Meteorite impact shatter cones – adiabatic shear bands?

Abstract
Shatter cones are distinctive, striated, conical fractures found in shocked rocks at meteorite impact structures. They are estimated to form at shock pressures from 2 to 25 GPa and range in size from a few millimeters up to more than 10 meters in length. Axes of the cones are aligned with the direction of maximum shock compression. Although shatter cones have been used for decades as a key field indicator to identify impact sites, the mechanism by which they form is not well understood. Evidence of extreme heating localized at shatter cone surfaces, along with their orientation along planes which experience maximum shear stress during shock compression, suggest that the cones may form by adiabatic shear banding. This possibility is explored through 3D numerical simulations using a crack band model – a technique for simulating fracture or shear banding with a continuum, strain softening, elasto-plastic model. Simulations of planar, plastic shocks show that a small flaw or inhomogeneity can trigger the formation of a conical shear band with apex pointing toward the shock source. These results suggest that adiabatic shear banding is a plausible formation mechanism for shatter cones.