Isotopic evidence for the origin of sulfur in the Herrin (no. 6) coal member of Illinois     

Linda M. Westgate  Thomas F. Anderson 《International Journal of Coal Geology》1984,4(1):1-20

The sulfur isotopic composition of the Herrin (No. 6) Coal from several localities in the Illinois Basin was measured. The sediments immediately overlying these coal beds range from marine shales and limestones to non-marine shales. Organic sulfur, disseminated pyrite, and massive pyrite were extracted from hand samples taken in vertical sections.The $\text{δ}{}^{34}\text{S}$ values from low-sulfur coals (< 0.8% organic sulfur) underlying nonmarine shale were +3.4 to +7.3%₀ for organic sulfur, +1.8 to +16.8%₀ for massive pyrite, and +3.9 to +23.8%₀ for disseminated pyrite. In contrast, the $\text{δ}{}^{34}\text{S}\text{values from high-sulfur coals}$ (> 0.8% organic sulfur) underlying marine sediments were more variable: organic sulfur, ?7.7 to +0.5%₀, pyrites, ?17.8 to +28.5%₀. In both types of coal, organic sulfur is typically enriched in ³⁴S relative to pyritic sulfur.In general, δ ³⁴S values increased from the top to the base of the bed. Vertical and lateral variations in δ ³⁴S are small for organic sulfur but are large for pyritic sulfur. The sulfur content is relatively constant throughout the bed, with organic sulfur content greater than disseminated pyrite content. The results indicate that most of the organic sulfur in high-sulfur coals is derived from post-depositional reactions with a ³⁴S-depleted source. This source is probably related to bacterial reduction of dissolved sulfate in Carboniferous seawater during a marine transgression after peat deposition. The data suggest that sulfate reduction occurred in an open system initially, and then continued in a closed system as sea water penetrated the bed.Organic sulfur in the low-sulfur coals appears to reflect the original plant sulfur, although diagenetic changes in content and isotopic composition of this fraction cannot be ruled out. The wide variability of the δ ³⁴S in pyrite fractions suggests a complex origin involving varying extents of microbial H₂S production from sulfate reservoirs of different isotopic compositions. The precipitation of pyrite may have begun soon after deposition and continued throughout the coalification process.  相似文献   

Precambrian sedimentary carbonates: carbon and oxygen isotope geochemistry and implications for the terrestrial oxygen budget   总被引：2，自引：0，他引：2  

Manfred Schidlowski  Rudolf Eichmann  Christian E. Junge 《Precambrian Research》1975,2(1):1-69

Carbon isotope values of 260 Precambrian limestones and dolomites (most of them being substantially unaltered) have yielded an overall mean of $\text{δ}{}^{13}\text{C}\text{= +0.4 ± 2.7‰}$ vs. PDB; the corresponding oxygen values average at $\text{δ}{}^{13}\text{O = +20.0 ± 4.2‰}$ vs. SMOW. Like the overall mean, the δ ¹³C values furnished by individual carbonate occurrences are, as a rule, fairly “modern” and almost constant as from the very beginning of the sedimentary record. A remarkable exception are the “heavy” dolomites of the Middle Precambrian Lomagundi Group, Rhodesia, with $\text{δ}{}^{13}\text{C}\text{= +9.4 ± 2.0‰}$ vs. PDB. As a result of our measurements, the sporadic occurrence in the geological past of anomalously heavy carbonates seems to be established.The approximate constancy around zero per mill of the δ ¹³C values of marine carbonates through geologic time would imply a corresponding constancy of the relative proportion of organic carbon in the total sedimentary carbon reservoir since about 3.3 · 10⁹ y ago (with C_org/C_total ? 0.2). Utilizing this ratio and current models for the accumulation of the sedimentary mass as a function of time, we get a reasonable approximation for the absolute quantity of organic carbon buried in sediments and, accordingly, of photosynthetic oxygen released. Within the constraints of our model (based on a terrestrial degassing constant λ = 1.16 · 10^?9 y^?1) close to 80% of the amount of oxygen contained in the present oxygen budget should have been released prior to 3 · 10⁹ y ago. Since geological evidence indicates an O₂-deficient environment during the Early and most parts of the Middle Precambrian, there is reason to believe that the distribution of this oxygen between the “bound” and the “molecular” reservoir was different from that of today (with effective O₂-consuming reactions bringing about an instantaneous transfer to the crust of any molecular oxygen released). Accordingly, the amount of C_org in the ancient sedimentary reservoir as derived from our isotope data is just a measure of the gross amount of photosynthetic oxygen produced, withholding any information as to how this oxygen was partitioned between the principal geochemical reservoirs. As a whole, the carbon isotope data accrued provide evidence of an extremely early origin of life on Earth since the impact of organic carbon on the geochemical carbon cycle can be traced back to almost 3.5 · 10⁹y.  相似文献   

