Determination of uranium and thorium in meteorites by the delayed neutron method     

G.L. Cumming 《Chemical Geology》1974,13(4):257-267

Delayed neutron measurements of U and Th in three meteorites yield the following values:

Crustal development in the Agnew region,Western Australia,as shown by Rb/Sr isotopic and geochemical studies     

J.A Cooper  R.W Nesbitt  J.P Platt  G.E Mortimer 《Precambrian Research》1978,7(1):31-59

Rb/Sr geochronology on a folded greenstone-granitoid complex in the Agnew area, Western Australia, yields four distinct ages of igneous activity that conform with stratigraphic and intrusive relationships. They are (using $\text{λ}{}^{87}\text{Rb}\text{= 1.42 · 10}{}^{\mathrm{?11}}\text{a}{}^{\mathrm{?1}}$, NBS 70A = 522 ppm Rb and 65.3 ppm Sr):

High precision intercalibration of 40Ar-39Ar standards     

J.C Roddick 《Geochimica et cosmochimica acta》1983,47(5):887-898

Intercalibration of one intralaboratory and three interlaboratory standards used in ⁴⁰Ar-³⁹Ar dating has been carried out. In order to provide homogeneous values for ${}^{40}\text{Ar}{}^1{}^{40}\text{K}$ the standards were prepared by careful handpicking. To control the neutron fluence in the Herald Reactor (A.W.R.E.) 16 aliquots of the standards were arranged along 0.6 × 60 cm of a single silica tube. The corrections for all known interferences from K, Ca, Cl were carefully assessed. Two of the hornblende standards, Hb3gr and MMHb-1 appear homogeneous at the 0.1% level while the other two standards, LP-6 and FY12a are not completely homogeneous. The mean values of ${}^{40}\text{Ar}{}^1{}^{40}\text{K}$ when referenced to the previously determined value for Hb3gr (turner et al., 1971) are:

An experimental study of alkali metal distributions in feldspars and micas     

A.E. Beswick 《Geochimica et cosmochimica acta》1973,37(2):183-208

K and Rb distributions between aqueous alkali chloride vapour phase (0.7 molar) and coexisting phlogopites and sanidines have been investigated in the range 500 to 800°C at 2000 kg/cm² total pressure.Complete solid solution of RbMg₃AlSi₃O₁₀(OH)₂ in KMg₃AlSi₃O₁₀(OH)₂ exists at and above 700°C. At 500°C a possible miscibility gap between approximately 0.2 and 0.6 mole fraction of the Rb end-member is indicated.Only limited solid solution of Rb AlSi₃O₈ in KAlSi₃O₈ has been found at all temperatures investigated.Distribution coefficients, expressed as $\text{K}{}_{\mathrm{d}}\text{= (}\text{Rb/K}\text{)}$ in solid/(Rb/K) in vapour, are appreciably temperature-dependent but at each temperature are independent of composition for low Rb end-member mole fractions in the solids. The determined $\text{K}{}_{\mathrm{D}}$ values and their approximate Rb end-member mole fraction ($\text{X}{}_{\mathrm{RM}}$) ranges of constancy are summarized as follows: (°C)$\text{T}$$\text{K}{}_{\mathrm{D}}{}^{\mathrm{Phlog/Vap.}}$$\text{X}{}_{\mathrm{RM}}$$\text{K}{}_{\mathrm{D}}{}^{\mathrm{Sandi/Vap.}}$$\text{X}{}_{\mathrm{rm}}$

Phase relations in the system NaCl-KCl-H₂O. Part I: Differential thermal analysis of the NaCl-KCl liquidas at 1 atmosphere and 500, 1000, 1500, and 2000 bars     

I-Ming Chou 《Geochimica et cosmochimica acta》1982,46(10):1957-1962

A simple differential thermal analysis (DTA) technique has been developed to study phase relations of various chemical systems at elevated pressures and temperatures. The DTA system has been calibrated against known melting temperatures in the system NaCl-KCl. Isobaric sections of the liquidus in the system NaCl-KCl have been determined at pressures of 1 atmosphere and 500, 1000, 1500, and 2000 bars. Using the least-squares method, the following equation was used to fit the experimental data: where T is the liquidus temperature, X_KCl is mole fraction of KCl, and a_i (listed below) are the derived empirical constants.

