Microstructural and geochemical response of muscovite to impact metamorphism

Bolide impacts can have profound effects on Earth, causing biogeochemical changes that may obliterate, initiate, or even diversify life. Thus, identifying and dating impact structures, especially in ancient rocks, can provide crucial temporal context for understanding the role of impacts in Earth’s evolution. We present novel characterization of muscovite from shocked pegmatites of the Yarrabubba structure in Western Australia. Shocked muscovite developed kink bands that underwent chemical modification, increasing the celadonite content, interpreted to be coeval with the impact event. In situ Rb−Sr (2463 ± 25 Ma) and 40Ar/39Ar dates (ca. 2464 Ma; probability peak) from low-strain, chemically unmodified muscovite overlap with zircon U−Pb dates (2440 ± 16 Ma) of pegmatite crystallization. Conversely, in situ 40Ar/39Ar dates from high-strain, celadonite-enriched lamellae define a complex age spectrum with a ca. 2266 Ma probability peak, overlapping the Yarrabubba impact age. Our findings indicate that muscovite, a major crustal mineral, can retain unique microstructural and geochemical features formed during impact metamorphism, and that targeted 40Ar/39Ar analysis can provide a reliable upper limit for the impact age.