Contributions to Mineralogy and Petrology

, Volume 95, Issue 4, pp 407–419

A-type granites: geochemical characteristics, discrimination and petrogenesis


  • Joseph B. Whalen
    • Geological Survey of Canada
  • Kenneth L. Currie
    • Geological Survey of Canada
  • Bruce W. Chappell
    • Department of GeologyThe Australian National University

DOI: 10.1007/BF00402202

Cite this article as:
Whalen, J.B., Currie, K.L. & Chappell, B.W. Contrib Mineral Petrol (1987) 95: 407. doi:10.1007/BF00402202


New analyses of 131 samples of A-type (alkaline or anorogenic) granites substantiate previously recognized chemical features, namely high SiO2, Na2O+K2O, Fe/Mg, Ga/Al, Zr, Nb, Ga, Y and Ce, and low CaO and Sr. Good discrimination can be obtained between A-type granites and most orogenic granites (M-, I and S-types) on plots employing Ga/Al, various major element ratios and Y, Ce, Nb and Zr. These discrimination diagrams are thought to be relatively insensitive to moderate degrees of alteration. A-type granites generally do not exhibit evidence of being strongly differentiated, and within individual suites can show a transition from strongly alkaline varieties toward subalkaline compositions. Highly fractionated, felsic I- and S-type granites can have Ga/Al ratios and some major and trace element values which overlap those of typical A-type granites.

A-type granites probably result mainly from partial melting of F and/or Cl enriched dry, granulitic residue remaining in the lower crust after extraction of an orogenic granite. Such melts are only moderately and locally modified by metasomatism or crystal fractionation. A-type melts occurred world-wide throughout geological time in a variety of tectonic settings and do not necessarily indicate an anorogenic or rifting environment.

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© Springer-Verlag 1987