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the deformation and crushing of minerals within rock during tectonic movements. Cataclasis occurs chiefly along and near tectonic ruptures (faults, displacements, overthrusts), where the relative shifts of rock sections have caused the grinding of minerals. Weak cataclasis can be ascertained only by examining a thin section of a crystal under polarized light and is shown by an “undulating decline,” notably in quartz crystals. Under the same conditions, stronger cataclasis results in a “mosaic decline,” indicating that various sections of the crystal have acquired through deformation a different orientation of the optic axes. Still stronger cataclasis is exhibited in the crushing of individual granules (granulation), which results in a “concrete” structure (larger angular or circular granules remain among the finely crushed material). The rock is transformed into mylonite, a compact, frequently silicified mass consisting of minute fusiform, lenticular, and flaky mineral fragments difficult to distinguish under a microscope.
In soft rocks, cataclasis may be seen in the formation of “clays of crushing” and “rock flour.” In the process of cataclasis, feldspars, micas, calcite, and certain other minerals are bent and split along the cleavage planes.
The zones that have undergone cataclasis are permeable to the movement of mineral aqueous solutions, including ore-bearing ones, and this causes the accumulation of various ores. The structure of rock that has undergone cataclasis is termed cata-clastic.
REFERENCEEliseev, N. A. Metamorfizm. Leningrad, 1959.
V. V. BELOUSOV