Oxygen isotope fractionations involving pyroxenes: The calibration of mineral-pair geothermometers     

Alan Matthews  Julian R. Goldsmith  Robert N. Clayton 《Geochimica et cosmochimica acta》1983,47(3):631-644

Oxygen isotope fractionations between wollastonite, diopside, jadeite, hedenbergite and water have been experimentally studied at high pressures (1<- PH₂O ≥ 24 kbar) and temperatures (400/dg ≤ T <- 800/dgC) using the three-isotope method (Matsuhisa et al., 1978). Initial ${}^{18}\text{O}{}^{16}\text{O}$ fractionations were made close to equilibrium and initial ${}^{17}\text{O}{}^{16}\text{O}$ ratios were well removed from equilibrium, allowing accurate determinations of the equilibrium ${}^{18}\text{O}{}^{16}\text{O}$ fractionations and of the extent of isotopic exchange. Scanning electron microscope and rate studies show that the wollastonite-water and diopside-water exchange reactions occur largely by solution-precipitation (Ostwald Ripening) mechanisms. Equilibrium ${}^{18}\text{O}{}^{16}\text{O}$ fractionations between water and the minerals wollastonite, diopside, and hedenbergite are in close agreement with one another, whereas significantly more positive fractionations are found for jadeite-water. These isotopic substitution effects can be ascribed to replacement of SiOM bonds (M is a divalent metal cation in octahedral coordination) by higher frequency SiOAl bonds. The fractionations determined in this study can be combined with quartz- and feldspar-water data of Matsuhisa et al. (1979) and revised magnetite-water data of O'NEIL (1963), to provide a coherent set of mineral-pair fractionations satisfactorily represented by straight lines through the origin on a conventional graph of In /ga versus T^?2. Mineral-water data, on the other hand, cannot readily be fitted to the simple relationship suggested by Bottinga and Javoy (1973). Coefficients “A” for the mineral-pair fractionations 1000 ln α = A × 10⁶T^?2 are:

Studies in diffusion—III. Oxygen in feldspars: an ion microprobe determination     

B.J Giletti  M.P Semet  R.A Yund 《Geochimica et cosmochimica acta》1978,42(1):45-57

Self-diffusion of oxygen in adularia, anorthite, albite, oligoclase and labradorite has been measured by isotope exchange of oxygen between natural feldspars and hydrothermal water enriched in ¹⁸O. The analysis consisted of measuring the ¹⁸O/¹⁶O gradient inward from the feldspar surface using an ion microprobe, and fitting a solution of the diffusion equation to the data. Depth of the sputtered hole was measured with an optical interferometer. Linear Arrhenius plots were obtained:

Oxygen and carbon isotope geochemistry of the Krivoy rog iron formation,Ukranian SSR     

E.C. Perry  S.N. Ahmad 《Lithos》1981,14(2):83-92

Oxygen and carbon isotope analyses of samples from three mines in the Krivoy Rog iron formation, Ukranian SSR, are reported here. Maximum and minimum quartz-magnetite fractionation values ($\text{Δ}{}_{\mathrm{<mtext>QM</mtext>}}$) and inferred temperature range in degrees centrigrade for each mine are:

Oxygen isotope fractionation between zoisite and water     

Alan Matthews  Julian R. Goldsmith  Robert N. Clayton 《Geochimica et cosmochimica acta》1983,47(3):645-654

