Partitioning of Rare Earth Elements Between Hibonite and Melt and Implications for Nebular Condensation of the Rare Earth Elements     

Michael J. Drake  William V. Boynton 《Meteoritics & planetary science》1988,23(1):75-80

Abstract— The partitioning of the rare earth elements (REE) between hibonite and silicate melt has been investigated at 1470 °C in the system calcium tschermak's molecule-diopside. Oxygen fugacity was varied between air and the iron-wustite buffer using conventional gas mixing, and to “infinitely reducing” using Sr²⁺ as a surrogate for Eu²⁺. The partition coefficient (D) pattern is light REE enriched with D(La) = 7.15 and D(Yb) = 0.1. D(Eu) varied from about 2 in air to about 0.55 in an “infinitely reducing” atmosphere. Experiments were reversed for Eu and, by implication, a close approach to equilibrium was achieved for other elements. Absolute activity coefficients for REE in hibonite were estimated, yielding γ_La = 330, γ_Eu3+ = 1200, and γ_Yb = 24 000. These results suggest that unless the principal phase(s) into which a trace element is dissolving and the activity—composition relationships for that trace element in that phase(s) are known, condensation temperatures based on assumed ideal solution behavior will generally be in error.  相似文献   

Erratum to: “Culmination of the flare activity of group 10786 in July 2005: X-ray observations from near-Mars and near-Earth orbits”     

M. A. Livshits  D. V. Golovin  L. K. Kashapova  I. G. Mitrofanov  A. S. Kozyrev  M. L. Litvak  A. B. Sanin  V. I. Tret’yakov  W. Boynton  K. Shinohara  D. Hamara 《Astronomy Reports》2011,55(10):943-943

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Role of Late Winter–Spring Wind Influencing Summer Hypoxia in Chesapeake Bay     

Younjoo J. Lee  Walter R. Boynton  Ming Li  Yun Li 《Estuaries and Coasts》2013,36(4):683-696

We examined the processes influencing summer hypoxia in the mainstem portion of Chesapeake Bay. The analysis was based on the Chesapeake Bay Monitoring Program data collected between 1985 and 2007. Self-organizing map (SOM) analysis indicates that bottom water dissolved oxygen (DO) starts to be depleted in the upper mesohaline area during late spring, and hypoxia expands down-estuary by early summer. The seasonal hypoxia in the bay appears to be related to multiple variables, (e.g., river discharge, nutrient loading, stratification, phytoplankton biomass, and wind condition), but most of them are intercorrelated. The winter–spring Susquehanna River flow contributes to not only spring–summer buoyancy effects on estuarine circulation dynamics but also nutrient loading from the land-promoting phytoplankton growth. In addition, we found that summer hypoxia is significantly correlated with the late winter–spring (February–April) northeasterly–southwesterly (NE–SW) wind. Based on winter–spring (January–May) conditions, a predictive tool was developed to forecast summer (June–August) hypoxia using river discharge and NE–SW wind. We hypothesized that the late winter–spring wind pattern may affect the transport of spring bloom biomass to the western shoal or the deep channel of the bay that either alleviates or increases the summer hypoxic volume in the midbay region, respectively. To examine this hypothesis, residual flow fields were analyzed using a hydrodynamic ocean model (Regional Ocean Modeling System; ROMS) between 2000 and 2003, two hydrologically similar years but years with different wind conditions during the spring bloom period. Simulation model results suggest that relatively larger amounts of organic matter could be transported into the deep channel in 2003 (severe hypoxia; frequent northeasterly wind) than 2000 (moderate hypoxia; frequent southwesterly wind).  相似文献   

Water distribution in Martian permafrost regions from joint analysis of HEND (Mars Odyssey) and MOLA (Mars Global Surveyor) data     

N. E. Demidov  W. V. Boynton  D. A. Gilichinsky  M. T. Zuber  A. S. Kozyrev  M. L. Litvak  I. G. Mitrofanov  A. B. Sanin  R. S. Saunders  D. E. Smith  V. I. Tretyakov  D. Hamara 《Astronomy Letters》2008,34(10):713-723

We jointly analyze data from the High-Energy Neutron Detector (HEND) onboard the NASA Mars Odyssey spacecraft and data from the Mars Orbiter Laser Altimeter (MOLA) onboard the Mars Global Surveyor spacecraft. The former instrument measures the content of hydrogen (in the form of H₂O or OH) in the subsurface layer of soil and the latter instrument measures the surface albedo with respect to the flux of solar energy. We have checked the presence of a correlation between these two data sets in various Martian latitude bands. A significant correlation has been found between these data at latitudes poleward of 40° in the northern hemisphere and at latitudes 40°–60° in the southern hemisphere. This correlation is interpreted as evidence for the presence of stable water ice in these regions under a dry layer of soil whose thickness is determined by the condition for equilibrium between the condensation of water from the atmosphere and its sublimation when heated by solar radiation. For these regions, we have derived an empirical relation between the flux of absorbed solar radiation and the thickness of the top dry layer. It allows the burial depth of the water ice table to be predicted with a sub-kilometer resolution based on near-infrared albedo measurements. We have found no correlation in the southern hemisphere at latitudes >60°, although neutron data also suggest that water ice is present in this region under a layer of dry soil. We conclude that the thickness of the dry layer in this region does not correspond to the equilibrium condition between the water ice table and the atmosphere.  相似文献   

