橄榄岩蛇纹石化过程中氢气和烷烃的形成   总被引：1，自引：1，他引：0  

黄瑞芳  孙卫东  丁兴  刘吉强  詹文欢 《岩石学报》2015,31(7):1901-1907

蛇纹石化过程中形成氢气、烷烃和有机酸,为海底热液区生命活动提供物质和能量来源,可能对地球和其他行星早期生命起源和演化有重要影响。目前关于蛇纹石化过程中氢气和烷烃形成的研究大多以橄榄石为初始物,且温度和压力较低(≤300℃,500bar)。本研究通过一系列的水热实验,研究300~500℃、1~3kbar时橄榄石、斜方辉石、单斜辉石、橄榄岩、玄武岩以及玄武岩与橄榄岩混合物发生蛇纹石化反应后氢气和烷烃的生成。300℃、3kbar时,橄榄石蛇纹石化后产生的氢气远大于辉石蚀变后产生氢气的量。随着温度的增加,400~500℃、3kbar时,橄榄石蚀变程度极低,产生氢气的量低于斜方辉石。单斜辉石实验后没有发生蚀变,不产生氢气和烷烃。400~500℃、3kbar时,橄榄岩蛇纹石化后产生的氢气和烷烃远高于橄榄石、斜方辉石和单斜辉石。玄武岩蛇纹石化后生成氢气和甲烷的量低于橄榄岩,但与玄武岩和橄榄岩混合物相当。这是因为玄武岩的单斜辉石蚀变后形成富铁的透辉石(~8.1%FeO),透辉石的Fe以Fe2+为主,这降低了Fe3+和氢气的量。以上表明,橄榄岩的蛇纹石化不同于橄榄石和斜方辉石。不仅是海底热液蚀变产生氢气和甲烷,洋壳俯冲过程中地幔楔橄榄岩蛇纹石化也会生成氢气和甲烷,但由于洋壳玄武岩的加入,氢气和甲烷的量会远小于橄榄岩蚀变时的量。  相似文献   

CH4 and N2O dynamics of a Larix gmelinii forest in a continuous permafrost region of central Siberia during the growing season     

《Polar Science》2014,8(2):156-165

Forest soils are generally sinks of CH₄ and sources of N₂O. To characterize the dynamics of these major greenhouse gases in central Siberia during the growing season, we measured fluxes from forest soil and assessed the relationships between CH₄ and N₂O fluxes and forest floor vegetation types, soil temperature, and moisture conditions. At the soil surface, both CH₄ uptake and emission (−6.6 to 3.1 μg CH₄–C m⁻² h⁻¹) were observed, and CH₄ fluxes did not differ among vegetation types. CH₄ flux was positively correlated with soil moisture, but not with soil temperature. The small CH₄ uptake compared with previous reports was due to CH₄ production in response to high precipitation. N₂O was also emitted and taken up by soil (−0.2 to 0.4 μg N₂O–N m⁻² h⁻¹), and N₂O fluxes did not differ among vegetation types. N₂O flux was negatively correlated with soil moisture and not correlated with soil temperature. Our findings suggest that high soil moisture and low availability of mineral nitrogen resulted in N₂O uptake due to denitrification. Furthermore, both CH₄ and N₂O were emitted from a river at the site; these were produced in the basin of the riverbank rather than deep in the soil.  相似文献   

Mineral-forming and diagenetic processes related to Tertiary hydrocarbon seepage at the Bohemian Massif/Outer Western Carpathians interface: Evidence from the Hrabůvka quarry,Moravia, Czech Republic     