Oxygen isotope fractionations between zoisite and water have been studied at 400–700°C, PH₂O = 13.4 kbar, using the three-isotope method described by Matsuhisaet al. (1978) and Matthewset al. (1983a). The zoisite-waier exchange reaction takes place extremely slowly and consequently direct-exchange calibration of equilibrium ${}^{18}\text{O}{}^{16}\text{O}$ fractionation factors was possible only at 600 and 700°C. Fractionation factors at 400–600°C were determined from samples hydrothermally crystallized from a glass of the anhydrous zoisite composition. At 600°C, both exchange procedures gave identical fractionations within experimental error. Scanning electron microscope studies showed that the zoisite-water exchange reaction occurs largely by solution-precipitation mass-transfer mechanisms. The slow kinetics of zoisite-water exchange may be typical of hydrous silicates, since additional experiments on tremolite-water and chlorite-water exchange also showed very low rates. When the zoisite-water fractionation factors determined in this study are combined with the quartz and albite-water data of Matsuhisaet al. (1979) and the calcite-water data of O'Nellet al. (1969), mineral-pair fractionations are obtained for which the coefficients “A” in the equation 1000 In α = A × 10⁶T^?2 are:

The kinetics of silica-water reactions     

J.D. Rimstidt  H.L. Barnes 《Geochimica et cosmochimica acta》1980,44(11):1683-1699

A differential rate equation for silica-water reactions from 0–300°C has been derived based on stoichiometry and activities of the reactants in the reaction SiO₂(s) + 2H₂O(l) = H₄SiO₄(aq) where ($\text{A}\text{M}$) = (the relative interfacial area between the solid and aqueous phases/the relative mass of water in the system), and k₊ and k_? are the rate constants for, respectively, dissolution and precipitation. The rate constant for precipitation of all silica phases is $\text{log k}{}_{\mathrm{?}}\text{= ? 0.707 ?}\text{2598}\text{T}\text{(T, K)}$ and E_act for this reaction is 49.8 kJ mol^?1. Corresponding equilibrium constants for this reaction with quartz, cristobalite, or amorphous silica were expressed as $\text{log K = a + bT +}\text{c}\text{T}$. Using $\text{K =}\text{k}{}_{\mathrm{+}}\text{k}{}_{\mathrm{?}}$, k was expressed as $\text{log k}{}_{\mathrm{+}}\text{= a + bT +}\text{c}\text{T}$ and a corresponding activation energy calculated:

Sorption of noble gases by solids,with reference to meteorites. II. Chromite and carbon     

Jongmann Yang  Edward Anders 《Geochimica et cosmochimica acta》1982,46(6):861-875

We studied trapping of noble-gases by chromite and carbon: two putative carriers of primordial noble gases in meteorites. Nineteen samples were synthesized in a Ne-Ar-Kr-Xe atmosphere at 440 K to 720 K, by the following reactions: Fe,Cr + 4H₂O → (Fe,Cr)₃O₄ + 4H₂ (1) or Fe,Cr + 4CO → (Fe,Cr)₃O₄ + 4C + carbides (2)The reactant metal films were prepared either by vacuum evaporation of alloy or by thermal decomposition of Fe- and Cr-carbonyls. The products—including Fe₃O₄, Cr₂O₃, carbides, and unreacted metal—were partially separated by selective solvents, such as HCl, H₂SO₄?H₃PO₄, or HClO₄. Samples were characterized by XRD, SEM, and atomic absorption; noble gases were measured by mass spectrometry. Surface areas, as measured by the BET method, were 2 to 100 m²/g.All samples are dominated by an adsorbed noble gas component that is largely released upon heating at ?400°C or slight etching. Elemental abundance patterns show that this component is derived from the highest-pressure noble gas reservoir seen by the sample—atmosphere or synthesis vessel—indicating that desorption or exchange rates at room T are slow on the time scale of our experiments (up to 1 year). Adsorptive capacity is reduced by up to 2 orders of magnitude upon light etching with HClO₄ (though the surface area actually doubles in this treatment) and, less drastically, by heating. Apparently some active adsorption sites are destroyed by these treatments. A trapped component (typically 30% of the total) is readily detectable only in samples synthesized at partial pressures close to or greater than atmospheric.Noble gas contents roughly obey Henry's Law, but show only slight, if any, correlations with composition, surface area, or adsorption temperature. (Geometric) mean distribution coefficients for bulk samples and HCl-residues are, in 10^?3 cc STP/g atm: Xe (100), Kr (15), Ar (3.5), Ne (0.62). Elemental fractionations are large and variable, but are essentially similar for the adsorbed and trapped components, or for chromite and carbon. They bracket the values for the corresponding meteoritic minerals.

