Natural and experimental structural evolution of dispersed organic matter in mudstones: The Shimanto accretionary complex, southwest Japan
Natural and experimental structural evolution of dispersed organic matter in mudstones: The Shimanto accretionary complex, southwest Japan
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DOI：
10.1111/iar.12318
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发表时间：
2019-07
期刊：
影响因子：
1.5
通讯作者：
Yoshihiro Nakamura;H. Hara;H. Kagi
中科院分区：
文献类型：
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作者：
Yoshihiro Nakamura;H. Hara;H. Kagi
利用显微傅里叶变换红外光谱和显微拉曼光谱研究了日本西南部Shimanto增生杂岩中分散有机质（OM）热成熟引起的结构变化。从D1-和G-波段FWHM值、拉曼谱带分离（RBS）和D1-和G-波段强度比（ID 1/IG比）推断，从成岩带到锚定带（IC值：0.75-0.30），天然分散的有机质表现出系统的结构变化。红外光谱表明，随着温度的升高，脂肪族CH x，芳香族CH x和含氧结构的损失。这些变化与由无序逆冲断层所限定的热结构中的不连续性相一致。动力学热解实验表明，合成OM的ID 1/IG比与热处理时间呈幂律关系。使用ID 1/IG比拟合温度依赖性的动力学模型，并使用Arrhenius方程估计有效活化能为106 ±17 kJ/mol。通过幂律速率和Avrami模型估计的活化能具有0.93的最小二乘相关系数，表明碳化的温度依赖性。估算的有效活化能与煤、木质素、纤维素和半纤维素在热降解过程中的活化能一致。另一方面，随着加热温度和时间的增加，OM的RBS和D1-和G-波段FWHM值显示出更复杂的变化，并且难以在热解实验期间约束速率参数。我们的数据表明，ID 1/IG比是由一个简单的热激活过程控制，而RBS和D1和G波段FWHM值可以受到岩石静压力，流体活动，氢指数，和主机岩性，以及温度。泥岩中分散有机质的结构演化在自然和无水封闭实验系统之间存在差异。基于显微拉曼光谱的天然碳化作用可作为热成熟度的有限指标，特别是对于成岩带中分散的有机质。
Structural changes induced by thermal maturation of dispersed organic matter (OM) in the Shimanto accretionary complex, southwest Japan, were investigated using micro‐Fourier‐transform infrared spectroscopy and micro‐Raman spectroscopy. Natural dispersed OM exhibits systematic structural changes inferred from D1‐ and G‐band FWHM values, Raman band separation (RBS), and intensity ratios of the D1‐ and G‐bands (ID1/IG ratio) from diagenetic zone to anchizone (IC values: 0.75–0.30). Infrared spectra indicate a loss of aliphatic CH x, aromatic CH x, and oxygen‐containing structures as temperature increases. These changes are consistent with discontinuities in thermal structures bounded by out‐of‐sequence thrusts. Kinetic pyrolysis experiments indicate that the ID1/IG ratio of synthesized OM has a power law relationship with heat treatment time. Kinetic models of temperature dependence were fitted using the ID1/IG ratio, and an effective activation energy of 106 ±17 kJ/mol was estimated using an Arrhenius equation. The activation energies estimated by power law rate and Avrami models have a least‐square correlation coefficient of 0.93, indicating the temperature dependence of carbonization. The estimated effective activation energy is consistent with that of coal, lignin, cellulose, and hemicellulose during thermal degradation. On the other hand, RBS, and D1‐ and G‐band FWHM values of OM display more complex changes with increasing heating temperature and time, and it is difficult to constrain rate parameters during pyrolysis experiments. Our data indicate that the ID1/IG ratio is controlled by a simple thermally activated process, whereas RBS and D1‐ and G‐band FWHM values can be affected by lithostatic pressure, fluid activity, hydrogen index, and host lithology, as well as temperature. Structural evolution of dispersed OM in mudstones differs between natural and anhydrous closed experimental systems. Natural carbonization based on micro‐Raman spectroscopy should be applied for a limited indicator of thermal maturation, especially for dispersed OM in diagenetic zone.