Isotopic and incompatible element constraints on the genesis of island arc volcanics from Cold Bay and Amak Island,Aleutians, and implications for mantle structure     

J.D Morris  S.R Hart 《Geochimica et cosmochimica acta》1983,47(11):2015-2030

Cold Bay and Amak Island, two Quaternary volcanic centers in the eastern Aleutians, are orthogonal relative to the trench and separated by ~50 km. Sr, Nd and Pb isotopic compositions of the calc-alkaline andesite magmas show no sign of contamination from continental crust (average ${}^{87}\text{Sr}{}^{86}\text{Sr}\text{= 0.70323}$, ${}^{143}\text{Nd}{}^{144}\text{Nd}\text{= 0.51301}$, ${}^{206}\text{Pb}{}^{204}\text{Pb}\text{= 18.82}$, ${}^{207}\text{Pb}{}^{204}\text{Pb}\text{= 15.571}$). These samples plot within the mantle arrays for Sr-Nd and for Pb and are similar to arcs such as the Marianas and New Britain (Sr-Nd) and Marianas and Tonga (Pb). Incompatible element ratios for the Aleutian andesites (K/Rb ~ 332, K/Cs ~ 10,600, K/Sr ~ 22.4, K/Ba ~ 18.3, Ba/La ~ 60) are within the range reported for arc basalts, despite the difference in degree of fractionation.Average K content, K/Rb, K/Ba and K/Sr are approximately the same for basalts from arcs and from oceanic islands (OIB); K/Cs is a factor of 4 lower and Ba/La almost 3 times higher in arcs. Abundance ratio correlations indicate that arcs are enriched in Cs and depleted in La relative to OIB, with other incompatible element abundances very similar. Histograms of Sr and Nd isotopic compositions for MORB, OIB, and intraoceanic arcs show remarkably similar peaks and distribution patterns for intraoceanic arcs and OIB.A “plum pudding” model for the upper mantle best accommodates a) geochemical coherence of OIB and IAV, b) the existence of mantle plumes at some oceanic islands, and c) the presence of a MORB-type source at back arc spreading centers. In this model, OIB plums are imbedded in a MORB matrix; small degrees of melting generate OIB-type magmas while larger degrees of melting dilute the OIB magma with MORB matrix melts.OIB plums are merely less robust lower mantle plumes (i.e., blobs) which are distributed throughout the upper mantle by convection. The existence of at least two types of OIB, as indicated by Sr, Nd, and Pb isotopes, suggests that nuggets of recycled oceanic lithosphère may coexist with lower-mantle plums and that both may be tapped in arcs and intraplate environments.  相似文献   

Sr and Pb isotopes,U and Th chemistry of the alkaline Monteregian and White Mountain igneous provinces,eastern North America     

G.Nelson Eby 《Geochimica et cosmochimica acta》1985,49(5):1143-1153

The Monteregian Hills and younger White Mountain alkaline intrusions were emplaced into the Cambro-Ordovician sediments of the St. Lawrence Lowlands and the folded and thrusted Lower Paleozoic sequence of the Appalachian orogen. Age relations indicate that there is a fine-scale structure to the igneous activity, with slightly undersaturated to critically saturated rocks emplaced between 141 and 128 Ma and strongly undersaturated rocks emplaced between 121 and 117 Ma.Sr and Pb isotopic data for the mantle-derived alkali picrite, alkali olivine basalt and basanite magmas, indicate derivation from a depleted mantle similar to that which produces present-day oceanic island basalts. For the most isotopically primitive samples, decay-corrected ${}^{87}\text{Sr}{}^{86}\text{Sr}\text{= 0.7030–0.7037}$, ${}^{206}\text{Pb}{}^{204}\text{Pb}\text{= 19.05–19.72}$, ${}^{207}\text{Pb}{}^{204}\text{Pb}\text{= 15.56–15.65}$, and ${}^{208}\text{Pb}{}^{204}\text{Pb}\text{= 38.64–39.26}$. On Pb-Sr isotope correlation diagrams the data define trends similar to those for MOR basalts, implying mantle heterogeneity which requires the presence of a component enriched in radiogenic Pb relative to Sr. The interaction of these isotopically primitive magmas with the crust can be defined in terms of a three component system: depleted mantle-Grenville age crust-Lower Paleozoic age crust. The granitic magmas were apparently derived from the Lower Paleozoic crust of the Appalachian orogen.For the mantle-derived magmas, Th/U ratios vary from 2.5 (estimated ratio for MORB source) to 5.1, with the mean value near that of the bulk earth. The variations in Th/U suggest mantle heterogeneity on a local scale, and the high Th/U of some samples suggests that the mantle was enriched in incompatible elements shortly before melting. The magmas derived by partial melting of the crust have Th/U of 3.3 to 8.7, and the higher ratios are associated with rocks crystallized from magmas that originated by melting of Lower Paleozoic sediments.The Sr and Pb isotopic data support the conclusion of Bellet al. (1982) that the subcontinental mantle under eastern Canada underwent a Precambrian depletion event. This depleted mantle apparently extends under the White Mountain province and is isotopically similar to the mantle which gives rise to oceanic island basalts. In contrast, Pb isotopic ratios for the New England Seamount chain (TARAS and HART, 1983), which apparently represents the oceanic extension of this magmatic activity, are significantly more radiogenic. It is possible that a mantle plume provided the heat energy, and perhaps metasomatic fluids, to trigger melting in the subcontinental mantle, whereas in the case of the oceanic extension the plume directly contributed to the observed magmatism, as reflected in the more radiogenic Pb ratios.  相似文献   

