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1.
Direct measurements on water samples from several CO2-charged warm springs are significantly higher than values calculated from field pH and alkalinity (and other constituents). In addition, calcite saturation indices calculated from field pH and solution composition indicated supersaturation in samples which, on the basis of hydrogeologic concepts, should be near saturation or undersaturated. We attribute these discrepancies to uncertainties in field pH, resulting from CO2 outgassing during pH measurement. Because samples for direct measurement can be taken with minimal disturbance to the water chemistry, we have used the measured to back calculate an estimate of the field pH and the carbon isotopic composition of the water before outgassing. By reconstructing water chemistry in this way, we find generally consistent grouping of , pH, and degree of calcite saturation in samples taken from the same source at different times, an observation which we expect based on our understanding of the hydrogeology and geochemistry of the ground-water systems. This suggests that for very careful geochemical work, particularly on ground-waters much above ambient temperature, measurements may provide more information on the system and a better estimate of its state of saturation with respect to carbonate minerals than can field measurements of pH. 相似文献
2.
We have studied fission tracks in phosphates from one gas-poor chondrite and three gas-rich chondrites to determine their thermal history and brecciation time scales. More than 70 percent of the tracks in whitlockites in these meteorites are due to the decay of extinct Pu244.Whitlockites separated from Bhola, a gas-poor chondrite, have and a model fission track age of 4.0 Gyr for a . Brecciation of the Bhola meteorite must have occurred at ?4.3 Gyr to account for the metal data (Scott and Rajan, 1981). A minimum cooling rate of in the temperature interval 800 to 300 K obtained from the track data is a factor of seven higher than the metallographic cooling rate ().For the gas-rich chondrites, the in whitlockites are: Weston, 32–148; Fayetteville, 21–227; and St. Mesmin, 26–137. Whitlockites from all these meteorites give model fission track ages of 4.4 Gyr assuming a . The final brecciation event definitely did not reset the track clock in phosphates of St. Mesmin. Our data suggest that it is also true for Weston and Fayetteville. We conclude that our observed fission track ages date the end of metamorphic cooling in the meteorite parent bodies and support the planetesimal model for the formation of xenolithic chondrites. 相似文献
3.
Stephen E Haggerty 《Geochimica et cosmochimica acta》1973,37(4):857-867
Electron microprobe analyses of the spinel mineral group, ilmenite and rutile have been carried out on part of the Luna 20 soil sample. The spinel group shows an almost continuous trend from MgAl8O4 to FeCr2O4 and a discontinuous trend from FeCr2O4 to Fe2TiO4. Well defined non-linear relationships exist within the spinel group for Fe-Mg substitution, for divalent () versus trivalent (), and for divalent versus . For Cr-Al substitution the relationship is linear and is negative for Mg-rich spinel and positive for Fe-Ti rich spinel. In general a combination of aluminous-rich chromite and ulvöspinel in the Luna 16 samples, combined with the chromian-pleonaste in Apollo 14 define comparable major compositional trends to those observed in Luna 20. Ilmenite is present in trace amounts. It is exsolved from pleonaste and pyroxene, is present in subsolidusreduced ulvöspinel and has undergone reequilibration to produce oriented intergrowths of chromite + rutile. Primary ilmenite is among the most magnesian-rieh (6 wt.% MgO) yet found in the lunar samples. The high MgO, inferred high Cr2O3 concentrations and the iron content of rutile (2.5 wt.% FeO) suggest crystallization at high temperatures and pressures for some components of the Luna 20 soil. 相似文献
4.
The cordierite-gedrite-cummingtonite rocks occur in the zone of sulphide mineralization. Field and petrographic evidences suggest formation of these rocks from the schists which are associated with them. Time relations between crystallization and deformation, as evident by textural relations, suggest that this transformation constitutes a progressive sequence in time during prograde metamorphism in the area. Bulk chemical compositions of the cordierite-gedrite-cummingtonite rocks plot in the compositional range of the chlorite schists in the AKF, ACF and AFM diagrams. The AFM diagram shows a discontinuity in the topology as revealed by the intersection of the coexisting garnet-chlorite join with the three-phase field of cordierite-gedrite-garnet, suggesting the reaction: . The reaction took place under conditions of , brought about by dilution of pore fluid by B, Cl, F, S, etc., which reduce the activity of water. 相似文献
5.
