An Experimental Petrological Study of Gabbro in Chintan, Taipei County, at Atmospheric Pressure

Abstract

A gab bro from Chintan, Sindian, was sub jected to ex per i ments at at mo spheric pres sure to study the frac tional crys tal li za tion of the gabbroic melt. The range of ex per i men tal tem per a tures was from 1120 to 1262°C, and the du ra tions were from about 16 to 150 hours. The min eral phases and the glass com po si tions in the quench ing prod ucts were analyzed with the SEM-EDS.The ex per i men tal re sults showed that the liquidus tem per a ture of the gab bro of Chintan is 1261°C. Fe-Ti ox ides crys tal lized at 1261°C. Plagioclase and chro mite crys tal lized at 1233 and 1196°C, re spec tively. Fi nally, pyroxene crys tal lized at 1178°C. The sol i dus tem per a ture is es ti mated to be about 1110°C and the melt ing in ter val is about 151°C. By com par ing the re sults of the runs with Au 75 -Pd 25 cap sules, the iron loss of melt to the plat i num en ve lopes at 1238°C over 18 hours can be neglected.The frac tional crys tal li za tion of the gabbroic melt at at mo spheric pres sure is con trolled by iron-ti ta nium ox ides, plagioclase, chro mite, and pyroxene. The dif fer en ti a tion trend of the gabbroic melts moves around in the cen ter of the AFM di a gram and can not fractionate into microsyenitic and al kali feld spar syenitic melts on the ground.