Distribution coefficients of Eu and Sr for plagioclase-liquid and clinopyroxene-liquid equilibria in oceanic ridge basalt: an experimental study     

Richard J. Williams 《Geochimica et cosmochimica acta》1974,38(9):1415-1433

The distribution coefficients of Eu and Sr for plagioclase-liquid and clinopyroxene-liquid pairs as a function of temperature and oxygen fugacity were experimentally investigated using an oceanic ridge basalt enriched with Eu and Sr as the starting material. Experiments were conducted between 1190° and 1140°C over a range of oxygen fugacities between 10^?8 and 10^?14 atm.The molar distribution coefficients are given by the equations: log^PL_Sr = 7320/T ? 4.62logK^CPX_Sr = 18020/T ? 13.10. Similarly, the weight fraction distribution coefficients are given by the equations: logD^PL_Sr = 6570/T ? 4.30logD^CPX_Sr = 18434/T ? 13.62.Although the mole fraction distribution coefficients have a smaller dependence on bulk composition than do the weight fraction distribution coefficients, they are not independent of bulk composition, thereby restricting the application of these experimental results to rocks similar to oceanic ridge basalts in bulk composition.Because the Sr distribution coefficients are independent of oxygen fugacity, they may be used as geothermometers. If the temperature can be determined independently — for example, with the Sr distribution coefficients, the Eu distribution coefficients may be used as oxygen geobarometers. Throughout the range of oxygen fugacities ascribed to terrestrial and lunar basalts, plagioclase concentrates Eu but clinopyroxene rejects Eu.  相似文献   

The geochemistry of basalts from a back-arc spreading centre in the East Scotia Sea     

Andrew D. Saunders  John Tarney 《Geochimica et cosmochimica acta》1979,43(4):555-572

Rapid sea floor spreading has taken place over the last 8 Myr behind the South Sandwich island arc, producing a regular set of magnetic lineations. Suites of fresh basalts have been dredged from four widely separated localities along the spreading axis. Dredges 20 and 23 yielded sub-alkaline olivine tholeiites, dredge 22 recovered vesicular tholeiites with minor normative olivine, while dredge 24 contained a fractionated suite of highly vesicular quartz-normative basalts with higher $\text{Fe}\text{Mg}$. The concentrations of the incompatible elements Ti, P, Zr, Hf, Nb, Ta, Y and the REE increase systematically from dredge 24 through dredges 22 and 20 to dredge 23 and there is a comparable increase in $\text{Ce}{}_{\mathrm{N}}\text{Yb}{}_{\mathrm{N}}$. Quantitative modelling suggests that all the basalts can be derived from an essentially similar mantle source (with respect to these elements) through varying degrees of partial melting, but involving some residual clinopyroxene. Basalts from dredge 24 have unusually low concentrations of Ti, P, Zr, Nb, Y, REE and Ni, similar to the values in arc tholeiites, and the more primitive dredge 24 liquids seem to have been generated through high degrees of partial melting (~ 30%) leaving a dunitic residue. Transitional arc tholeiite characteristics are also apparent in the relatively high K, Rb, Ba contents and ${}^{87}\text{Sr}{}^{86}\text{Sr}$ ratios of dredge 24 and 22 basalts, though Nd isotope ratios are uniform. It is considered that fluids derived from the dehydrating subducted slab may have locally penetrated the source regions of the back-arc basalts, carrying K, Rb, Ba and seawater-enriched ⁸⁷Sr, and producing conditions of magma generation similar to that of arc tholeiites. However, it is unlikely that the sources for these and other marginal basin basalts differ fundamentally from the range of mantle sources feeding normal mid-ocean ridges.  相似文献   