《Marine and Petroleum Geology》2014

Ancient hydrocarbon seepage occurred in the Hrabůvka quarry at the boundary between the basement of the Bohemian Massif (represented by folded Lower Carboniferous siliciclastics of the Culm facies) and Tertiary sedimentary cover of the Carpathian Foredeep (formed by Lower Badenian siliciclastics and calcareous clays). The unconsolidated Lower Badenian sediments contain lithified domains composed of limestone and breccias with limestone cement, whereas the basement rocks are cut by subvertical neptunic dykes filled up by limestone and calcite-marcasite-pyrite veinlets representing sealed fluid conduits. The deeply negative δ¹³C values of both vein calcite and limestone (down to −38.1‰ V-PDB) indicate that oxidation of hydrocarbons was the major source of carbon for authigenic mineralization. A fluid inclusion study suggests low fluid temperatures (<50 °C) and low and variable salinities of aqueous fluids associated with hydrocarbons (0.7–6.7 wt. % NaCl eq.). The variability of δ¹⁸O values of authigenic carbonates (−1.7 to −8.2‰ V-PDB) could reflect either slight changes in temperature of escaping fluids (mostly within 15 °C), and/or some mixing with meteoric waters. The low δ³⁴S values of vein marcasite (∼–20‰ V-CDT) are consistent with bacterial reduction of sulfate in the hydrothermal system. Low C₁/(C₂+C₃) ratios in hydrocarbon gas extracted from authigenic carbonates (9.9 and 5.8) as well as the high δ¹³C values of methane (−31.8 and −32.4‰ V-PDB) are compatible with a thermogenic source of hydrocarbons. REE data indicate sequestration of REE from finely dispersed detrital material in the apical part of the hydrothermal system. The available data are compatible with two possible scenarios of fluid origin. The hydrocarbons could have been leached from underlying Paleozoic sedimentary sequence by aqueous fluids that infiltrated into the basement after Tertiary tectonic reactivation. Alternatively, an external source of hydrocarbon-bearing fluids can be found in the adjacent Outer Western Carpathians flysch nappes containing petroleum-producing lithologies. Nevertheless, a regional flow of hydrocarbon-bearing fluids is evidenced by the occurrence of very similar hydrocarbon-bearing vein mineralizations in a wider area.  相似文献   

地层渗透率与水合物含量关系的模拟研究(英文)   总被引：1，自引：1，他引：0  

赵倩  邓克俊  刘学伟 《应用地球物理》2011,8(2):101-109

本文通过人工变换T2分布和建立管-球模型模拟法研究含水合物地层渗透率与水合物含量之间的关系。首先,在渗透率的模拟试验中,我们改变了束缚水与可动水的比例、总孔隙度以及与之关联的T2分布。试验结果表明,相对渗透率与水合物含量之间的关系受到这些因素的制约。随后,我们用管-球模型表示水合物生长的孔隙空间,并把水合物的生长过程看成是向孔隙空间随机扔小球的过程。在此过程中,采用两种方法计算渗透率,一是Schlumberger’sT2公式(即SDR模型),二是Darcy定律与Poiseuille流动方程相结合的方法。前人的实验研究表明,在一定的水合物含量范围内,渗透率基本保持不变。以此为参考,我们将计算结果与之进行比较。我们发现,采用SDR模型时,渗透率的数值模拟曲线与Masuda模型N=15时的结果相近。而采用Darcy定律时,渗透率模拟值较高,但与实验结果的趋势相一致,都会出现渗透率的平直阶段。尤其,当水合物晶体在孔隙体内优先生成时,优先的概率越高,渗透率的平直范围越大。  相似文献   

Selection of coals of different maturities for CO₂ Storage by modelling of CH₄ and CO₂ adsorption isotherms     

Ch. GarnierG. Finqueneisel  T. ZimnyZ. Pokryszka  S. LafortuneP.D.C. Défossez  E.C. Gaucher 《International Journal of Coal Geology》2011,87(2):80-86

CO₂ injection in unmineable coal seams could be one interesting option for both storage and methane recovery processes. The objective of this study is to compare and model pure gas sorption isotherms (CO₂ and CH₄) for well-characterised coals of different maturities to determine the most suitable coal for CO₂ storage. Carbon dioxide and methane adsorption on several coals have been investigated using a gravimetric adsorption method. The experiments were carried out using both CO₂ and CH₄ pure gases at 25 °C from 0.1 to 5 MPa (1 to 50 bar). The experimental results were fitted using Temkin's approach but also with the corrected Langmuir's and the corrected Tóth's equations. The two last approaches are more accurate from a thermodynamical point of view, and have the advantage of taking into account the fact that experimental data (isotherms) correspond to excess adsorption capacities. These approaches allow better quantification of the adsorbed gas. Determined CO₂ adsorption capacities are from 0.5 to 2 mmol/g of dry coal. Modelling provides also the affinity parameters of the two gases for the different coals. We have shown these parameters determined with adsorption models could be used for classification and first selection of coals for CO₂ storage. The affinity ratio ranges from a value close to 1 for immature coals to 41 for high rank coals like anthracites. This ratio allows selecting coals having high CO₂ adsorption capacities. In our case, the modelling study of a significant number of coals from various ranks shows that anthracites seem to have the highest CO₂ storage capacities. Our study provides high quality affinity parameters and values of CO₂ and CH₄ adsorption capacities on various coals for the future modelling of CO₂ injection in coal seams.  相似文献   

http://www.sciencedirect.com/science/article/pii/S1674987110000344     

Jinfu Shu  Xiaojia Chen  I.-Ming Chou  Wenge Yang  Jingzhu Hu  Russell J. Hemley  Ho-kwang Mao 《地学前缘(英文版)》2011,2(1):93-100