The MgO-Al₂O₃-SiO₂ system: free energy of pyrope and Al₂O₃-enstatite     

S.K. Saxena 《Geochimica et cosmochimica acta》1981,45(6):821-825

Using the model of fictive ideal components, Gibbs free energies of formation of pyrope and Al₂O₃-enstatite have been determined from the experimental data on coexisting garnet and orthopyroxene and orthopyroxene and spinel in the temperature range of 1200–1600 K. The negative free energies in kJ/mol are:

Pallasites—metal composition,classification and relationships with iron meteorites     

Edward R.D Scott 《Geochimica et cosmochimica acta》1977,41(3):349-360

Concentrations of Au, As, Co, Ga, Ge, Ir, Ni and W were determined in the metal of 28 different pallasites plus 6 which are probably paired, to help elucidate their origin. Most divide into two clusters:

The chemical classification of iron meteorites—VII. A reinvestigation of irons with Ge concentrations between 25 and 80 ppm     

Edward R.D Scott  John T Wasson  V.F Buchwald 《Geochimica et cosmochimica acta》1973,37(8):1957-1983

We report Ni, Ga, Ge and Ir concentrations for 193 irons. The compositional trends in groups IIIA and IIIB are redefined, and the suggestion by Wasson and Kimberlin that they represent a single fractionation sequence (group IIIAB) is confirmed. A new group, HIE, is similar in its properties to group IIIA but distinguished by lower Ga/Ni and Ge/Ni ratios, larger bandwidths and the formation of haxonite (Fe, Ni)₂₃C₆ in each of its members. A sixth member, Hassi-Jekna, has been added to group IIIC, extending its Ge range up to 70 ppm. The characteristics of these groups can be summarized as follows:

Chemical classification of iron meteorites—VIII. Groups IC. IIE,IIIF and 97 other irons     

Edward R.D Scott  John T Wasson 《Geochimica et cosmochimica acta》1976,40(1):103-115

Concentrations of Ni, Ga, Ge and Ir in 106 iron meteorites are reported. Three new groups are defined: IC, IIE and IIIF containing 10, 12 and 5 members, respectively, raising the number of independent groups to 12. Group IC is a cohenite-rich group distantly related to IA. Group IIE consists of those irons previously designated Weekeroo Station type and five others having similar compositions though diverse structures. The IIE irons are compositionally similar to the mesosiderites and pallasites, and the three groups probably formed at similar heliocentric distances. The mixing of the globular IIE silicates with the metal probably occurred during shock events. Group IIIF is a well-defined group of low-Ni and low-Ge irons. The compositions of these groups are summarized as follows:

Low-temperature heat capacities of synthetic pyrope,grossular, and pyrope₆₀grossular₄₀     

H.T. Haselton  E.F. Westrum 《Geochimica et cosmochimica acta》1980,44(5):701-709

The heat capacities of synthetic pyrope (Mg₃Al₂Si₂O₁₂), grossular (Ca₃Al₂Si₃O₁₂) and a solid solution pyrope₆₀grossular₄₀ (Mg_1.8Ca_1.2Al₂Si₃O₁₂) have been measured by adiabatic calorimetry in the temperature range 10–350 K. The samples were crystallized from glasses in a conventional piston-cylinder apparatus.The molar thermophysical properties at 298.15 K (J mol^?1 K^?1) are:

Further evidence of the complexity of the racemization process in fossil shells with implications for amino acid racemization dating     

《Geochimica et cosmochimica acta》1987,51(4):839-846

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Paleomagnetism and the alpine tectonics of Eurasia V: The paleomagnetism of some mesozoic and cenozoic volcanic rocks from the lebanon     

C.B Gregor  S Mertzman  A.E.M Nairn  J Negendank 《Tectonophysics》1974,21(4):375-395

A sampling of Mesozoic and Tertiary basalts in Lebanon yielded the following information: