Zirconium silicates in a peralkaline granite: a record of the interplay of magmatic and hydrothermal processes

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Marco E. Ciriotti
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Zirconium silicates in a peralkaline granite: a record of the interplay of magmatic and hydrothermal processes

Messaggio da Marco E. Ciriotti » dom 24 lug, 2022 10:10

Referenza:
▪ Cegiełka, M., Bagiński, B., MacDonald, R., Belkin, H.E., Kotowski, J., Upton, B.G. (2022): Zirconium silicates in a peralkaline granite: a record of the interplay of magmatic and hydrothermal processes (Ilímaussaq complex, Greenland). Acta Geologica Polonica, 72, 235–245.

Abstract:
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.
Marco E. Ciriotti

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