Genesis of the Skagit Gneiss migmatites, Washington, and the distinction between possible mechanisms of migmatization

摘要: Some possible chemical and morphological criteria to distinguish different migmatization mechanisms are considered examples of the processes discussed. Leucosomes formed by anatexis likely contain K-feldspar should have a more sodic plagioclase than restite rocks. Metamorphic segregation can cause slight fractionation albite into leucosome only. Anatectic leucosomes might form irregular bodies or agmatize restite; close-spaced planar veins improbable. Leucosome hydrothermal be coarse grained pegmatitic, whereas water-rich anatectic melts may freeze readily aplites. The developed applied Skagit Gneiss migmatites, although temperature metamorphism was high (<700 °C), an model is rejected, as in earlier studies. Much that accompanied regional deformation due metamorphic segregation. Many other believed related extensive suite pegmatite dikes, probably origin, were emplaced at late stage. These dikes uniform composition (plagioclase ≃ An20), irrespective host rock, plagioclases some feldspathized schists tend toward this composition. Recent fluid-inclusion studies shown high-grade rocks mixed CO2-H2O fluid. Therefore, partial melting unlikely begin until temperatures well excess water-saturated granite solidus reached. Melts so coalesce migrate out source rock without producing migmatite zone. terranes predominantly processes, notably segregation, it represent particular type tectonic environment.