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1.
Mark Wilkinson 《Chemical Geology》2002,191(4):277-283
K-Ar ages of Gulf Coast shales do not correspond to diagenetic ‘events’, but are a combination of inherited detrital ages and authigenic overprints. The key to understanding K-Ar ages of shales is the fate of the 40Ar when the host minerals dissolve or react during the illitisation reaction: is 40Ar incorporated within the illite, or is it lost to the porewaters? Ages are modelled as due to a single illitisation reaction, assuming a uniform precursor sediment and open-system import of K. Both whole-rock and clay mineral fraction data can be reproduced by modelling. The 40Ar incorporated into illite is a surprisingly high proportion (75-100%) of that produced within detrital phases (smectite, K-feldspar, mica), perhaps implying that the illitisation reaction is a solid-state transformation, or that 40Ar is imported into the shales along with incoming K. The model does not provide a good fit to the data below 4000 m, when the illitisation reaction is apparently complete, but shales lose 40Ar by solid-state diffusion or recrystallisation. 相似文献
2.
The argon solubility of 38 liquids in the system Na2O-CaO-MgO-Al2O3-SiO2 (NCMAS) has been determined at 1873 K and 1 bar, the argon concentration of presaturated glasses being measured using a static mass spectrometer. For compositions in the subsystem diopside (CaMgSi2O6), nepheline (NaAlSiO4), albite (NaAlSi3O8), anorthite (CaAl2Si2O8), argon solubility is generally a linear function of the relative proportion of each end member, solubility being lowest in diopside melt (1.53 10−5 cm3 STP · g−1 · bar−1) and highest in albite melt (2.88 10−4 cm3 STP · g−1 · bar−1). For the tectosilicate joins studied (SiO2-Na2Al2O4, SiO2-CaAl2O4, SiO2-MgAl2O4) solubility decreases with decreasing silica content in all cases, being highest for Na-bearing liquids and lowest for Mg-bearing liquids at constant molar silica content. Where comparison is possible our results are in good agreement with data from the literature. When our data are considered in isolation we find that argon solubility shows an excellent correlation with calculated ionic porosity. The covariation of argon solubility and liquid density is also reasonable, that with molar volume less convincing and that with polymerization state (as defined by the ratio of the number of nonbridging oxygens and tetrahedral network forming cations; NBO/T) nonexistent. However, when our data are combined with those from the literature no well constrained correlation between argon solubility and ionic porosity is apparent. Based upon this observation and consideration of the temperature dependence of noble gas solubility it is concluded that ionic porosity is not a universally applicable parameter which may be used to predict noble gas solubility as a function of composition, temperature and pressure. Two new models for calculating argon solubility are proposed, both employing the notion of partial molar argon solubilities. The first uses oxide components, for which partial molar argon solubility is directly proportional to partial molar ionic porosity calculated at 1873 K, irrespective of the temperature of experimental equilibration. The second model, which offers the best fit to the available data, employs tetrahedral units rather than oxides as the proposed melt components. This latter model successfully accounts for reported argon solubilities in simple Al-free systems, in simple Al-bearing systems and in natural liquids. This is interpreted to infer that argon is incorporated in large sites in the liquid structure (such as the space within rings of n-tetrahedra) although further work is required to understand the quantitative links between melt structure and noble gas solubility. 相似文献
3.
采用分阶段加热爆裂法测定了不同成因热液矿床脉石英流体包裹体的氩同位素,计算出各温度段内大气氩的相对含量,从而,总结出大气降水热液矿床、再平衡岩浆水热液矿床等成矿流体的氩同位素组成特征及其演化规律。典型的大气降水热液矿床,其成矿流体以具有高大气Ar组分(约95%-100%)为特征;再平衡岩浆水热液矿床成矿流体的Ar同位素组成特征取决于与其有成因关系的初始岩浆水的Ar同位素组成及矿源层和围岩的性质,产于古老变质岩中的,一般以具有低大气Ar组分(约6%-20%)为特征,其它的再平衡岩浆水热液矿床在主成矿温度范围内一般为50%-60%左右。 相似文献
4.
The Cretaceous–Paleogene boundary (KPgB) was dated by the 40Ar/39Ar method herein from the western interior of North America at 65.48 ± 0.12 Ma (1σ), in good agreement with other recent published estimates. For the Deccan Traps, India, new argon ages as well as others available in the literature, are assessed for reliability based on (a) statistical reliability of plateau/isochron sections and (b) freshness of material dated utilizing the alteration index method. From tholeiitic lavas from the Composite Western Ghats Section (CWGS), only six ages are found to be reliable estimates of the time of crystallization. These ages along with the magnetic polarity of the lavas agree with the geomagnetic polarity time scale (GPTS) at ∼67–64 Ma. Alkaline rocks from the Anjar area of Kutch, provide three reliable ages that suggest a hiatus in lava extrusion around KPgB. For the Rajahmundry basalts, the upper flow’s age defines its formation during chron 29n; a single age from the lower reversed polarity flow appears somewhat dichotomous when plotted against the GPTS. The reliable lava ages indicate the most voluminous (reversed polarity) sections of the CWGS were extruded at a time statistically indistinguishable from that of the KPgB. The Deccan Trap – KPgB faunal extinction hypothesis remains plausible, but must compete with the latest report, favoring a very close temporal connection (∼0.03 m.y.) between the Chixculub (Impact) Crater and the KPgB. 相似文献
5.