Aragonite from deep sea ultramafic rocks     

E. Bonatti  J.R. Lawrence  P.R. Hamlyn  D. Breger 《Geochimica et cosmochimica acta》1980,44(8):1207-1214

Aragonite mineralization was observed in serpentinized peridotites from the Romanche and Vema Fracture Zones in the Atlantic and the Owen Fracture Zone in the Indian Ocean, either in veins or as radial aggregates in cavities within the serpentinites. Evidence of incipient dissolution of the aragonite crystals was observed in one case. The aragonites tend to have lower Mg content (< 0.03%) and higher Sr content (> 0.95%) relative to other marine aragonites. Their ${}^{18}\text{O}{}^{16}\text{O}$, ${}^{13}\text{C}{}^{12}\text{C}$ and ${}^{87}\text{Sr}{}^{86}\text{Sr}$ isotopic ratios suggest the aragonite was deposited at ocean floor temperatures from solutions derived from sea water circulating in fissures and fractures within the ultramafic rocks. The ${}^{18}\text{O}{}^{16}\text{O}$ ratios of the serpentines indicate serpentinization occurred at higher temperatures, probably deeper in the crust. Low-T reactions between circulating seawater and Mg-silicates (primarily serpentine and pyroxenes) caused high pH and enrichment of Mg and Ca in the solution, conditions favoring carbonate precipitation. Aragonite was formed rather than calcite presumably because the high Mg²⁺ concentration in the solution inhibited calcite precipitation. The high Sr content of the aragonites is probably related, at least in part, to their low temperature of formation. Opaque mineral grains containing over 8% NiO and over 40% MnO were observed concentrated along the margins of some of the aragonite veins, suggesting that Ni is one of the elements mobilized during reactions between ultramafic rocks and circulating seawater.  相似文献   

Geochimie et teneurs isotopiques des systèmes saisonniers de dissolution de la calcite dans un sol sur craie     

L. Dever  R. Durand  J.Ch. Fontes  P. Vachier 《Geochimica et cosmochimica acta》1982,46(10):1947-1956

In a soil developed on the Cretaceous chalk of the Eastern Paris basin, calcite dissolution begins at the surface. The soil water is rapidly saturated in calcite. Calcite dissolution follows two different pathways according to seasonal pedoclimatic conditions.During winter: the soil is only partly saturated in water and the CO₂ partial pressure is low (Ca 10^?3 atm.). As a consequence total inorganic dissolved carbon (TIDC) is a hundred times the carbon content of the gaseous phase. Equilibrium is usually observed between the two phases. It is a closed system. The measured carbon 14 activity (87,5%) and ¹³C content ($\text{δ}{}_{\mathrm{tidc}}{}^{13}\text{C = ?12,2\%0}$) of the drainage water are very close to theoretical values calculated for an ideal mixing system between gaseous and mineral phases (respectively characterized by the following isotopic values: $\text{δ}{}_{\mathrm{G}}{}^{13}\text{C = ?21,5\%0}$; $\text{A}{}_{\mathrm{G}}{}^{14}\text{C = 118\%}$; $\text{δ}{}_{\mathrm{M}}{}^{13}\text{C = +2,9\%0}$; $\text{A}{}_{\mathrm{M}}{}^{14}\text{C = 28\%}$).During spring and summer: the soil moisture decreases, the input of biogenic CO₂ induces an increase of the soil CO₂ partial pressure (Ca from 3.10^?3 atm to 7.10^?3 atm). The carbon content of the gaseous phase is higher by an order of magnitude compared to winter conditions. Therefore the aqueous phase is undersaturated in CO₂ with respect to the latter. This disequilibrium occurs as a result of unbalanced rates of CO₂ dissolution and CO₂ effusion toward atmosphère. It is an open system. The carbon isotopic ratio of the aqueous phase is regulated by that of the gaseous phase, as demonstrated by the agreement between measured and calculated isotopic compositions (respectively δ_{L mes} = from ?9,4%0 to ?11,5%0, δ_{l calc} = from ?9,8%0 to ?13,9%0 A_{L mes} = 119%, A_{L calc} = from 119% to 125%).The solutions originating from both systems (open and closed) move downwards without significant mixing together. It has also been observed that no significant variation of the TIDC isotopic composition occurs during precipitation of secondary calcite.  相似文献   