The system pargasite-H₂O-CO₂: a model for melting of a hydrous mineral with a mixed-volatile fluid—I. Experimental results to 8 kbar     

J.R Holloway 《Geochimica et cosmochimica acta》1973,37(3):651-666

The stability of the amphibole pargasite [NaCa₂Mg₄Al(Al₂Si₆))O₂₂(OH)₂] in the melting range has been determined at total pressures (P) of 1.2 to 8 kbar. The activity of H₂O was controlled independently of P by using mixtures of H₂O + CO₂ in the fluid phase. The mole fraction of H₂O in the fluid ($\text{X}{}_{\mathrm{H}}{}_2\text{O}{}^{\mathrm{1fl}}$) ranged from 1.0 to 0.2.At P < 4 kbar the stability temperature (T) of pargasite decreases with decreasing $\text{X}{}_{\mathrm{H}}{}_2\text{O}{}^{\mathrm{1fl}}$ at constant P. Above P ? 4 kbar stability T increases as $\text{X}{}_{\mathrm{H}}{}_2\text{O}{}^{\mathrm{1fl}}$ is decreased below one, passes through a T maximum and then decreases with a further decrease in $\text{X}{}_{\mathrm{H}}{}_2\text{O}{}^{\mathrm{1fl}}$. This behavior is due to a decrease in the H₂O content of the silicate liquid as $\text{X}{}_{\mathrm{H}}{}_2\text{O}{}^{\mathrm{1fl}}$ decreases. The magnitude of the T maximum increases from about 10°C (relative to the stability T for $\text{X}{}_{\mathrm{H}}{}_2\text{O}{}^{\mathrm{1fl}}\text{= 1}$) at P = 5 kbar to about 30°C at P = 8 kbar, and the position of the maximum shifts from $\text{X}{}_{\mathrm{H}}{}_2\text{O}{}^{\mathrm{1fl}}\text{? 0.6}$ at P = 5 kbar to $\text{X}{}_{\mathrm{H}}{}_2\text{O}{}^{\mathrm{1fl}}\text{? 0.4}$ at P = 8 kbar.The H₂O content of liquid coexisting with pargasite has been estimated as a function of at 5 and 8 kbar P, and can be used to estimate the H₂O content of magmas. Because pargasite is stable at low values of $\text{X}{}_{\mathrm{H}}{}_2\text{O}{}^{\mathrm{1fl}}$ at high P and T, hornblende can be an important phase in igneous processes even at relatively low H₂O fugacities.  相似文献   

Speciation of boron with Cu2+, Zn2+, Cd2+ and Pb2+ in 0.7 M KNO3 and in sea-water     

Constant M.G. van den Berg 《Geochimica et cosmochimica acta》1984,48(12):2613-2617

The stability constants, $\text{K}{}^1{}_{\mathrm{MB}}$, for borate complexes with the ions of Cu, Pb, Cd and Zn are determined in this work by DPASV in 0.7 M KNO₃ at metal concentrations of 10^?7 M. The acidity constants of the Cu²⁺ ion are determined by DPASV in the same conditions. The following values for log $\text{K}{}^1{}_{\mathrm{MB}}$ () have been obtained: CuB: 3.48, CuB₂: 6.13, PbB: 2.20, PbB₂: 4.41, ZnB: 0.9, ZnB₂: 3.32, CdB: 1.42, and CdB₂: 2.7, while the values for the acidity constants of Cu are $\text{pK}{}^1{}_{\mathrm{CuOH}}\text{= 7.66}$ and . At the low concentration of boron in 35%. S sea-water complexes with borate represent only about 0.2% Cu, 0.03% Pb, 0.02% Zn and 0.003% Cd.  相似文献   

