Jump to ContentJump to Main Navigation
Show Summary Details
More options …

American Mineralogist

Journal of Earth and Planetary Materials

Ed. by Baker, Don / Xu, Hongwu / Swainson, Ian

IMPACT FACTOR 2018: 2.631

CiteScore 2018: 2.55

SCImago Journal Rank (SJR) 2018: 1.355
Source Normalized Impact per Paper (SNIP) 2018: 1.103

See all formats and pricing
More options …
Volume 102, Issue 10


The system fayalite-albite-anorthite and the syenite problem

S.A. Morse
  • Corresponding author
  • Department of Geosciences, University of Massachusetts, Amherst, Massachusetts 01003-9297, U.S.A.
  • Email
  • Other articles by this author:
  • De Gruyter OnlineGoogle Scholar
/ J.B. Brady
Published Online: 2017-10-02 | DOI: https://doi.org/10.2138/am-2017-5762


The presence in a magma of fayalite, the iron end-member of the olivine binary series, affects the feldspars at pressure by lowering the temperatures at which they crystallize from the magma. Starting with estimates from published literature it becomes obvious that at pressure, fayalite becomes important because the pressure effects on the melting temperatures are very different: large for albite, and small for anorthite. In this experimental study, a powder of fayalite composition was combined with six finely ground natural feldspars from Ab to An97 to make six bulk compositions. Using graphite crucibles in piston-cylinder apparatus at a pressure of 5 kbar, a cotectic in the ternary system was found to range from 1141 °C at An(Fa) to 1124 °C at Ab(Fa), with fayalite contents from 68 to 17 wt%, respectively. The results can be used to show that ternary feldspars saturated with fayalite and Fe monoclinic pyroxene will crystallize at a 5 kbar multiphase eutectic 1010 °C—56 °C below a calculated azeotropic point on the Ab-Or join. The results are used to compare the end points of two very different layered intrusions, Skaergaard and Kiglapait, and to illuminate the nature and origins of syenite and trachyte, which are leucocratic rocks unsaturated with mafic minerals. Because fayalite-saturated melts are responsive to pressure unequally on the feldspar end-members, olivine of intermediate composition will have a damped but potentially significant effect on feldspar fractionation in the lower crust of the Earth, possibly affecting the origin of anorthosite and syenite.

Keywords: Fayalite; olivine; feldspar; fractionation; melting experiments; syenite origin

References cited

  • Bowen, N.L. (1945) Phase equilibria bearing on the origin and differentiation of alkaline rocks. American Journal of Science, 243A, 75–89.Google Scholar

  • Bowen, N.L., and Schairer, J.F. (1936) The system, albite-fayalite. Proceedings of the National Academy of Sciences, 22, 345–350.Google Scholar

  • Bryan, W.B., Thompson, G., Frey, F.A., and Dickey, J.S. (1976) Inferred geologic settings and differentiation in basalts from the Deep-Sea Drilling Project. Journal of Geophysical Research, 81(23), 4285–4304.Google Scholar

  • Fuhrman, M.L., Frost, B.R., and Lindsley, D.H. (1988) Crystallization conditions of the Sybille Monzosyenite, Laramie Anorthosite Complex, Wyoming. Journal of Petrology, 29, 699–729.Google Scholar

  • Goldsmith, J.R. (1980) Melting and breakdown reactions of anorthite at high temperatures and pressures. American Mineralogist, 65, 272–284.Google Scholar

  • Grove, T.L., Kinzler, R.J., and Bryan, W.B. (1992) Fractionation of mid-ocean ridge basalt (MORB). American Geophysical Union Monograph, 71, 281–310.Google Scholar

  • Lange, R.A. (2003) The fusion curve of albite revisited and the compressibility of NaAlSi3O8 liquid with pressure. American Mineralogist, 88, 109–120.Google Scholar

  • Le Maitre, R.W. (1976) The chemical variability of some common igneous rocks. Journal of Petrology, 17, 589–598.Google Scholar

  • Lindsley, D.H. (1966) Pressure-temperature relations in the system FeO-SiO2. Carnegie Institution of Washington Yearbook, 65, 244–247.Google Scholar

