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1.
Calcic diopside megacrysts, called Granny Smith nodules, in the Kimberley area and Jagersfontein kimberlites are sheared, commonly contain lenticles of ilmenite and intergrowths of phlogopite, and have a distinctive apple-green color. These diopsides have Ca(Ca + Mg) > 0.45, Mg(Mg + Fe) > 0.90, 0.2?0.4 wt% TiO2 and 0.5–3 wt% Cr2O3. They have Na > (Al + Cr), in contrast to diopsides in peridotite xenoliths and those that form subcalcic discrete nodules, but in this respect are similar to diopsides in amphibole-bearing MARID nodules and mica-rich glimmerites. Granny Smith megacrysts are not cognate (Kramers, 1979); their parental magmas (in an igneous or metasomatic sense) may have been parts of the spectrum between kimberlites and lamproites.  相似文献   

2.
Sources of sedimentary humic substances: vascular plant debris   总被引:1,自引:0,他引:1  
A modern Washington continental shelf sediment was fractionated densimetrically using either an organic solvent, CBrCl3, or aqueous ZnCl2. The resulting low density materials (<2.06 g/ml) account for only 1% of the sediment mass but contain 25% of the sedimentary organic carbon and 53% of the lignin. The C/N ratios (30–40) and lignin phenol yields (Λ = 8) and compositions indicate that the low density materials are essentially pure vascular plant debris which is slightly enriched in woody (versus nonwoody) tissues compared to the bulk sediment. The low density materials yield approximately one-third of their organic carbon as humic substances and contribute 23% and 14% of the total sedimentary humic and fulvic acids, respectively. Assuming that the lignin remaining in the sedimentary fraction is also contained in plant fragments that yield similar levels of humic substances, then 50% and 30% of the total humic and fulvic acids, respectively, arise directly from plant debris.Base-extraction of fresh and naturally degraded vascular plant materials reveals that significant levels of humic and fulvic acids are obtained using classical extraction techniques. Approximately 1–2% of the carbon from fresh woods and 10–25% from leaves and bark were isolated as humic acids and 2–4 times those levels as fulvic acids. A highly degraded hardwood yielded up to 44% of its carbon as humic and fulvic acids. The humic acids from fresh plants are generally enriched in lignin components relative to carbohydrates and recognizable biochemicals account for up to 50% of the total carbon. Humic and fulvic acids extracted directly from sedimentary plant debris could be responsible for a major fraction of the biochemical component of humic substances.  相似文献   

3.
Bark samples isolated from brown coal deposits in Victoria, Australia, and buried wood from Rhizophora mangle have been studies by high-resolution solid-state nuclear magnetic resonance (NMR) techniques. Dipolar dephasing 13C NMR appears to be a useful method of detecting the presence of tannins in geochemical samples including barks, buried woods, peats and leaf litter. It is shown that tannins are selectively preserved in bark during coalification to the brown coal stage.  相似文献   

4.
Thai silicified woods were examined using electron probe microanalysis, yielding chemical data that characterised the samples into two groups: low and high silica contents (82—94 wt% and 94—98 wt%). The elements analysed in order of abundance include Si > Fe > Ca > Na > Al > Ti > K > Mg > Mn > Zr. Iron plays a major role in the colour range (red, orange, yellow, brown, grey and black) of the samples. Calcium is associated with Fe in the darker colours of the wood. Pseudo-crystallochemistry has been used for the substitution of trace elements for Si4+ in silica polymorphs. The atomic channels that run parallel to the c-axis of silica polymorphs or lattice defects, or even the charge balance for trivalent-ion substitution for Si4+, can accommodate monovalent ions (K+ and Na+). Vacant and atomic cavities, which are charged balanced by trivalent ions [Al3+ or Fe3+ substituting for Si4+], are commonly occupied by divalent ions (Ca2+, Mg2+ and Mn2+). Quadrivalent ions, Ti4+ and Zr4+ are non-structurally incorporated but form clusters of mineral inclusions in the samples. Several other trace-element contents are also in the form of mineral/fluid inclusions hosted in the woods.  相似文献   