Prediction of Gibbs free energies of calcite-type carbonates and the equilibrium distribution of trace elements between carbonates and aqueous solutions     

Dimitri A Sverjensky 《Geochimica et cosmochimica acta》1984,48(5):1127-1134

A linear correlation exists between the standard Gibbs free energies of formation of calcite-type carbonates (MCO3) and the corresponding conventional standard Gibbs free energies of formation of the aqueous divalent cations (M2+) at 25 °C and 1 bar ΔGMCO30 = m(ΔGf,M2+0) ? 141,200 cal · mole?1 where m is equal to 0.9715. This relationship enables prediction of the standard free energies of formation of numerous hypothetical carbonates with the calcite structure. Associated uncertainties typically range from about ± 250 to 600 cal · mole?1. An important consequence of the above correlation is that the thermodynamic equilibrium constant for the distribution of two trace elements M and N between carbonate mineral and aqueous solution at 25 °C and 1 bar is proportional to the free energy difference between the corresponding two aqueous ions: In Combination of predicted standard free energies, entropies and volumes of carbonate minerals at 25°C and 1 bar with standard free energies of aqueous ions and the equation of state in Helgesonet al. (1981) enables prediction of the thermodynamic equilibrium constant for trace element distribution between carbonates and aqueous solutions at elevated temperatures and pressures. Interpretation of the thermodynamic equilibrium constant in terms of concentration ratios in the aqueous phase is considerably simplified if pairs of divalent trace elements are considered that have very similar ionic radii (e.g., $\text{Sr}{}^{\mathrm{2+}}\text{Pb}{}^{\mathrm{2+}}$, $\text{Mg}{}^{\mathrm{2+}}\text{Zn}{}^{\mathrm{2+}}$). In combination with data for the stabilities of complex ions in aqueous solutions, the above calculations enable useful limits to be placed on the concentrations of trace elements in hydrothermal solutions.  相似文献   

The variation of the marine ${}^{87}\text{Sr}{}^{86}\text{Sr}$ ratio during Phanerozonic time: interpretation using a flux model     

Garrett W. Brass 《Geochimica et cosmochimica acta》1976,40(7):721-730

The ${}^{87}\text{Sr}{}^{86}\text{Sr}$ ratio in sea water has varied over geologic time due to the addition of strontium to the sea from rocks with a variety of ${}^{87}\text{Sr}{}^{86}\text{Sr}$ ratios. The measurements by Petermanet al. (Geochim. Cosmochim. Acta34, 105–120, 1970) of the value of the marine ${}^{87}\text{Sr}{}^{86}\text{Sr}$ ratio have been confirmed by several other workers and by some new measurements on JOIDES samples. They form the basis of a model calculation of the relative proportions of ‘basaltic’ (${}^{87}\text{Sr}{}^{86}\text{Sr}\text{= 0.704}$) and ‘granitic’ (${}^{87}\text{Sr}{}^{86}\text{Sr}\text{= 0.718}$) strontium being supplied to the sea. For the last 200 million years, the proportions of these two sources appear to reflect the history of global tectonics; ‘basaltic’ during rifting and increasingly ‘granitic’ during the present episodes of uplift and continental collision  相似文献   

Strontium isotope geology of the South Mountain batholith,Nova Scotia     

D.B. Clarke  A.N. Halliday 《Geochimica et cosmochimica acta》1980,44(8):1045-1058

The South Mountain batholith of southwestern Nova Scotia is a large, peraluminous, granodiorite-granite complex which intrudes mainly greenschist facies metasediments of the Cambro-Ordovician Meguma Group. Using Rb-Sr isochrons constructed from whole rocks and mineral separates, the present study shows a variation in age and initial ratios of the intrusive phases of the batholith as follows: biotite granodiorite (371.8 ± 2.2 Ma, (${}^{87}\text{Sr}{}^{86}\text{Sr}\text{)}{}_{\mathrm{i}}$ ranges from 0.7076 ± 0.0003 to 0.7090 ± 0.0003, with the average = 0.7081); adamellite (364.3 ± 1.3 Ma, $\text{(}{}^{87}\text{Sr}{}^{86}\text{Sr}\text{)}{}_{\mathrm{i}}\text{= 0.70942 ± 35}$); porphyry (361.2 ± 1.4 Ma, $\text{(}{}^{87}\text{Sr}{}^{86}\text{Sr}\text{)}{}_{\mathrm{i}}\text{= 0.71021 ± 119}$); using λ⁸⁷Rb = 1.42 × 10^?11yr^?1.A suite of Meguma country rock samples showed a variation of ${}^{87}\text{Sr}{}^{86}\text{Sr}\text{= 0.7113?0.7177}$ at the time of intrusion of the batholith. A number of xenoliths of this material occurring in the marginal granodiorite had partially equilibrated isotopically with the granodiorite at a higher ${}^{87}\text{Sr}{}^{86}\text{Sr}$ ratio than elsewhere in the granodiorites. This evidence demonstrates that isotopic (and probably some accompanying bulk chemical) contamination by the Meguma rocks has been an important factor in determining the ultimate chemical composition and mineralogy of the South Mountain batholith.The $\text{(}{}^{87}\text{Sr}{}^{86}\text{Sr}\text{)}{}_{372}\text{= 0.7081}$ of the early granodiorites indicates that the parent magma of the South Mountain batholith was derived from a source unlike the Meguma Group. The precise nature of the source region cannot be determined by Rb-Sr work unless the degree of contamination with Megumalike material is known.  相似文献   