Density calculations for silicate liquids. I. Revised method for aluminosilicate compositions     

Y Bottinga  D Weill  P Richet 《Geochimica et cosmochimica acta》1982,46(6):909-919

Equations are developed for calculating the density of aluminosilicate liquids as a function of composition and temperature. The mean molar volume at reference temperature T_r, is given by $\text{V}{}_{\mathrm{r}}\text{= ∑X}{}_{\mathrm{i}}\text{V}\text{?}{}^{\mathrm{o}}{}_{\mathrm{i}}\text{+ X}{}_{\mathrm{A}}\text{V}\text{?}{}^{\mathrm{o}}{}_{\mathrm{A}}$, where the summation is taken over all oxide components except A1₂O₃, X stands for mole fraction, terms are constants derived independently from an analysis of volume-composition relations in alumina-free silicate liquids, and $\text{V}\text{?}{}^{\mathrm{o}}{}_{\mathrm{A}}$ is the composition-dependent apparent partial molar volume of Al₂O₃. The thermal expansion coefficient of aluminosilicate liquids is given by $\text{α = ∑X}{}_{\mathrm{i}}\text{}\text{?}\text{ga}{}_{\mathrm{i}}{}^{\mathrm{o}}\text{+ X}{}_{\mathrm{A}}\text{}\text{?}\text{ga}{}_{\mathrm{A}}{}^{\mathrm{o}}$, where $\text{}\text{?}\text{ga}{}_{\mathrm{i}}{}^{\mathrm{o}}$ terms are constants independent of temperature and composition, and $\text{}\text{?}\text{ga}{}^{\mathrm{o}}{}_{\mathrm{A}}$ is a composition-dependent term representing the effect of Al₂O₃ on the thermal expansion. Parameters necessary to calculate the volume of silicate liquids at any temperature T according to V(T) = V_rexp[α(T-T_r)], where T_r = 1400°C have been evaluated by least-square analysis of selected density measurements in aluminosilicate melts. Mean molar volumes of aluminosilicate liquids calculated according to the model equation conform to experimentally measured volumes with a root mean square difference of 0.28 $\text{cc}\text{mole}$ and an average absolute difference of 0.90% for 248 experimental observations. The compositional dependence of $\text{V}\text{?}{}^{\mathrm{o}}{}_{\mathrm{A}}$ is discussed in terms of several possible interpretations of the structural role of Al³⁺ in aluminosilicate melts.  相似文献   

Theoretical prediction of phase relations among aqueous solutions and minerals: Salton Sea geothermal system     

Dennis K. Bird  Denis L. Norton 《Geochimica et cosmochimica acta》1981,45(9):1479-1494

  相似文献   

Diffusion of ions in sea water and in deep-sea sediments   总被引：3，自引：0，他引：3  

Sandra Gregory 《Geochimica et cosmochimica acta》1974,38(5):703-714

The tracer-diffusion coefficient of ions in water, D_j⁰, and in sea water, $\text{D}{}_{\mathrm{j}}{}^1$, differ by no more than zero to 8 per cent. When sea water diffuses into a dilute solution of water, in order to maintain the electro-neutrality, the average diffusion coefficients of major cations become greater but of major anions smaller than their respective $\text{D}{}_{\mathrm{j}}{}^1$ or D_j⁰ values. The tracer diffusion coefficients of ions in deep-sea sediments, D_j,sed., can be related to $\text{D}{}_{\mathrm{j}}{}^1$ by $\text{D}{}_{\mathrm{j,sed.}}\text{= D}{}_{\mathrm{j}}{}^1\text{·}\text{α}\text{θ}{}^2$, where θ is the tortuosity of the bulk sediment and a a constant close to one.  相似文献   

Volatile contents and ferric-ferrous ratios of basalt,ferrobasalt, andesite and rhyodacite glasses from the Galapagos 95.5°W propagating rift     

Charles D Byers  David M Christie  David W Muenow  John M Sinton 《Geochimica et cosmochimica acta》1984,48(11):2239-2245