5.
6.
Noble gas data are reported for 12 E-chondrites. Combined with literature data, they show that K-Ar ages are >4 Æ for 14 out of 18 meteorites, yet U, Th-He ages are often shorter, perhaps due to late, mild reheating. Cosmic-ray exposure ages differ systematically between types 4 and 6, with E4's mostly below 16 Myr and E6's above 30 Myr. This may mean that the E-chondrite parent body contains predominantly a single petrologic type on the (~ 1 km) scale of individual impacts, in contrast to the more thoroughly mixed parent bodies of the ordinary chondrites.The heavy noble gases consist of at least two primordial components: the usual planetary component (36Ar132Xe ~ 80) and a less fractionated, ‘subsolar’ component (2700 ≤ 36Ar132Xe ≤ 3800). The latter is found in highest concentration in the E4 chondrite South Oman (36Ar = 760 × 10?8cc/g, 36Ar132Xe = 2700). The isotopic compositions of both components are similar to typical planetary values, indicating that some factor other than mass controlled the noble gas elemental ratios. The heavy Xe isotopes occasionally show some of the lowest 134Xe132Xe and 136Xe132Xe ratios measured in bulk chondrites, suggestive of nearly fission-free Xe (e.g. 136Xe132Xe = 0.3095 ± 0.0020). Amounts of planetary gas in E4 E6 chondrites fall in the range for ordinary chondrites of types 4–6, but, in contrast to the ordinary chondrites. fail to correlate with petrologic type or volatile trace element contents. Another unusual feature of E-chondrites is that primordial Ne is present even in most 4's and 5's (20Nep ~ 1 to 7 × 10?8cc/g). with an isotopic composition consistent with planetary Ne.Analyses of mineral separates show that the planetary gases are concentrated in an HF- and HCl-insoluble mineral similar to phase Q, the poorly characterized, HNO3-soluble carrier of primordial gases in carbonaceous and ordinary chondrites. The subsolar gases, on the other hand, are located in an HCl- and HNO3-resistant phase, possibly enstatite or a minor phase included in enstatite. Much of the 129Xer (50% for E4's, > 70% for E6's) is in HCl-resistant but HF-soluble sites, suggestive of a silicate.A similar subsolar component may be responsible for the high 36Ar132Xe ratios of some C3's, unequilibrated ordinary chondrites, and the unique aubrite Shallowater. The planet Venus also has a high ArKr ratio, well above the planetary range, and hence may have acquired its noble gases from an E-chondrite-like material, similar to South Oman.  相似文献   

7.
The carbon isotopic composition of 66 inclusion-containing diamonds from the Premier kimberlite, South Africa, 93 inclusion-containing diamonds and four diamonds of two diamond-bearing peridotite xenoliths from the Finsch kimberlite, South Africa was measured. The data suggest a relationship between the carbon isotopic composition of the diamonds and the chemical composition of the associated silicates. For both kimberlites similar trends are noted for diamonds containing peridotite-suite inclusions (P-type) and for diamonds containing eclogite-suite inclusions (E-type): Higher δ13C P-type diamonds tend to have inclusions lower in SiO2 (ol), Al2O3 (opx, gt), Cr2O3, MgO, Mg(Mg + Fe) (ol, opx, gt) and higher in FeO (ol, opx, gt) and CaO (gt). Higher δ13C E-type diamonds tend to have inclusions lower in SiO2, Al2O3 (gt, cpx), MgO, Mg(Mg + Fe) (gt), Na2O, K2O, TiO2 (cpx) and higher in CaO, Ca(Ca + Mg) (gt, cpx).Consideration of a number of different models that have been proposed for the genesis of kimberlites, their xenoliths and diamonds shows that they are all consistent with the conclusion that in the mantle, regions exist that are characterized by different mean carbon isotopic compositions.  相似文献   

