Two forsterite-bearing FUN inclusions in the Allende meteorite     

Robert N. Clayton  Glenn J. MacPherson  Ian D. Hutcheon  Andrew M. Davis  Lawrence Grossman  Toshiko K. Mayeda  Carol Molini-Velsko  John M. Allen  Ahmed El Goresy 《Geochimica et cosmochimica acta》1984,48(3):535-548

We have discovered two FUN inclusions, CG-14 and TE, among a group of five forsterite-rich inclusions in Allende, two of which are described for the first time herein. All five consist of euhedral forsterite and spinel crystals poikilitically enclosed by fassaite. Forsterite and spinel are usually segregated from one another, sometimes into a spinel-rich mantle and a forsterite-rich core. Some inclusions contain vesicles, indicating that they were once molten. The crystallization sequence inferred from textures is: spinel, forsterite, fassaite and, finally, Mg-rich melilite. One concentrically-zoned inclusion contains melilite in its mantle whose composition lies on the opposite side of the liquidus minimum in the melilite binary from that in its core. This suggests that segregation of forsterite from spinel in all of these inclusions could be due to volatilization of MgO and SiO₂ relative to Al₂O₃ and CaO from the outsides of droplets. CG-14 is relatively uniformly enriched in refractory elements relative to Cl chondrites by a factor similar to that for Ca-, Al-rich coarse-grained inclusions except for Ca, Al and Hf which are unusually low. No Ce anomaly such as found in FUN inclusions Cl and HAL is present in CG-14. Whole-rock samples of CG-14 and TE are more strongly mass-fractionated in oxygen relative to “normal” Allende inclusions than the FUN inclusion EK 1-4-1 and less so than Cl. Relative to bulk Allende, both inclusions have strongly massfractionated magnesium and silicon and ²⁵Mg excesses or deficits of ²⁴Mg or ²⁶Mg. CG-14 has a ²⁹Si excess or a deficit of ²⁸Si or ³⁰Si. Volatilization loss cannot be responsible for the magnesium and silicon isotope fractionations, as this would require prohibitively large mass loss from these magnesium-rich inclusions. The remarkable similarity in textures between FUN and non-FUN inclusions implies similar thermal histories, arguing against different rates of evaporative loss of major elements. Sputtering alone may be insufficient to account for the magnitude and direction of oxygen isotope fractionation in FUN inclusions.  相似文献   

X-ray absorption spectroscopic studies of silicate glasses and minerals     

Georges Calas  Gordon E. Brown Jr.  Glenn A. Waychunas  Jacqueline Petiau 《Physics and Chemistry of Minerals》1987,15(1):19-29

Selected results of x-ray absorption spectroscopy (XAS) studies of amorphous silicates and minerals are presented in order to show their utility in providing short-and, in certain cases, medium-range structural and bonding information for cations and anions. EXAFS and XANES studies of amorphous silicates are reviewed with the objective of illustrating variations in structural environments of the various types of glass-forming cations, including Si, Al, Na, K, Ca, Ti, Fe, Yb, and U. Al is shown to occur in tetrahedral coordination in all aluminosilicate glasses examined, including peraluminous compositions. The weakly bonded Na and Ca cations are shown to occur in sites with observed coordination numbers (ranging from 6 to 7) and distances similar to those predicted by molecular dynamics simulations. Elements like Ti, which form bonds of intermediate strength, may show some order beyond the first coordination shell at low concentrations in silicate glasses. EXAFS studies of Yb and U in silicate glasses at trace to minor concentration levels provide unique structural information about the environments of these cations. K-edges and XANES of transition element sulfides, third-row tetrahedral oxyanions, and oxygen in minerals are interpreted in terms of band theory or molecular orbital theory.  相似文献   

Drainage of agricultural land: U.S. Soil Conservation Service, 1973. Water Information Center Inc., Port Washington,N. Y., 423 pp., U.S. $7.95     

Glenn O. Schwab 《Earth》1973,9(4):380-381

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A corundum-rich inclusion in the Murchison carbonaceous chondrite     

Miryam Bar-Matthews  Ian D Hutcheon  Glenn J MacPherson  Lawrence Grossman 《Geochimica et cosmochimica acta》1982,46(1):31-41