  • Lindsley, D.H. (1968) Melting relations of plagioclase at high pressure. In Isachsen, Y.W., Ed., Origin of anorthosite and related rocks, New York State Museum and Science Service Memoir, 18, 39–46.Google Scholar

  • McBirney, A.R., and Naslund, H.R. (1990) The differentiation of the Skaergaard intrusion: A discussion of Hunter and Sparks (Contributions to Mineralogy and Petrology 95:451–461). Contributions to Mineralogy and Petrology, 104, 235–240.Google Scholar

  • Morse, S.A. (1981) Kiglapait geochemistry IV: The major elements. Geochimica et Cosmochimica Acta, 45, 461–479.Google Scholar

  • Morse, S.A. (1994) Basalts and Phase Diagrams. Corrected and reprinted by Krieger, Melbourne, Florida, 493 pp.Google Scholar

  • Morse, S.A. (2014) Plagioclase fractionation in troctolitic magma. Journal of Petrology, 55, 2403–2418.Google Scholar

  • Morse, S.A. (2015 a) Linear partitioning in binary solutions: A review with a novel partitioning array. American Mineralogist, 100, 1021–1032.Google Scholar

  • Morse, S.A. (2015b) Kiglapait Intrusion, Labrador. In B. Charlier, O. Namur, R. Latypov, C. Tegner, Eds., Layered Intrusions, p. 589–648. Springer.Google Scholar

  • Morse, S.A. (2017) Kiglapait Mineralogy V: Feldspars in a hot dry magma. American Mineralogist, 102, 2069–2080.Google Scholar

  • Morse, S.A., and Brady, J.B. (2017) Thermal history of the Kiglapait Upper Zone. Journal of Petrology, in press.Google Scholar

  • Morse, S.A. and Ross, M. (2004) Kiglapait mineralogy IV: The augite series. American Mineralogist, 89, 1380–1395.Google Scholar

  • Morse, S.A., Brady, J.B., and Sporleder, B.A. (2004) Experimental petrology of the Kiglapait intrusion: Cotectic trace for the Lower Zone at 5kb in graphite. Journal of Petrology, 45, 2225–2259.Google Scholar

  • Schairer, J.F. (1942) The system CaO-FeO-Al2O3-SiO2. I. Results of quenching experiments on five joins. American Ceramic Society Journal, 25, 241–274.Google Scholar

  • Schairer, J.F., and Yoder, H.S. (1967) The system albite-anorthite-forsterite at 1 atmosphere. Yearbook Carnegie Institution of Washington, 65, 204–209.Google Scholar

  • Upton, B.G.J. (2013) Tectono-magmatic evolution of the younger Gardar southern rift, South Greenland. Geological Survey of Denmark and Greenland Bulletin 29, 124 pp.Google Scholar

  • Upton, B.G.J., Martin, A.R., and Stephenson, D. (1990) Evolution of the Tugtutôq Central Complex, South Greenland: A high-level, rift-axial, late-Gardar centre. Journal of Volcanology and Geothermal Research 43, 195–214.Google Scholar

  • Wager, L.R., and Brown, G.M. (1967) Layered Igneous Rocks, 588 pp. Freeman, San Francisco.Google Scholar

  • Waldbaum, D.R., and Thompson, J.B. Jr. (1969) Mixing properties of sanidine crystalline solutions. I. Phase diagrams from equations of state. American Mineralogist, 54, 1274–1298.Google Scholar

  • Watson, E.B., Wark, D.A., Price, J.D., and Van Orman, J.A. (2002) Mapping the thermal structure of solid-media pressure assemblies. Contributions to Mineralogy and Petrology, 142, 640–652.Google Scholar

  • Watt, S.W. (1966) Chemical analyses from the Gardar Igneous Province, South Greenland. Rapport Grønlands Geologiske Undersøgelse, 6, 92.Google Scholar

About the article

Received: 2016-03-11

Accepted: 2017-06-08

Published Online: 2017-10-02

Published in Print: 2017-10-26

Citation Information: American Mineralogist, Volume 102, Issue 10, Pages 2077–2083, ISSN (Online) 1945-3027, ISSN (Print) 0003-004X, DOI: https://doi.org/10.2138/am-2017-5762.

Export Citation

© 2017 by Walter de Gruyter Berlin/Boston.

Comments (0)

Please log in or register to comment.
Log in