This looks very much like a lower- to mid-crustal mylonite, but it was formed quite shallow in the drust during thin-skinned tectonics of the External units in the Betics. The reason that it looks like a much deeper rock is that it is made of gypsum, which is very soft and deforms in a ductile manner under quite moderate conditions.
That means that if teher is any gypsum around it gets entrained onto slipping fault systems and lubricates the fault helping to keep strain locallised onto relatively narrow shear surfaces. We can see the way that the gypsum beds have been entrained in the thrusts by looking at the structural cross section of teh Eastern betics.
15 окт 2024
