I could imagine it's possible in nature if a large mountain range is to be formed from a continental collision, and the section you're looking at just so happens to have seen no volcanic activity. The mountain range would have to be significant in depth. The material exposed to the surface would be exposed to erosion, to strip away any sedimentary deposits, while the rocks deepest in the Lithosphere are exposed to enough heat and pressure to drastically alter them, forming gneiss in some cases, but not enough so that they melt, meaning they're technically still metamorphic rocks, not igneous. The metamorphic materials deepest down could initially have been granite, diorite, or gabbro; the process of being heated and squeezed by the surrounding rocks could be enough to alter them.
Technically, though, you'd still see some sedimentary deposits, even unlithified such as the soil at the top of your embark, and probably some igneous deposits like material that melted and cooled again, maybe within faults in the mountain block, or that failed to be metamorphosed to an extent great enough to be technically defined as a metamorphic rock. Part of the process of granite being transformed into gneiss is that the minerals, when under pressure, align their long axis perpendicular to the pressure, as this reduces the strain on them. They also generally form bands of the same or similar minerals. In gneiss, you might see bands of lighter minerals - quartz or feldspar - and darker minerals - mica and biotite or amphibole(hornblende), arranged in alternating layers, whereas in granite crystals of these minerals would be arranged more haphazardly.
As far as DF goes, I've never personally seen it before, but it seems like something that could happen. I'm not sure how the game even chooses where to place what materials.
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Topic: Metamorphic Fascism (Read 1183 times)