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191.
192.
Calibration of the anchizone: a critical comparison of illite 'crystallinity'scales used for definition 总被引:7,自引:0,他引:7
H. J. KISCH 《Journal of Metamorphic Geology》1990,8(1):31-46
Instrumental settings for determination of illite/muscovite 'crystallinity'(half-height width of the 10-Å X-ray diffraction peak) and the limits of the anchimetamorphic zone adopted by various authors fall into several groups.
The variation in the limiting peak widths between the authors that have adopted Kubler's Neuchâtel boundary values of 0.42° and 0.25°Δ2θ can be interpreted in terms of variation in the instrumental settings. The choice of time constants higher than those given by the formula causes peak broadening; this effect is particularly marked at high scan rates. The peak broadening is by constant increments that are virtually independent of the absolute peak width.
The differences between the Kubler (Neuchâtel)-derived limiting values and some other scales are appreciably greater than can be accounted for by these differences in instrumental settings: many of these scales are not equivalent. In particular, the limits adopted by Dunoyer de Segonzac (1969) and subsequent workers at Strasbourg are too broad; their anchizone represents a range of grades of metamorphism lower than that of Kubler, widely overlapping the latter's 'diagenetic'zone. Those adopted by some other, mainly French, authors are too narrow.
The limits of the anchizone should be calibrated by inter-laboratory standards, and the instrumental settings should be specified in full. 相似文献
The variation in the limiting peak widths between the authors that have adopted Kubler's Neuchâtel boundary values of 0.42° and 0.25°Δ2θ can be interpreted in terms of variation in the instrumental settings. The choice of time constants higher than those given by the formula causes peak broadening; this effect is particularly marked at high scan rates. The peak broadening is by constant increments that are virtually independent of the absolute peak width.
The differences between the Kubler (Neuchâtel)-derived limiting values and some other scales are appreciably greater than can be accounted for by these differences in instrumental settings: many of these scales are not equivalent. In particular, the limits adopted by Dunoyer de Segonzac (1969) and subsequent workers at Strasbourg are too broad; their anchizone represents a range of grades of metamorphism lower than that of Kubler, widely overlapping the latter's 'diagenetic'zone. Those adopted by some other, mainly French, authors are too narrow.
The limits of the anchizone should be calibrated by inter-laboratory standards, and the instrumental settings should be specified in full. 相似文献
193.
I. M. Gorokhov M. A. Semikhatov M. M. Arakelyants E. A. Fallick N. N. Mel’nikov T. L. Turchenko T. A. Ivanovskaya T. S. Zaitseva E. P. Kutyavin 《Stratigraphy and Geological Correlation》2006,14(3):260-274
Clay subfractions (SFs) of <0.1, 0.1–0.2, 0.2–0.3, 0.3–0.6, 0.6–2 and 2–5 μm separated from Middle Riphean shales of the Debengda Formation are studied using the TEM, XRD, K-Ar and Rb-Sr isotopic methods. The oxygen and hydrogen isotope compositions in the SFs are studied as well. The low-temperature illite-smectite is dominant mineral in all the SFs except for the coarsest ones. The XRD, chemical and isotopic data imply that two generations of authigenic illite-smectite different in age are mixed in the SFs. The illite crystallinity index decreases in parallel with size diminishing of clay particles. As compared to coarser SFs, illite of fine-grained subfractions is enriched in Al relative to Fe and Mg, contains more K, and reveals higher K/Rb and Rb/Sr ratios. The Rb-Sr age calculated by means of the leachochron (“inner isochron”) method declines gradually from 1254-1272 Ma in the coarsest SFs to 1038-1044 Ma in finest ones, while the K-Ar age decreases simultaneously from 1225–1240 to 1080 Ma. The established positive correlation of δ18O and δD values with dimensions of clay particles in the SFs seems to be also consistent with the mixing systematics. The isotopic systematics along with data on mineral composition and morphology lead to the conclusion that mixedlayer illite-smectite was formed in the Debengda shales during two periods 1211–1272 and 1038–1080 Ma ago. The first period is likely close to the deposition time of sediments and corresponds to events of burial catagenesis, whereas the second one is correlative with the regional uplift and changes in hydrological regime during the pre-Khaipakh break in sedimentation. 相似文献
194.
