首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 15 毫秒
1.
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   

2.
Definition of low-grade metamorphic zones using illite crystallinity   总被引：4，自引：0，他引：4  
Abstract Two major problems which exist in the use of illite crystallinity to define low-grade metamorphic zones are the variety of values chosen for the zone boundaries and the persistent use of three different indices of crystallinity. Although measurement techniques, which cause much of the interlaboratory variation, can be standardized, it is shown that there is, nevertheless, significant additional variation which demands calibration on standards. The greatest variations are due to choices of different absolute values of crystallinity to define zone boundaries. The problem of relating measurements between different indices is approached by fitting mathematical relationships to pairs of measurements from the same sample. A power–law relationship is a satisfactory fit to the Kubler–Weaver and Weaver–Weber pairs, while the Kubler–Weber indices are linearly related. These relationships are used to transform definitions of the diagenetic zone, anchizone and epizone from one index to the others, although they apply strictly only to the data set from which they are derived. This results in compatibility between the three zones and shows that previous definitions to the anchizone in different indices have been chosen at incompatible values. The boundaries of Kubler's anchizone (0.42 and 0.25 Δ2θ) are 0.4 and 0.215 Δ2θ in this study, which become 5.1 and 14.6 in the Weaver index and 278 and 149 in the Weber index. An error analysis shows that percentage errors in both Kubler and Weaver indices increase with crystallinity; the Kubler measurements are marginally preferred at all grades.  相似文献   

3.
40Ar/39Ar step-heating data were collected from micron to submicron grain-sizes of correlative illite- and muscovite-rich Cambrian pelitic rocks from the western United States that range in metamorphic grade from the shallow diagenetic zone (zeolite facies) to the epizone (greenschist facies). With increasing metamorphic grade, maximum ages from 40Ar/39Ar release spectra decrease, as do total gas ages and retention ages. Previous studies have explained similar results as arising dominantly or entirely from the dissolution of detrital muscovite and precipitation/recrystallization of neo-formed illite. While recognizing the importance of these processes in evaluating our results, we suggest that the inverse correlation between apparent age and metamorphic grade is controlled, primarily, by thermally activated volume diffusion, analogous to the decrease in apparent ages with depth observed for many thermochronometers in borehole experiments. Our results suggest that complete resetting of the illite/muscovite Ar thermochronometer occurs between the high anchizone and epizone, or at roughly 300 °C. This empirical result is in agreement with previous calculations based on muscovite diffusion parameters, which indicate that muscovite grains with radii of 0.05–2 μm should have closure temperatures between 250 and 350 °C. At high anchizone conditions, we observe a reversal in the age/grain-size relationship (the finest grain-size produces the oldest apparent age), which may mark the stage in prograde subgreenschist facies metamorphism of pelitic rocks at which neo-formed illite/muscovite crystallites typically surpass the size of detrital muscovite grains. It is also approximately the stage at which neo-formed illite/muscovite crystallites develop sufficient Ar retentivity to produce geologically meaningful 40Ar/39Ar ages. Results from our sampling transect of Cambrian strata establish a framework for interpreting illite/muscovite 40Ar/39Ar age spectra at different stages of low-grade metamorphism and also illuminate the transformation of illite to muscovite. At Frenchman Mtn., NV, where the Cambrian Bright Angel Formation is at zeolite facies conditions, illite/muscovite 40Ar/39Ar data suggest a detrital muscovite component with an apparent age ≥967 Ma. The correlative Carrara Fm. is at anchizone conditions in the Panamint and Resting Spring Ranges of eastern California, and in these locations, illite/muscovite 40Ar/39Ar data suggest an early Permian episode of subgreenschist facies metamorphism. The same type of data from equivalent strata at epizone conditions (greenschist facies) in the footwall of the Bullfrog/Fluorspar Canyon detachment in southern Nevada reveals a period of slow-to-moderate Late Cretaceous cooling.  相似文献   

4.
由伊利石结晶度研究桂西右江地区区域极低级变质作用   总被引：10，自引：0，他引：10  
运用伊利石结晶度Kübler指数将桂西右江地区下三叠统罗楼群和中三叠统百逢组下段划归为浅层变质带(K.I△2θ°为0.22～0.25);将中三叠统百逢组上段和河口组划归为近变质带,中三叠统百逢组上段为高级近变质带(K.I△2θ°为0.26～0.33);中三叠统上部河口组为低级近变质带(K.I△2θ°为0.38～0.40),不排除局部为成岩带的可能.地层柱自下向上,伊利石结晶度Kübler指数由小变大,变质程度由高变低,而且,变质作用级别与岩层在地层柱中位置协调以及变质带边界与地层界线趋于一致,证明为区域埋藏极低级变质作用.凌云明山金矿区剖面矿体和百逢组各层段伊利石结晶度Kübler指数为0.42～0.50,属成岩带,且没有明显时空变化规律.  相似文献   