The statistical analysis and interpretation of imperfectly-fitted Rb-Sr isochrons from polymetamorphic terrains     

M. Cameron  K.D. Collerson  W. Compston  R. Morton 《Geochimica et cosmochimica acta》1981,45(7):1087-1097

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The enrichment of 34S in the solfataras of the Nea Kameni volcano,Santorini archipelago,Greece     

H.W. Hubberten  H. Nielsen  H. Puchelt 《Chemical Geology》1975,16(3):197-205

Sulfur isotope investigations carried out on elemental sulfur and sulfates of the Nea Kameni solfataras, Santorini, Aegean Sea, Greece, show a clear enrichment in the heavy sulfur isotope ³⁴S against the assumed primordial ${}^{32}\text{S}{}^{34}\text{S}$ ratio of 22,220. Within the same crater, different vents, only a few meters apart from each other, produced δ differences up to 10‰, which remained constant for several years. This enrichment is most probably due to contamination by heavy sulfur from a nonvolcanic source. An enrichment in the same order of magnitude was observed in sulfur of recent and older lavas ($\text{δ}{}^{34}\text{S}\text{= ?1 ? +11‰}$).Potential contaminants like sulfide sulfur in hydrothermal ore veins of Athinios has a δ ³⁴S mean value close to 0‰, sulfide and sulfate in the sedimentary basement has a δ ³⁴S mean value of $\text{+2.6‰.}$ Seawater sulfate from the area gives a value of $\text{δ}{}^{34}\text{S}\text{= 20‰}$, while sulfide from bacterial reduction of pore-water sulfate in recent iron ore sediments has δ ³⁴S values between ?8 and $\text{?5‰.}$ Sulfate remaining in the pore solutions gave $\text{δ}{}^{34}\text{S}\text{= +27‰}$.The most probable explanation for the observed high δ ³⁴S values in the solfataric sulfur and in some of the lavas of the Santorini area is contamination of the volcanic vents by Mediterranean Sea water.  相似文献   

The incorporation of Mg²⁺ and Sr²⁺ into calcite overgrowths: influences of growth rate and solution composition     

Alfonso Mucci  John W Morse 《Geochimica et cosmochimica acta》1983,47(2):217-233

The concentrations of Mg²⁺ and Sr²⁺ incorporated within calcite overgrowths precipitated from seawater and related solutions, determined at 25°C, were independent of the precipitation rate over approximately an order of magnitude. The saturation states used to produce this range of precipitation rates varied from 3 to 17 depending on the composition of the solution.The amount of Mg²⁺ incorporated in the overgrowths was not directly proportional to $\text{Mg}{}^{\mathrm{2+}}\text{Ca}{}^{\mathrm{2+}}$ in solution over the entire range (1–20) of ratios studied. Below a ratio of 7.5, the overgrowth was enriched in MgCO₃ relative to what is predicted by the constant distribution coefficient measured above a ratio of 7.5. This increased MgCO₃ correlates with the relative enrichment of adsorbed Mg²⁺. Above a ratio of 7.5 the concentration of MgCO₃ in the calcite overgrowths followed a classical thermodynamic behavior characterized by a constant distribution coefficient of 0.0123 (±0.008 std dev).The concentration of SrCO₃ incorporated in the overgrowths was linearly related to the MgCO₃ content of the overgrowths, and is attributed to increased solubility of SrCO₃ in calcite due to the incorporation of the smaller Mg²⁺ ions.The kinetic data indicate that the growth mechanism involves the adsorption of the cations on the surface of the calcite prior to dehydration and final incorporation. It is suggested that dehydration of cations at the surface is the rate controlling step.  相似文献   

