155 / 2015-08-03 16:57:10

The geothermomter study of carbonaceous material in metasedimentary by Raman spectrum

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It is challenge to calculate the metamorphic temperature of rock accurately,conventional geothermomter often use characteristic mineral to determine the metamorphic temperature.And it is impossible to measure quantitatively the peak temperature during the metamorphic processes.Raman spectrum of carbonaceous material (RSCM )themomter can get quantitative parameters that may be used as proxies for thermal metamorphism in this region. Previous work has demonstrated that Raman spectroscopy is a non-intrusive, non-destructive analytical technique to describe the degree of graphitization of CM .As a matter of fact, Raman micospectroscopy has become the most widely used tool to study archean life、thermal metamorphism in formation of mountain belts and evidence of planet life.
Our paper choose a series sample from different P-T conditions, including Animikie group from Lake superior area、Marble Bar chert and tumbiana stromatolite in the Pilbara craton western Australia and HuTuo group of north china.By using laser Raman micospectroscopy,we get CM raman spectrum to calculate the T.Meanwhile,we analysis the paragenetic mineral to get T0.
Previous works have assumed the graphitization process to be irreversible, with no effects on the CM structure during retrogression. Therefore, CM structure that may be used as proxies for thermal metamorphism in this region.The raman spectrum of graphite bar, exhibits first-order bands（1100–1800 cm-1) and second-order bands (2500–3100 cm-1), Previous works have assumed that increasingλ0 have no effects on first-order bands. So we choose several defect bands at 1200 (D4), 1350 (D1), 1500 (D3) and1620(D2) cm-1to develop a robust peak-fitting method to calculate the metamorphic temperature.There are three RSCM themomther such as Beyssac.O et al（2002）、Rahl . Jeffrey M et al（2005）、Lahfid et al（2010）.We use this three. method for different metamorphic grade sample to calculate T;And compared with T0 that get from conventional mineral geothermomter.From our paper we know
1）With increasing P–T conditions, The D1 band occur at 1580 -1600cm-1, The G band is at 1130 -1350cm-1; And D1band FWHF、Area decrease as the temperature increasing,It demonstrated CM structure approach to order graphite.
2)Compare to T0, T get from RSCM themomter is accuracy, so RSCM themomter is practicable.For the other side, we also know the method of Rahl . Jeffrey M et al（2005）is most exact.