5.
This study uses clay mineral assemblages, illite ??crystallinity?? (IC), chlorite ??crystallinity?? (CC), illite polytypes, the b cell-dimension of K-white mica, mineral geothermo-geobarometers and homogenization temperatures of fluid inclusions to investigate the transition from diagenesis to metamorphism in a 7?km thick Triassic flysch sequence in the well Hongcan 1, eastern Tibetan plateau. The 7,012.8?m deep borehole penetrated flysch of Upper to the Middle Triassic age and represents a unique chance to characterize low temperature metamorphic processes in an unusually thick sedimentary sequence developed on thickened continental crust. Mineral assemblage analysis reveals a burial metamorphic pattern with kaolinite and chlorite/smectite mix-layer phases present in the upper 1,500?m, and illite/smectite mixed-layer phases extending to a depth of 3,000?m. The metamorphic index mineral, graphite, was detected in sedimentary rock below 5,000?m using Raman spectroscopy. There exists a good correlation between IC and CC within the prograde burial sequence; with CC anchizonal boundaries of 0.242 and 0.314°2?? (upper and lower boundaries, respectively) corresponding to Kübler??s IC limits at 0.25 and 0.42°2??. Illite polytypism also shows an increase in the 2M 1 polytype with increasing depth, with ca. 60?% 2M 1 abundance compared to the 1M type at the surface, to 100?% 2M 1 at the bottom of the borehole. Fluid inclusion analysis show HHC-rich bearing fluids correspond to the diagenetic zone, CH4-rich bearing fluids appear at transitional zone from diagenetic to low anchizone and H2O-rich bearing fluids mark the high anchizone to epizone. Based on chlorite chemical geothermometer, calcite?Cdolomite geothermo-barometers as well as homogenization temperature of fluid inclusions, a paleotemperature range of 118?C348?°C is estimated for the well with a pressure facies of low to intermediate type.  相似文献   

6.
40Ar/39Ar incremental-release analyses were carried out on whole-rock and constituent white mica (illite)-rich size fractions (0.63–1 to 6.3–20 m) within two very-low grade, penetratively cleaved metatuffs of contrasting anchizonal metamorphic grade (northeastern Rheinisches Schiefergebirge, Federal Republic of Germany). One sample from the upper anchizone displays internally concordant 40Ar/39Ar spectra with plateau ages ranging between ca. 316 and 325 Ma. These are similar to conventional K-Ar ages determined for the whole-rock and size fractions. Together the isotopic results suggest that cleavage formed at ca. 320 Ma during a concomitant very-low grade metamorphism. This is consistent with biostratigraphic controls which suggest that metamorphism and cleavage formation occurred during the Westphalian.A metatuff sample from the middle anchizone records more internally discordant 40Ar/39Ar age spectra with total-gas ages ranging from 366 to 372 Ma. These are ca. 35–45 Ma older than corresponding conventional K-Ar ages, indicating marked recoil-loss of 39Ar occurred during irradiation. Transmission electron microscopy reveals that white mica grains within size fractions from the upper anchizone sample have clearly defined, straight edges whereas those within the middle anchizone samples are embayed and diffuse. This results in an increase in surface/volume ratio and therefore greater susceptibility for recoil-loss of 39Ar in the middle anchizone sample. Grain-edge morphology appears to be a major factor in determining the extent of recoil-loss of 39Ar during 40Ar/39Ar analysis of fine-grained size fractions.  相似文献   

