Abstract
Grossular-andradite (grandite) garnet, precipitated from hydrothermal solutions associated with contact metamorphism in the Oslo rift, shows complex oscillatory chemical zonation. Immiscibility in the grandite system at T ≤ 400 °C, P ≈ 500 bars has been demonstrated by coexisting, unzoned isotropic and anisotropic grandite garnets in skarn zones around hydrothermal veins. A set ofthree first-order differential equations model the garnet zonation as a function of internal and external factors. The model simultaneously accounts for immiscibility in the grandite system, dissipation of energy during epitaxial growth ofone garnet phase upon another, and external forcings such as variations in the composition of the hydrothermal fluid(s) from which the garnets precipitate. It is demonstrated how simple (periodic) external forcings may lead to very complex (nonperiodic) zonation patterns within regions of immiscibility.
Although the observed zonation profiles may have resulted from transient rather than stationary erowth processes, the model indicates that stationary nonperiodic and chaotic gowth dynamics may arise in the grandite system under the influence of quasi-periodic external templates.
