On critical observations that constrain models of terrestrial hypervelocity impact craters

Abstract

AbstractImpact structures in the crystalline rocks of the Canadian Shield range over two orders of magnitude in size and display morphologies recognized elsewhere in the solar system. This contribution draws upon new examinations of drill core from Canadian craters to reaffirm some relationships, modify others, and refine the transitions from simple to complex with central peak to peak‐ring structures. These include recognizing the hyperbolic form of transient craters, sharpening the allochthon–parautochthon distinction, and proposing new formulae for key relationships. It emphasizes the role of dynamic tensile strength and the attenuation of tensile rarefaction waves in determining the size of both transient and final crater dimensions. On Earth, depth (d) to diameter (D) ratios are not invariant at about 1:10 but change smoothly with size from 1:3 at Brent through 1:5 to 1:10 in the largest; that is, d = 0.4 D0.75. In craters in crystalline rocks, the central peak grows at about uplift = 0.175 D until, at D about 28 km, the uplift rises above the original surface then collapses to form a peak‐ring structure. These relationships demonstrate the dominant role of gravity in attenuating tensile rarefaction waves and controlling transient crater depth and overall size relative to the volume shocked.