Regional and local structural controls on the emplacement of 1326 Southern African kimberlites and related rocks (kimberlites sensu lato, 11% of which are dated) are analysed using a framework of lineaments defined by combining geology, aeromagnetics, gravity and geomorphological data. Spatial analysis of occurrences within clusters of kimberlites less than 100km across resolves variable trends, depending on the age and position of the cluster; but on a regional scale the distribution of these clusters is statistically controlled by four lineament trends: 040°, 096°, 134°and 165°. Similar regional trends are observed as aspect lineaments that can be followed over large distances from modelling the variation in dip direction of the Southern African topography. These observations suggest that different geological parameters exert a control on the distribution of kimberlites. Local structures may include en-echelon fault arrays, Riedel, R'-, P-or T-structures within trans-continental lithosphere structures (cryptic continental corridors). Many cryptic continental corridors are collinear with fracture zones along the Atlantic and Indian continental margins of Southern Africa, and may have found their origin in events resulting from plate reorganization during the break-up of the supercontinent Gondwana. Fault resistance may have rapidly changed the stress state of the African continent causing the deep lithospheric faults to be the loci of episodic extension, allowing kimberlite fluids to ascend through the faults and cluster within near-surface structures. A progressive age variation of kimberlite magmatism in Southern Africa may be attributed to stress propagation along deep lithospheric fractures.

The fossil records of the living orders of mammals do not extend much earlier than the latest Cretaceous/early Palaeocene (Alroy, 1999;Foote et al., 1999). If this evidence indeed reflects the time of origin of the orders, rather than indicating the inadequacy of the fossil record (Martin

No abstract

z a ) 'The duty of the geologist and the prospector is in fact to deliver the goods' Abstract: Archaean cratons are fragments of old continents that are more richly endowed with mineral deposits than younger terrains. The mineral deposits of different cratons are also diversely enriched with useful (to humankind) chemical elements. Cratons are therefore mineral-diversity hotspots that represent regional geochemical heterogeneities in the early Earth, evidence for which remains encoded on each craton as unique metallogenic 'fingerprints'. Some of the younger cratons (<3.0 Ga, e.g. Superior Province, Yilgarn and Zimbabwe) have strong Au, Cu, Pb and Zn imprints. Older (>3.0 Ga) cratons, however, are remarkably enriched in siderophile elements such as Ni, Cr, PGE, in both their crustal and mantle sections (e.g. Pilbara and Kaapvaal Cratons). Still other Archaean cratons are relatively enriched in Sn, W, U and Th (e.g. Amazonian, Leo-Man, Ntem and South China Cratons). How most of these fragments of old continents inherited their rich and diverse metallogenlc characteristics is unresolved. Their dominant metallogenic inventories were formed near the time of their separation from the mantle; thereafter the inherited metals were frequently remobilized and redistributed during subsequent tectono-metamorphic, magmatic and erosion-deposition processes (e.g. tin in South America; platinum and gold in Southern Africa). Because different cratons are likely to represent only small remnants of once much larger and probably varied Archaean continents, part of the total metal inventories of Archaean continents must have been recycled back into the mantle. Using six selected element groups from our extensive in-house GIS database of Gondwana mineral deposits, we derive the metallogenic fingerprints of 11 Archaean cratons of the southern hemisphere, and compare these against metallogenic fingerprints of the same elements in younger crust of three continents (Africa, Australia and South America). We confirm that the mineral deposit density and diversity of Earth's continental lithosphere has decreased with time. We conclude that metallogenic elements were transferred more efficiently from the mantle to the continental lithosphere in the Archaean and/or that subsequently (<2.5 Ga) recycling of these elements (mineral deposits) back into the mantle became more effective.