Porphyroclast of the month - February 14th

摘要

This month, especially for the 14th of February, we have the honor to introduce a new special structure in the "photograph of the month" section, which has just been discovered. We hope that it expresses the general feeling of rocks and structures towards the people who study them.rnThe structure is a microcline porphyroclast in mylonitised mig-matite of the Maria da Fe Shear Zone, Brazil. This strike-slip shear Zone is related to the Ribeira Fold Belt, and is characterized by deformation at medium grade conditions around 590 Ma. The porphyroclast formed by the shedding of a thin mantle of small feldspar grains. The shear sense in the shear zone and in the section is sinistral, but this is hidden because it is not the message the structure wishes to convey.