Chemical controls on the solubility of Zr-bearing phases in simplified peralkaline melts and application to the Strange Lake intrusion, Quebec-Labrador

The solubility of Zr-bearing minerals was measured in H2O-saturated, peralk aline haplobasaltic, haplosyenitic and haplogranitic melts +/- Cl +/- F at 800 degrees C and 1 kbar. In halogen-free and F-bearing melts, the solubili ty of Zr-bearing phases reached a maximum of 4 and 3.5 wt.% ZrO2, respectiv ely, in melts with 57 to 60 wt.% silica. No such maximum was observed for C l-bearing compositions, which became saturated in a Zr-bearing phase at ZrO 2melt concentrations of 2 to 2.2 wt.%. A silica concentration of 57 to 60 w t.% represents a threshold above which zircon is the saturating Zr-bearing phase for all compositions. For compositions with SiO2 content below this r ange, wadeite (K2ZrSi3O9) crystallizes in the halogen-free experiments, whe reas ZrO2 is the saturating phase in the F- and Cl-bearing experiments. The positive slope of the wadeite saturation curve on X(ZrO2) - X(SiO2) plots suggests that increasing activity of silica increases the solubility of wad eite. Since this behavior of wadeite is not expected based on a simple diss olution mechanism, a more complex equilibrium involving different structura l units is proposed. Observations that zircon is scarce, whereas elpidite ( Na2ZrSi6O15. 3H(2)O) and other alkali and alkaline-earth zirconosilicates a re abundant in the Strange Lake peralkaline intrusive complex in northern Q uebec - Labrador, indicate that the parent magma did not saturate with a Zr -bearing mineral until it cooled to a low temperature, probably less than 6 00 degrees C.