Petrological Implication of the Albite Rims in the Felsic Gneisses of the Fuping Complex

Abstract:The albite rim is present in most felsic gneisses of the Fuping Complex. The presence of the rim indicates the coexistence of plagioclase and K‐feldspar in the rock. The rim is formed immediately after the myrmekite, and both textures were derived from the alteration of K‐feldspar. The difference is that that there is no quartz present in the rim, and the rim is nearly albite and the anorthite content of the rim plagioclase is substantially lower than that of the myrmekite plagioclase. Formed at 400–500°C the albite rim was derived from the K‐feldspar composition adjustment in the late or post‐magmatism stage. As the temperature decreased, the equilibrium between K‐feldspar and plagioclase could be maintained, and reactions between the minerals occurred. The leucocratic veins in the complex show distinguished magma or migmatitic characteristics. The rim might form in the late magma or deuteric stage. The formation of the rim implies obvious granitic magma‐ or melt‐injection activity. Typical metamorphic rocks cannot produce the rims. Anatexis after medium‐high grade metamorphism might be subordinate. If present, the anatexis is water‐present, but the rim texture cannot be taken as the symbol of anatexis.