Zirconium silicates in a peralkaline granite: a record of the interplay of magmatic and hydrothermal processes (Ilímaussaq complex, Greenland)
Authors
Małgorzata Cegiełka
Institute of Geological Sciences, Polish Academy of Sciences, Research Centre in Warsaw, ul. Twarda 51/55, 00-818 Warsaw
Bogusław Bagiński
Department of Geochemistry, Mineralogy and Petrology, Faculty of Geology, University of Warsaw,
ul. Żwirki i Wigury 93, 02-089 Warsaw
Ray Macdonald
Environment Centre, Lancaster University, Lancaster LA1 4YQ
Harvey E. Belkin
11142 Forest Edge Drive, Reston, VA 20190
Jakub Kotowski
Department of Geochemistry, Mineralogy and Petrology, Faculty of Geology, University of Warsaw,
ul. Żwirki i Wigury 93, 02-089 Warsaw
Brian G.J. Upton
Grant Institute, University of Edinburgh, James Hutton Rd., Edinburgh EH9 3FE
Compositional and textural data are presented for zircon, secondary Zr-silicates, catapleiite and elpidite in a peralkaline granite from the Ilímaussaq complex, south Greenland. The zircon is essentially stoichiometric, with (Zr + Hf + Si) = 1.96–1.98 a.p.f.u. The secondary Zr-silicates show a wide range of Zr/Si atomic ratios (0.13–0.79). The catapleiite varies from close to stoichiometric to a Na-depleted type showing cation deficiency (5.2–5.8 a.p.f.u.). Elpidite shows similar variations (7.2–9.0 a.p.f.u.). Textural relationships between the Zr phases are interpreted to show that magmatic zircon interacted with hydrous fluids exsolved from the magma to form the secondary Zr-silicates. Formation of catapleiite was late‑magmatic, in equilibrium with a Na-Si-bearing fluid. This was followed by the crystallization of elpidite, the fluid having a different Na/Si ratio. Both catapleiite and elpidite experienced Na-loss during late-stage hydrothermal alteration.
