A study on the b0 parameter and crystallinity index of K-white micas from low-grade metapelites in Deokpyeong and Miwon areas, central Ogcheon metamorphic belt, Korea.

In order to elucidate metamorphic conditions of metasedimentary rocks of central Ogcheon metamorphic belt, we investigated the b₀ parameter and the crystallinity index (CI) of K-white micas from low-grade metapelites. The CI values of muscovite from seventy-eight samples range from 0.08° to 0.19° Δ2θ with an average of 0.12±0.01° Δ2θ, and show no remarkable difference between structurally upper Pibanryeong and lower Poeun lithotectonic units. Slate and phyllite of the Poeun unit have the b₀ parameters of 8.993–9.031 Å with an average of 9.010±0.007 Å (n=63), whereas those in the vicinity of Poeun granite have slightly lower values of 8.988–9.010 Å with an average of 8.998±0.006 Å (n=33). On the other hand, b₀ parameters of pelitic schists in the Pibanryeong unit vary from 8.995 Å to 9.042 Å (n=29) with an average of 9.009±0.013 Å that is similar to 9.003±0.009 Å (n=26) in the Poeun unit. These results suggest that low-grade metapelites of central Ogcheon metamorphic belt have experienced a mediumpressure type metamorphism, reaching up to the upper greenschist facies (biotite zone) condition. Moreover, metamorphic pressures estimated from the b₀ values show no apparent discontinuity across the unit boundary, implying an insignificant vertical displacement along this boundary after the peak metamorphism. [ABSTRACT FROM AUTHOR]