Equations are developed for calculating the density of aluminosilicate liquids as a function of composition and temperature. The mean molar volume at reference temperature Tr, is given by , 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 is the composition-dependent apparent partial molar volume of Al2O3. The thermal expansion coefficient of aluminosilicate liquids is given by , where terms are constants independent of temperature and composition, and 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) = Vrexp[α(T-Tr)], where Tr = 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 and an average absolute difference of 0.90% for 248 experimental observations. The compositional dependence of is discussed in terms of several possible interpretations of the structural role of Al3+ in aluminosilicate melts. 相似文献
6.
The isotopic composition of Ag and the concentration of Ag and Pd have been determined in Canyon Diablo (IA), Grant (IIIB), Hoba, Santa Clara, Tlacotepec and Warburton Range (IVB), Piñon and Deep Springs (anom.). Troilite from Grant and Santa Clara have also been analyzed. All of these meteorites, with the exception of Canyon Diablo, give in the metal phase that is greater than the terrestrial value with the enrichments of 107Ag ranging from ~2% to 212%. These data show that Ag of anomalous isotopic composition is common to all IVB and anomalous meteorites. The results on Grant suggest that the anomalies may be widespread including more common meteorite groups. There is a general correlation of with except for the data from FeS of Santa Clara. It is concluded that the excess 107Ag is the result of decay of 107Pd, a nuclide that is extinct at present with an abundance of of about 3 × 10?5. The troilite in Grant exhibits normal to within errors, a high Ag concentration and a low ratio of ~0.17. Grant metal has that is ~2% greater than normal and a high ratio of ~ 103. The data from Grant appear to represent a 107Pd-107Ag isochron and indicate that the cooling rate at elevated temperatures was sufficiently rapid to preserve substantial isotopic differences between metal and troilite. Troilite in Santa Clara was found to contain Ag with a very high ratio (108% above normal), an Ag concentration only a factor of three above the metal and a high value of ~1.3 × 104. The troilite has a higher than the metal. These data are not compatible with a simple model of in situ decay and subsequent local Ag redistribution between metal and troilite during cooling. These data suggest that Ag in Santa Clara and possibly other IVB meteorites is made up of almost pure 107Ag produced from 107Pd decay and 109Ag produced by nuclear reactions with only a small amount of “normal” Ag. This indicates an intense energetic particle bombardment history in the early solar system (~1020 p/m2) which occurred after the formation of small planetary bodies. We infer that a T-Tauri activity by the early sun contributed to some late stage “nucleosynthesis” and the heating of a dust cloud. In addition, implications on the early thermal evolution of iron meteorites are presented based on 107Pd decay and models of the cooling history. 相似文献
7.
Tadao Nishiyama 《Geochimica et cosmochimica acta》1983,47(2):283-294
This paper describes an application of a steady diffusion model (Joesten, 1977) to an olivineplagioclase corona and some new results about a theoretical background on the steady diffusion equations.The olivine-plagioclase corona in a metanorite from Mt. Ikoma. Japan, has a layer sequence of olivinecummingtonite-hornblende + spinel-plagioclase. An analysis of a set of steady diffusion equations for the corona in the four-component system, MgO-AlO-SiO2-Na0.1Ca0.9O0.95 (NC) with excess H2O. successfully gives the exchange cycle (Fisher, 1973) in the layer sequence with specific values of the phenomenological coefficients' ratios; , and . The factor which controls most strictly the stability of the layer sequence under isobaric-isothermal conditions is .Theoretical considerations on the steady diffusion equations show that the L-ratios does not depend on concentrations even if the phenomenological coefficients themselves are functions of concentrations. Equivalence of the steady state condition and the minimum rate of entropy production law (Prigogine, 1967) is also proved for the system with fixed chemical potential gradients under isobaric-isothermal conditions, such as reaction bands. These results give a strong background for the model. 相似文献
8.
The fractionation factors () 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 () approximating the observed fractionation. 相似文献
9.
