An experimental study of olivine lamproite: first results from the diamond stability field

Liquidus experiments on an olivine lamproite have been performed at pressures between 45 and 55 kbar in the presence of a reduced fluid with H₂O > CH₄. Results show that olivine is the liquidus phase up to pressures in excess of 50 kbar, above which olivine, orthopyroxene, and phlogopite occur together at the liquidus. The results are consistent with the hypothesis that a range of primary magmas from leucite lamproite to olivine lamproite can be derived by partial melting of phlogopite harzburgite as a function of pressure between <15 and >60 kbar under reducing conditions. Simple interpretation of the results in terms of a homogeneous phlogopite harzburgite, however, belies a complex melting process. The phase relations are also consistent with melting of a veined source rock in which neither vein nor wall-rock consists of phlogopite harzburgite.