Preferential distribution along transcontinental corridors of kimberlites and related rocks of Southern Africa

Abstract

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