Origin of large-volume pseudotachylite in terrestrial impact structures

Large-volume pseudotachylite bodies, which consist of angular and rounded wall-rock fragments enveloped by a microcrystalline or glassy matrix, are not formed through a single fragmentation and melt generation process. Instead, these centimeter- to kilometer-scale structures form as fragment- and melt-filled tension fractures due to differential rotation of target rock during cratering. This discovery, based on observations from Sudbury (Canada) and Vredefort (South Africa), challenges existing hypotheses and suggests that pseudotachylite characteristics arise from the drainage of initially superheated impact melt into these fractures. The study provides a unified process to explain highly variable pseudotachylite features, advancing our understanding of complex crater formation mechanics.

Riller, U., Lieger, D., Gibson, R. L., Grieve, R. A. F., & Stöffler, D. (2010). Origin of large-volume pseudotachylite in terrestrial impact structures. Geology, 38(7), 619–622. https://doi.org/10.1130/g30806.1