The structural stability of methane hydrate under pressure at room temperature was examined by both in-situ single-crystal and powder X-ray diffraction techniques on samples with structure typesⅠ,Ⅱ,and H in diamond-anvil cells.The diffraction data for typesⅡ(sⅡ) and H(sH) were refined to the known structures with space groups Fd3m and P6_3/mmc,respectively.Upon compression,sⅠmethane hydrate transforms to the sⅡphase at 120 MPa,and then to the sH phase at 600 MPa.The sⅡmethane hydrate was found to coexist...  相似文献   

Vodyanitskii mud volcano,Sorokin trough,Black Sea: Geological characterization and quantification of gas bubble streams     

Heiko Sahling  Gerhard Bohrmann  Yuriy G. Artemov  André Bahr  Markus Brüning  Stephan A. Klapp  Ingo Klaucke  Elena Kozlova  Aneta Nikolovska  Thomas Pape  Anja Reitz  Klaus Wallmann 《Marine and Petroleum Geology》2009

Vodyanitskii mud volcano is located at a depth of about 2070 m in the Sorokin Trough, Black sea. It is a 500-m wide and 20-m high cone surrounded by a depression, which is typical of many mud volcanoes in the Black Sea. 75 kHz sidescan sonar show different generations of mud flows that include mud breccia, authigenic carbonates, and gas hydrates that were sampled by gravity coring. The fluids that flow through or erupt with the mud are enriched in chloride (up to ∼650 mmol L⁻¹ at ∼150-cm sediment depth) suggesting a deep source, which is similar to the fluids of the close-by Dvurechenskii mud volcano. Direct observation with the remotely operated vehicle Quest revealed gas bubbles emanating at two distinct sites at the crest of the mud volcano, which confirms earlier observations of bubble-induced hydroacoustic anomalies in echosounder records. The sediments at the main bubble emission site show a thermal anomaly with temperatures at ∼60 cm sediment depth that were 0.9 °C warmer than the bottom water. Chemical and isotopic analyses of the emanated gas revealed that it consisted primarily of methane (99.8%) and was of microbial origin (δD-CH₄ = −170.8‰ (SMOW), δ¹³C-CH₄ = −61.0‰ (V-PDB), δ¹³C-C₂H₆ = −44.0‰ (V-PDB)). The gas flux was estimated using the video observations of the ROV. Assuming that the flux is constant with time, about 0.9 ± 0.5 × 10⁶ mol of methane is released every year. This value is of the same order-of-magnitude as reported fluxes of dissolved methane released with pore water at other mud volcanoes. This suggests that bubble emanation is a significant pathway transporting methane from the sediments into the water column.  相似文献   

A rapid method for preparing low volume CH4 and CO2 gas samples for 14C AMS analysis     

《Organic Geochemistry》2015

¹⁴C measurements of CH₄ in environmental samples (e.g. soil gas, lake water, gas hydrates) can advance understanding of C cycling in terrestrial and marine systems. The measurements are particularly useful for detecting the release of old C from climate sensitive environments such as peatlands and hydrate fields. However, because ¹⁴C CH₄ measurements tend to be complex and time consuming, they are uncommon. Here, we describe a novel vacuum line system for the preparation of CH₄ and CO₂ from environmental samples for ¹⁴C analysis using accelerator mass spectrometry (AMS). The vacuum line is a flow-through system that allows rapid preparation of samples (1 h for CH₄ and CO₂, 30 min for CH₄ alone), complete separation of CH₄ and CO₂ and is an easy addition to multipurpose CO₂ vacuum lines already in use. We evaluated the line using CH₄ and CO₂ standards with different ¹⁴C content. For CH₄ and CO₂, respectively, the total line blank was 0.4 ± 0.2 and 1.4 ± 0.6 μg C, the ¹⁴C background 51.1 ± 1.2 and 48.4 ± 1.5 kyr and the precision (based on pooled standard deviation) 0.9‰ and 1.3‰. The line was designed for sample volumes of ca. 180 ml containing 0.5–1% CH₄ and CO₂, but can be adjusted to handle lower concentration and larger volume samples. This rapid and convenient method for the preparation of CH₄ and CO₂ in environmental samples for ¹⁴C AMS analysis should provide more opportunities for the use of ¹⁴C CH₄ measurements in C cycle studies.  相似文献   

