TY - JOUR

T1 - The influence of H2O-H2 fluids and redox conditions on melting temperatures in the haplogranite system

AU - Schmidt, Burkhard C.

AU - Holtz, François

AU - Scaillet, Bruno

AU - Pichavant, Michel

N1 - Funding Information: Acknowledgements This research constituted a part of Burkhard C. Schmidt’s Ph.D. thesis, supported by a grant of the French Ministry for Research and Education. The authors thank Jean-Michel Bény and Olivier Rouer for assistance with Raman spectroscopy and electron microprobe analysis, respectively. The manuscript benefitted from the reviews of Hans Keppler and Robert W. Luth. We also thank Werner Schreyer for his editorial handling. Copyright: Copyright 2017 Elsevier B.V., All rights reserved.

PY - 1997/2/26

Y1 - 1997/2/26

N2 - Solidus temperatures of quartz-alkali feldspar assemblages in the haplogranite system (Qz-Ab-Or) and subsystems in the presence of H2O-H2 fluids have been determined at 1, 2, 5 and 8 kbar vapour pressure to constrain the effects of redox conditions on phase relations in quartzofeldspathic assemblages. The hydrogen fugacity (fH2) in the fluid phase has been controlled using the Shaw membrane technique for moderately reducing conditions (fH2 < 60 bars) at 1 and 2 kbar total pressure. Solid oxygen buffer assemblages in double capsule experiments have been used to obtain more reducing conditions at 1 and 2 kbar and for all investigations at 5 and 8 kbar. The systems Qz-Or-H2O-H2 and Qz-Ab-H2O-H2 have only been investigated at moderately reducing conditions (1 and 5 kbar) and the system Qz-Ab-Or-H2O-H2 has been investigated at redox conditions down to IW (1 to 8 kbar). The results obtained for the water saturated solidi are in good agreement with those of previous studies. At a given pressure, the solidus temperature is found to be constant (within the experimental precision of ± 5°C) in the fH2 ange of 0-75 bars, At higher fH2, generated by the oxygen buffers FeO-Fe3O4 (WM) and Fe-FeO (IW), the solidus temperatures increase with increasing H2 content in the vapour phase. The solidus curves obtained at 2 and 5 kbar have similar shapes to those determined for the same quartz - alkali feldspar assemblages with H2O-CO2- or H2O-N2-bearing systems. This suggests that H2 has the behaviour of an inert diluent of the fluid phase and that H2 solubility in aluminosilicate melts is very low. The application of the results to geological relevant conditions [HM (hematite-magnetite) > fO2 > WM] shows that increasing fH2, produces a slight increase of the solidus temperatures (up to 30°C) of quartz-alkali feldspar assemblages in the presence of H2O-H2 fluids between 1 and 5 kbar total pressure.

AB - Solidus temperatures of quartz-alkali feldspar assemblages in the haplogranite system (Qz-Ab-Or) and subsystems in the presence of H2O-H2 fluids have been determined at 1, 2, 5 and 8 kbar vapour pressure to constrain the effects of redox conditions on phase relations in quartzofeldspathic assemblages. The hydrogen fugacity (fH2) in the fluid phase has been controlled using the Shaw membrane technique for moderately reducing conditions (fH2 < 60 bars) at 1 and 2 kbar total pressure. Solid oxygen buffer assemblages in double capsule experiments have been used to obtain more reducing conditions at 1 and 2 kbar and for all investigations at 5 and 8 kbar. The systems Qz-Or-H2O-H2 and Qz-Ab-H2O-H2 have only been investigated at moderately reducing conditions (1 and 5 kbar) and the system Qz-Ab-Or-H2O-H2 has been investigated at redox conditions down to IW (1 to 8 kbar). The results obtained for the water saturated solidi are in good agreement with those of previous studies. At a given pressure, the solidus temperature is found to be constant (within the experimental precision of ± 5°C) in the fH2 ange of 0-75 bars, At higher fH2, generated by the oxygen buffers FeO-Fe3O4 (WM) and Fe-FeO (IW), the solidus temperatures increase with increasing H2 content in the vapour phase. The solidus curves obtained at 2 and 5 kbar have similar shapes to those determined for the same quartz - alkali feldspar assemblages with H2O-CO2- or H2O-N2-bearing systems. This suggests that H2 has the behaviour of an inert diluent of the fluid phase and that H2 solubility in aluminosilicate melts is very low. The application of the results to geological relevant conditions [HM (hematite-magnetite) > fO2 > WM] shows that increasing fH2, produces a slight increase of the solidus temperatures (up to 30°C) of quartz-alkali feldspar assemblages in the presence of H2O-H2 fluids between 1 and 5 kbar total pressure.

UR - http://www.scopus.com/inward/record.url?scp=0000897381&partnerID=8YFLogxK

U2 - 10.1007/s004100050258

DO - 10.1007/s004100050258

M3 - Article

AN - SCOPUS:0000897381

VL - 126

SP - 386

EP - 400

JO - Contributions to Mineralogy and Petrology

JF - Contributions to Mineralogy and Petrology

SN - 0010-7999

IS - 4

ER -