Insights into rock deformation from observations of the Chicxulub impact crater: Impact bulking, role of cohesion, and contrasts with tectonic plate boundary faults
Abstract
Understanding rock deformation caused by major geologic events is a critical to geohazard research and the evolution of planetary surfaces. Hypervelocity asteroid impact is the most energetic of these processes followed by subduction zone earthquakes. In both settings, geophysical data image structural interfaces and elements that record rock deformation. Also, in both cases, ground-truth is required through geological observations in outcrop or drill core.
In 1773 Coulomb presented the first formal discussion of failure criterion including two key aspects: cohesion and resistance to sliding (friction). Plate tectonic studies of faulting, especially plate boundary faults capable of producing large but infrequent earthquakes, appropriately focus on the friction term. Indeed, cohesion may only have a role in terms of cohesion healing of damaged zones surrounding major earthquake generating faults. However, recent results from the International Ocean Discovery Program- International Continental scientific Drilling Program Expedition 364 that cored and logged the peak ring of the Chicxulub impact crater highlights the key importance of loss of cohesion during the initial phase of cratering wherein rock strength is regained within 10 minutes as the final crater is formed We present seismic images, physical properties data, and drill core observations from Expedition 364 with comparisons to seismic and drilling studies of subduction megathrusts and their surrounding rocks. In particular, our observations at Chicxulub support permanent porosity enhancement (dilation or impact bulking) by shock, pervasive fracturing and loss of target rock cohesion that is steadily regained through formation of a central uplift and its subsequent collapse to form a topographic peak ring. Deformation passes through short stages of cataclasis, ultra-cataclasis, and then shear faulting with an effective target rock block size that enlarges throughout the process supporting acoustic fluidization as the weakening mechanism. Seismically, only the final large-scale faulting is observable as well as the presence of a low-velocity, low-density, yet topographically elevated peak ring. In tectonic terms, the entirety of the peak ring is a damaged zone with physical properties permanently affected by the impact process.- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFMMR42A..08G
- Keywords:
-
- 5112 Microstructure;
- PHYSICAL PROPERTIES OF ROCKS;
- 7209 Earthquake dynamics;
- SEISMOLOGY;
- 8034 Rheology and friction of fault zones;
- STRUCTURAL GEOLOGY;
- 8159 Rheology: crust and lithosphere;
- TECTONOPHYSICS