The crystallinity of carbonaceous material (CM) in metasedimentary schists in the Yuli belt, eastern Taiwan, shows unusual diversity. The difference between the maximum and minimum temperatures estimated by a Raman CM geothermometer reaches 200 °C, which is much wider than those in other metamorphic belts and contact aureoles. In light of these results, we considered two possible explanations: (1) a mixture of detrital and metamorphic graphite grains, and (2) a mixture of different reactive CM during short-lived metamorphism. One sample shows a near-bimodal peak, suggesting the former hypothesis, while the other two samples show a continuous single peak, suggesting the latter possibility. Detailed analyses of CM crystallinities have the potential to extract information relating not only to the peak metamorphic temperature, but also to the pre-metamorphic history or the duration of heating in a metamorphic belt.

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