8.
A total of 268 thermal spring samples were analyzed for total soluble As using reduced molybdenum-blue; 27 of these samples were also analyzed for total Sb using flame atomic absorption spectrometry. At Yellowstone the ClAs atomic ratio is nearly constant among neutral-alkaline springs with Cl > 100 mg L?1, and within restricted geographic areas, indicating no differential effects of adiabatic vs. conductive cooling on arsenic. The ClAs ratio increases with silica and decreases with decreasing ClΣCO3; the latter relationship is best exemplified for springs along the extensively sampled SE-NW trend within the Lone Star-Upper-Midway Basin region. The relationship between ClAs and ClΣCO3 at Yellowstone suggests a possible rock leaching rather than magmatic origin for much of the Park's total As flux. Condensed vapor springs are low in both As and Cl. Very high ClAs ratios ( > 1000) are associated exclusively with highly diluted (Cl < 100 mg L?1) mixed springs in the Norris and Shoshone Basins and in the Upper White Creek and Firehole Lake areas of Lower Basin. The high ratios are associated with acidity and/or oxygen and iron; they indicate precipitation of As following massive dilution of the Asbearing high-Cl parent water.Yellowstone Sb ranged from 0.009 at Mammoth to 0.166 mg L?1 at Joseph's Coat Spring. Within basins, the ClSb ratio increases as the ClΣCO3 ratio decreases, in marked contrast to As. Mixed springs also have elevated ClSb ratios. White (1967) and Weissberg (1969) previously reported stibnite (Sb2S3), but not orpiment (As2S3), precipitating in the near surface zone of alkaline geothermal systems.  相似文献   

9.
Dissolved humic material from three locations on the Ogeechee River Estuary near Savannah, GA, was ultrafiltered into three size fractions and used for kinetic experiments with Cu(II). A Cu(II)-humic mixture was reacted with a colorimetric reagent for Cu(II) and absorbance observed from 50 msec to at least 1835 sec corresponding to rate constants from 0.001–40 sec?1. The apparent dissociation rate constants were distributed over a wide range, with most bound Cu(II) having k > 1 sec?1 (t12 < 0.7 sec). Nearly all the variation seen in the kinetic distribution was among size fractions; as size fraction decreased, the distribution of bound Cu(II) shifted to larger rate constants. Location of sampling stations on the estuary had little effect on results.  相似文献   

10.
Experimental quartz solubilities in H2O (Anderson and Burnham, 1965, 1967) were used together with equations of state for quartz and aqueous species (Helgesonet al., 1978; Walther and Helgeson, 1977) to calculate the dielectric constant of H2O (?H2O) at pressures and temperatures greater than those for which experimental measurements (Heger, 1969; Lukashovet al., 1975) are available (0.001 ? P ? 5 kb and 0 ? T ? 600°C). Estimates of ?H2O computed in this way for 2 kb (which are the most reliable) range from 9.6 at 600°C to 5.6 at 800°C. These values are 0.5 and 0.8 units greater, respectively, than corresponding values estimated by Quist and Marshall (1965), but they differ by <0.3 units from extrapolated values computed from Pitzer's (1983) adaptation of the Kirkwood (1939) equation. The estimates of ?H2O generated from quartz solubilities at 2 kb were fit with a power function of temperature, which was then used together with equations and data given by Helgeson and Kirkham (1974a,b, 1976) Helgesonet al. (1981), and Helgeson (1982b, 1984) to calculate Born functions, Debye Hückel parameters, and the thermodynamic properties of Na+, K+, Mg++, Ca++, and other aqueous species of geologic interest at temperatures to 900°C.  相似文献   

