Graphite Crystallinity and Metamorphic Temperature Estimates Using RSCM Geothermometryin the Storsjön-Edsbyn Deformation Zone, Sweden

Sammanfattning

Graphite is a significant mineral in the geological field due to its ability to estimate the metamorphic temperature of its host rock. This study investigates the crystallinity and thermal maturity of graphite-bearing metamorphic rocks from two localities in central Sweden. One from the western part of the Ljusdal unit (MA9005) and another from the northwestern part of the Bergslagen unit (SLH241008A). Both areas are a part of the Svecofennian orogeny and are situated in the Storsjön-Edsbyn Deformation Zone (SEDZ).Optical microscopy was used to examine the graphite as well as identify the mineral assemblage of the rocks and the textural position of graphite relative to the temperature estimations. Raman spectroscopy was performed on thin sections to assess graphite crystallinity and estimate the metamorphic temperature using the Raman spectroscopy on carbonaceous matter (RSCM method). The spectral data, including D1, D2 and G, were analyzed using a software called Fityk, after applying baseline correction and Voigt peak fitting. Multiple data point was compared throughout the two samples.The results revealed that temperature estimation reached beyond the calibration range, exceeding 650°C. This result is higher than the previously documented metamorphic temperature of the area. Importantly, the highly ordered graphite withstood pervasive hydrothermal alteration of the studied rocks, demonstrating the advantages of RCSM thermometry in highly altered rocks.