A gab bro from Chintan, Sindian, was subjected to experiments at atmospheric pressure to study the fractional crystallization of the gabbroic melt. The range of experimental temperatures was from 1120 to 1262¢XC, and the durations were from about 16 to 150 hours. The mineral phases and the glass compositions in the quenching products were analyzed with the SEM-EDS.
The experimental results showed that the liquidus temperature of the gab bro of Chintan is 1261°C. Fe-Ti ox ides crystallized at 1261°C. Plagioclase and chromite crystallized at 1233 and 1196°C, respectively. Finally, pyroxene crystallized at 1178°C. The solidus temperature is estimated to be about 1110°C and the melting interval is about 151°C. By comparing the results of the runs with Au75-Pd25 capsules, the iron loss of melt to the platinum envelopes at 1238°C over 18 hours can be neglected.
The fractional crystallization of the gabbroic melt at atmospheric pres sure is controlled by iron-titanium oxides, lagioclase, chromite, and pyroxene. The differentiation trend of the gabbroic melts moves around in the center of the AFM diagram and can not fractionate into microsyenitic and alkali feldspar syenitic melts on the ground.