7.
The Oued Belif 48 and Koudiat El Halfa 5 borehole samples have been analysed in order to reveal the mineralogical composition of the Triassic successions and their burial history within the geological evolution of the Tethysian southern margin. Oued Belif 48 borehole belongs to Nefza district which is a part of the “Nappe zone” (Tellian unit, north-western Tunisia). Koudiat El Halfa 5 borehole crosses the Koudiat El Halfa diapir (north–west of the north–south axis, Central Atlas). In this paper, the burial degree of evaporitic Triassic samples was determined by the “illite crystallinity” index and by the evolution of the other phyllosilicates, essentially chlorite, talc and illite/chlorite and illite/smectite mixed layers. The studied samples of the two boreholes are characterized by the presence of abundant clay minerals. The <2-μm grain-size fraction of the samples is mostly composed of illite, chlorite and smectite and may contain a slight percentage of swelling layers (illite/smectite and illite/chlorite). The illite crystallinity value measured on ethylene glycol solvated oriented mounts of the Oued Belif 48 samples oscillates globally between 1 and 2.5 characterizing the epizonal zone with a range of 300–400 °C temperatures. The measures of Koudiat El Halfa 5 samples crystallinity index show a value ranging from 2 to 4, which indicates the anchizone and early epizone burial stage (temperatures around 200 °C). These data can be explained by Miocene magmatic activities characterizing the Triassic material of Nefza district and also by burial phenomena effects.  相似文献   

8.
Modern ooids from Joulters Cay, when baked at 500 °C, turn various shades of black depending upon the organic content. Mucus-rich laminae occur at quasi-regular intervals of a few micrometres within the cortex. When mucus is still present, it turns black; when it is absent, there is a gap. The cortex consists of two types of aragonite: (1) 'batons' of circular cross-section capped by a single 0·1-μm (100-nm) ball, which can be interpreted as a single nannobacteria cell that precipitated the baton; (2) elongate crystals made of multiple rows of minute balls of about 0·03 μm (30 nm), which may or may not have been small organisms in the size range of viruses. There are also some crystals that show no evidence of organic precipitation. Hardground cementation begins with the formation of a terminal mucus-rich ring on the ooid that bakes black and is crowded with 0·1-μm (100-nm) balls. Some ooids are then joined by a meniscus also made of mucus with aragonite crystals. The final, most abundant hardground cement forms a fur of inorganic aragonite crystals often shaped like plywood sheets, although some 'organic', elongate crystals composed of ≈0·03 μm (≈30 nm) balls are also found in the later cement. For a century, ooids have been known to be closely associated with organic matter; this paper goes further and proposes that the bulk of the ooid may be precipitated by nannobacterial processes. Hardground formation, in the beginning, may also be a microbiological process, but most cementation is accomplished inorganically.  相似文献   

9.
Six samples of a single carbonate-rich unit of the Swiss Préalpes, progressively metamorphosed from diagenesis to deep anchizone, yield 40Ar/39Ar spectra with variably developed staircase patterns, consistent with mixtures of detrital mica and neocrystallized mixed-layer illite/smectite. The lowest temperature heating steps for different size fractions (2–6?μm and 6–20?μm) converge to ～40?Ma providing an imprecise, maximum age of regional metamorphism. A method is described for distinguishing and quantifying the amount of pre-existing detrital mica versus neoformed illite layer in the illite/smectite formed during Tertiary Alpine metamorphism by comparison of X-ray diffraction patterns with Newmod© simulations. In the least metamorphosed samples the illite/smectite contains ～65% neoformed illite, and this illite accounts for approximately 17% of all dioctahedral phyllosilicate minerals in the rock (e.g., detrital mica and illite/smectite). In contrast, the illite/smectite from the more strongly metamorphosed samples contains >97% neoformed illite, which accounts for ～70% to >90% of all dioctahedral phyllosilicate minerals. Phyllosilicate morphologies viewed by scanning electron microscopy are consistent with these estimates. A process of dissolution/reprecipitation is inferred as a mechanism for the growth of the neoformed phyllosilicates. A plot of neoformed illite content versus 40Ar/39Ar total fusion age yields a near-linear curve with an extrapolated age of 27?Ma for 100% neoformed dioctahedral phyllosilicates. This age is interpreted as the time of incipient metamorphism and is consistent with independent biostratigraphic constraints. Model 40Ar/39Ar age spectra constructed with the XRD simulation results correspond well to the experimental data and illustrate the changes in degassing properties of progressively metamorphosed mixtures of detrital mica and neoformed illite.  相似文献   

