Alkali-feldspars: Which solvus?

摘要: Variation in published alkali-feldspar solvus curves is discussed the light of concept complete (crystal-crystal) and exchange (crystal-fluid-crystal) equilibrium. Exchange equilibrium may lead to very regular solvus-like two-phase differing substantially from true binodal solvus; certain experimental strategies tend favour attainment persistence condition. New long duration experiments under “alkali excess” “alkali+silica conditions did not yield fledspar pairs significantly off bracketed obtained by Smith Parsons (1974) but behaviour shown influence course equilibration peralkaline experiments. Agreement bracketing several workers excellent (±2 mol. % Or) with a straight linear relationship between T crit P such that dT crit/dP≈16°/Kbar. These do exhibit breaks or sensitivity chemical environment, there no evidence changes shape increasing P.