The New Luizi Impact Structure (Democratic Republic of Congo) and Implications for Central Peak and Peak Ring Formation

Introduction: Rocks exposed within the uplifted central part of meteorite impact structures come from depths up to several kilometers and thus provide a unique opportunity to study subsurface crustal and, in some cases, potentially upper mantle material of planetary bodies. However, the crater-forming process that results in the formation of central peak and peak ring(s) is poorly understood. Much of our knowledge is based on extraterrestrial observations, as on Earth these types of impact structures with intricate structural features are very rarely exposed and preserved. Based on these planetary observations, it is widely accepted that central uplifts typically show a progression from central peak to peak ring basin morphology with increasing crater size. Here we report on the ~17 kilometer diameter Luizi structure (Democratic Republic of Congo), a pristine and moderately sized complex crater, with an intermediate ring (~5.2 km in diameter), and a ~2 km wide circular central ring around a central depression [1]. Previous work: The Luizi structure was first mentioned in a field geological report published in 1919 [2] in which it is described as a semi-circular basin. The general aspect of the structure, as visible using satellite data, was briefly discussed in [3,4]. The hypervelocity impact origin of the Luizi structure have been confirmed only very recently by Ferriere et al. [1] with the documentation of shatter cones, multiple sets of PDFs in quartz grains, and shocked feldspar grains. Results and discussion: We conducted a remote sensing study using available imagery and topographic data (Fig. 1), which revealed the dominant morphological features of the structure. Luizi exhibits, from the periphery to the center of the structure, a rim elevated up to ~300–350 m above the crater interior, an annular depression, an intermediate ring with a diameter of ~5.2 km, and a ~2 km wide circular central ring around a central depression (Figs. 1,2). All these features are well defined and can be easily recognized because of their sharp local topographic gradients. Using a digital elevation model (DEM) and derived cross-sections, we estimate the rim diameter of the structure to be ~17 km (Figs. 1,2 and [1]). A large fault zone oriented NNW-SSE, unrelated to the impact event, is also apparent on the right part of the Figure 1. Of great interest to the community is the fact that the overall morphology of the Luizi structure appears to be relatively well preserved based on comparisons with other similarly-sized impact craters (e.g., Haughton impact structure, Canada [5]). The absence of crater-filling impact breccias within the structure [1] suggests that at least 200–300 m of material were removed by erosion.

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