Volatiles and major elements in abyssal glasses ranging in composition from basalt, ferrobasalt, andesite to rhyodacite from the Galapagos Spreading Center (GSC) near 95°W were analyzed using electron microprobe and high temperature mass spectrometry. Total volatile content ranged from 0.32 wt.% to 2.74 wt.%. Volatile abundances of MORB glasses from the 95.5°W propagating rift are similar to those from the adjacent normal rift (avg. 0.34 wt.%) and lower than those of N-type MORB from the Mid-Atlantic Ridge (avg. 0.49 wt.%). Although both propagating and non-propagating rift glasses contain trace amounts of methane (<0.01 wt.%) and carbon monoxide (0.04 wt.%), significantly higher 100 $\text{Fe}{}_2\text{O}{}_3\text{FeO}\text{+ Fe}{}_2\text{O}{}_3$ ratios are observed for the primitive propagating rift glasses. Water contents of the most primitive GSC glasses are ~0.09 wt.% suggesting a water content for the mantle source of ~0.02 wt.% which indicates that source masses with very low water content can be involved in the generation of MORB.In fractionated ferrobasalt, andesite and rhyodacite glasses from the 95.5°W propagating rift, increasing abundances of H₂O, Cl and F indicate highly incompatible behavior, whereas CO₂ and reduced carbon species appear to decrease in abundance with increasing differentiation. Ferric-ferrous ratios increase from basalt to andesite and reduce to near zero in the rhyodacite. These values are not distinguishable from those previously reported for similar fractionated glasses from the Galapagos 85°W propagating rift, despite the apparent suppression of oxide precipitation in the 85°W suite.  相似文献   

The nature and origin of geochemical variation in Mid-Atlantic Ridge basalts from the Central North Atlantic     

William M. White  Jean-Guy Schilling 《Geochimica et cosmochimica acta》1978,42(10):1501-1516

Seventy-two basalts from 58 dredge stations located along the Mid-Atlantic Ridge from 29°N to 59°N have been analyzed for ${}^{87}\text{Sr}{}^{86}\text{Sr}$ and for K, Rb, Cc, Sr and Ba. The Sr-isotope profile along the ridge has three distinct maxima, one coinciding with the Azores platform (0.70345), one at 45°N (0.70340) and the third at 35°N, in the vicinity of the Oceanographer Fracture Zone. Basalts from ridge segments between 29°N and 33°N, and 49°N and 59°N have ${}^{87}\text{Sr}{}^{86}\text{Sr}$ ratios typical of ‘normal’ mid-ocean ridge basalts (0.70230–0.70280). Profiles of K, Rb, Cs, Sr, Bz, Rb/Sr and Ba/Sr are similar to the ${}^{87}\text{Sr}{}^{86}\text{Sr}$ profile, but Rb/K, Cs/K and Ba/K show broad maxima between 35°N and 45°N.These variations result from chemical and isotopic heterogeneity in the mantle, and are interpreted as caused by a mantle plume beneath the Azores which mixes with the LIL-element-depleted asthenosphere. Additional plumes may exist beneath 45°N and 35°N.Compared to the LIL-element-depleted asthenosphere, the Azores mantle plume is 10 to 30 times enriched in LIL elements with very small (? 0.1) bulk crystal/melt partition coefficients (Rb, Cs, Ba, La). Mildly incompatible elements (0.1 < D < 1) (Sr, Sm, Yb) are only 0.8–3 times enriched. These, observations suggest that LIL element differences between these two mantle reservoirs resulted from processes involving solid-liquid equilibria and not vapor-solid or vapor-liquid equilibria. Isotope systematics indicate that neither mantle reservoir remained a closed system since the formation of the Earth, but it is not possible to determine the time at which heterogeneity first developed.  相似文献   

Constantes de formation des complexes hydroxydés de l'aluminium en solution aqueuse de 20 a 70°C     

Yves Couturier  Gil Michard  Gérard Sarazin 《Geochimica et cosmochimica acta》1984,48(4):649-659