A corundum-hibonite inclusion, BB-5, has been found in the Murchison carbonaceous chondrite. This is the first reported occurrence of corundum as a major phase in any refractory inclusion, even though this mineral is predicted by thermodynamic calculations to be the first condensate from a cooling gas of solar composition. Ion microprobe measurements of Mg isotopic compositions yield the unexpected result for such an early condensate that ²⁶Mg excesses are small: δ_N²⁶Mg = 7.0 ± 1.6%. for hibonite and 5.0 ± 4.8%. for corundum, despite very large ${}^{27}\text{Al}{}^{24}\text{Mg}$ ratios, 130 and 2.74 × 10⁴, respectively. Within the errors, δ_N²⁶Mg does not vary over this exceedingly large range of ${}^{27}\text{Al}{}^{24}\text{Mg}$ ratios. The extreme temperature required to melt this inclusion makes a liquid origin unlikely, except possibly by hypervelocity impact involving refractory bodies. If, instead, BB-5 is a direct gas-solid condensate, textural evidence implies that corundum formed first and later reacted to produce hibonite. In this model, BB-5's uniform enrichment in ²⁶Mg must be a characteristic of the reservoir from which it condensed. Because severe difficulties are encountered in making such a reservoir by prior decay of ²⁶Al, nebular heterogeneity in magnesium isotopic composition is a preferred explanation.  相似文献   

Seismic stratigraphy and sedimentation history of the East Mariana Basin,western Pacific     

Thomas H. Shipley  Jill M. Whitman  Frederick K. Duennebier  Lisa D. Petersen 《Earth and Planetary Science Letters》1983,64(2):257-275

An interpretation of the seismic stratigraphy and sedimentation history of the East Mariana Basin has been made using recently collected seismic reflection and refraction data. This Mesozoic(?) age basin, between the Marshall Islands and the Mariana Trench, is subdivided into three regions. The central region with about 1000 m of sediment probably records Jurassic to Late Cretaceous sedimentation of a pelagic biogenic and clay-rich section overlain by a thick section of mainly Cenozoic carbonates shed from nearby volcanic platforms. A western region is characterized by a thinner sediment cover and a shallower acoustic basement with a similar sedimentation history except that the upper section is thinner as a consequence of fewer nearby volcanic highs. Extensive Late Cretaceous mid-plate volcanics apparently masks the lower section and forms acoustic basement. The shallower eastern region (east of 157.5°E) contains WNW-trending ridges which may be either fracture zones or high-amplitude abyssal hills. The sedimentation appears controlled by the same factors as in the other regions but the area was bypassed by most Cenozoic basin-filling turbidites because of its elevation.The isostatistically corrected basement depths between the three regions suggest that the crust in the east may be substantially younger than in the rest of the East Mariana Basin, perhaps Cretaceous in age. This requires the existence of a tectonic boundary within the basin.  相似文献   

Bio-controlled thermostasis involving the sulfur cycle   总被引：4，自引：0，他引：4  

Glenn E. Shaw 《Climatic change》1983,5(3):297-303

The Gaia hypothesis proposed by Lovelock and Margulis presumes the existence of an unspecified biological means of ameliorating climate that has operated since the emergence of life 3500 Myr ago: Recently it was suggested that the mechanism of thermostasis may involve biospheric cycling of atmospheric carbon dioxide. We suggest an alternative hypothesis of biothermostasis operating through the sulfur cycle, rather than the carbon cycle. The mechanism would operate by altering planetary albedo through the selective creation of biospheric organic sulfide gases which go on to metamorphize into submicron particles and introduce cooling. In contrast to the carbon-cycle mechanism, sulfur-based cooling would have the ability to ameliorate climate well into the future, in principle over stellar Main Sequence time intervals. The main feature of interest is that the S cycle represents a particularly favorable thermodynamic pathway, involving three to four orders of magnitude less mass of active material cycled through the biospheric-atmospheric system (in response to a given temperature-imposed stress) than would be the case for a greenhouse gas hypothesis. There is no evidence that the suggested biospheric controlled particle-albedo change mechanism is actually operating, but we speculate that the probability of its rising importance and perhaps eventual dominance will improve when the partial pressure of atmospheric CO₂ drops low enough to impose stress on metabolic processes. The intriguing thing about the process is its extremely high efficiency.  相似文献   

