Pseudotachylite

Pseudotachylite is a glassy or finely crystalline rock that forms during frictional melting associated with seismic faulting. It is essentially a fault rock, meaning it is a product of rock deformation. The intense heat generated by the rapid movement along a fault plane can melt the surrounding rock, which then cools quickly to form this characteristic material. This rapid cooling prevents the formation of large mineral crystals, resulting in a fine-grained texture, often with a dull, aphanitic appearance.

The composition of pseudotachylite varies depending on the host rocks that were melted. It can appear as veins or breccias within larger fault zones. The presence of pseudotachylite is a strong indicator of significant seismic activity and the associated high strain rates and temperatures. Scientists study pseudotachylite to understand the conditions under which earthquakes occur, including the temperatures reached at fault zones and the mechanisms of fault rupture. It can also be found in other high-energy impact events, such as meteorite impacts, where similar frictional melting can occur.