Recognition of Detrital Carbonaceous Material in the Ryoke Metamorphic Belt by Using Raman Thermometry: Implications for Thermal Structure and Detrital Origin

Raman spectroscopy of carbonaceous material (RSCM) thermometry is an effective method to determine the thermal structure of metasedimentary domains with high spatial resolution. The mean value of numerous measurements in a single sample is used for temperature estimation. A potential complicating factor is the presence of detrital carbonaceous material (CM) that can introduce bias in the results. Detrital CM generally shows a high degree of crystallinity making it difficult to discriminate detrital and metamorphic CM in high-grade metamorphic domains. Application of the RSCM thermometry to 100 metamudstone samples from the Hongusan area of the Ryoke metamorphic belt reveals multimodal degrees of crystallinity of CM in many samples indicating the common presence of detrital CM grains. Application of a new procedure to filter out the effects of detrital CM reveals a thermal structure that can be explained as the result of the overprinting of two distinct thermal regimes related to regional and subsequent contact metamorphism. The ability to recognize the presence of detrital CM and measure its crystallinity can be used to infer the metamorphic grade present in the hinterland from which the detrital material is derived. A combination of this information on metamorphic temperature with geochemical and radiometric age data reported in the literature indicates that the detrital CM was derived from basement rocks of the Korean Peninsula.

Automated summary

Raman spectroscopy of carbonaceous material (RSCM) thermometry is a useful method to determine the thermal structure of metasedimentary domains with high spatial resolution. The presence of detrital carbonaceous material (CM) can introduce bias in the results, but a new filtering procedure can effectively remove the effects of detrital CM. By analyzing metamudstone samples from the Hongusan area, it is observed that the thermal structure can be explained by the overprinting of two distinct thermal regimes. Recognizing the presence of detrital CM and measuring its crystallinity can help infer the metamorphic grade and the source of detrital material.