抄録
In the Donachui River area of the Santa Marta Mountains, Precambrian metamorphic rocks of amphibolite facies and three large Mesozoic masses are exposed. The metamorphism is considered to be associated with a large-scale granitization and probably superimposed on an earlier granulitic facies metamorphism. Many retrogressive minerals are also observed in the metamorphic rocks.
From the obliquities and optics of K-feldspar, the following three events are recognized in the metamorphic process. (1) a hair- or string-perthitic orthoclase (Δ=0, 2VX=59°-65°) was formed during the main phase of metamorphim; (2) this orthoclase was mostly transformed into maximum microcline (Δ=0.84-0.99, 2VX=76°-83°) with grading texture during the cataclastic movement; (3) some orthoclases have been transformed into intermediate microcline (Δ=0.77-0.81, 2VX=68°-72°) and the maximum microcline has been converted into “dirty” microcline (Δ=0.86-0.92, 2VX=76°-85°) showing ambiguous grating texture and containing abundant second generation perthitic albite during the retrogressive metamorphism.
Most K-feldspar in Mesozoic granites is orthoclase.
