VAPORIZATION OF ALUMINUM FROM SILICATE ME LT

We present experimental data on the pulsed laser evaporation (temperat ure similar to 4000K and time similar to 10(-3) s) of several aluminou s minerals (nepheline, leucite, jadeite, spodumene, oligoclase, microc line, sanidine, and phlogopite) and obsidian. These results confirmed the vaporization sequence of major components from the melt: SiO2 grea ter than or equal to greater than or equal to Na2O > K2O approximate t o Al2O3, which we obtained in earlier experiments on alkali feldspar e vaporation and which differs from the sequence of individual vaporizat ion of pure oxides. An increase in relative volatilization of alumina was observed with increasing silica content in the melt. Evidence is p resented on a cluster mechanism of alumina vaporization in the form of ''nepheline'' cluster with Na : Al : Si = 1 : 1 : 1 and in the sodium -free form with Al : Si = 1 : 1. The proportions of the Al cluster for ms in vapor depend on the initial composition of the evaporated target . The maximum abundance of ''nepheline'' clusters was observed at the evaporation of targets with initial ratios of Na/Al approximate to 0.5 -0.6. The experimental results are important for the problem of impact matter fractionation on the stage of planet accretion and early grani te formation.