f Bushveld Cooling And Palaeomagnetism

Early palaeomagnetic studies on the Bushveld Complex yielded widely separated poles for the various zones suggesting that the Bushveld Complex was emplaced over an extended period of time, possibly in separate pulses over a period of ~50 million years. However, modern high resolution age data have revealed that the Bushveld Complex was emplaced in a relatively short time span, likely to be less than 1 million years. These new age data prompted new palaeomagnetic studies that resulted in a single pole for all of the zones of the Bushveld Complex from magnetite with high unblocking (HB) components. These new studies also documented 7 reversals within the 8 km thick sequence of Bushveld Complex lithologies. These reversals were initially interpreted as occurring sequentially in stratigraphic order; however careful examination of the cooling process in conjunction with the reversals reveals that they are duplicated as the Bushveld Complex cools from the top and the bottom. Thus the stratigraphic location of the reversal also depends strongly on the thickness of the Bushveld Complex. In order to examine details of these reversals and their relationship to the cooling process, we are using data from the triaxial fluxgate magnetometers used in borehole orientation systems to identify the precise stratigraphic location of reversals in borehole core.