Charles D Byers David W Muenow Michael O Garcia 《Geochimica et cosmochimica acta》1983,47(9):1551-1558
Glasses from submarine lavas recovered by the ALVIN submersible from the Galapagos Spreading Center (GSC) near 86°W have been analyzed by electron microprobe for major elements and by high-temperature mass spectrometry for volatiles. The samples studied range in composition from basalt to andesite and are more evolved than typical MORBs. Previous studies indicate that they are related to normal MORB by extensive crystal fractionation in small, isolated magma chambers. The H2O, Cl and F contents of these lavas are substantially higher than any previously reported for MORBs. H2O, Cl and F abundances increase linearly with P2O5 content, which is used as an indicator of the extent of crystal fractionation. The ratios measured in the andesite glasses progressively decrease with increasing P2O5 content and are probably related to fractionation of Fe-Tioxides. Reduced carbon gas species, principally CH4 and CO, were discovered in these glasses. The presence of reduced carbon species in GSC glasses may be indicative of a more reduced oxidation state of the upper mantle than is commonly assumed. 相似文献
10.
Archean clastic sedimentary rocks are well exposed in the Pilbara Block of Western Australia. Shales from turbidites in the Gorge Creek Group (ca. 3.4 Ae) and shales from the Whim Creek Group (ca. 2.7 Ae) have been examined. The Gorge Creek Group samples, characterized by muscovite-quartzchlorite mineralogy, are enriched in incompatible elements (K, Th, U, LREE) by factors of about two, when compared to younger Archean shales from the Yilgarn Block. Alkali and alkaline earth elements are depleted in a systematic fashion, according to size, when compared with an estimate of Archean upper crust abundances. This depletion is less notable in the Whim Creek Group. Such a pattern indicates the source of these rocks underwent a rather severe episode of weathering. The Gorge Creek Group also has fairly high B content (85 ± 29 ppm) which may indicate normal marine conditions during deposition.Rare earth element (REE) patterns for the Pilbara samples are characterized by light REE enrichment () and no or very slight Eu depletion (). A source comprised of about 80% felsic igneous rocks without large negative Eu-anomalies (felsic volcanics, tonalites, trondhjemites) and 20% mafic-ultramafic volcanics is indicated by the trace element data. Very high abundances of Cr and Ni cannot be explained by any reasonable provenance model and a secondary enrichment process is called for. 相似文献
11.
Solubility product of galena at 298°K: A possible explanation for apparent supersaturation in nature
The synthetic chelating agent ethylenediaminetetraacetic acid (EDTA) has been used to evaluate the stoichiometric solubility product of galena (PbS) at 298°K: This method circumvents the possible uncertainties in the stoichiometry and stability of lead sulfide complexes. At infinite dilution, , and at an ionic strength corresponding to seawater (), . Using the value of at infinite dilution, and the free energies of formation of HS? and Pb2+ at 298°K (literature values), the free energy of formation of PbS at 298°K is computed to be . Galena is shown to be more than two orders of magnitude more soluble than indicated by calculations based on previous thermodynamic data. 相似文献
12.
age spectrum analyses of three microcline separates from the Separation Point Batholith, northwest Nelson, New Zealand, which cooled slowly (~5°C-Ma?1) through the temperature zone of partial radiogenic 40Ar accumulation are characterized by a linear age increase over the first 65 percent of gas release with the lowest ages (~80 Ma) corresponding to the time that the samples cooled below about 100°C. The last 35 percent of 39Ar released from the microclines yields plateau ages (103,99 and 93 Ma) which reflect the different bulk mineral ages, and correspond to cooling temperatures between about 130 to 160°C. Theoretical calculations confirm the likelihood of diffusion gradients in feldspars cooling at rates ≤5°C-Ma?1. Diffusion parameters calculated from the 39Ar release yield an activation energy, E = 28.8 ± 1.9 kcal-mol?1, and a frequency factor/grain size parameter, . This Arrhenius relationship corresponds to a closure temperature of 132 ± 13°C which is very similar to the independently estimated temperature. From the observed diffusion compensation correlation, this implies an average diffusion half-width of about 3 μm, similar to the half-width of the perthite lamellae in the feldspars. The range in microcline K-Ar ages from the Separation Point Batholith is the result of relatively small temperature differences within the pluton during cooling. Comparison of the diffusion laws determined for microcline with those for anorthoclases and other homogeneous K-feldspars (E = 40 to 52 kcal-mol?1) reveals that Ar diffusion is more highly temperature dependent in the disordered structural state than in the ordered structural state. Previously published U-shaped age spectra are probably the result of the superimposition of excess 40Ar upon diffusion profiles of the kind described here. 相似文献
13.
