The behaviours of Mg and Ca in some types of ultramaphic alkaline melts in the presence of H 2 O at high temperature and pressure (the experimental data)

Resumo

The sample has been investigated, which was composed of olivine-melilite rock from the
south-western part of the Kugda intrusion, situated in the eastern margin of the Maimecha-Kotuiskay
alkaline- ultramaphic province (northern part of Siberia platform). The experiments were carried
out using a high-pressure apparatus of the "piston-cylinder" type. The pressure was 5-15 kb and
the temperature -800-1250 0 C. The water content in the system was 3 and 9 wt. All experiments
were carried out in hermetically sealed Pt or Au ampoules. The samples were chemically analyzed
using a scanning electron microscope (SEM). Besides, the chemical composition of the experimental
phases was determined by means of more than 40 electron microprobe in 20 experimental samples.
For phase identification the X-ray method was used too. The structural peculiarities of rocks and
mineral compositions were studied by optical methods in polished and thin sections prior and
after the experiment. It was shown that at pressures above 7.5-8 kb the olivine-melilite melt is
separated into two melts: pyroxenite and melilite. Most part of Mg in this system was concentrated
in a high temperature phase of diopside type. The remaining melt was depleted of Mg and enriched
by Ca. The mineralization vapour practically did not contain Mg. The main components of the
mineralization vapour were Ca, Na, Si and Fe.