11.
Analysis of modern Metasequoia leaves revealed the presence of the structural polyester cutin, guaiacyl lignin units and polysaccharides. Analysis of environmentally decayed Metasequoia leaves revealed that guaiacyl lignin units and cellulose were degraded more than vinyl phenol (the last being the primary pyrolysis product of cutin and plant cuticles) suggesting that cutin is more stable than lignin and cellulose during degradation, contrary to some previous studies. This observation is supported by electron microscopy showing changes in the cellular structure and cuticle of modern, decayed and fossil Metasequoia leaves. Metasequoia fossils from the Eocene of Republic (Washington State) showed a significant aliphatic component, but biopolymeric lignin and polysaccharides were not detected. Fossils from the Eocene of Axel Heiberg revealed the presence of lignin and an aliphatic polymer up to C29 with cellulose, and fossils from the Miocene Clarkia deposit (Idaho) revealed lignin and an aliphatic polymer up to C27 without any polysaccharides. Modern Metasequoia needles heated experimentally in confined conditions generated a macromolecular composition with an aliphatic polymer up to C32 and additional phenolic compounds similar to those present in the fossils. Experimental heating of cutin is known to generate an aliphatic polymer with carbon chain length units <C20. Thus, the n-alkyl component with chain length units >C20 in the heated Metasequoia needles is a product of incorporation of longer chain plant waxes, indicated by the odd/even predominance of the >C27 n-alkanes. The resistant nature of cutin compared to lignin and polysaccharides explains the presence of an n-alkyl component (<C20) in fossil leaves even when polysaccharides are absent and lignin has decayed; cutin and its diagenetically altered products contribute significantly to the presence of aliphatic components in terrestrially derived sedimentary organic matter.  相似文献   

12.
The concentrations of noble gas isotopes of He, Ne and Ar have been measured in eight mineral separates of the Bruderheim chondrite. The cosmic-ray-produced nuclides 21Ne and 38Ar were correlated by a computer least-squares fitting program with the elemental composition in each separate of potential targets for nuclear production yielding the following production equations: [21Ne, 10?8 cm3/g] = k(0.45[Mg] + 0.085[Si] + 0.060[S] + 0.017[Ca] + 0.0044[Fe + Ni]); [38Ar, 10?8 cm3/g] = k(2.6[K] + 0.37[Ca] + 0.08[Ti + Cr + Mn] + 0.021[Fe + Ni]) with elemental concentrations in weight per cent and k equal to the reciprocal of the cosmic-ray exposure age of Bruderheim. The P(S)/P(Cr + Mn + Fe + Ni) weight production ratio for 3He was determined to be 1.53; relative productions of 3He from O, Mg and Si and 21Ne from Al proved to be incalculable.  相似文献   

13.
The relationship between chemical composition and microscopic appearance of present-day wood-derived materials and Victorian xylites and gelified soft brown coal woods, Latrobe Valley, Australia, is discussed. The present-day wood-derived material consists of milled wood and lignin and holocellulose fractions prepared from an angiosperm, Eucalyptus regnans and a gymnosperm, Pinus radiata. The xylites and least gelified soft brown coal woods resemble the P. radiata lignin fraction; the latter contains residual cellulose.The atomic H/C ratio was found to be a useful guide to the degree of gelification. Increase in the degree of gelification was accompanied not only by an increase in the total huminite reflectance, but also by an increase in the reflectance of the individual huminite submacerals. The loss of hymotelinite autofluorescence under ultraviolet and blue light excitation with increase in the degree of gelification of Victorian soft brown coal woods was ascribed primarily to the elimination of cellulose and, possibly, modification of the lignin structure of xylite.  相似文献   

14.
15.
Equations and graphs have been devised to correct for the adverse effects of magnesium upon the Na-K-Ca chemical geothermometer. Either the equations or graphs can be used to determine appropriate temperature corrections for given waters with calculated NaKCa temperatures > 70°C and R < 50, where R = {Mg(Mg + Ca + K)} × 100 with cation concentrations expressed in equivalents. Waters with R > 50 are probably derived from relatively cool aquifers with temperatures approximately equal to the measured spring temperature, irrespective of much higher calculated Na-K-Ca temperatures.  相似文献   

