GEOLOGY, September 2011 851 INTRODUCTION Impact cratering is a fundamental and virtu- ally instantaneous geological process that has contributed to the formation and evolution of our solar system (e.g., French, 1968; Shoemaker, 1977), involving extreme pressures, tempera- tures, and high strain rates (e.g., Stöffler, 1972; Melosh, 1989). Although millions of impact cra- ters are known on Mars and the Moon, to date only 181 confirmed meteorite impact structures are currently recognized on Earth, only 18 of which are located in the African continent (Fig. DR1 in the GSA Data Repository 1 ). In contrast to most other planetary bodies, Earth’s surface is constantly renewed by plate tectonics and ero- sion, and a large part of it is not easily acces- sible, either because of the presence of oceans, dense vegetation, and/or the political situation in some regions of the globe. The recognition and confirmation of new hypervelocity impact struc- tures, particularly complex craters (>2–4 km in size), is thus extremely important for improving our understanding of the terrestrial cratering record and for the improvement of our knowl- edge of impact cratering processes in general. A unique result of complex crater formation is that material from depth is brought to the surface; the original position and distribution of the target rocks are modified when, because of gravitational instability of the transient cav- ity, inward and upward movement of the crater floor leads to formation of a central uplift (e.g., Melosh, 1989). Redistribution of rock can also occur during the subsequent collapse of an ini- tially oversteepened and/or weak central uplift. The mechanics of central uplift formation remain unclear and there are large apparent dif- ferences between the behavior of sedimentary versus crystalline rocks. For many impact sites and on all other planetary bodies besides Earth, these central uplifts provide the only samples of the deep subsurface. The central uplift is also commonly on Earth the only remnant of an impact crater to be preserved following erosion, and thus represents the only material available with which to identify and character- ize impact structures. Therefore, studying the formation of, and distribution of shock features within, a central uplift is crucial to further our understanding on the crater-forming process. Although these types of impact structures with intricate structural features are abundant on other planets, they are very rarely exposed and preserved on Earth. Here we report on a detailed analysis of the Luizi structure, located in Democratic Republic of Congo, combining a remote sensing study with geological field observations and petro- graphic examination of rock samples collected during our 2010 field campaign. We demon- strate that this structure is a complex meteorite impact crater, the first one to be confirmed in Central Africa (Fig. DR1). Because of its size and its complex crater morphology, i.e., an inner ring and a central depression, together with its relatively simple geology, we propose that Luizi is an excellent site for contributing to our under- standing of the formation of mid-sized impact craters on Earth and on other planetary bodies. LUIZI STRUCTURE Previous Work The Luizi structure, centered at 10°10′13.5″S and 28°00′27.0″E on the Kundelungu Plateau of the Katanga province, lies in an underexplored region of the southeastern Democratic Republic of Congo (Fig. 1). The first and only field geo- logical report on the Luizi structure appeared in Grosse (1919), in which the author described an ~20 km semicircular basin, with the dominant rocks consisting of more or less fractured thick- bedded quartzitic arkose, dipping from 5° to 20° at the basin edge and from 60° to 90° in the inner basin. Since that time, owing to the politi- cal situation and logistical challenges of work- ing in Democratic Republic of Congo, the study of Luizi has been restricted to remote sensing techniques. As such, we identified this structure as an analogue for planetary exploration, where only satellite imagery is available. Our motiva- tion to study the Luizi structure came from a brief note in a publication by Dumont (1990), in which an impact origin was suggested for Luizi purely on the basis of its circular mor- phology. Given that other terrestrial geological processes, such as magmatism, salt diapirism, caldera collapse, or sinkhole formation, are also capable of producing more or less circu- lar features, unambiguous shock deformation features, such as planar deformation features (PDFs) in quartz, or traces of extraterrestrial matter (e.g., siderophile element anomalies), are essential to confirm the impact origin of a structure (French and Short, 1968; Stöffler, Geology, September 2011; v. 39; no. 9; p. 851–854; doi:10.1130/G31990.1; 4 figures; Data Repository item 2011247. © 2011 The Geological Society of America. For permission to copy, contact Copyright Permissions, GSA, or editing@geosociety.org. 1 GSA Data Repository item 2011247, Figure DR1 (distribution map of the confirmed meteorite im- pact structures on Earth) and Table DR1 (universal- stage microscope data), is available online at www .geosociety.org/pubs/ft2011.htm, or on request from editing@geosociety.org or Documents Secretary, GSA, P.O. Box 9140, Boulder, CO 80301, USA. *Current address: Natural History Museum, Burgring 7, A-1010 Vienna, Austria; E-mail: ludovic .ferriere@nhm-wien.ac.at. † E-mails: lubala.toto@unilu.ac.cd; gosinski@ uwo.ca. The newly confirmed Luizi impact structure, Democratic Republic of Congo—Insights into central uplift formation and post-impact erosion Ludovic Ferrière 1 *, François R.T. Lubala 2† , Gordon R. Osinski 1,3† , and Pierre K. Kaseti 2 1 Department of Earth Sciences, University of Western Ontario, 1151 Richmond Street, London, Ontario N6A 5B7, Canada 2 Department of Geology, University of Lubumbashi, P.O. Box 1825, Lubumbashi, Democratic Republic of Congo 3 Department of Physics & Astronomy, University of Western Ontario, 1151 Richmond Street, London, Ontario N6A 5B7, Canada ABSTRACT 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, cen- tral 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 intermedi- ate 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 macro- scopic 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 struc- tures 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. as doi:10.1130/G31990.1 Geology, published online on 5 August 2011