) that intruded semi-molten and darker metamorphic rocks but didn’t form where we see them now?
I have seen many migmatites. Estonian coastline is littered with this material that were brought here by the continental glacier in the Pleistocene. Bedrock in Southern Finland is largely composed of high-grade metamorphic rocks. Thus, migmatite is a really common rock type here. Even the term “migmatite” was brought into the geological terminology by a Finnish petrologist Jakob Sederholm in 1907.
I tend to support the view that both formation processes were probably involved. Not necessarily always simultaneously but one here and another there. Therefore this dispute may somewhat resemble the famous arguments between blind men who all had very different opinions how elephant might look like.
Whatever the truth, I think we all agree that these rocks are pretty. Here is one nicely folded example, this time from Norway near Geirangerfjord. This rock is part of a local bedrock. I don’t remember exactly but the width of the view might be one meter or slightly more. This rock face is horizontal, I just took a picture of the rocks I was standing on.
Migmatite near Geirangerfjord in Norway.