16.
A data base summarising the stability constants of more than 500 complexes is used to calculate speciation pictures for 58 trace elements in model seawater (pH 8.2) and freshwaters (pH 6 and 9). Consideration of the results provides a general summary of the chemical periodicity of the speciation of trace components in natural waters. The polarising power of an element ((cation charge)2/(radius), z2/r) provides a useful index to the degree of hydrolysis in aqueous solution. The fully hydrolysed elements with a high polarising power form distinct groupings in the periodic table. The relative magnitudes of the acid dissociation constants are summarised by Pauling's rules and the speciation of the fully hydrolysed elements in natural waters largely depends on pH and, to a lesser extent, on interactions with the major cations. The remaining cations of low and intermediate polarising power can be subdivided according to their tendency to form covalent bonds. An empirical parameter Δβ(= logβ0MF ? log β0MCl) is used to define (a)-type (Δβ > 2), borderline (a)-type (2 >Δβ > 0), (b)-type (Δβ < ?2) and borderline (b)-type (0 >Δβ > ?2) cations. Again these various categories form coherent groupings on the periodic table. By considering the interactions of cations from the various categories with the inorganic ligands commonly encountered in natural waters it is possible to assign the ligands themselves to ‘hard’ (e.g. F?, SO42?), ‘intermediate’ (e.g. OH?, CO2?3) and ‘soft’ categories (e.g. Cl?). These concepts can be summarised by constructing a Complexation Field Diagram in which the various cations are located on a plot of z2r vs δβ. The extension of the model to include redox equilibria and additional ligands is described.  相似文献   

17.
The Betts Cove ophiolite includes the components of typical ocean crust: pillow lavas, sheeted dikes, gabbros and ultramafics. However, the trace element geochemistry of basaltic rocks is unusual. Three geochemical units are recognized within the lava and dike members. Within the pillow lavas, the geochemical units correspond to stratigraphic units. Upper lavas have ‘normal’ (i.e., typical for ocean floor basalts) TiO2 contents (0.75 to 2.0 wt%), heavy rare earth elements (HREE) values in the range 6–20× chondrites and chondrite-normalized REE patterns with relative LREE depletion. Intermediate lavas have TiO2 contents between 0.30 and 0.50 wt%, HREE contents from 4–7× chondrites and extreme relative LREE depletion. Lower lavas have anomalously low TiO2 contents (<0.30 wt%) and unusual convex-downwards REE patterns with REE abundances around 2–5 × chondrite. These geochemical differences can be explained if the three groups were derived from different mantle sources. Independent mantle sources for the three units are consistent with their different 143Nd144Nd ratios varying at 480 m.y.B.P. from 0.51222 in a lower lava to 0.51238 in an upper lava. The upper lavas may be partial melts of a source similar in composition to that of modern MORB, the intermediate lavas may be from a very depleted oceanic mantle (second stage melt), and the lower lavas may have formed by melting an extremely depleted mantle that had been invaded by a LREE-enriched fluid. A possible tectonic environment where these different sources could be juxtaposed is a back-arc or inter-arc basin.  相似文献   

