Petrotectonics

(also structural petrology), a division of petrography concerned with the structures of tectonites, that is, rocks that have undergone dynamic metamorphism. Petrotec-tonics was developed by the German scientist B. Sander in 1930.

In petrotectonics, spatially oriented specimens of the rocks under study are taken from geologic sections. The orientation of cleavage, of optic axes, and of other crystallographic elements in a large amount of grains of one or several minerals is measured in microsections of a Fedorov stage. These data are plotted on a stereographic net. The patterns of the resulting diagrams permit scientists to ascertain the symmetry and nature of the tectonic movements that caused the metamorphism. Experimental investigations of the mechanism of plastic deformation of various minerals and rocks under high hydrostatic pressures and temperatures are carried out for a more complete interpretation of the diagrams.