Conditions of kaolin illitization in the Permo-Triassic sandstones from the SE Iberian Ranges, Spain
J.D. Martín-Martín D. Gmez-Gras T. Sanfeliu A. Permanyer J.A. Núez D. Parcerisa 《Journal of Geochemical Exploration》2006,89(1-3):263
Kaolin is a widespread authigenic clay mineral in the Permo-Triassic sandstones from the marginal areas of the SE Iberian Basin. However, relatively more extensive illitization of kaolin occurs in the SW basin margin compared with the slight occurrence in the NE margin. SEM analysis of sandstones reveals that illite replaced small kaolinite crystals while blocky dickite remained unaltered. Kaolin illitization is suggested to take place in relation to the maximum burial depth reached during Late Cretaceous post-rift stage. Vitrinite reflectance data denotes a maximum burial temperature of 118 °C and 144 °C in the NE basin margin and in the SW basin margin, respectively. Thus, the extent of illitization in the SW margin is attributed to the higher Tpeak reached by the Permo-Triassic succession. Regarding the lack of K-feldspars observed in the sandstones and interbedded mudrocks, the source of K+ is mainly related to the alteration of detrital mica. 相似文献
195.
Hiroyasu Murakami 《Resource Geology》2008,58(1):1-24
Hydrothermal alteration, involving chiefly chlorite and illite, is extensively distributed within host rocks of the Pleistocene Hishikari Lower Andesites (HLA) and the Cretaceous Shimanto Supergroup (SSG) in the underground mining area of the Hishikari epithermal gold deposit, Kagoshima, Japan. Approximately 60% of the mineable auriferous quartz‐adularia veins in the Honko vein system occur in sedimentary rocks of the SSG, whereas all the veins of the Yamada vein system occur in volcanic rocks of the HLA. Variations in the abundance and chemical composition of hydrothermal minerals and magnetic susceptibility of the hydrothermally altered rocks of the HLA and SSG were analyzed. In volcanic rocks of the HLA, hydrothermal minerals such as quartz, chlorite, adularia, illite, and pyrite replaced primary minerals. The amount of hydrothermal minerals in the volcanic rocks including chlorite, adularia, illite, and pyrite as well as the altered and/or replaced pyroxenes and plagioclase phenocrysts increases toward the veins in the Honko vein system. The vein‐centered variation in mineral assemblage is pronounced within up to 25 m from the veins in the peripheral area of the Honko vein system, whereas it is not as apparent in the Yamada vein system. The hydrothermal minerals in sandstone of the SSG occur mainly as seams less than a few millimeters thick and are sporadically observed in halos along the veins and/or the seams. The alteration halos in sandstone of the SSG are restricted to within 1 m of the veins. In the peripheral area of the Honko vein system, chlorite in volcanic rocks is characterized by increasing in Al in its tetrahedral layer and the Fe/Fe + Mg ratio toward the veins, while illite in volcanic rocks has relatively low K and a restricted range of Fe/Fe + Mg ratios. Temperature estimates derived from chlorite geothermometry rise toward the veins within the volcanic rocks. The magnetic susceptibility of tuff breccia of the HLA varies from 21 to less than 0.01 × 10?3 SI within a span of 40 m from the veins and has significant variation relative to that of andesite (27–0.06 × 10?3 SI). The variation peripheral to the Honko vein system correlates with an increase in the abundance of hematite pseudomorphs after magnetite, the percentage of adularia and chlorite with high Fe/Fe + Mg ratios, and the degree of plagioclase alteration with decreasing distance to the veins. In contrast, sedimentary rocks of the SSG maintain a consistent magnetic susceptibility across the alteration zone, within a narrow range from 0.3 to 0.2 × 10?3 SI. Magnetic susceptibility of volcanic rocks of the HLA, especially tuff breccia, could serve as an effective exploration tool for identifying altered volcanic rocks. 相似文献
196.
A series of pyrolysis experiments, utilizing two different immature kerogens (from the Monterey and Green River Formations) mixed with common sedimentary minerals (calcite, illite, or Na-montmorillonite), was conducted to study the impact of the mineral matrix on the bitumen that was generated. Calcite has no significant influence on the thermal evolution of bitumen and also shows virtually no adsorption capacity for any of the pyrolysate. In contrast, montmorillonite and illite, to a lesser extent, alter bitumen during dry pyrolysis. Montmorillonite and illite also display strong adsorption capacities for the polar constituents of bitumen. By this process, hydrocarbons are substantially concentrated within the pyrolysate that is not strongly adsorbed on the clay matrices. The effects of the clay minerals are significantly reduced during hydrous pyrolysis. The strong adsorption capacities of montmorillonite and illite, as well as their thermocatalytic properties, may in part explain why light oils and gases are generated from certain argillaceous source-rock assemblages, whereas heavy immature oils are often derived from carbonate source rocks. 相似文献
197.
