ALBERT

Description: Rocks exposed within the uplifted central part of meteorite impact structures come from significant stratigraphic depths, in some cases as much as several kilometers. On Earth, central uplifts are commonly the final and only feature of an impact crater that remains after the rest of the structure is lost to erosion. However, the crater-forming process that results in the formation of intricate features such as central peak and peak rings is poorly understood. Much of our knowledge is based on extraterrestrial observations; as on Earth, there are very few unequivocal examples of impact craters with well-preserved peak and ring morphologies, because of erosion. In this study we describe the [~]17-km-diameter Luizi structure (Katanga region, Democratic Republic of Congo), a moderate-sized complex crater, with an intermediate ring ([~]5.2 km in diameter), and an [~]2-km-wide circular central ring around a central depression. For the first time, unique evidence of shock metamorphism, in the form of macroscopic shatter cones and multiple sets of microscopic planar deformation features in quartz and feldspar grains, is described, confirming the meteorite impact origin of the structure. Our observations at Luizi provide insights into the formation of mid-sized impact craters on Earth, adding to the evidence that, in the case of sedimentary target lithologies, structural ring structures within the central uplift may form by the collapse of an unstable central peak. Given the preservation state of the Luizi crater, it cannot be excluded that structural rings may be a common feature for mid-size craters developed in layered target rocks.