Major-element, trace-element and isotopic compositions of approximately 1200 basalts (< 53 wt. % SiO2) from intra-oceanic island arcs have been compiled to assess the nature and possible sources of primitive island-arc basalts (IAB). The chemical characteristics of IAB are examined with reference to those of mid-ocean ridge basalts (MORB) and intraplate oceanic basalts (IPB). Major-element compositions of primitive [] IAB and MORB are similar, but differ significantly from IPB. In general, IAB do not have higher Al2O3, lower TiO2 or a lack of Fe enrichment compared to primitive MORB but many do have greater K2O contents. Differences in major- and minor-element contents between more evolved IAB and MORB result from the dominance of plagioclase + olivine crystal fractionation in MORB magmas vs. clinopyroxene + olivine controlled fractionation in IAB suites. This difference in crystallization history may be related to the higher PH2O or greater depth of crystallization of IAB magmas compared to those inferred for MORB.IAB are characteristically enriched in large-ion-lithophile (LIL) elements and depleted in high-field-strength ions (e.g., Zr, Nb and Hf) relative to normal MORB (N-type) and IPB. The enrichment of some LIL elements (e.g., Sr, Rb, Ba and Pb) relative to the rare-earth elements in IAB is difficult to explain by simple partial melting alone and suggests a multistage petrogenesis involving an LIL-enriched component. Low abundances of high-field-strength ions in evolved IAB are explicable in terms of fractional crystallization, but the cause for consistently low abundances in primitive IAB remains problematic.Island-arc lavas contain greater concentrations of volatiles and have higher and Cl/F ratios than either MORB or IPB, suggesting involvement of a slab-derived volatile component. However, this is not consistent with data which indicate that only near-trench volcanics have been significantly affected by dehydration of the oceanic crust.Sr-, Nd-, Pb- and O-isotopic data, in conjunction with the trace-element data, clearly indicate that IAB are derived from heterogeneous, LIL-depleted mantle sources most similar to those which give rise to enriched MORB (E-type). The marked shift towards higher in IAB compared to oceanic lavas with similar values cannot be explained simply by the addition of radiogenic Sr from the slab. Variable degrees of contamination from a crustally-derived sedimentary component is consistent with the isotopic and trace-element data from a number of arcs. However, the lack of correlation between LIL/REE ratios and more radiogenic isotopic ratios suggests that this enrichment/contamination process is complex. A multi-stage petrogenetic model involving subducted oceanic crust (± sediments), dehydration/volatile transfer, and partial melting of metasomatized mantle beneath island arcs is considered the most reasonable, although least constrained, method to generate a variety of primitive IAB. 相似文献
14.
