Petrography of Shock-Metamorphosed Crystalline Rocks and Impactites

The gneisses of the crystalline basement, mainly garnet-biotite varieties including graphite-bearing ones were transformed under the influence of a powerful shock wave and carry numerous shock metamorphic features. They represent the initial substrate for the appearance of large volume of an impact melt induced by shock. This melt solidified in the form of fragment-bearing continuous masses (tagamites) or in the form of bombs, lapilli and ash particles mixed with crushed material of altered to a variable degree crystalline and sedimentary rocks (suevites). Tagamites and suevites, among which, according to petrographic features, a number of varieties are distinguished, represent the main types of rocks containing impact diamonds. These rocks were partially altered during cooling by the action of meteoric water.