Mizarela Lithological Contact

This is certainly one of the geosites in the Arouca Geopark where we can best observe the macroscopic characteristics that allow us to distinguish between schist and granitoid rocks, since they are presented side by side as a result of the abrupt lithological contact in an approximate NW-SE direction and with an inclination of close to 90 degrees. This is considered to be an excellent place for practicing geological mapping techniques. The granite takes the form of a residual relief, protruding from the landscape, as is the case throughout the Serra da Freita plateau. This rock, known as Serra da Freita granite, is a syn-tectonic magmatic rock, leuco to mesocratic, with a phaneritic texture and medium grain size. Although it is described as a two-mica granite, curiously, at this site, there is a clear dominance of muscovite over biotite. On the other hand, the rocks previously referred to as “schists” correspond mostly to mica schists, affected by medium-grade regional metamorphism, where it is possible to observe a NW-SE to WSW-ESE, subvertical schistosity. In the biotite mica schists, porphyroblasts of staurolite and andalusite stand out. There is also some sillimanite (fibrolite), a mineral that can only be observed under the microscope, but whose presence indicates that the rocks are in the sillimanite zone of regional metamorphism. The staurolite crystals can reach dimensions of several centimeters and are sometimes maculated.