Measurements of the isotopic composition of nitrogen in the solar system are summarized. We show that the 30% change, during the last 3 to 4 billion years, of in solar-wind-bearing lunar soils and breccias probably does not reflect changes in this ratio at the solar surface. Such changes, whether by spallation or thermonuclear reactions are ruled out by comparing the yields of 15N with those of other rare isotopes such as 9Be, 11B, 3He or 13C, even if an arbitrary degree of solar mixing is introduced. Moreover, we calculate that the solar activity required for producing significant amounts of 15N by spallation at the solar surface should have resulted in a particle bombardment of the Moon of an intensity that would have produced amounts of spallation isotopes (e.g.15N, 21Ne, 38Ar, 131Xe) several orders of magnitude in excess of what is actually found in the whole regolith.We argue that accretion of interstellar matter also does not work as a cause for a significant change of the photospheric ratio. Evidence is presented that the mixing depth at the solar surface on a time scale of ?109 years is (10?2 ?10?1) M⊙ Mixing to this depth renders accretion of interstellar matter as a source of compositional changes at the solar surface inefficient, even if allowance is made for the expected large difference in the accretion rates of condensed and gaseous matter. A quantitative treatment of several alternatives of solar accretion leads to serious contradictions (e.g. with the low Ne abundances in planetary atmospheres or with the amounts of nitrogen that should have been directly accreted by the Moon), and we conclude that accretion during the main sequence life of the Sun is an unlikely source of changes in at the solar surface.A ratio of is our best estimate for average solar system material and for the Sun. We propose that a rare, very light nitrogen component (called LPN) is admixed in varying amounts to planetary matter. Undiluted LPN has not been found in meteorites or planetary atmospheres, but we show that the combined effects of LPN admixture and isotope fractionation can in principle account for the variability of observed in the planetary system. Determination of the Jovian ratio with an accuracy of ~10% would crucially test our interpretation of the nitrogen isotope observations. 相似文献
15.
The partial molal volume () of silicic acid in 0.725 m NaCl at 20°C has been calculated from (1) direct volume changes due to the dissolution of anhydrous sodium silicate and (2) some literature values for the partial molal volumes of NaOH and water. , unconnected for electrostriction effects, was found to be 53 ± 2 ml mole?1. , corrected for volume changes due to solvent electrostriction by charged Si species, was estimated to be in the range 58–62 ml mole?1; this range is 7–11 ml mole?1 greater than the calculated from Willey's (Mar. Chem. 2, 239–250, 1974) solubility data obtained from the dissolution, in seawater, of amorphous silica subjected to hydrostatic pressure. Our does, however, agree within experimental error with the calculated from Jones and Pytkowicz's (Bull. Soc. Roy. Sci. Liege 42, 118–120, 1973) data for the solubility of amorphous silica in seawater at high pressure and is nearly in agreement with Willey's (Ph.D. thesis, Dalhousie University, 1975) solubility data for amorphous silica in 0.6 m NaCl. 相似文献
16.
Robert L. Cullers Subramanian Ramakrishnan Pieter Berendsen Tom Griffin 《Geochimica et cosmochimica acta》1985,49(6):1383-1402
Lamproite sills and their associated sedimentary and contact metamorphic rocks from Woodson County, Kansas have been analyzed for major elements, selected trace elements, and strontium isotopic composition. These lamproites, like lamproites elsewhere, are alkalic (molecular ), are ultrapotassic , are enriched in incompatible elements (LREE or light rare-earth elements, Ba, Th, Hf, Ta, Sr, Rb), and have moderate to high initial strontium isotopic compositions (0.7042 and 0.7102). The silica-saturated magma (olivine-hypersthene normative) of the Silver City lamproite could have formed by about 2 percent melting of a phlogopite-garnet lherzolite under high ratios in which the Iherzolite was enriched before melting in the incompatible elements by metasomatism. The Rose Dome lamproite probably formed in a similar fashion although the extreme alteration due to addition of carbonate presumably from the underlying limestone makes its origin less certain. Significant fractional crystallization of phases that occur as phenocrysts (diopside, olivine, K-richterite, and phlogopite) in the Silver City magma and that concentrate Co, Cr, and Sc are precluded as the magma moved from the source toward the surface due to the high abundances of Co, Cr, and Sc in the magma similar to that predicted by direct melting of the metasomatized Iherzolite.Ba and, to a lesser extent, K and Rb and have been transported from the intrusions at shallow depth into the surrounding contact metamorphic zone. The Silver City lamproite has vertical fractionation of some elements due either to volatile transport or to variations in the abundance of phenocrysts relative to groundmass most probably due to flow differentiation although multiple injection or fractional crystallization cannot be conclusively rejected. 相似文献
17.
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 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 values and their approximate Rb end-member mole fraction () ranges of constancy are summarized as follows: (°C)
(°C)T | ||||
500 | 0–0.2 | 0–0.07 | ||
700 | 0–0.2 | 0–0.1 | ||
800 | 0–0.2 | 0–0.1 |