摘要 | 激光拉曼光谱技术被称为“分子指纹”,对于物质结构的分析具有独特的价值,
因其具备非接触、无需样品预处理、探测多种组分等优点,该技术已被成功地应
用于深海极端环境气体、液体的原位定量分析以及天然气水合物的原位探测,但
是对于极端环境的岩石研究较少。本文利用自主研发的 RiP(Raman insertion
Probe)系统对台西南盆地福尔摩沙脊冷泉区(Site F)和珠江口盆地东部冷泉区(Site P)的自生碳酸盐岩进行了对比分析,基于激光拉曼光谱揭示了不同地质环境中自生碳酸盐岩的显著变化。除此之外,本文对 Site F 不同位置的自生碳酸盐岩进行了系统的原位探测。综合上述研究得到以下的几点结论:
(1)物质成分的差异对拉曼频移造成一定的影响。 Site F 碳酸盐主峰的拉曼
频移在 1084~1087 cm-1 ,相对于 Site P 的碳酸盐主峰拉曼频移小了 3 个波数。排除了系统的误差和拟合方法的干扰,对拉曼光谱采集的位置进行 SEM
(Scanning Electron Microscope)和 EDS(Energy Dispersive Spectrum)分析,结果表明二者具有显著的组分差异,说明元素组成的差异会对拉曼频移造成影响。
(2)冷泉区标志性的矿物为文石、方解石等。 Site F 和 Site P 的方解石的拉
曼光谱没有显著变化, 碳酸根的拉曼频移和半峰宽很相似,表明在 Site P 方解石的元素组成没有发生明显变化以及结晶度未受到损害。反之,文石的拉曼光谱变化较为显著,相比于 Site F 碳酸盐岩的拉曼光谱, Site P 文石的半峰宽变大以及拉曼频移向高频移动,说明 Site P 文石的结晶度受到了破坏,组分也发生了变化。这些结果表明 Site P 海水理化环境的变化会对文石结晶度造成明显的影响。结合过去的研究, 本文认为过去南海底部富 CO2 的深层水可能在 Site P 的冷泉活动停止后加速了该地区的碳酸盐岩的侵蚀。
(3)对 Site F 边缘地带、中间地带、气泡中心地带的自生碳酸盐岩进行了
原位拉曼光谱的采集工作。 设定相同的积分光谱采集参数,从边缘到气泡喷口中
心碳酸盐拉曼强度逐渐增加。中间地带主要分布着以方解石为主的自生碳酸盐岩,说明形成于海底深部的以方解石为主的自生碳酸盐岩由于构造抬升或者上部侵蚀而逐渐暴露在海底。在气泡喷口中心广泛分布着以文石为主的自生碳酸盐岩,表明了一种高硫酸根含量的流体环境。除此之外,气泡喷口中心的自生碳酸盐岩里也检测到类胡萝卜素的存在,关于这二者的联系值得进一步的探索。基于前人工作,结合本论文获取的原位光谱数据、高清海底影像、地球物理数据, 我们建立了 Site F 的地貌分布模式图,加深了对 Site F 的认识。原位探测能够提供样品的初步信息,使采样工作具有了一定的方向性和目的性。 |
其他摘要 | 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 1084~1087cm-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 richCO2 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.
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