天然气水合物成因探讨

天然气水合物是未来的能源资源。其分布于极地地区、深海地区及深水湖泊中。在海洋里,天然气水合物主要分布于外大陆边缘和洋岛的周围,其分布与近代火山的分布范围具有一致性。同位素组成表明天然气水合物甲烷主要是由自养产甲烷菌还原CO₂形成的。典型的大陆边缘沉积物有机碳含量低（＜0．5％～1．0％）,不足以产生天然气水合物带高含量的甲烷。赋存天然气水合物的沉积物时代主要为晚中新世-晚上新世,具有一定的时限性,并且天然气水合物与火山灰或火山砂共存,表明其形成与火山-热液体系有一定联系。火山与天然气水合物空间上的一致性表明,天然气水合物甲烷的底物可能主要是由洋底火山喷发带来的CO2。由前人研究结果推断 HCO^－₃在脱去两个O原子的同时,可能发生了亲核重排,羟基 H原子迁移到 C原子上,形成了甲酰基（HCO^－）,使甲烷的第一个 H原子来源于水。探讨了甲烷及其水合物的形成机制,提出了天然气水合物成因模型。     

伊利石40Ar-39Ar定年技术在松辽盆地北部下白垩统泉头组四段物源和油气成藏时代研究中的应用

利用特别研制的纯化装置有效地除弃有机杂质气体,松辽盆地下白垩统泉头组四段砂岩储层伊利石40Ar-39Ar激光阶段加热分析获得了逐渐上升的阶梯型年龄谱.低温阶段伊利石的年龄小于地层年龄,大于但可能接近于油气成藏最早的年龄;高温阶段坪年龄明显老于地层年龄,反映了陆源碎屑伊利石的年龄,用于探讨盆地沉积物的物源.松辽盆地北部下...     

鄂尔多斯盆地东北部二叠系油气成藏的时间和期次

提要：油气成藏年代学是多旋回叠合盆地油气成藏动力学研究的热点问题。运用钻井岩心样品的自生伊利石同位素定年和流体包裹体间接定年方法,探讨分析了鄂尔多斯盆地东北部二叠系多期次油气成藏的时间和期次。含油气砂岩自生伊利石年龄以较宽的时间域分布在178~108 Ma,测年数据的统计分布特征指示二叠系原生油气成藏时间主要集中在175~155 Ma和145~115 Ma两组主值年龄区间,相应的峰值年龄为165 Ma和130 Ma。流体包裹体测温数据的统计分析与其宿主砂岩磷灰石裂变径迹热史模拟路径的投影关系表明,二叠系不同层段共同经历了与90~78 ℃和125~118 ℃两组统计峰温相应的162~153 Ma和140~128 Ma两期原生油气成藏事件,其中的上二叠统则还经历了统计峰温接近98 ℃、峰值年龄接近30 Ma的一期次生油气成藏事件。由此认为,鄂尔多斯盆地东北部二叠系不同层段在中生代早—中期的多旋回沉降增温过程至少经历了165~153 Ma和140~128 Ma的两期原生油气成藏作用,上二叠统则在晚白垩世以来盆地后期抬升改造阶段的构造动热转换过程经历了接近30 Ma的一期次生油气成藏作用。     

Authigenic minerals from the Paola Ridge (southern Tyrrhenian Sea): Evidences of episodic methane seepage