10.
Carbonate mud from three small isolated carbonate platforms of Belize (Central America) is largely a product of the breakdown of skeletal grains. The composition of the 63-20- and 20-4-µm fractions of 37 samples was determined by point counting under SEM; composition of the <4-µm fraction was assessed qualitatively under SEM. The 63-4-µm fractions are dominated by fragments of mollusks, the codiacean alga Halimeda, and other skeletal types. About one-third of the particles in the 63-4-µm fractions remained unidentified, probably due to obliteration of diagnostic features by early recrystallization processes such as micritization. Nanograins (<1 µm) and short (3-5 µm) aragonite needles are most common in the <4-µm fraction. These grains are interpreted to be largely fragments of codiacean algae (Halimeda, Penicillus). The 20-4- and <4-µm sediment fractions are composed of 80 and 75% aragonite on average, respectively. Trace element composition of strontium averages 7,900 ppm in the 20-4-µm fraction and in codiacean algae samples, and 5,600 ppm in the <4-µm fraction. Geochemical (trace element) data also argue against inorganic aragonite precipitation within the water column, and favor a skeletal origin. The lower strontium contents in the <4-µm fraction as compared with the 20-4-µm fraction may also be a consequence of early recrystallization processes.  相似文献   

11.
周健  王河锦 《地质论评》2002,48(4):361-364
运用X射线衍射分析技术，计算了成岩带、近变质带粘土矿物C^*方向的粒度。根据阿尔卑斯造山带前陆碎屑岩粘土矿物粒度与伊利石结晶指数的关系，推导出了伊利石、绿泥石、蒙脱石、伊蒙混层、高岭石和叶蜡石的c^*方向粒度变化趋势曲线。结果表明，大多数产于成岩带和近变质带的粘矿物其c6*方向粒工为几至几十纳米。成岩带和近为质带是一维天然纳为级土帮物的产地。  相似文献   

12.
The Neoproterozoic and Lower Paleozoic along the profile of Yuanguping in western Hunan Province, China underwent anchimetamorphism. The illite crystallinity (IC) of the <2 μm fractions ranges from 0.23-0.34°△2θfor the Neoproterozoic to 0.23-0.35°△A2θ for the Lower Paleozoic (calibrated with the Kisch IC set, Kisch, 1991). This indicates that the metamorphic grade of the Neoproterozoic and Lower Paleozoic is the anchizone. The peak metamorphic temperature is estimated to be 290-210℃. This result does not agree with the greenschist or subgreenschist facies of the Banxi Group, nor with the lower-greenschist facies or sedimentary cover of the Sinian to Lower Paleozoic, as most previous researchers thought. The illite (K-mica) b0 values range from 0.9074 to 0.8963 (nm) for the Neoproterozoic and the Lower Paleozoic. Based on cumulative frequency curves of the illite (K-mica) b0, the peak metamorphic pressure of the Banxi Group was derived to be of a type that is slightly higher than that of the N. Ne  相似文献   

13.
White mica from the Liassic black shales and slates in Central Switzerland was analysed by transmission electron microscopy (TEM) and electron microprobe to determine its textural and compositional evolution during very low-grade prograde metamorphism. Samples were studied from the diagenetic zone, anchizone and epizone (T ≈100°–450 °C). Phyllosilicate minerals analysed include illite/smectite (I/S), phengite, muscovite, brammallite, paragonite, margarite and glauconite. Textural evolution primarily is towards larger, more defect-free grains with compositions that approach those of their respective end-members. The smectite-to-illite transformation reduced the amounts of the exchange components SiK?1Al?1, MgSiAl?2, and Fe3+Al?1. These trends continue to a lesser degree in the anchizone and epizone. Correlations between the proportion of smectite in I/S and the composition of I/S indicate that smectite layers may contain a high layer charge. Illite in I/S bears a compositional resemblance to macrocrystalline phengite in some samples, but is different in others. Paragonite first appears in the upper diagenetic zone or lower anchizone as an interlayer-deficient brammallite, and it may be mixed with muscovite on the nanometre scale. Owing to the small calculated structure factor for paragonite-muscovite superstructures, conventional X-ray powder diffraction cannot distinguish between mixed-layer structures and a homogeneous compositionally intermediate solid solutions. However, indirect TEM evidence shows that irregularly shaped domains of Na- and K-rich mica exist below 10 nm. Subsequent coarsening of domains at higher grades produced discrete paragonite grains at the margins of muscovite crystals or in laths parallel to the basal plane of the host muscovite. Margarite appears in the epizone and follows a textural evolution similar to paragonite in that mixtures of margarite, paragonite, and muscovite may initially occur on the nanometre scale. However, no evidence of interlayer-poor margarite has been found.  相似文献   