广西东攀剖面二叠系顶部粘土矿物特征及古气候意义 总被引:2,自引:1,他引:1
对广西东攀剖面二叠系顶部20个样品中的粘土矿物进行X射线衍射分析。伊利石结晶度值显示这些样品形成于中晚成岩带的地质环境;伊利石、蒙脱石纵向分布规律和伊利石结晶度与伊利石含量的关系表明伊利石除陆源碎屑来源外,可能有部分为蒙脱石伊利石化而成;伊利石结晶度变化曲线和伊蒙混层类型的变化规律表明,本区粘土矿物组合与含量的变化除受到后期成岩作用的影响外,还明显地受沉积因素的控制;伊利石结晶度、伊利石化学指数、高岭石和伊利石的含量、伊蒙混层类型显示东攀剖面以9、10层界线上方5cm为界,古气候由干冷变为湿暖;水介质由偏碱性向酸性转变。 相似文献
198.
Mixed layer clay minerals, vitrinite reflectance and geochemical data from Rock-Eval pyrolysis were used to constrain the burial evolution of the Mesozoic–Cenozoic successions exposed at the Kuh-e-Asmari (Dezful Embayment) and Sim anticlines (Fars province) in the Zagros fold-and-thrust belt. In both areas, Late Cretaceous to Pliocene rocks, show low levels of thermal maturity in the immature stages of hydrocarbon generation and early diagenetic conditions (R0 I–S and Ro% values < 0.5). At depths of 2–4 km, Tmax values (435–450 °C) from organic-rich layers of the Sargelu, Garau and Kazhdumi source rocks in the Kuh-e-Asmari anticline indicate mid to late mature stages of hydrocarbon generation. One dimensional thermal models allowed us to define the onset of oil generation for the Middle Jurassic to Eocene source rocks and pointed out that sedimentary burial is the main factor responsible for measured levels of thermal maturity. Specifically, the Sargelu and Garau Formations entered the oil window prior to Zagros folding in Late Cretaceous times, the Kazhdumi Formation during middle Miocene (syn-folding stage), and the Pabdeh Formation in the Late Miocene–Pliocene after the Zagros folding. In the end, the present-day distribution of oil fields in the Dezful Embayment and gas fields in the Fars region is primarily controlled by lithofacies changes and organic matter preservation at the time of source rock sedimentation. Burial conditions during Zagros folding had minor to negligible influence. 相似文献
199.
The tight sandstones of the Cretaceous Quantou formation are the main exploration target for hydrocarbons in the southern Songliao basin. Authigenic quartz is a significant cementing material in these sandstones, significantly reducing porosity and permeability. For efficient predicting and extrapolating the petrophysical properties within these tight sandstones, the quartz cement and its origin need to be better understood. The tight sandstones have been examined by a variety of methods. The sandstones are mostly lithic arkoses and feldspathic litharenites, compositionally immature with an average framework composition of Q43F26L31, which are characterized by abundant volcanic rock fragments. Mixed-layer illite/smectite (I/S) ordered interstratified with R = 1 and R = 3 is the dominating clay mineral in the studied sandstone reservoirs. Two different types of quartz cementation modes, namely quartz grain overgrowth and pore-filling authigenic quartz, have been identified through petrographic observations, CL and SEM analysis. Homogenization temperatures of the aqueous fluid inclusions indicate that both quartz overgrowths and pore-filling authigenic quartz formed with a continuous process from about 70 °C to 130 °C. Sources for quartz cement produced are the conversion of volcanic fragments, smectite to illite reaction and pressure solution at micro stylolites. Potassium for the illitization of smectite has been sourced from K-feldspar dissolution and albitization. Silica sourced from K-feldspars dissolution and kaolinite to illite conversion is probably only minor amount and volumetrically insignificant. The internal supplied silica precipitate within a closed system where the transport mechanism is diffusion. The quartz cementation can destroy both porosity and permeability, but strengthen the rock framework and increase the rock brittleness effectively at the same time. 相似文献
200.
宁德下洋伊利石矿呈脉状产出,贮存于晚侏罗世南园组火山碎屑岩石中,共发现有3个矿体。矿石可分为石英一伊利石型及叶蜡石伊利石型。矿体受北东向断裂控制,由火山碎屑岩经过热液交代形成。 相似文献