Paola Ridge, along the NW Calabrian margin (southern Tyrrhenian Sea), is one of the few reported deep sea sites of precipitation of authigenic carbonates in the Tyrrhenian Sea. Here, the changing composition of the seeping fluids and the dynamic nature of the seepage induced the precipitation of pyrite, siderite and other carbonate phases. The occurrence of this array of authigenic precipitates is thought to be related to fluctuation of the sulfate-methane transition zone (SMTZ).Concretions of authigenic minerals formed in the near sub-bottom sediments of the Paola Ridge were investigated for their geochemical and isotopic composition. These concretions were collected in an area characterized by the presence of two alleged mud volcanoes and three mud diapirs. The mud diapirs are dotted by pockmarks and dissected by normal faults, and are known for having been a site of fluid seepage for at least the past 40 kyrs. Present-day venting activity occurs alongside the two alleged mud volcanoes and is dominated by CO₂-rich discharging fluids. This discover led us to question the hypothesis of the mud volcanoes and investigate the origin of the fluids in each different domed structure of the study area.In this study, we used stable isotopes (carbon and oxygen) of carbonates coupled with rare earth element (REE) composition of different carbonate and non-carbonate phases for tracing fluid composition and early diagenesis of authigenic precipitates. The analyses on authigenic precipitates were coupled with chemical investigation of venting gas and sea-water.Authigenic calcite/aragonite concretions, from surficial sediments on diapiric structures, have depleted ¹³C isotopic composition and slightly positive δ¹⁸O values. By contrast, siderite concretions, generally found within the first 6 m of sediments on the alleged mud volcanoes, yielded positive δ¹³C and δ¹⁸O values. The siderite REE pattern shows consistent LREE (light REE) fractionation, MREE (medium REE) enrichment and positive Gd and La anomalies. As shown by the REE distribution, the ¹³C-depleted composition and their association with chemosymbiotic fauna, calcite/aragonite precipitated at time of moderate to high methane flux close to the seafloor, under the influence of bottom seawater. Authigenic siderite, on the other hand, formed in the subseafloor, during periods of lower gas discharges under prolonged anoxic conditions within sediments in equilibrium with ¹³C-rich dissolved inorganic carbon (DIC) and ¹⁸O-rich water, likely related to methanogenesis and intermittent venting of deep-sourced CO₂.     

Mid-Cretaceous hydrothermal vents and authigenic carbonates in a transform margin, Basque-Cantabrian Basin (western Pyrenees): a multidisciplinary study

A comprehensive study of authigenic carbonates and associated fauna in Late Albian organic‐rich, deep‐water deposits (the Black Flysch Group) reveals that carbonate precipitation was a by‐product of the anaerobic oxidation of hydrocarbon‐rich hydrothermal fluids. The authigenic carbonates are exposed along the Kardala and Alkolea sea cliffs in the western Pyrenees. The two vent carbonates occur 1 km apart adjacent to the synsedimentary, right‐reverse Mutriku fault, but in contrasting structural domains: the Kardala carbonates occur on a structural ridge (hangingwall) and the Alkolea carbonates are positioned at the base of an erosional scarp (folded downward footwall). The similarity in pattern of the carbonate phases and complex paragenetic events for both vent precipitates implies that hydrothermal fluid generation processes and pore‐water evolution during early and late diagenesis were similar. Nevertheless, a comparison of the geochemistry, fossil fauna and morphology of carbonate structures of both precipitates suggests that the vented hydrocarbon type, flow intensity and temperature of hydrothermal fluids were different. At the Kardala vent, intense focused flow of hot (up to 109 °C), oil‐rich fluids were generated, allowing the development of a relatively abundant chemosynthesis‐based fauna. In contrast, at the Alkolea vent, diffuse flows of warm, thermogenic methane‐rich fluids were expelled to the sea floor and no chemosynthetic fauna developed. These differences are related to the contrasting structural setting of each locality. Similar δ¹³C_org values for both pyrobitumen‐fills and host unit organic matter suggest that the hydrocarbon source was the Black Flysch Group. Contact alteration of these organic‐rich sediments by syndepositional hydrothermal fluids generated hydrothermal petroleum (oil and gas hydrocarbons) which probably migrated updip to the sea floor by contemporary compression tectonics.     

断层泥自生伊利石年龄分析及其在龙门山断裂带的应用

韧性剪切带的活动年龄及其相关的隆升/剥蚀速率可以通过各种同位素技术进行直接测定和计算。相比较而言,由于形成于浅部低温环境,老的碎屑物质和新的重结晶物质相互掺杂,脆性断裂的同位素年龄往往代表的是一个混合年龄,难以反映其真实的活动时间。近些年来,断层泥自生伊利石定年方法在地表脆性断裂的年代学研究中展现出了良好的应用前景。文中介绍了断层泥中自生伊利石的生成过程、形貌特征和定年原理,并简要介绍了样品的处理过程和伊利石多型相对含量的确定方法。近几年,这种方法逐渐被应用于龙门山断裂带及其山前飞来峰活动时代的确定,为青藏高原东缘早期的构造活动提供了直接的年代证据。     

浙南渡船头伊利石矿的热膨胀性及其机理研究

对我国浙南温州渡船头伊利石矿的热膨胀性及其机理进行了研究。结果表明，在室温－１３００℃温度区间内，其热膨胀性表现为先收缩后膨胀再收缩的特性，其中在１３００℃之后不同类型矿石的热膨胀性亦不同。伊利石的这种热膨胀性与其在加热过程中晶体结构及物相的变化密切相关。伊利石矿中的铁质杂质矿物对其热膨胀性有很大影响。     

