Shock metamorphism exclusively occurs locally around impact craters and possibly around some diatremes. It is characterized by extremely high P/T conditions (tens of hundred of kilobars) over very short time spans. These conditions result from the passing of a shock wave through the rocks.
Figure 2: Aerial view of Meteor (or Barringer) Crater, Arizona (USA). This broadly circular bowl is ca 180 m deep and over ca 1250 m in diameter. The ridge or rim surrounding the crater is 100 to 60 m above the plateau and is composed of angular debris. The debris was ejected from the crater when a meteorite impacted;
Source: Michael Collier, AGI webpage.