Solid rock behaves like fluid during large-impact cratering: rock deformation mechanisms unvailed
24. Oktober 2018, von Tom Jaeppinen
Since its discovery in 1991, the 200-km Chicxulub meteorite impact structure, burried under carbonate rock of the Yucatán platform, Mexico, has often been the focus of scientific attention, mostly regarding the cause of the Cretaceous-Paleogene (K-Pg) mass extinction. The impact structure contains an inner topographic ring rising above an otherwise flat crater floor and thus forms a so-called peak-ring impact structures known also from terrestrial bodies of the solar system. Craters the size of Chicxulub form within a few minutes. In order to flow rapidly over large distances, impacted rocks need to weaken drastically, but subsequently have to regain sufficient strength to build and sustain topographic rings. The mechanisms of rock deformation that accomplish such extreme change in mechanical behaviour during cratering have been debated for decades.
Recent drilling into the Chicxulub peak ring funded by the Internation Ocean Discovery Program (IODP) and the International Continental Scientific Drilling Program (ICDP) unveiled an unprecedented record of rock deformation mechanisms. As Ulrich Riller and the IODP-ICDP Expedition 364 science party report in the October 25 issue of the journal “Nature” the mechanisms indicate catastrophic rock weakening upon impact followed by an increase in rock strength that culminated in peak-ring formation during cratering. The observations point to quasi-continuous rock flow and support the hypothesis of acoustic fluidisation as the dominant physical process controlling initial cratering. During this cratering stage, rock behaves like a viscous mass through high-frequency pressure oscillations around the lithostatic pressure. Acoustic fluidization is followed by increasingly localised faulting terminating in a single, approximatey 100 m thick, thrust zone evident in the drill core. The team was able to transmit the results in a numeric model, which simulates the formation of the crater and peak ring. The results of the research team have far-reaching consequences for understanding the formation of large impact craters in the solar system.
Riller, U., Poelchau, M.H., Rae, A.S.P., Schulte, F.M., Collins, G.S., Melosh, H.J., Grieve, R.A.F., Morgan, J.V., Gulick, S.P.S., Lofi, J., Diaw, A., McCall, N. Kring, D.A., and IODP-ICDP Expedition 364 Science Party, 2018. Rock fluidisation during peak-ring formation of large impact structures. Nature 562, 511–518. DOI: 10.1038/s41586-018-0607-z
Further Information:
University of Hamburg press release
University of Hamburg Newsroom: Zehn Minuten, die die Welt veränderten
MIN press release (german)
Min press release (english)