基于氮气吸附-核磁共振-氩离子抛光场发射扫描电镜研究川西须五段泥质岩储层孔隙结构 总被引：7，自引：5，他引：2
微观孔隙作为泥质岩的有效储集空间,其孔隙结构参数是作为气藏评价及资源量估算的重要依据。本文应用氮气吸附法(NAM)、核磁共振法(NMR)、氩离子抛光及场发射扫描电镜(AIP-FESEM)研究川西须五段泥质岩微观孔隙特征,结果表明:1氩离子抛光及场发射扫描电镜在表征微观孔隙形态与类别时有一定优势,但定量表征孔隙参数时,受图像二值化阈值的影响,表征结果偏差较大,可结合氮气吸附法来定量表征其孔径大小;2核磁共振受岩石骨架影响小,能够更精细反映岩石的物性条件,可定量计算孔隙度与可动流体饱和度,但对样品的孔隙形态反映较差;3综合上述三种方法,在须五段泥质岩中可识别出一定量的纳米级中、大孔,孔径大多介于几十纳米到几百纳米之间,孔隙连通性差,孔隙度主要介于2.3%~7.4%之间,孔隙类型以粒间孔、晶间孔最发育,有机孔隙、微裂缝次之,粒内孔隙最不发育。总体而言,融合了三种技术方法能更精确、更全面地反映泥质岩孔隙结构特征,能得到更完善的储层孔隙结构参数,在定量表征泥质岩孔隙结构中具有广泛的应用前景。 相似文献
6.
The Machaoying fault zone extends along the southern margin of the North China Craton (NCC) and controlled the regional structures and hydrothermal mineral systems in this area. The fault underwent at least two major deformational phases, as revealed by macro- and micro-structural observations from a well-developed segment of the fault in the Hongzhuang–Baitu area, located south of the Xiong'er Mountains. Early ductile deformation is characterized by thrusting from north to south, which was subsequently overprinted by late brittle faulting. Syntectonic strain shadows of biotite are preserved around rotated porphyroclasts of quartz amygdales in mylonite. The biotite yields a 40Ar–39Ar plateau age of 524.9 ± 1.9 Ma, which is interpreted as the time of regional thrusting along the Machaoying fault zone. The thrusting may be temporally correlated with an Early Cambrian discontinuity in sedimentation observed in the rocks sequences of the NCC, suggesting a compressional regime in this area and a craton-wide tectonic event. Many 540–500 Ma tectonic events have been previously identified in the Qinling–Qilian–Kunlun Orogenic Belt of central China and in massifs in northeastern China, both of which surround the NCC, and some of these were interpreted to be associated with assembly of Gondwana. However, paleomagnetic data indicate that the NCC was unlikely to have been connected with Gondwana in the Early Cambrian and thus our new biotite date cannot record deformation along the Gondwanan margin. Dating of K-feldspar from a quartz–K-feldspar vein formed along one of the brittle faults of the Machaoying fault zone yields a much younger 40Ar–39Ar plateau age of 119.5 ± 0.7 Ma. This is a minimum age for the brittle deformation along the southern margin of the NCC, which also overlaps the age of widespread gold and molybdenum mineralization in the region. 相似文献
7.
As part of the DarkSide program of direct dark matter searches using two-phase argon TPCs, a prototype detector with an active volume containing 10 kg of liquid argon, DarkSide-10, was built and operated underground in the Gran Sasso National Laboratory in Italy. A critically important parameter for such devices is the scintillation light yield, as photon statistics limits the rejection of electron-recoil backgrounds by pulse shape discrimination. We have measured the light yield of DarkSide-10 using the readily-identifiable full-absorption peaks from gamma ray sources combined with single-photoelectron calibrations using low-occupancy laser pulses. For gamma lines of energies in the range 122–1275 keV, we get light yields averaging 8.887±0.003(stat)±0.444(sys) p.e./keVee. With additional purification, the light yield measured at 511 keV increased to 9.142±0.006(stat) p.e./keVee. 相似文献
8.
