Experimental study of partial melting of biotite-orthopyroxene-quartz bearing assemblages in the system KAlO2-MgO-FeO-SiO2-H2O
Graphchikov, Alexander A.; Konilov, Alexander N.
European Journal of Mineralogy Volume 8 Number 1 (1996), p. 143 - 152
published: Feb 22, 1996
manuscript accepted: Aug 28, 1995
manuscript received: May 2, 1994
ArtNo. ESP147050801015, Price: 29.00 €
Abstract Melting temperatures of biotite-orthopyroxene-quartz assemblages were determined experimentally using biotites with various Fe-contents in the system KAIO2-MgO-FeO-SiO2-H2O, in the pressure range 100-500 MPa and under the quartz-fayalite-magnetite fO2 buffer. All experiments were performed with synthetic phases. Water contents in the starting mixtures ranged from 11 to 78 wt.%. The compositions of coexisting minerals and melts were determined by electron microprobe. The analysis of glass (quenched liquids) in the experimental products showed them to have about 79 wt.% SiCh, with very low Fe and Mg contents which do not change with changing Fe-content of the system or temperature. The Fe/(Fe+Mg) ratio of the melt is greater than in the biotite and coexisting orthopyroxene. Solidus temperatures of biotite-orthopyroxene-quartz assemblages decrease considerably with increasing Fecontent in biotite. This means that water-saturated as well as fluid-absent (dehydration) melting of biotite-quartz assemblages may occur at temperatures between 700 and 800°C. Natural biotites are probably stabilized up to higher melting temperatures by the presence of titanium and aluminium.