14.
Thirty-five illite and muscovite concentrates were extracted from Triassic and Permian claystones, shales, slates and phyllites along a cross-section from the diagenetic Alpine foreland (Tabular Jura and borehole samples beneath the Molasse Basin) to the anchi- and epimetamorphic Helvetic Zone of the Central Alps. Concentrates and thin sections were investigated by microscopic, X-ray, infrared, Mössbauer, thermal (DTA and TG), wet chemical, electron microprobe, K-Ar, Rb-Sr, 40Ar/39Ar and stable isotope methods.With increasing metamorphic grade based on illite crystallinity data (XRD and IR) the following continuous changes are observed: (i) the 1Md2M1 polymorph transformation is completed in the higher grade anchizone; (ii) K2O increases from 6–8 wt. % (diagenetic zone) to 8.5–10% (anchizone) to 10–11.5% (epizone), reflecting an increase in the total negative layer charge from 1.2 to 2.0; (iii) a decrease of the chemical variation of the mica population with detrital muscovite surviving up to the anchizone/ epizone boundary; iv) a shift of an endothermic peak in differential thermal curves from 500 to 750° C; (v) K-Ar and Rb-Sr apparent ages of the fraction <2 m decrease from the diagenetic zone to the epizone, K-Ar ages being generally lower than Rb-Sr ages. The critical temperature for total Ar resetting is estimated to be 260±30° C. K-Ar and Rb-Sr ages become concordant when the anchizone/ epizone boundary is approached. The stable isotope data, on the other hand, show no change with metamorphic grade but are dependent on stratigraphic age.These results suggest that the prograde evolution from 1 Md illite to 2M1 muscovite involves a continuous lattice restructuration without rupture of the tetrahedral and octahedral bonds and change of the hydroxyl radicals, however this is not a recrystallization process. This restructuration is completed approximately at the anchizone/epizone boundary. The isotopic data indicate significant diffusive loss of 40Ar and 87Sr prior to any observable lattice reorganization. The restructuration progressively introduces a consistent repartition of Ar and K in the mineral lattices and is outlined by the 40Ar/39Ar age spectra.Concordant K-Ar and Rb-Sr ages of around 35-30 Ma. with concomitant concordant 40Ar/39Ar release spectra are representative for the main phase of Alpine metamorphism (Calanda phase) in the Glarus Alps. A second age group between 25 and 20 Ma. can probably be attributed to movements along the Glarus thrust (Ruchi phase), while values down to 9 Ma., in regions with higher metamorphic conditions, suggest thermal conditions persisting at least until the middle Tortonian.  相似文献   

15.
Incipient metamorphism in the Lower Palaeozoic marginal basin of Wales   总被引：1，自引：0，他引：1  
Abstract A diagenctic through anchizone to epizone transition is demonstrated in pelitic rocks of the Lower Palaeozoic marginal basin of Wales by examination of variations in phyllo-silicate mineralogy, illite crystallinity and bo parameter of white micas. This transition represents a temperature range from ∼ 150°C to ∼ 400°C and the metamorphism is of a low-pressure facies series type, with a geothermal gradient of ∼ 40°Ckm-1. Variations in grade can be correlated largely with the original basin and shelf form, suggesting a depth-related metamorphism. However, in areas closer to the site of Caledonian plate collision an increasingly syn-tectonic metamorphic event is apparent.
Correlation of pelite data with metabasite assemblages is variable, the most consistent relationship being between epizone crystallinity values andepidote-actinolite (greenschist facies) assemblages. Diagenetic clay mineral assemblages are found associated with prehnite-pumpellyite assemblages in metabasites and it is suggested that the latter represent non-buffered, and therefore non-diagnostic, assemblages.  相似文献   

16.
内蒙古东北地区上古生界伊利石研究   总被引：3，自引：1，他引：2  
胡大千  于介江 《岩石学报》2009,25(8):2017-2022
内蒙古东北地区上古生界主要是一套泥质岩石,其详细深入的矿物学工作尚不多见.本文利用JSM-6700F场发射电镜及INCA能谱仪,探讨了伊利石在成岩.极低级变质作用过程中的行为.采用D/max-2500 X-射线衍射仪,研究了伊利石的结晶度、多型和b0值.伊利石结晶度变化于0.28～0.77,除去构造应力对伊利石结晶度指数值的影响,研究区伊利石结晶度指数应>0.34,反映晚古生代地层主体属于晚期成岩带和低级近变质带.伊利石(白云母)多型分三种类型,分别是1Md型、1Md+2M1混合型和2M1型,是晚期成岩带和低级近变质带的产物.伊利石(白云母)b0值变化于8.9892 ～9.0404 之间,b0平均值9.0196 ,属中压相.  相似文献   

