| Popis: |
Two-mica monzogranites to leucogranites and biotite-rich, cordierite-bearing tonalites to monzogranites form two distinct groups of peraluminous granitoids. They can be distinguished by mineral and rock associations and by the variation of their peraluminosity during differentiation. Except for the rare muscovite-bearing granitoids produced by extreme fractionation or local contamination of metaluminous magmas, the majority of peraluminous granitoids are produced by partial melting of crustal rocks. Production of either muscovite-bearing granites or biotite-rich, cordierite-bearing granitoids does not depend only on the nature of the sources, but is also controlled by the physical parameters of partial melting and consequently by the way anatexis of a thickened crust is enhanced. Biotite-rich, cordierite-bearing granitoids are generated where mantle-derived magmas are injected into or have underplated crustal rocks; two-mica granites are generated where thickened crust is affected by major crustal shears or thrusts. Correlations between differentiation and peraluminosity indicate the dominant role of either restite unmixing or fractional crystallization in the production and evolution of the various types of peraluminous granitoids. |