Stability constants of hydroxocomplexes of Al(III):Al(OH)²⁺ and A1(OH)₄^? have been measured in the 20–70°C temperature range by reactions involving only dissolved species. The stability constant ${}^1\text{K}{}_1$ of the first complex ion is studied by measuring pH of solutions of aluminium salts at several concentrations. ${}^1\text{β}{}_4$ of aluminate ion is deduced from equilibrium constants of the reaction between the trioxalato aluminium (III) complex ion and Al³⁺ in acid medium, and between the same complex ion and A1(OH)₄^? in alkaline medium. The K values and the associated ΔH are ${}^1\text{K}{}_1\text{= 10}{}^{\mathrm{?5.00}}$ and ΔH₁ = 11.8 Kcal; ${}^1\text{β}{}_4\text{= 10}{}^{\mathrm{?22.20}}$ and ΔH₄ = 42.45 Kcal. These last results are not in agreement with the values of recent tables for $\text{ΔG}{}^0\text{?}$ and $\text{ΔH}{}^0\text{?}$ of Al³⁺ and Al(OH)₄^?. We suggest a consistent set of data for dissolved and solid Al species and for some aluminosilicates.  相似文献   

Magmatic evolution of a volcano studied by ²³⁰Th-²³⁸U disequilibrium and trace elements systematics: The Etna case     

M Condomines  J.C Tanguy  G Kieffer  C.J Allègre 《Geochimica et cosmochimica acta》1982,46(8):1397-1416

Age determinations of several lava flows from Etna through ²³⁰Th-²³⁸U disequilibrium (internal isochrons) yield a precise chronology of the volcano's history for the last 200,000 years, and emphasize the main episodes in the formation of this huge complex strato-volcano. Study of $\text{(}{}^{230}\text{Th}{}^{232}\text{Th}\text{)}{}_0$ initial ratios of lavas together with their trace-element compositions yields a consistent model of magmatic evolution implying the existence, for 200,000 years, of a deep reservoir of alkalic magma periodically mixed with magmas of tholeiitic affinity. These short periods of mixing appear to be related to the formation of the large calderas of Etna. In addition to these processes affecting the deep reservoir, fractional crystallization also occurred in more superficial levels of the volcanic edifice, thereby yielding several series of differentiation of relatively short duration. As for its geochemistry, Etna's volcanism is of oceanic type but with its own characteristics and in a peculiar geodynamic context, at the edge of the African Plate.  相似文献   

Use of Pitzer's equations to determine the media effect on the formation of lead chloro complexes     

Frank.J. Millero  Robert H. Byrne 《Geochimica et cosmochimica acta》1984,48(5):1145-1150

The spectrophotometric measurements of chloro complexes of lead in aqueous HCl, NaCl, MgCl₂ and CaCl₂ solutions at 25°C have been analyzed using Pitzer's specific interaction equations. Parameters for activity coefficients of the complexes PbCl⁺, PbCl₂⁰ and PbCl₃^? have been determined for the various media. Values of $\text{K}{}_1\text{= 30.0 ± 0.6}$, $\text{K}{}_2\text{= 106.7 ± 2.1}$ and $\text{K}{}_3\text{= 73.0 ± 1.5}$ were obtained for the cumulative formation constants. [$\text{Pb}{}^{\mathrm{2+}}\text{+ nCl}{}^{\mathrm{?}}\text{→ PbCl}{}_{\mathrm{n}}{}^{\mathrm{2?n}}\text{)}$]. These values are in reasonable agreement with literature data. The Pitzer parameters for the PbCl ion pairs in various media were used to calculate the speciation of Pb²⁺ in an artificial seawater solution.  相似文献   

Total individual ion activity coefficients of calcium and carbonate in seawater at 25°C and 35%. salinity,and implications to the agreement between apparent and thermodynamic constants of calcite and aragonite     

L.Niel Plummer  Eric T. Sundquist 《Geochimica et cosmochimica acta》1982,46(2):247-258

We have calculated the total individual ion activity coefficients of carbonate and calcium, and , in seawater. Using the ratios of stoichiometric and thermodynamic constants of carbonic acid dissociation and total mean activity coefficient data measured in seawater, we have obtained values which differ significantly from those widely accepted in the literature. In seawater at 25°C and 35%. salinity the (molal) values of and are $\text{0.038 ± 0.002}$ and $\text{0.173 ± 0.010}$, respectively. These values of and are independent of liquid junction errors and internally consistent with the value . By defining and on a common scale (), the product is independent of the assigned value of and may be determined directly from thermodynamic measurements in seawater. Using the value and new thermodynamic equilibrium constants for calcite and aragonite, we show that the apparent constants of calcite and aragonite are consistent with the thermodynamic equilibrium constants at 25°C and 35%. salinity. The demonstrated consistency between thermodynamic and apparent constants of calcite and aragonite does not support a hypothesis of stable Mg-calcite coatings on calcite or aragonite surfaces in seawater, and suggests that the calcite critical carbonate ion curve of Broecker and Takahashi (1978, Deep-Sea Research25, 65–95) defines the calcite equilibrium boundary in the oceans, within the uncertainty of the data.  相似文献   

