ON THE FIRST EXPERIMENTAL PHREATOMAGMATIC EXPLOSION OF A KIMBERLITE MELT

Detailed field investigations of kimberlite pipes of the Upper Cretace ous Gibeon Kimberlite Field in southern Namibia revealed geologic feat ures which do neither agree with extensive nor with explosive vesicula tion. In the pipe Hanaus 2, vesicle-free magmatic kimberlite intruded the diatreme as a plug. Here we report on the first experiments in whi ch phreatomagmatic explosions were produced with remolten natural, non -fragmental magmatic kimberlite from the Hanaus 2 central plug as a be st fit model kimberlite magma system. After water was injected into th e melt under controlled conditions, the resulting water-melt mix was t riggered by a low-energy shock wave (<1 J) and a violent explosion was obtained: High-energy shock waves of several 1000 J were generated an d pyroclasts were ejected with a maximum speed > 400 m/s. (C) 1998 Els evier Science B.V.