Archaeal polar lipids in subseafloor sediments from the Nankai Trough: Implications for the distribution of methanogens in the deep marine subsurface     

《Organic Geochemistry》2015

Although the methane in marine methane hydrates is mainly of microbial origin, information about the distribution of methanogens in subseafloor sediments is limited. To address this issue, we analyzed sediment core samples from two sites in the Nankai Trough, off the Pacific coast of central Japan, including those bearing methane hydrates from depths > 100 m below the seafloor (mbsf), for isopranyl ether-linked polar lipids (i.e. with polar head groups of phosphate, sugar, or both) as biomarkers of archaea, including methanogens. In most samples, including the deepest (381 mbsf), archaeol, and sn-2- and sn-3-hydroxyarchaeols were detected as their hydrolyzed derivatives. Concentrations of these three archaeal lipids correlated strongly with each other, suggesting a common biological source. The δ¹³C values of phytane derived from the phytanyl groups in the archaeal lipids were distinctly higher than those of methane, indicating that methanogens rather than anaerobic methanotrophic archaea were the major biological source. Depth profiles of polar sn-2-hydroxyarchaeol concentration were consistent with those of the potential methane production activity previously estimated from incubation of core sediments from the same sites. This observation, together with results of previous studies showing the presence of sn-2-hydroxyarchaeol mainly in shallow young sediments, strongly suggests that this polar lipid is a valid biomarker for in situ methanogens in sediments. There was a strong correlation between the concentration of polar sn-2-hydroxyarchaeol and that of total organic carbon, suggesting that bulk organic matter concentration is a primary control on the distribution of methanogens in sediments.  相似文献   

Biomarker evidence for Botryococcus and a methane cycle in the Eocene Huadian oil shale,NE China     

《Organic Geochemistry》2015

The saturated and unsaturated hydrocarbons of two samples (HD-19 and HD-21) from the same section of the Middle Eocene lacustrine Huadian oil shale in NE China were identified and shown to be mainly from algal and bacterial sources. Comparison of the two samples provided an opportunity to explore the contribution from telalginite to the hydrocarbon profiles. Cells identified from microscopy as Botryococcus in the telalginite of HD-21 were confirmed as belonging to the L race of B. braunii from the presence of monoaromatic lycopane derivatives and small amounts of several lycopadienes. Lycopane was abundant and was probably derived from biohydrogenation of lycopadienes and related lipids on the basis of δ¹³C values. Hopane distributions showed a dominance of those with the biological 17β,21β-stereochemistry, as expected for an immature shale, with low amounts of 17β,21α-hopanes (moretanes) and 17α,21β-hopanes. Two hopenes were also abundant and assigned as C₂₉ and C₃₀ neohop-13(18)-enes, which occurred together with the C₂₉ and C₃₀ hop-17(21)-enes. These had depleted carbon isotope values (−43.7‰ to −50.8‰), indicative of production by methane oxidizing bacteria (methanotrophs). The high proportion of hopanoids with carbon numbers < C₃₂ indicates extensive post-depositional diagenetic alteration of bacteriohopanepolyols as well as a direct input of C₃₀ hopanoids. The data clearly indicate that there was active utilization of methane in this lacustrine depositional setting, but isoprenoid hydrocarbon biomarkers for methanogens, such as pentamethylicosane (PMI) and squalane, were in surprisingly low abundance. It is possible that these bacterial contributions were present as polar lipids. The origins of an unusual C₃₈ isoprenoid alkane assigned as bipristane are uncertain, but may be from methanogens. Steranes and sterenes were relatively minor components, but abundant diasterenes and 4-methyldiasterenes were present, reflecting significant conversion of the original lipid composition by way of clay-catalysed diagenesis. The biomarker data suggest that the bottom waters in the original depositional environment had low O₂ content, but the sediments were probably neither sulfidic nor strongly reducing. The high content of organic matter in the shale likely reflects both high (but fluctuating) productivity due to eutrophic conditions in the overlying water and good preservation in the sediments.  相似文献