Laser Raman Spectroscopy Application Of Exposed Authigenic Carbonates In The South China Sea For In Situ Detection And The Analyses In Laboratory

Laser Raman technology is named"molecular fingerprint",and has a great advantage of analyzing material structure.The technique has been used to analyze the gases,liquid in the extreme environment and in situ detection of gas hydrate due to the characterizes of non-contact,non-prepared of samples,analyzing various components,however,the application of the laser Raman spectroscopy to the rocks in the extreme environment has few reports.In this paper,we applied the RiP?Raman insertion Probe?system to collect the Raman spectra of authigenic carbonates in the Formosa Ridge offshore the southwest Taiwan Basin and the east of the of the Pear River Mouth Basin.The Raman spectra show the apparent changes of the authigenic carbonates in different cold seeps.In addition,we also took in situ detection of the authigenic carbonate in different locations in Site F.The conclusions are the followings:?1?The differences at components make influence on the Raman shift.The Raman shift of dominant carbonate Raman peaks in Site F is at the range of 1084¹087cm^-1,which is smaller 3 wavenumbers than that in Site P.Excluding the interference of the RiP system and fitting ways.Taking the analyses SEM and EDS of spots where collect Raman spectra,the results showed that differences at the components of the samples made influence on the Raman shift.?2?The typical minerals in the cold seeps are aragonites and calcites.The Raman spectra of calcites in Site F and Site P don't have differences.The similarities of the Raman shifts and full width at half maximum?FWHM?showed that the components and degree of crystallization of calcites don't have differences.In contrast,the Raman spectra of aragonites in Site F and Site P are different.Compared the aragonites in Site F,the Raman shift becomes higher and FWHM of aragonites becomes bigger in Site P,suggesting the components and degree of crystallization of aragonite changed a lot.The phenomenon showed the physicochemical environment in Site P made effects on the degree of crystallization of aragonite.Based on the previous research,we think the rich-CO₂ deep water in South China Sea may accelerate the erosion of carbonate in the area after the cease of seep activities.?3?We took in situ detection of the authigenic carbonates at the edge area of the Site F,the middle area of the Site F and bubbles vent of the Site F.The Raman intensity becomes stronger at the same integration spectral acquisition parameters from the edge area to bubbles vent.At the middle area of the Site F,the Raman spectra of calcites suggested the calcite-dominated authigenic carbonates below the seafloor may suffer from erosion or tectonic uplift and exposed on the seafloor.At the bubbles vent,the aragonite-dominated authigenic carbonates on the seafloor,suggesting the high sulfate content in the environment.In addition,we also detected the carotene in the authigenic carbonates in the bubbles vent.The relationship between the authigenic carbonate and carotene needs deeper research.Finally,we build a landform model based on the in situ Raman spectra of authigenic carbonate,the high definition image of Site F,geophysical data,and previous research,which contributes to knowing about the landforms of Site F.In situ detection provides the preliminary information,which contributes to guiding the sampling works..