A New Method for Simultaneous Measurement of Cl⁻, Br⁻, NO₃⁻, SCN⁻, and I⁻ at Sub-ppm Levels in Ground Water     

Klaus J. Stetzenbach  Glenn M. Thompson 《Ground water》1983,21(1):36-41

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Anomalies in temperature and rainfall during warm Arctic seasons     

Jill Jäger  William W. Kellogg 《Climatic change》1983,5(1):39-60

The regional patterns of change of temperature and rainfall that might accompany a global warming due to increased carbon dioxide can be studied by experiments with theoretical models of the climate system, by reconstructing the climates of past warm epochs, and by determining the anomalies of temperature and precipitation that prevailed during years or seasons when the Arctic region was unusually warm. The current study pursues the last course, making use of the northern hemisphere meteorological data record for the period 1931–1978. Hemispheric maps of anomalies of both temperature and precipitation are presented for the 10 warmest Arctic seasons and years, and for differences between the 5 warmest and 5 coldest consecutive Arctic winters. Wintertime anomalies are generally greatest and dominate in determining the annual averages. The hemispheric temperature anomalies for these data sets are similar to those determined earlier by the first author (Williams, 1980) using 1900–1969 data, but the precipitation anomalies (for North America alone) show more variation, partly due to the method of computing the anomalies. Work reported here begun while a visitor to the National Center for Atmospheric Research. The National Center for Atmospheric Research is sponsored by the National Science Foundation.  相似文献   

In situ oxygen,magnesium, and silicon isotopic compositions of the FUN inclusion Vigarano 1623-5     

Johanna Marin-Carbonne  Kevin D. McKeegan  Andrew M. Davis  Glenn J. MacPherson  Ruslan A. Mendybaev  Frank M. Richter 《Meteoritics & planetary science》2023,58(4):546-571

Oxygen, magnesium, and silicon isotopic abundances in Vigarano 1623-5 were studied using secondary ion mass spectrometry to investigate correlations between isotopic and petrologic properties of this unique forsterite-bearing FUN inclusion. Vigarano 1623-5 displays large, correlated mass-dependent fractionation effects, tightly linked to mineralogy within distinct petrologic units of the inclusion. The pyroxene-rich and melilite-rich interior parts of the inclusion display highly mass-fractionated isotopic compositions of oxygen, magnesium, and silicon, consistent with Rayleigh distillation during evaporation of a melt with initial oxygen composition close to a solar composition. However, the chemical composition, enriched in magnesium and silicon, suggests a precursor already fractionated by prior melt evaporation. A discontinuous igneous rim was produced by a flash-melting event followed by isotopic exchange in the rim melilite with planetary-like oxygen, mechanical fragmentation, and reassembly with an accretionary rim of heterogeneous materials. Al-rich minerals in 1623-5 show evidence for having crystallized with live ²⁶Al but at less than the “canonical” level of most CV calcium-aluminum-rich inclusions. However, well-defined ²⁶Al-²⁶Mg isochrons are not found and temporal implications are ambiguous.  相似文献   

Preface to Owen P. Bricker III Special Issue of Aquatic Geochemistry     

Suzanne B. Bricker  Fred T. Mackenzie  Jill S. Baron  Jason R. Price 《Aquatic Geochemistry》2014,20(2-3):81-86

This special volume of aquatic geochemistry is dedicated to the memory of Owen Peterson Bricker III (1936–2011) and serves as a tribute to his life and career. Owen had a distinguished and productive research career in both academics at Johns Hopkins University (Fig. 1) and as a public servant with the Maryland Geological Survey, the US Environmental Protection Agency, and the US Geological Survey. He was a pioneer and leader in aqueous geochemistry, who applied a study approach that quantified mineral weathering reactions and equilibrium thermodynamic relations to better understand the chemical evolution of stream water in small watersheds. He will be especially remembered for his efforts to establish rigorous field studies in small catchments around the United States as a means of quantifying the sources of acid-neutralizing capacity that affect the chemical status and biological health of natural waters.