Kinetic and thermodynamic factors controlling the distribution of SO₃²⁻ and Na⁺ in calcites and selected aragonites     

Eurybiades Busenberg  L. Niel Plummer 《Geochimica et cosmochimica acta》1985,49(3):713-725

Significant amounts of SO₄^2?, Na⁺, and OH^? are incorporated in marine biogenic calcites. Biogenic high Mg-calcites average about 1 mole percent SO₄^2?. Aragonites and most biogenic low Mg-calcites contain significant amounts of Na⁺, but very low concentrations of SO₄^2?. The SO₄^2? content of non-biogenic calcites and aragonites investigated was below 100 ppm. The presence of Na⁺ and SO₄^2? increases the unit cell size of calcites. The solid-solutions show a solubility minimum at about 0.5 mole percent SO₄^2? beyond which the solubility rapidly increases. The solubility product of calcites containing 3 mole percent SO₄^2? is the same as that of aragonite. Na⁺ appears to have very little effect on the solubility product of calcites. The amounts of Na⁺ and SO₄^2? incorporated in calcites vary as a function of the rate of crystal growth. The variation of the distribution coefficient ($\text{D}$) of SO₄^2? in calcite at 25.0°C and 0.50 molal NaCl is described by the equation $\text{D = k}{}_0\text{+ k}{}_1\text{R}$ where $\text{k}{}_0$ and $\text{k}{}_1$ are constants equal to $\text{6.16 × 10}{}^{\mathrm{?6}}$ and $\text{3.941 × 10}{}^{\mathrm{?6}}$, respectively, and $\text{R}$ is the rate of crystal growth of calcite in mg·min^?1·g^?1 of seed. The data on Na⁺ are consistent with the hypothesis that a significant amount of Na⁺ occupies interstitial positions in the calcite structure. The distribution of Na⁺ follows a Freundlich isotherm and not the Berthelot-Nernst distribution law. The numerical value of the Na⁺ distribution coefficient in calcite is probably dependent on the number of defects in the calcite structure. The Na⁺ contents of calcites are not very accurate indicators of environmental salinities.  相似文献   

Strontium isotopic studies of the volcanic rocks of the Saunda arc,Indonesia, and their petrogenetic implications     

D.J Whitford 《Geochimica et cosmochimica acta》1975,39(9):1287-1302

Pleistocene and Recent lavas from the Sunda arc range from those showing affinities with the island arc tholeiitic series, through a spectrum of calc-alkaline to high-K alkaline rocks. The tholeiitic rocks have relatively low ${}^{87}\text{Sr}{}^{86}\text{Sr}$ ratios averaging 0–7043; the calc-alkaline rocks show a wide range (from 0.7038 to 0.7059, averaging 0.7048); the high-K alkaline rocks average 0.7045. A rhyolitic ignimbrite from Sumatra has an ${}^{87}\text{Sr}{}^{86}\text{Sr}$ ratio of 0.7139.The relationship between ${}^{87}\text{Sr}{}^{86}\text{Sr}$ and major and trace element geochemistry is variable and complex. Lavas from the same volcano sometimes show significant differences in ${}^{87}\text{Sr}{}^{86}\text{Sr}$ despite close geochemical relationships. Rocks of the calc-alkaline suite show a regular decrease in ${}^{87}\text{Sr}{}^{86}\text{Sr}$ from West Java to Bali and there is some evidence for increasing ${}^{87}\text{Sr}{}^{86}\text{Sr}$ with increasing depth to the Benioff zone. Calc-alkaline and tholeiitic rocks from the Sunda arc have significantly higher ${}^{87}\text{Sr}{}^{86}\text{Sr}$ ratios than those from other island arcs, except from those arcs where continental crustal involvement has been inferred (e.g. New Zealand).A model of ⁸⁷Sr enrichment due to isotopic equilibration of oceanic crust with sea water and disequilibrium melting in the slab and/or mantle is favoured to explain the Sr isotopic composition of the tholeiitic and normal calc-alkaline lavas. Calc-alkaline lavas with high ${}^{87}\text{Sr}{}^{86}\text{Sr}$ ratios are best explained by either sialic contamination, or the presence of alkali basalt as a component of the downgoing slab. The Sr isotopic data for the high-K alkaline lavas suggest a mantle origin. The high ${}^{87}\text{Sr}{}^{86}\text{Sr}$ ratio in the Lake Toba rhyolite implies a crustal origin.  相似文献   