18.
We used a reproducible seeded growth technique with a pH-stat to study the kinetics of calcite precipitation at 25°C. We performed different experiments at initial Ca2+ and HCO3? concentrations ranging from 0.7–2 and 4–7 mmol L?1, pH values ranging from 8.25 to 8.70, pCO2 values ranging from 0.0006 to 0.01 atm, and ionic strengths ranging from 0.015 to 0.10 mol L?1. With this experimental data set, we used initial rate measurements and integral methods to test several precipitation rate equations. Rate equations that possess a disequilibrium functional dependence, such as the BURTON et al. (1951) dislocation model, forms of the Davies and Jones (1955) model, and the model used by Reddy and Nancollas (1973), did not adequately describe the kinetics of calcite precipitation at pH greater than 8 and pCO2 less than 0.01 atm. Rate equations that describe independent dissolution and precipitation mechanisms with elementary reactions, such as the equation presented by Plummeret al. (1978), and nancollas and Reddy (1971) were more successful. However, Plummer's model did not adequately describe the rate of all experiments due to the presence of an OH? surface term in the precipitation rate equation. The elementary reaction of the Nancollas and Reddy model is written in terms of bulk Ca2+ and CO3? concentrations, and appears to be the most successful model which describes calcite precipitation at pH > 8 and pCO2 < 0.01 atm. The Nancollas and Reddy model, altered to account for varying ionic strengths, adequately described the rate of all experiments and yielded a precipitation rate constant of 118.2 ± 13.9 dm6 mol?1 m?2 s?1, with an apparent Arrhenius activation energy of 48.1 kJ mol?1.  相似文献   

19.
Noble gas elemental and isotopic abundances were measured in steam from four wells in the Baca geothermal reservoir located in the Valles Caldera, New Mexico. The 40Ar36Ar ratio and noble gas elemental abundances relative to 36Ar are all strongly correlated with 1/36Ar, the inverse of the argon content. Ratios of (α,n)-produced 21Ne1 and radiogenic 40Ar1 to total 4He (dominantly radiogenic) are nearly constant at 2.1 × 10?8 and 0.20, respectively. The 3He4He ratio covers a restricted range of 3.9 to 4.8 times atmospheric. The high 3He content of the gas indicates the presence of a helium component ultimately derived from the mantle. Kr and Xe isotopic compositions are close to atmospheric; excess 129Xe1 is <0.25% of the total 129Xe.The high degree of linear correlation among the various noble gas results strongly suggests that the Baca reservoir contains two distinct fluids that are produced in varying proportions from individual wells. The noble gases in fluid A (~2900 mg/1 C1) are air-like, but with lighter gases and isotopes preferentially enriched. The fluid A 36Ar content is low, only 13% that of 10°C air-saturated water (ASW). The second fluid, B (~ 1700 mg/1 C1), is the dominant carrier of the radiogenic and mantle-derived gases. The heavier non-radiogenic gases are preferentially enriched in fluid B, and its 36Ar content is very low, only 5–7% ASW. The source of the noble gases in fluid A is tentatively ascribed to leaching of the relatively young (<1.4 m.y.) volcanic Bandelier Tuff. The radiogenic gases and mantle-derived helium in fluid B suggest a deeper source, possibly including gases escaping from a magma.  相似文献   

20.
The distribution of primordial 3He in the crust of Italy has been investigated through a survey of groundwaters, hot-springs, exploration and production geothermal wells. The mantle-derived component varies from 0% to > 60% and reaches a maximum at Vulcano in the Eolian Islands. 3He anomalies occur where the conductive heat flow is relatively high, but the relationships between heat flow and anomaly are uncertain.The distribution of 3He in the main reservoir and cap rock to the Larderello geothermal system shows that the mantle-derived 3He varies from ~5% to ~40% of total He and reaches a maximum in fluids extracted from a depth of ca. 3 km within the basement. Bomb-produced tritiogenic 3He appears to make a near-negligible contribution. Well 107 at Larderello has been monitored over a period of 17 months and the 3He4He ratio (R) varies from 1.4 to 1.6 times the atmospheric ratio (Ra) whilst He/Ne varies from 9 to 160. A model is proposed for the Larderello geothermal system whereby mantle-derived heat and volatiles are advected to shallow (6–8 km) depths in association with melts and released into the main geothermal reservoir at Larderello in a non-uniform manner possibly associated with fracturing. Isotopic and elemental equilibrium of gaseous species (C, O, H) appears to have taken place in the basement to the main reservoir from where fluid with R/Ra ≥ 3.2 has been extracted.  相似文献   

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