Evolution of the Raman spectrum of carbonaceous material in low-grade metasediments of the Glarus Alps (Switzerland)

P>The Raman spectrum of carbonaceous material (CM) from advanced diagenesis (similar to 200 degrees C) to low-grade metamorphism (similar to 320 degrees C) is documented in the Helvetic flysch of the Glarus Alps (Switzerland). The spectrum is complex, with several defect bands at similar to 1200 (D4), similar to 1350 (D1), similar to 1500 (D3) and similar to 1620 (D2) cm-1. We document the evolution of these bands relative to the 'graphite' G band with increasing metamorphic grade, and we show that this qualitative evolution may be used as a proxy for temperature in the Glarus Alps. We develop a robust peak-fitting method and propose quantitative parameters that may be used as proxies for thermal metamorphism in this region. Further work in other geological contexts is needed to assess whether the spectral evolution observed in the Glarus Alps may be generalized and to critically assess the potential for calibrating a general, empirical and quantitative thermometer based on the Raman spectrum of CM in low-grade rocks.