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The Lukanga Swamp in central Zambia has previously been proposed as the site of a large (52 km diameter) impact structure on the basis of alleged observation of shock-diagnostic planar deformation features (PDFs) in quartz of breccia from the southern margin of the swamp. The southern margin of the swamp, marked by the Nyama Dislocation Zone, consists of quartzite and silicified meta-siltstone, shale, sedimentary quartz breccia, and fault breccia. Structures and textures in the meta-sediments are syn-sedimentary, whereas fault breccia displays tectonic fabrics. In thin section, quartz in sedimentary quartz breccia displays widely spaced, randomly oriented, subparallel, non-planar fluid inclusion trails, which were earlier misidentified to represent decorated PDFs formed by meteoritic impact. Siderophile element abundances (

Two distinct tectonostratigraphic terranes, separated by repeatedly reactivated deformation zones, are recognised in the Precambrian of southern Ethiopia: (1) granite-gneiss terrane, which is classified into sub-terranes and complexes, and (2) ophiolitic fold and thrust belts. The granite-gneiss terrane consists of para- and orthoquartzofeldspathic gneisses and granitoids, intercalated with amphibolites and sillimanite–kyanite-bearing schists. The paragneisses resemble gneisses from northern Kenya that were derived from sediments that filled the Kenyan sector of the “Mozambique Belt basin” between 1200 and 820 Ma. The volume of sediments formed during this period is comparatively small in southern Ethiopia, implying that the “Mozambique Belt basin” became progressively narrower northwards. The granitoid rocks in the study area vary from granitic gneisses to undeformed granites and range compositionally from diorites to granites. The granitoid gneisses form an integral part of the granite-gneiss terrane, but are rare in the ophiolitic fold and thrust belts. The ophiolitic fold and thrust belts are composed of mafic, ultramafic and metasedimentary rocks in various proportions. Undeformed granitoids are also developed in these belts. Eight granitoids from southern Ethiopia have been dated by U–Pb single zircon SHRIMP and laser probe 40Ar–39Ar dating. The SHRIMP ages range from ∼880 to 526 Ma, and are interpreted as close approximations of the respective magmatic emplacement ages. The 40Ar–39Ar data range from 550 to 500 Ma. The available geochronological data and field studies allowed classification of the granitoids of the Precambrian of southern Ethiopia into seven generations: Gt1 (>880 Ma); Gt2 (800–770 Ma); Gt3 (770–720 Ma); Gt4 (720–700 Ma); Gt5 (700–600 Ma); Gt6 (580–550 Ma); and Gt7 (550–500 Ma). The period 550–500 Ma (Gt7) is marked by emplacement of late- to post-tectonic and post-orogenic granitoids and presumably represents the latest tectonothermal event marking the end of the East African Orogen. Five tectonothermal events belonging to the East African Orogen are recognised in the Precambrian of southern Ethiopia: (1) Adola (1157±2 to 1030±40 Ma); (2) Bulbul–Awata (∼876±5 Ma); (3) Megado (800–750 Ma); (4) Moyale (700–550 Ma); and (5) Berguda (550–500 Ma).

The Anna's Rust Sheet (ARS) and a suite of mineralogically and chemically related intrusions in the core and collar of the Vredefort Dome (in particular, the Vredefort Mafic Complex: VMC) represent a newly recognised type of high Ti gabbro in this central part of the Kaapvaal Craton. This lithology, referred to as the Vredefort Type IV mafic intrusion, is distinguished from chemically similar Type V intrusions (the Karoo dolerites) by the presence of glomeroporphyritic plagioclase and higher Th content and from Type III intrusions (≈ 1600 Ma gabbro) by the lack of cross-cutting pseudotachylitic breccia veinlets. Petrographic features and both major and trace element compositions of all Type IV intrusions are very similar. Based on its Rb-Sr isotope age and character, a gabbroic intrusion from Majuba Colliery (Mpumalanga Province) is also thought to belong to the ARS (Type IV) suite of tholeiitic intrusions. Rb-Sr isotopic analysis resulted in a preferred age of 1052±11 Ma (2ω) for biotite and plagioclase data for ARS, VMC and Majuba samples. The Rb-Sr age for the ARS is further supported by 40 Ar- 39 Ar stepheating ages for plagioclase and pyroxene separates from two ARS and VMC samples, which favour formation of this gabbroic intrusion at ca 1000 Ma ago. These results suggest that an ≈ 120 m thick sheet intrusion may be present throughout a major part of the Vredefort Dome. While Kibaran-age ( ca 1–1.2 Ga) alkaline, both mafic and felsic, magmatism, as well as tectonic and hydrothermal activity at that time, have been known in the central Kaapvaal Craton, a widespread tholeiitic magmatic component has now been added to this record. There is a strong likelihood that this magmatic event occurred throughout the southern African subcontinent and perhaps into Antarctica.

