Abstract
Carbonaceous materials (CMs) have been widely used to assess temperatures in sedimentary and metamorphic carbonate rocks. The use of Raman spectroscopy of carbonaceous material (RSCM) is largely devoted to the study of deformed rocks hosted in thrust-tectonic settings. Raman spectroscopy of carbonaceous material successfully allows the study of carbonate rocks at a temperature as high as 650 °C. In this study, a set of carbonate-mylonite rocks (Italian Alps) were investigated using micro-Raman spectroscopy, in order to infer the deformation conditions associated with the Alpine thrusts, expected to occur at T < 350 °C. Micro-Raman spectra were collected using two sources: green (532 nm) and red (632.8 nm) lasers. Several deconvolution procedures and parameters were tested to optimize the collected spectrum morphologies for the laser sources, also in accordance with the low temperature expected. The obtained temperatures highlight two clusters: one at 340–350 °C for the samples collected in the axial part of the Alpine chain, and the other at 200–240 °C for those collected in the external thrust-and-fold belt. These results agree with the independent geological and petrological constraints. Consistent results were obtained using 532 and 632.8 nm laser sources when the appropriate deconvolution approach was used.
Highlights
Micro-Raman spectroscopy has been proved to be a worthwhile technique for characterizing carbonaceous materials (CMs) in widely different rock types [1,2,3,4,5,6,7,8,9,10,11]
Different authors investigated the best profile deconvolution approach with which to obtain quantitative parameters required to apply the Raman spectroscopy of carbonaceous material (RSCM) as a geothermometer [3,5,9,10,15,16,17,18,19,20]
The aim of this study is to extend the applicability of the CM-based geothermometer to lower temperatures and evaluate suitable deconvolution procedures using two different laser sources
Summary
Micro-Raman spectroscopy has been proved to be a worthwhile technique for characterizing carbonaceous materials (CMs) in widely different rock types [1,2,3,4,5,6,7,8,9,10,11] As it concerns the petrographic field, the degree of crystalline order of CMs in the sample has been proved to be dependent on the temperature conditions attained by the hosting rock during the metamorphic process [1,12,13,14]. CMs, and subscript A indicates that the ratio is based on peak areas This geothermometer is described by Beyssac et al, as reliable for temperatures in the range of 330–650 ◦ C [1] as, at lower temperatures, the R2 parameter displays no significant variations. Different authors investigated the best profile deconvolution approach with which to obtain quantitative parameters required to apply the Raman spectroscopy of carbonaceous material (RSCM) as a geothermometer [3,5,9,10,15,16,17,18,19,20]
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