The partial molal volume of silicic acid in 0.725 M NaCl at 1°C determined by the neutralization of Na₂SiO₃     

J.Peter Hershey  Iver W Duedall 《Geochimica et cosmochimica acta》1983,47(11):1931-1936

The partial molal volume of silicic acid ($\text{V}\text{?}\text{(Si(OH)}{}_4\text{)}$) in 0.725 M NaCl at 1°C was calculated from the measured volume change (Δ$\text{V}\text{?}{}_{\mathrm{n}}$) due to the neutralization of anhydrous sodium metasilicate with HCl and the $\text{V}\text{?}\text{(HCl)}$ and $\text{V}\text{?}\text{(NaCl)}$ obtained from the literature. $\text{V}\text{?}\text{(Si(OH)}{}_4\text{) = 59.0 cm}{}^3\text{mol}\text{? 1}$, determined under experimental conditions of pH = 2.2, compares favorably with $\text{V}\text{?}\text{(Si(OH)}{}_4\text{) = 58.9 cm}{}^3\text{mol}{}^{\mathrm{?1}}$ calculated from the measured volume change due to the hydrolysis of the meta-silicate salt at pH = 11 and from the partial molal volume due to electrostriction ($\text{V}\text{?}{}_{\mathrm{elect}}$) of water by charged Si species present in the solution at the high pH. This agreement lends support to a semiempirical model for calculating $\text{V}\text{?}{}_{\mathrm{elect}}$ in developed by Millero (1969). $\text{V}\text{?}\text{(NaOH) = ? 5.45 cm}{}^3\text{mol}{}^{\mathrm{?1}}$ in 0.725 M NaCl needed for this calculation was also determined in this work. The rate of polymerization of Si(OH)₄ at 1°C was monitored to insure that the monomer Si(OH)₄ was the main Si species present during the determination of $\text{V}\text{?}\text{(Si(OH)}{}_4\text{)}$ by neutralization of the alkali silicate. $\text{V}\text{?}\text{(Si(OH)}{}_4\text{)}$ determined in this study compares favorably with the value calculated from high pressure solubility measurements.  相似文献   

Methane-producing bacteria: natural fractionations of the stable carbon isotopes   总被引：1，自引：0，他引：1  

Larry M. Games  J.M. HayesRobert  P. Gunsalus 《Geochimica et cosmochimica acta》1978,42(8):1295-1297

The ${}^{13}\text{C}{}^{12}\text{C}$ fractionation factors ($\text{CO}{}_2\text{CH}{}_4$) for the reduction of CO₂ to CH₄ by pure cultures of methane-producing bacteria are, for Methanosarcina barkeri at 40°C, 1.045 ± 0.002; for Methanobacterium strain M.o.H. at 40°C, 1.061 ± 0.002; and, for Methanobacterium thermoautotrophicum at 65°C, 1.025 ± 0.002. These observations suggest that the acetic acid used by acetate dissimilating bacteria, if they play an important role in natural methane production, must have an intramolecular isotopic fractionation ($\text{CO}{}_2\text{H}\text{CH}{}_3$) approximating the observed $\text{CO}{}_2\text{CH}{}_4$ fractionation.  相似文献   

Dissociation constants for alkali earth and sodium borate ion pairs from 10 to 50°C     

E.J. Reardon 《Chemical Geology》1976,18(4):309-325

Potentiometric measurements in dilute sodium borate solutions with added alkali earth chlordie salts yield the following expressions for the dissociation constants of alkali earth borate ion pairs from 10 to 50°C:where T is in °K. Enthalpies for the dissociation reactions at 25°C are less than 1 kcal./mole for all the alkali earth borate ion pairs.Values for pK(NaH₂BO₃°) from 5 to 55°C computed from the experimental data of Owen and King are in good agreement with those determined potentiometrically. The average value from both methods is 0.22 ± 0.1 at 25°C.Application to seawater of computed pK's for MgH₂BO₃⁺, CaH₂BO₃⁺ and NaH₂BO₃⁰ yields an apparent dissociation constant for boric acid of 8.73 vs. 8.70 measured by Lyman, 8.68 by Buch and 8.73 by Byrne and Kester.  相似文献   

