Volcanology of the kimberlitic Gibeon Volcanic Field, southern Namibia

The Gibeon Kimberlite Field consists of at least 42 diatremes and numerous dikes. It shows a systematic location of carbonatites and highly evolved kimberlites towards the margins of the field, suggesting a close genetic and, hence, age relationship between these rocks. Age determinations from kimberlites and carbonatites uniformly point towards an Upper Cretaceous volcanic activity. As the kimberlite diatremes commonly cut downwards on the dikes, the kimberlite dikes and diatremes must be genetically closely related with each other. The kimberlite diatremes are assumed to have formed on the dikes when kimberlite magma contacted groundwater resulting in phreatomagmatic explosions. In a second, non-explosive phase in a few diatremes, kimberlite magma intruded and formed plugs at shallow diatreme levels of 320 to 420 m below the original surface.