Phase relations in albite granite-H2O-HF system and their petrogenetic application

Phase relations were experimentally determined in albite granite-H2O-HF sys tem with 2, 4 and 6 wt.% fluorine at 100 MPa pressure. With the increase of fluorine content from 2 to 6 wt.% in the system, liquidus temperature incr eased from 768 to 790 degrees C and the solidus temperature decreased from 540 to 490 degrees C. Maximum temperature of quartz and topaz stability fie ld increased with F content, whereas that of alkali-feldspar decreased and its stability field disappeared at 6 wt.% fluorine. The mineral assemblage of topaz granite (quartz + albite + K-feldspar + mica + topaz) was stable a bove solidus at F less than or equal to 4 wt.%, and that of topaz greisen ( quartz + topaz + mica) was stable above solidus at F = 6 wt.%. The experime nts showed that the residual melt with high F content can be formed by frac tional crystallization of a leucogranitic melt with relatively low F conten t. These experimental results provide reliable evidences for the formation of topaz granite and topaz greisen at low temperature magmatic conditions.