Metamorphic fluid origins in the Osborne Fe oxide–Cu–Au deposit,Australia: evidence from noble gases and halogens 总被引：1，自引：1，他引：0
The Osborne iron oxide–copper–gold (IOCG) deposit is hosted by amphibolite facies metasedimentary rocks and associated with
pegmatite sheets formed by anatexis during peak metamorphism. Eleven samples of ore-related hydrothermal quartz and two pegmatitic
quartz–feldspar samples contain similarly complex fluid inclusion assemblages that include variably saline (<12–65 wt% salts)
aqueous and liquid carbon dioxide varieties that are typical of IOCG mineralisation. The diverse fluid inclusion types present
in each of these different samples have been investigated by neutron-activated noble gas analysis using a combination of semi-selective
thermal and mechanical decrepitation techniques. Ore-related quartz contains aqueous and carbonic fluid inclusions that have
similar 40Ar/36Ar values of between 300 and 2,200. The highest-salinity fluid inclusions (47–65 wt% salts) have calculated 36Ar concentrations of approximately 1–5 ppb, which are more variable than air-saturated water (ASW = 1.3–2.7 ppb). These fluid
inclusions have extremely variable Br/Cl values of between 3.8 × 10−3 and 0.3 × 10−3, and I/Cl values of between 27 × 10−6 and 2.4 × 10−6 (all ratios are molar). Fluid inclusions in the two pegmatite samples have similar 40Ar/36Ar values of ≤1,700 and an overlapping range of Br/Cl and I/Cl values. High-salinity fluid inclusions in the pegmatite samples
have 2.5–21 ppb 36Ar, that overlap the range determined for ore-related samples in only one case. The fluid inclusions in both sample groups
have 84Kr/36Ar and 129Xe/36Ar ratios that are mainly in the range of air and air-saturated water and are similar to mid-crustal rocks and fluids from
other settings. The uniformly low 40Ar/36Ar values (<2,200) and extremely variable Br/Cl and I/Cl values do not favour a singular or dominant fluid origin from basement-
or mantle-derived magmatic fluids related to A-type magmatism. Instead, the data are compatible with the involvement of metamorphic
fluids that have interacted with anatectic melts to variable extents. The ‘metamorphic’ fluids probably represent a mixture
of (1) inherited sedimentary pore fluids and (2) locally derived metamorphic volatilisation products. The lowest Br/Cl and
I/Cl values and the ultra-high salinities are most easily explained by the dissolution of evaporites. The data demonstrate
that externally derived magmatic fluids are not a ubiquitous component of IOCG ore-forming systems, but are compatible with
models in which IOCG mineralisation is localised at sites of mixing between fluids of different origin.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorised users. 相似文献
9.
尽管40Ar和36Ar之间质量相差达1/10,但是受放射性成因40Ar的影响,一般认为难以进行氩同位素分馏研究.本文通过自行设计的一套氩扩散迁移实验分析系统,对比研究了氩在不同的扩散介质条件下扩散迁移前后氩同位素组成变化情况,证实氩在致密的扩散介质条件下以分子流形式从一个储库向另一个储库的迁移过程中,由于36Ar和40Ar的迁移速率不同,扩散后的40Ar/36Ar值比扩散前的值要小,也即发生了氩同位素分馏.氩同位素分馏的特征表现为最初的一段时间内分馏程度逐步增强,在一定时间后,由于储库之间压力逐渐达到平衡,分馏程度逐步减小.研究自然界中存在的氩同位素分馏,不仅可以判别油气田中油气运移的方向、增强油气远景评价和地球化学勘探,而且对深源岩浆的起源、迁移等研究也可提供新的研究思路和途径. 相似文献
10.
Focusing on physical processes, we aim at constraining the dynamics of argon (Ar), a biogeochemically inert gas, within first year sea ice, using observation data and a one-dimensional halo-thermodynamic sea ice model, including parameterization of gas physics. The incorporation and transport of dissolved Ar within sea ice and its rejection via gas-enriched brine drainage to the ocean, are modeled following fluid transport equations through sea ice. Gas bubbles nucleate within sea ice when Ar is above saturation and when the total partial pressure of all three major atmospheric gases (N2, O2 and Ar) is above the brine hydrostatic pressure. The uplift of gas bubbles due to buoyancy is allowed when the brine network is connected with a brine volume above a given threshold. Ice-atmosphere Ar fluxes are formulated as a diffusive process proportional to the differential partial pressure of Ar between brine inclusions and the atmosphere. Two simulations corresponding to two case studies that took place at Point Barrow (Alaska, 2009) and during an ice-tank experiment (INTERICE IV, Hamburg, Germany, 2009) are presented. Basal entrapment and vertical transport due to brine motion enable a qualitatively sound representation of the vertical profile of the total Ar (i.e. the Ar dissolved in brine inclusions and contained in gas bubbles; TAr). Sensitivity analyses suggest that gas bubble nucleation and rise are of most importance to describe gas dynamics within sea ice. Ice-atmosphere Ar fluxes and the associated parameters do not drastically change the simulated TAr. Ar dynamics are dominated by uptake, transport by brine dynamics and bubble nucleation in winter and early spring; and by an intense and rapid release of gas bubbles to the atmosphere in spring. Important physical processes driving gas dynamics in sea ice are identified, pointing to the need for further field and experimental studies. 相似文献