Multi-ringed basin A multi-ringed basin (also a multi-ring impact basin) is not a simple bowl-shaped crater, or a peak ring crater, but one containing multiple concentric topographic rings;[1] a multi-ringed basin could be described as a massive impact crater, surrounded by circular chains of mountains[2] resembling rings on a bull's-eye. A multi-ringed basin may have an area of many thousands of square kilometres.[3] An impact crater of diameter bigger than about 180 miles (290 km) is referred to as a basin.[4] StructureMore common peak ring craters have: (1) a peak-ring, i.e., a crater rim, which is generally circular, and; (2) a mountainous region which surrounds the center of the crater basin. In contrast, a multi-ringed basin has multiple peak-rings displaying as further concentric circles. In extremely large collisions, the rebound of the surface after impact can obliterate any trace of the initial impact point. Usually, a peak ring crater has a high structure with a terrace and has slump structures inside of it. In adjacent rings, the ratio of the diameters approximates √2:1 ≈ 1.41 to 1.[5][6][7] Formation.png) Multi-ring basins are some of the largest, oldest, rarest and least understood of impact craters. There are various hypotheses to explain the formation of multi-ringed basins, however there is currently no consensus.[8][9] In 2016, research brought forward new hypotheses about the formation of the lunar mare called Mare Orientale on Earth's Moon.[10] Prior to this research, the most accepted explanation was the 'slumping/megaterrace' model, which suggested that a deep bowl-shaped basin forms during the impact and that subsidence along faults later produces the ring formations, though this hypothesis was always considered problematic because of evidence that the rings were produced simultaneously with the impact that formed the basin.[9]: 80–81 The new research produced a model confirming instantaneous formation of all rings, a mechanism in which ductile subsurface rocks flowed towards the center of the basin as the crust rebounded, causing concentric cracking and slippage that formed the outer rings, and that the unstable central peak collapsing formed the inner ring.[10] Examples
Chicxulub crater in Mexico has a sufficient area to have been a multi-ringed basin.[12] See also
References
|