Experimental paleotemperature equation for planktonic foraminifera     

Jonathan Erez  Boaz Luz 《Geochimica et cosmochimica acta》1983,47(6):1025-1031

Small live individuals of Globigerinoides sacculifer which were cultured in the laboratory reached maturity and produced garnets. Fifty to ninety percent of their skeleton weight was deposited under controlled water temperature (14° to 30°C) and water isotopic composition, and a correction was made to account for the isotopic composition of the original skeleton using control groups.Comparison of. the actual growth temperatures with the calculated temperature based on paleotemperature equations for inorganic CaCO₃ indicate that the foraminifera precipitate their CaCO₃ in isotopic equilibrium. Comparison with equations developed for biogenic calcite give a similarly good fit. Linear regression with Craig's (1965) equation yields: $\text{t = ?0.07 + 1.01}\text{t}\text{?}\text{(r= 0.95)}$ where t is the actual growth temperature and $\text{t}\text{?}$ Is the calculated paleotemperature. The intercept and the slope of this linear equation show that the familiar paleotemperature equation developed originally for mollusca carbonate, is equally applicable for the planktonic foraminifer G. sacculifer.Second order regression of the culture temperature and the delta difference (δ¹⁸Oc ? δ¹⁸Ow) yield a correlation coefficient of r = 0.95: $\text{t}\text{?}\text{= 17.0 ? 4.52(δ}{}^{18}\text{Oc ? δ}{}^{18}\text{Ow) + 0.03(δ}{}^{18}\text{Oc ? δ}{}^{18}\text{Ow)}{}^2$$\text{t}\text{?}\text{, δ}{}^{18}\text{Oc}$ and δ¹⁸Ow are the estimated temperature, the isotopic composition of the shell carbonate and the sea water respectively.A possible cause for nonequilibnum isotopic compositions reported earlier for living planktonic foraminifera is the improper combustion of the organic matter.  相似文献   

Rutile solubility and titanium coordination in silicate melts     

James E Dickinson  Paul C Hess 《Geochimica et cosmochimica acta》1985,49(11):2289-2296

The solubility of rutile has been determined in a series of compositions in the K₂O-Al₂O₃-SiO₂ system ($\text{K}{}^1\text{=}\text{K}{}_2\text{O}\text{(K}{}_2\text{O}$ + Al₂O₃) = 0.38–0.90), and the CaO-Al₂O₃-SiO₂ system ($\text{C}{}^1\text{=}\text{CaO}\text{(CaO + Al}{}_2\text{O}{}_3\text{)}\text{= 0.47–0.59}$). Isothermal results in the KAS system at 1325°C, 1400°C, and 1475°C show rutile solubility to be a strong function of the $\text{K}{}^1$ ratio. For example, at 1475°C the amount of TiO₂ required for rutile saturation varies from 9.5 wt% ($\text{K}{}^1\text{= 0.38}$) to 11.5 wt% ($\text{K}{}^1\text{= 0.48}$) to 41.2 wt% ($\text{K}{}^1\text{= 0.90}$). In the CAS system at 1475°C, rutile solubility is not a strong function of $\text{C}{}^1$. The amount of TiO₂ required for saturation varies from 14 wt% ($\text{C}{}^1\text{= 0.48}$) to 16.2 wt% ($\text{C}{}^1\text{= 0.59}$).The solubility changes in KAS melts are interpreted to be due to the formation of strong complexes between Ti and K⁺ in excess of that needed to charge balance Al³⁺. The suggested stoichiometry of this complex is K₂Ti₂O₅ or K₂Ti₃O₇. In CAS melts, the data suggest that Ca²⁺ in excess of A1³⁺ is not as effective at complexing with Ti as is K⁺. The greater solubility of rutile in CAS melts when $\text{C}{}^1$ is less than 0.54 compared to KAS melts of equal $\text{K}{}^1$ ratio results primarily from competition between Ti and Al for complexing cations (Ca vs. K).TiK_β x-ray emission spectra of KAS glasses ($\text{K}{}^1\text{= 0.43–0.60}$) with 7 mole% added TiO₂, rutile, and Ba₂TiO₄, demonstrate that the average Ti-O bond length in these glasses is equal to that of rutile rather than Ba₂TiO₄, implying that Ti in these compositions is 6-fold rather than 4-fold coordinated. Re-examination of published spectroscopic data in light of these results and the solubility data, suggests that the 6-fold coordination polyhedron of Ti is highly distorted, with at least one Ti-O bond grossly undersatisfied in terms of Pauling's rules.  相似文献   

Etude systématique des isotopes de l'oxygène,du carbone et du strontium dans les carbonatites     

