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

CIGCES, Department of Geological Sciences, University of Cape Town, Rondebosch 7701, South Africa De Beers Exploration Division, GeoScience Centre, PO Box 82232, Southdale 2135, South Africa

Maarten J. de Wit

CIGCES, Department of Geological Sciences, University of Cape Town, Rondebosch 7701, South Africa e-mail: maarten{at}cigces.uct.ac.za

Christien Thiart

CIGCES and Department of Statistical Sciences, University of Cape Town, Rondebosch 7701, South Africa e-mail: christie{at}cigces.uct.ac.za

Paul H.G.M. Dirks

School of Earth Sciences, University of the Witwatersrand, Wits 2050, South Africa e-mail: dirksp{at}geosciences.wits.ac.za

Giulio Viola, Ian J. Basson and Eva Anckar

Department of Geological Sciences, University of Cape Town, Rondebosch 7701, South Africa email: gviola{at}geology.uct.ac.za, ibasson{at}geology.uct.ac.za eanckar{at}geology.uct.ac.za

Correspondence: Corresponding author: e-mail: hielke.jelsma{at}debeersgroup.com

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.

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