Quantitative structural data on the Okavango N110°E-trending giant mafic dyke swarm in the northern Karoo Large Igneous Province (LIP., NE Botswana) are based on >170 (exposed) and 423 (detected by ground magnetics) dykes on a ca. 80 km-long section lying at high-angle to the densest zone of the dyke complex. This study partially covers also a second Karoo dyke swarm striking N70°E. Within each swarm, individual dykes are sub-vertical, parallel to the entire swarm. The average thickness of dykes within the two swarms is 18 m (N110°) and 27 m (N70°), but with marked variations in the N110°E dyke system correlated to the lithology of host-rocks (Archaean metamorphic basement vs Permo-Triassic sedimentary cover). The frequency of N110°E Karoo dykes increases markedly in two densest zones (ca. 10 km-wide each) on both sides and along an identified Proterozoic N110°E-trending dyke zone. The cumulative width of Karoo dykes (87% of the total population) is 6315 m along reference section, implying an average dyke-induced crustal dilatation of 12.2 % on the 52 km-long section projected perpendicular to the N110° trend of the dyke swarm. During the Karoo igneous event, crustal extension in NE Botswana is primarily accommodated through dyke intrusion rather than normal faulting. The two sets of coeval Karoo dyke swarms documented in NE Botswana occur along preexisting basement structures, reactivated as oblique (N110°E) and pure extension (N70°E) fractures during a single N160°E-directed extension. Because of the inherited origin of the two giant Karoo dyke swarms in NE Botswana, the Nuanetsi radiating dyke system can no longer be taken for a proof of a deep mantle plume.
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