Françoise Pineau  Marc Javoy  Claude J Allegre 《Geochimica et cosmochimica acta》1973,37(11):2363-2377

${}^{18}\text{O}{}^{16}\text{O}$, ${}^{13}\text{C}{}^{12}\text{C}$ and ${}^{87}\text{Sr}{}^{86}\text{Sr}$ ratios have been measured on the same samples for carbonatite complexes. The results show that besides the ‘carbonatite box’ of Tayloret al. (1967) there exist higher δ¹⁸O and δ¹³C values than can be explained by late magmatic or deuteric processes. These processes correspond to high concentrations of CO₂ and lead to big enrichments in ¹⁸O and ¹³C as well as in some ‘volatile’ elements. Strontium results are consistent with a model of selective contamination of deep-seated material by highly radiogenic strontium. The whole study leads to the opinion that parent magmas of carbonatites differentiated in a crustal environment with or without significant contamination.  相似文献   

A strontium isotopic study of Smackover brines and associated solids,southern Arkansas     

Alan M. Stueber  Paul Pushkar  Ernest A. Hetherington 《Geochimica et cosmochimica acta》1984,48(8):1637-1649

The isotopic composition of Sr has been measured in brine samples from the Upper Jurassic Smackover Formation in southern Arkansas; ${}^{87}\text{Sr}{}^{86}\text{Sr}$ ratios range from 0.7071 to 0.7101. With one exception, the 32 Smackover brines contain Sr which is significantly more radiogenic than the Sr in Late Jurassic sea water, indicating sizable Sr contributions from detrital sources. Isotopic analyses of core samples from rock units associated with the brines and regional stratigraphic relationships suggest that the radiogenic Sr was released from detrital minerals in Bossier shale to interstitial fluids expelled from the underlying Louann Salt in the North Louisiana salt basin. These fluids migrated through the Bossier Formation updip to the South Arkansas shelf, where they entered the upper Smackover carbonate grainstone. The radiogenic fluids mixed with Sr-rich interstitial marine waters that had the isotopic composition of Late Jurassic sea water; mixing in variable proportions resulted in the random distribution pattern of variable ${}^{87}\text{Sr}{}^{86}\text{Sr}$ ratios that is observed in Smackover brines within the 5000 km² study area. Isotopic analyses of nonskeletal carbonate grains and coexisting coarse calcspar cement from the upper Smackover grainstone imply that the grains were diagenetically stabilized in the presence of interstitial marine waters, whereas the calcspar cement is a relatively late diagenetic phase precipitated after the arrival of radiogenic fluids.  相似文献   

The RbSr isotope system as an index of origin and diagenetic evolution of southern Pacific red clays     

Norbert Clauer  Michel Hoffert  Anne-Marie Karpoff 《Geochimica et cosmochimica acta》1982,46(12):2659-2664

Morphological, mineralogical, chemical and RbSr isotopic studies have been made on Fesmectites (nontronites) from southern Pacific red clays cored near the Marquisas Islands. These minerals have at the top of the core, an ${}^{87}\text{Sr}{}^{86}\text{Sr}$ ratio of 0.70917 ± 0.00007, which indicates an authigenic origin in isotopic equilibrium with seawater. Weak leaching experiments with 1N HCl show that the nontronites also contain a volcanic component with a lower ${}^{87}\text{Sr}{}^{86}\text{Sr}$ ratio which, combined with the morphology of the particles, suggests a transportation by bottom currents of clay formed elsewhere.During burial, the nontronites experience diagenetic modifications resulting in an increase in Fe, K and Rb contents, a concomitant decrease of Mg, Ca, Ti, Na and Sr, and a preferential migration of radiogenic ⁸⁷Sr from the clays into the surrounding pore waters.The ${}^{87}\text{Sr}{}^{86}\text{Sr}$ ratio of the Sr adsorbed on the outermost surfaces of the nontronites does not change with depth in the core, and is, therefore, independent of diagenetic influence, which is rather characterized by the ${}^{87}\text{Sr}{}^{86}\text{Sr}$ ratios of the interstitial waters. The isotopic composition of both the adsorbed Sr and that of the pore fluids may yield useful information on the crystallization environment and subsequent history of deep sea red clays.  相似文献   

