Formation of pseudotachylitic breccias in the central uplifts of very large impact structures: Scaling the melt formation

A groundbreaking study reveals that pseudotachylitic breccias (PTB), enigmatic friction-melt-like structures found in impact craters, can form from local melt reservoirs rather than requiring intrusion of distant impact melt. Researchers analyzed a 1.5 × 3 × 0.04 m granite slab from the Vredefort Dome, South Africa—the central uplift of a >250 km diameter impact structure—to estimate melt volumes. Their calculations show that a 1 m³ PTB-bearing host rock can accommodate up to 52 dm³ of melt, with larger breccia zones potentially deriving from local reservoirs during rapid decompression phases linked to crater formation or post-impact collapse. This challenges long-standing debates on PTB origins, suggesting decompression melting during central uplift formation is a plausible mechanism.

MOHR‐WESTHEIDE, T., & REIMOLD, W. U. (2011). Formation of pseudotachylitic breccias in the central uplifts of very large impact structures: Scaling the melt formation. Meteoritics & Planetary Science, 46(4), 543–555. Portico. https://doi.org/10.1111/j.1945-5100.2011.01173.x