When two rock formations slide past one another during an earthquake, the friction generated melts the rock to create a liquid layer that eases further movement. At 1000–1550 °C, interface temperatures during sliding exceed the melting points of most minerals. Even so, examination of exhumed faults does not reveal evidence of the uniform, equilibrium melting that occurs at high temperature. In the case of quartzite rock (shown in the figure), the melting is especially puzzling. Minority components in the quartzite that have lower melting temperatures than their host will melt and resolidify. But so too does some of the quartzite, whose melting temperature is 1726 °C.
To identify the processes at play, Sung Keun Lee of Seoul National University and Raehee Han of Gyeongsang National University—both in South Korea—and their colleagues cleaved a cylindrical sample of Brazilian quartzite perpendicular to its axis and loaded the two disk-shaped pieces into a...