17.
X-ray diffraction methods for estimating the metamorphic grade of diagenetic, anchizone and epizone in metapelites are reviewed and applied to samples from a 7000?m+ borehole in western China and surface samples from the surrounding Zoigê area. Kübler’s illite crystallinity (IC) measurements provide more consistent results than calculated values of percentage of illite in the I/S mixed layers and percentage of I/S mixed layers. Down-borehole IC values display a typical burial metamorphic relationship between stratigraphic level and IC. A method for preparing very low grade metamorphic maps is described, and isograds plotted on a regional geological map at selected values of IC, delineating a high temperature diagenetic zone, an anchizone, and an epizone. The map shows that IC values are controlled by stratigraphic level in the north of the study area (i.e. burial metamorphism), and proximity to an igneous intrusive body in the south (i.e. contact metamorphism).  相似文献   

18.
Abstract Fairly strong (r= 0.75–0.85) positive linear correlations were found between crystallinity indices (peak widths) measured on the first two basal reflections of chlorite and those of illite–muscovite in <2-μm fractions of a representative shale–slate–phyllite series from Palaeozoic and Mesozoic formations of northeast Hungary. The metamorphic grade ranges from late or deep diagenesis through anchizone to epizone conditions. Chlorite crystallinity values measured on air-dried and ethylene-glycol-solvated samples suggest that the effects of expandable interlayers are negligable, especially in the higher grade (～temperature) part of the series. However, the greater scattering of crystallinity values for the chlorite 001 reflection compared to those of the 002 reflection may be related to the effects of minor amounts of interlayered and/or discrete smectite and/or vermiculite. With increasing metamorphic grade and advancing equilibrium recrystallization, the chlorite compositions in different samples become more homogenous. No correlation exists between crystallinity and changes in chlorite composition as estimated from the intensity ratios of basal reflections. Hence an increase of domain size and a decrease of lattice distortion with increasing grade (～temperature) may be decisive factors affecting chlorite crystallinity. Chlorite crystallinity can be applied as a reliable regional, statistical technique complementary with, or instead of, the illite crystallinity method. The illite and chlorite crystallinity scales used here are related to Kübler's epi-, anchi- and diagenetic zones and correlated with coal rank, conodont colour alteration and mineral facies data. As the effects of the detrital white mica can be observed even in the <2-μm fractions of anchizonal metapelites, the anchizone boundaries determined solely on the base of ‘fixed’illite crystallinity values may vary with amounts of detrital and newly formed muscovite–illite. Hence a complex approach utilizing more than one method for determination of grade is preferred for petrogenetic purposes, even if relationships between crystallinity scales, coal rank and mineral facies also vary strongly in different tectonic settings and lithologies.  相似文献   

19.
伊利石结晶度及其在低温变质研究中若干问题的讨论   总被引：4，自引：0，他引：4  
王河锦  陶晓风  M.Rahn 《地学前缘》2007,14(1):151-156
文中介绍与伊利石结晶度相关的伊利石矿物新的定名方案;讨论了伊利石结晶度的结晶学基础与Scherrer方程式的关系;讨论了三个重要的伊利石结晶度指数Weaver、K櫣bler和Weber指数的关系,并介绍推导的Weaver、K櫣bler和Weber指数的理论关系式;评价了衍射仪测量条件对结晶度数值的影响和三套伊利石结晶度标样的作用以及成岩带、变质带与葡萄石-绿纤石相、沸石相、绿纤石-阳起石亚相对比的依据。建议(1)停用绢云母一词;(2)建立可供各实验室使用的具有晶体结构和晶体化学参数和多型参数的伊利石结晶度标样;(3)建议多开展规范的可进行国际对比的低温变质研究,划分出与国际上一致的成岩带和近变质带,不仅利于低温变质作用理论的研究,而且由于成岩带到近变质转变带是重要的煤气油的生成带,也利于中国煤气油资源的勘探与开发,利于国民经济的长远持续发展。  相似文献   

20.
王河锦  徐庆生 《地质论评》2000,46(6):588-593
根据实验结果,衍射峰半高宽随接收狭缝增大而呈二次工线线性增大。扫描速度与扫描步长的确定应遵守Ｗａｎｇ（１９９４）提出的关系式,并确定在相对误差小于〈５％的范围内。固定样品条件,选定最优实验条件下使用国际标样标定系统偏差是伊利石结晶测量中必不可少的重要步骤。不固定样品条件和实验条件,同一样品的伊利石工值将因条件的变化而不同;固定样品和实验条件而不使用国际标样标定系统偏差,则无法与他人数据进行对比,其  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号