Low-angle collision with Earth: The elliptical impact crater Matt Wilson, Northern Territory, Australia

Abstract

Nearly all meteorite impact craters on Earth are circular. However, ~4% of craters should be formed by impacts at angles lower than 12° from the horizontal, which should result in elongated crater structures. The crater-forming process that produces elliptical shapes is poorly understood. We document the first elliptical crater on Earth that contains a central uplift and that provides insights into the mechanisms of crater formation at a critical threshold angle of 10°–15°. The dimensions of the Proterozoic Matt Wilson impact structure, Northern Territory, Australia, are 7.5 by 6.3 km, corresponding to an aspect ratio of 1.2, with its long axis trending northeast-southwest. The exposed crater floor shows a preferred stacking of thrust sheets within the central uplift and in the surrounding syncline, indicating northeast-southwest shortening and a material transport top-to-the-SW. This is consistent with an up-range to down-range motion of rock, caused by remnant horizontal momentum transferred from the impacting projectile to the target. This preferential deformation interferes with a radially oriented convergent material flow characteristic for crater collapse. The Matt Wilson crater provides evidence for the usefulness of structural asymmetries as a diagnostic tool to infer impact vectors. The new impact crater is confirmed by the presence of planar deformation features, planar fractures in quartz grains, and its structural inventory.