A large, deeply eroded impact structure, known as the Morokweng impact structure, has recently been positively identified in the North West Province of South Africa, centred on the Ganyesa Dome about 80 km northwest of Vryburg. The marked geomorphic effect of the Morokweng impact event at 145 ± 2 Ma is identified through large-scale analysis of the long-term evolution of the Molopo River drainage system. A comparison of the pre- and post-impact drainage patterns shows that a dramatic change in both drainage direction and pattern occurred after the impact event. Prior to the impact, the regional drainage direction of the proto-Molopo had been towards the northwest, where it connected with the major southwest trending drainage line of the Permo-Carboniferous (∼300 Ma) Kalahari Basin. Reconstruction of the post-impact drainage pattern, as it existed in the Late Cretaceous (∼ 75 Ma), just before the formation of the rejuvenated Cenozoic Kalahari Basin, shows a generally southward flowing system with annular drainage pattern components. With the filling of the Kalahari Basin since Tertiary times, the affinity between the Molopo drainage and the Morokweng impact structure became less obvious.

In contrast to Europe, where geoconservation is actively pursued in most countries and where two international symposia on this subject have been staged in 1991 and 1996, geoconservation in Africa has indeed a very poor record. Considering the wealth of outstanding geological sites and the importance African stratigraphy has within the global geological record, pro-active geoconservation on this continent has not featured very prominently to date. In the interest of science, education and tourism, unique and typical geosites need to be identified, catalogued, and prioritised with the aim being their protection. Most African countries do not have vibrant non-governmental organisations such as a strong geological society, which could drive projects like geoconservation, or strong support from the private sector for environmental work. Here, a case is made for the role that established National Geological Surveys, some of which are already involved with retroactive environmental geological work, could play in the forefront of pro-active geoconservation and site protection.

New drill core data are provided which support earlier interpretations that the Kalkkop structure, a 600–630 m wide, near-circular feature south-southwest of Graaff-Reinet in the Eastern Cape Province of South Africa, is a meteorite impact crater. Shock metamorphosed clasts in suevitic crater fill and ReOs isotope data of this breccia indicate the presence of a minor (0.05%) meteoritic component in the suevite. The new data come from a 1992 borehole, which transected the complete crater fill and extended from about 160 to 380 m depth into the sedimentary basement belonging to the Koonap Formation of the Beaufort Group (Karoo Supergroup). Dyke breccias were found in the otherwise coherent Beaufort Group sediments forming the floor to the Kalkkop Crater. Mostly narrow zones of different breccia types, including injections of lithic impact breccia, a possible pseudotachylite veinlet and cataclasite occur predominantly in an approximately 65 m wide zone below the crater floor, with a few other cataclasite occurrences found lower down in the basement. Stratigraphical crater constraints provide information for the depth-diameter scaling and breccia volumes associated with such small, bowl-shaped impact craters formed in sedimentary targets. UTh series dating of limestone samples from near the top and the bottom of the crater sediment fill constraints the age of the Kalkkop impact event to about 250 ± 50 ka, similar to the age of the Pretoria Saltpan impact crater, also located in South Africa. The variety of different breccia types (polymict and monomict impact breccias; local formations of pseudotachylitic and cataclastic breccias) observed in the crater fill of the Kalkkop Crater indicates the need to carefully distinguish different breccia types in order to assess the respective importance of each formation.

The importance of large impact events for the evolution of all bodies in the Solar System has been recognised by a large proportion of the geological community only in the past 15 years. More than 150 impact structures are now known on the Earth's surface. The origin of the Vredefort dome, a ca 70 kilometre wide structural uplift terrane in the centre of the economically important Witwatersrand basin, by either endogenic or impact processes, has long been controversial. Detailed microdeformation studies have recently proven that the dome represents the central uplift of one of the largest (original diameter: ca 300 kilometres) and oldest (2023 ± 4 Ma) known terrestrial impact structures. The Vredefort structure is not only of importance because of its controversial origin and particular setting in the centre of the economically important Witwatersrand basin. This structure is also the type locality for pseudotachylitic breccia and well-known for its abundant shatter cones and the enigmatic Vredefort granophyre. A wealth of new data on the Vredefort structure have become available in recent years: detailed microdeformation studies have revealed the presence of bona fide shock metamorphic effects in quartz and zircon; UPb dating of single zircons from pseudotachylitic breccia have provided reliable age information regarding the time of impact and have permitted temporal separation of the Vredefort impact event from the emplacement of the 2050 Ma Bushveld complex. This achievement has major implications for the understanding of the impact-related thermal and hydrothermal effects in the Witwatersrand basin as a whole and the regional metamorphic evolution. As continued study of the Vredefort structure has the potential to contribute much more to the understanding of large impact cratering events and their potential geological and economic effects, besides contributing to the general geological knowledge of the evolution of the Kaapvaal craton, this paper reviews the current knowledge on the Vredefort structure and to emphasise those areas in need of future investigation.