Kiglapait geochemistry V: Strontium     

S.A Morse 《Geochimica et cosmochimica acta》1982,46(2):223-234

The Kiglapait intrusion contains 330 ppm Sr and has $\text{Sr}\text{Ca}\text{= 5 × 10}{}^{\mathrm{?3}}$ and $\text{Rb}\text{Sr}\text{= 3 × 10}{}^{\mathrm{?3}}$, as determined by summation over the Layered Group of the intrusion. Wholerocks in the Lower Zone contain 403 F_L^0.141 ppm Sr, where F_L is the fraction of liquid remaining; Sr drops to 180 ppm at the peak of augite production (F_L = 0.11) and rises to a maximum of 430 ppm in the Upper Zone before decreasing to 172 ppm at the end of crystallization. Feldspars in the Lower Zone contain 532 F_L^0.090 ppm Sr, increasing to 680 ppm in the Upper Zone before decreasing to 310 ppm at the end. Clinopyroxenes contain 15 to 30 ppm Sr and have a mineral-melt distribution coefficient D = 0.06 except near the top of the intrusion where D = 0.10.The calculated feldspar-liquid distribution coefficient has an average value near 1.75 but shows four distinct trends when plotted against X_An of feldspar. The first two of these are strongly correlated with the modal augite content of the liquid, on average by the relation D = 1.4 + 0.02 Aug^L. The third (decreasing) trend is due to co-crystallization of apatite, and the fourth (increasing) trend can best be attributed to a triclinic-monoclinic symmetry change in the feldspar at An₂₆, 1030°C. The compound feldspar-liquid distribution coefficient K_D for $\text{Sr}\text{Ca}$ bears out these deductions in detail and yields ΔG_r for the Sr-Ca exchange ranging from nearly zero at the base of the Lower Zone to ?26 kJ/gramatom at the end of crystallization. The compound feldspar-liquid distribution coefficient K_D for $\text{Rb}\text{Sr}$ varies from 0.3 in the Lower Zone to 1.1 at the end of crystallization.The ratio $\text{Ca}{}^{\mathrm{F}}\text{Ca}{}^{\mathrm{L}}$ is about 1.45 for troctolitic liquids containing 5% augite, for which K_D (Sr-Ca) = 1.0 and D_Ca = D_Sr. For common basaltic liquids containing 20% augite, the Kiglapait data predict $\text{solSr}{}^{\mathrm{F}}\text{Sr}{}^{\mathrm{L}}\text{= 1.8}$, as commonly found elsewhere. The strong dependence of D_sr on augite content of the liquid illuminates the role of liquid composition and structure in determining the feldspar-liquid distribution coefficient. Conversely, a discontinuous change in the trend of D_Sr when apatite arrives shows that the effect is due to apatite crystallization itself, not to the continuous variation of the liquid as it becomes enriched in apatite component.  相似文献   

⁸⁷Sr/⁸⁶Sr composition of seawater during the Phanerozoic     

Ján Veizer  William Compston 《Geochimica et cosmochimica acta》1974,38(9):1461-1484

${}^{87}\text{Sr}{}^{86}\text{Sr}$ measurements of 108 sedimentary carbonate rocks have been used to trace variations in the strontium isotopic composition of seawater during the Phanerozoic. The lowest ⁸⁷Sr/⁸⁶Sr observed for any suite of carbonates is taken as the best approximation to the value in well-mixed contemporary seawater. Our data support the existence of low ${}^{87}\text{Sr}{}^{86}\text{Sr}$ in the Cretaceous and Late Jurassic but they do not support further structure beyond a general trend through the Phanerozoic, which may correlate with the continental denudation rate.  相似文献   

Importance of alteration of volcanic material in the sediments of deep sea drilling site 323: chemistry, 18O16O and 87Sr86Sr     

J.R. Lawrence  J.I. Drever  T.F. Anderson  H.K. Brueckner 《Geochimica et cosmochimica acta》1979,43(4):573-588

A downhole decrease in ¹⁸O, Mg²⁺ and K⁺, an increase in Ca²⁺ and a low ${}^{87}\text{Sr}{}^{86}\text{Sr}$ ratio of 0.7067 in the pore fluids of DSDP site 323 were caused principally by the alteration of volcanic material. These chemical and isotopic patterns were produced by the alteration, in order of decreasing importance of: a 60-m thick basal layer of volcanic ash; the underlying basalts; and igneous components in the 640-m thick upper sequence composed largely of terrigenous material. A significant portion of the alteration of the ash in the basal sequence must have occurred before the deposition of the upper sediments, perhaps under the influence of advecting solutions. The rest of the alteration occurred during the deposition of the thick upper sediments. Mass balance considerations and the low δ¹⁸O values of most of the alteration products suggest that much of the later alteration occurred progressively over the last 13 Myr. The principal alteration products were smectite, potassium feldspar, clinoptilolite and calcite.  相似文献