Thermodynamic stability studies of the basic copper carbonate mineral,malachite     

James L Symes  Dana R Kester 《Geochimica et cosmochimica acta》1984,48(11):2219-2229

Natural malachite is a well defined solid demonstrating reproducible solubility behavior over a wide range of pH. The following equilibrium constants associated with the malachite dissolution equilibrium at 25°C, 1 atm were determined: (infinite dilution) (0.72 ionic strength) (36.9‰ salinity seawater). The temperature dependence of a “mixed” equilibrium constant, K_sp⁺, of the form: has been measured at I = 0.72, yielding the relationship: within a 5–25°C temperature range. The effect of pressure on the solubility of malachite in water and seawater was estimated from partial molar volume and compressibility data. For 25 °C at infinite dilution $\text{K'}{}_{\mathrm{sp}}\text{(1000 bar)}\text{K'}{}_{\mathrm{sp}}\text{(0)}\text{= 240}$ and in seawater $\text{K′}{}_{\mathrm{sp}}\text{(1000)}\text{K'}{}_{\mathrm{sp}}\text{(0)}\text{= 44}$.Comparison of stoichiometric and apparent malachite equilibrium constants has been used to estimate the extent of copper(II) ion interaction at the ionic strength of seawater. In dilute carbonate medium (total alkalinity, TA = 2.4 meq/kg H₂O, pH 8.3), 2.9% of total dissolved copper exists as the free copper(II) ion and in seawater (S = 36.9%., TA = 2.3 meq/kg H₂O, pH = 8.1), $\text{[Cu}{}^{\mathrm{2+}}\text{]}\text{T(Cu)}$ is 3.1%.Total dissolved copper levels of approximately 450–750 nMol/Kg are necessary to attain malachite saturation conditions in the open ocean. Observations of malachite particles suspended in seawater must be explained by precipitation or solid phase substitution reactions from localized environments rather than by direct precipitation from bulk seawater.  相似文献   

Diffusivity of oxygen in jadeite and diopside melts at high pressures     

N. Shimizu  I. Kushiro 《Geochimica et cosmochimica acta》1984,48(6):1295-1303

The diffusivity of oxygen was determined in melts of Jadeite (NaAlSi₂O₆) and diopside (CaMgSi₂O₆) compositions using diffusion couples with ¹⁸O as a tracer. In the Jadeite melt, the diffusivity of oxygen increases from $\text{6.87}{}_{\mathrm{?0.25}}{}^{\mathrm{+0.28}}\text{× 10}{}^{\mathrm{?10}}\text{cm}{}^2\text{/}\text{sec}$ at 5 Kb to $\text{1.32 ± 0.08 × 10}{}^{\mathrm{?9}}\text{cm}{}^2\text{/}\text{sec}$ at 20 Kb at constant temperature (1400°C), whereas in the diopside melt at 1650°C, the diffusivity decreases from $\text{7.30}{}_{\mathrm{?0.18}}{}^{0.29}\text{× 10}{}^{\mathrm{?7}}\text{cm}{}^2\text{/}\text{sec}$ at 10 Kb to $\text{5.28}{}_{\mathrm{?0.55}}{}^{\mathrm{+0.60}}\text{× 10}{}^{\mathrm{?7}}\text{cm}{}^2\text{/}\text{sec}$ at 17 Kb. These results demonstrate that the diffusivity is inversely correlated with the viscosity of the melt. For the jadeite melt, in particular, the inverse correlation is very well approximated by the Eyring equation using the diameter of oxygen ions as a unit distance of translation, suggesting that the viscous flow is rate-limited by the diffusion of individual oxygen ions. In the diopside melt, the activation volume is slightly greater than the molar volume of oxygen ion, indicating that the individual oxygen ion is the diffusion unit. The negative activation volume obtained for the jadeite melt is interpreted as the volume decrease associated with a diffusive jump of an oxygen ion due to local collapse of the network structure.  相似文献