her ited ▁dy ke - indu ced ▁f ract ures ▁Mant le ▁pl ume ▁hypothesis ▁Pass ive ▁mel ting ▁of ▁G ond w ana ▁super cont inent ▁ ▁Model ▁ 1 : ▁In her ited ▁and ▁dy ke - indu ced ▁f ract ures ▁ ▁A ▁number ▁of ▁dy kes ▁in ▁the ▁Ok av ango ▁dy ke ▁sw arm ▁are ▁dated ▁as ▁Pro ter oz o ic ▁age ▁( main ly ▁~ 8 8 4 ▁Ma ), ▁which ▁indicates ▁the ▁orientation ▁of ▁the ▁dy ke ▁sw arm ▁was ▁determined ▁before ▁the ▁occurrence ▁of ▁Kar oo ▁mag mat ism . ▁ ▁It ▁is ▁suggested ▁that ▁the ▁dy ke ▁emp lacement ▁in ▁the ▁Kar oo ▁triple ▁j unction ▁was ▁controlled ▁by ▁some ▁rock ▁structures ▁of ▁the ▁pre - Kar oo ▁bas ement ▁rocks . ▁The ▁rock ▁fab rics ▁at ▁cr aton ▁boundaries ▁and ▁bas ement ▁rock ▁control ▁the ▁orientation ▁of ▁Ok av ango ▁dy ke ▁sw arm ▁The ▁Ok av ango ▁dy ke ▁sw arm ▁inherited ▁the ▁Pro ter oz o ic ▁f ract ures ▁in ▁association ▁with ▁the ▁previous ▁Pro ter oz o ic ▁dy ke ▁emp lacement ▁event . ▁ ▁The ▁well - develop ed ▁ch illed ▁margin ▁and ▁few ▁x en ol ith s ▁found ▁on ▁individual ▁dy kes ▁indicate ▁that ▁the ▁intr usion ▁of ▁a ▁dy ke ▁was ▁not ▁a ▁vig orous ▁event ▁at ▁ 1 8 0 ▁Ma . ▁The ▁dy ke ▁sw arm ▁could ▁extend ▁for ▁such ▁a ▁large ▁area ▁because ▁of ▁the ▁pre - ex isting ▁bas ement