EXPERIMENTAL STUDIES OF FELDSPAR CRYSTALL IZATION FROM THE GRANITIC MELT WITH VARIOUS WATER-CONTENT

Time and inhibition rate of the crystallisation of elongated alkaline feldspar crystals fro m the alaskitic granitic melt at C-H2O = 4 and 1 .9 mass% and P = 1 kbar was studied by use of priming. At low overcool ing the anisotropy of growth rate is observed (V-a greater than or equ al to V-c > V-b). At high overcooling (Delta T > 40-60 degrees C) all alkaline feldspar crystals were found to be elongated along the a-axis . At 40 degrees C the maximal value of growth rate of feldspar crystal s is observed, this phenomenon was found to be more distinct in melts saturated in relation to water. The experimental data were interpreted in terms of elongated crystal growth model, the latter satisfying the studied range of parameters.