NEW DATA ON PETROLOGY OF SIBERIA MEYMECHITES

Composition of primary melt of North-Siberia meymechites corresponds to that of alkaline komatiite and represents the strongly high-temperature (1600-degrees-C) and magnesia-rich (29 mass% MgO) member of Phanerozoic melts as was shown by the numerical calculations, thermometry and the study of compositions of melt inclusions in minerals. Crystallization differentiation of meymechite melts at the temperatures 1600-1150-degrees-C and fractionation degree 0-70% leads to formation of picrite-melanephelinite alkaline series of melts characteristic for alkaline component of Meymecha-Kotui province. Meymechite rocks form in the processes of cumulation of 35-55 mass% of Mg-olivine in alkaline komatiite melts in the temperature interval 1600-1400-degrees-C. The rocks have been depleted by Na (and by K in the strongly altered samples) during post-magmatic or at the final stages of magmatic processes. It has been supposed that initial meymechite melts were formed at the low degrees of melting of garnet peridotite followed by separation of the melt from restite in the depths 230-300 km at temperatures 1800-1900-degrees-C as a result of lower mantle diapirism from the depths > 700 km.