Illite crystallinity study of the Cretaceous Shimanto Belt in the Akaishi Mountains, eastern Southwest Japan

Abstract Illite crystallinity (IC) analyses in the Upper Cretaceous Shimanto accretionary complex of the southern Akaishi Mountains, eastern Southwest Japan confirm the applicability of this technique for evaluating the grade of diagenesis/metamorphism in a sediment-dominated accretionary complex. Reproducibility analyses of IC values show a variance of about 15% from the mean. Data from three traverses, which transect across-strike sections of ∼25 km, clearly demonstrate that the IC distributions have specific overall trends. The IC values belong to the lQwer anchizone and the zone of diagenesis. The IC distributions may be controlled locally by structural features, but there are no distinct relationships with regional-scale geological structures. This may indicate that the heterogeneous geothermal rise affected the pre-existing structural and diagenetic/metamorphic framework of the accretionary sequence. Along-strike variations of grade tend to increase toward the northeast where a Middle Miocene granitoid occurs. Hence, the original diagenetic/metamorphic framework of this part of the Shimanto Belt was presumably overprinted during the Middle Miocene.     

TEM and XRD determination of crystallite size and lattice strain as a function of illite crystallinity in pelitic rocks

Average crystallite size and mean-square strain of illite in rock specimens and clay separates were measured independently in TEM images and by single-line Fourier (Voigt method) profile analysis of the c. 1 nm peak of XRD patterns for a prograde sequence of pelitic rocks (illite crystallinity indices=0.17–0.58°Δ2θ) from the Gaspé Peninsula, Quebec. The TEM-determined crystallite sizes in clay separates approximate those determined by Fourier profile analyses and those calculated from illite crystallinity indices by the Scherrer equation, with the exception of the diagenetic sample. The crystallite sizes and mean-square strains of illite in rock samples exhibit a trend similar to that determined by profile analyses, but the average crystallite sizes are up to five times larger than those measured for clay separates. TEM images show that all rock samples have a wide range of crystallite sizes, and the proportions of larger crystallites increase with metamorphic grade. The diagenetic illite is defect-rich, fine-grained (mean thickness by volume=c. 70 nm), 1M_d material. Anchizonal illite tends to occur as separate aggregates of small 1M_d and larger 2M₁ crystals (c. 200 nm), comprising arrays of subparallel coalescing packets. The epizone sample has thick (c. 400 nm), defect-free crystals of muscovite occurring in stacks of parallel layers, or subhedral crystals intergrown with large-angle boundaries. Cleaved crystals that are free of intracrystalline layer terminations are dominant in clay separates of all samples, having ranges of smaller sizes with volume-average thicknesses of c. 43, 43, and 81 nm (c. 14, 28, 67 nm by the Voigt method), respectively, for the three zones. The results suggest that illite crystallinity indices do not provide a direct measure of a single microstructural state of illite in rocks, although they yield consistent limits for average crystallite sizes for the anchizone (23 & 48 nm here). Therefore, they serve as a general parameter of the degree of recrystallization on a relative basis, in part because the contributions of all peak-broadening variables (mixed layering, size and strain) decrease regularly with prograde regional metamorphism of pelites. The microstructural changes caused by rock disaggregation are probably a function of those variables as well. The data collectively demonstrate a trend from metastable, defect-rich, small crystals towards a stable assemblage of larger, defect-free crystals, through dissolution of strained crystals and neocrystallization, consistent with the Ostwald step rule.     

阿刀亥矿区CP2煤段粘土岩夹矸研究

内蒙大青山煤田ＣＰ２煤段含粘土岩夹矸多达４０余层。与上覆ＣＰ３砾岩段冲刷接触的煤段顶板和顶部粘土岩夹矸，为伊利石或伊利石－高岭石粘土岩。其下煤段中夹矸及底板为高岭石粘土岩，均发生了不同程度的铵云母化和一水硬铝石化。鳞片状、纤维状、条片状及晶粒假象铵云母沿粘土岩夹矸的节理裂隙呈脉状产出；微、细晶一水硬铝石沿碳质碎屑条带及富有机质的高岭石基质条带分布。这些特征表明，在有Ｋ＾＋离子带入的开放条件下，粘土