First- and second-order Raman spectra of carbonaceous material through successive contact and regional metamorphic events (Ryoke belt, SW Japan)

The evolution of both the first- and second-order Raman spectra carbonaceous material (CM) through successive contact regional metamorphic events is explored in western part Ryoke belt (Iwakuni-Yanai area, SW Japan). Thirty-two metasedimentary rock samples were collected along a N-S gradient locally affected by metamorphism before after main tectono-metamorphic event (DP1). First-order document decreasing peak area ratio R2 an increasing temperature T CM towards south surrounding granitoids. Domains with intermediate (535–600 °C) values match extent pre-DP1 aureole but also image so far unclear post-DP1 aureole. axial belt, likely unaffected granite intrusions, preserves southward from 425 to 660 °C. Second-order show single S1 band that splits into two peaks (S1- S1+) whose frequency difference ?S1 increases stepwise south. spatial distribution follows E–W trending zones. splitting indicates transition two-dimensional three-dimensional occurs at ~500 °C, which seems be common all belts worldwide. Despite was able record overprint there no clear observation delayed recrystallization, depends on crystallinity precursor. A discrepancy between parameters suggests they partly influence different factors; gives account thermal events, particularly those related localized metamorphism, whereas potentially yields information variations heating duration pressure. This demonstrates potential full spectrum for deciphering complex history orogenic systems. • Response pre-, syn- post-regional overprints. Extent revealed analysis material. Discrepancy features.