Identification and measurement of neutron-absorbing elements on Mercury’s surface     

David J. Lawrence  William C. Feldman  Timothy J. McCoy  William V. Boynton  Larry R. Nittler  Sean C. Solomon 《Icarus》2010,209(1):195-455

MESSENGER Neutron Spectrometer (NS) observations of cosmic-ray-generated thermal neutrons provide the first direct measurements of Mercury’s surface elemental composition. Specifically, we show that Mercury’s surface is enriched in neutron-absorbing elements and has a measured macroscopic neutron-absorption cross section of 45-81 × 10⁻⁴ cm²/g, a range similar to the neutron absorption of lunar basalts from Mare Crisium. The expected neutron-absorbing elements are Fe and Ti, with possible trace amounts of Gd and Sm. Fe and Ti, in particular, are important for understanding Mercury’s formation and how its surface may have changed over time through magmatic processes. With neutron Doppler filtering - a neutron energy separation technique based on spacecraft velocity - we demonstrate that Mercury’s surface composition cannot be matched by prior models, which have characteristically low abundances of Fe, Ti, Gd, and Sm. While neutron spectroscopy alone cannot separate the relative contributions of individual neutron-absorbing elements, these results provide strong new constraints on the nature of Mercury’s surface materials. For example, if all the measured neutron absorption were due to the presence of an Fe-Ti oxide and that oxide were ilmenite, then Mercury’s surface would have an ilmenite content of 7-18 wt.%. This result is in general agreement with the inference from color imaging and visible-near-infrared spectroscopy that Mercury’s overall low reflectance is consistent with a surface composition that is enriched in Fe-Ti oxides. The incorporation of substantial Fe and Ti in oxides would imply that the oxygen fugacity of basalts on Mercury is at the upper range of oxygen fugacities inferred for basalts on the Moon.  相似文献   

Quantitative geochemical mapping of martian elemental provinces     

Olivier Gasnault  G. Jeffrey Taylor  Suniti Karunatillake  James Dohm  Horton Newsom  Olivier Forni  Patrick Pinet  William V. Boynton 《Icarus》2010,207(1):226-341

We present an exploratory approach to the interpretation of the elemental maps produced by the Odyssey Gamma-Ray Spectrometer (GRS). These maps benefit from a direct detection of elemental mass fractions and are used to delineate and characterize elementally homogeneous provinces in the mid-latitudinal martian surface on the basis of chemistry alone. This approach is different from assessing the elemental composition of regions previously defined by their geologic context. Multivariate statistical approaches are discussed and a combination of principal component and clustering analyses is applied on the GRS-based hydrogen, chlorine, potassium, silicon, iron, and calcium maps. At least three principal components must be considered to properly describe the compositional variability seen in the maps. The main component is likely driven by the degree of mantling through a GRS perspective, i.e. by materials enriched in mobile elements (Cl, H) and finer than 10-20 cm, at horizontal and depth scales of hundreds of kilometers and tens of centimeters, respectively. Elemental diversity is found in both mantled and less-mantled provinces, suggesting both local and regional sources for the surficial materials. The less-mantled regions appear to have compositions which include basaltic igneous rocks. Although there is an absence of obvious natural clusters in the data, a solution between five and eight elemental provinces seems optimal and is discussed (Amazonis-Tharsis and Sabaea-Arabia, Tempe and the southern highlands, Chryse and Utopia, Elysium-Tartarus, Acidalia-Arabia). Future investigation of the defined elemental provinces will involve integrating other types of data and geological information.  相似文献   

RARE EARTH AND OTHER ELEMENTS IN COMPONENTS OF THE ABEE ENSTATITE CHONDRITE     

Robert M. Frazier  William V. Boynton 《Meteoritics & planetary science》1985,20(2):197-218

Abee clast samples, a matrix sample, a dark inclusion, magnetic and nonmagnetic samples, and bulk samples were analyzed by neutron activation analysis (NAA). The REE were determined by radiochemical NAA. Na, K, Sc, Cr, Mn, Fe, Co, Ni, Zn, As, Se, Sm, Ir, Au were determined by instrumental NAA. High abundances of As, Ir, and Au in the magnetic separate and the correlation of their abundances with the metal content of the clasts indicate that As, Ir, and Au chiefly occur in the metal. Correlations for Zn and Sc indicate that they chiefly occur in niningerite, but a significant amount of Sc may also occur in oldhamite. The dark inclusions do not follow the As and Zn correlations, suggesting that the dark inclusions and clasts are not equilibrated with each other. Correlation of the REE and oldhamite abundances for both the clasts and dark inclusions indicates that the REE chiefly occur in oldhamite. In view of the INAA and mineralogical evidence for non-equilibration among the clasts and a dark inclusion (Sears et al., 1981), the similar REE patterns for clasts (3,3) and dark inclusion (5,1), and the similar mineral composition of oldhamite in clast (3,3) and dark inclusion (5,1), suggest that the oldhamite in the clasts and dark inclusions is of a common origin, which Sears et al. (1981) showed could be formed by condensation. A Tb anomaly of a factor of 2 was found in sample (2,9 and 9,2), and a La anomaly of a factor of 2 was found in clast (3,3). The only other REE anomaly in Abee, a factor of 3.5 for Yb, was found by Nakamura and Masuda(1973). In view of the evidence for equilibration among the clasts, this anomaly must have been introduced shortly before the brecciation process and indicates that no significant reheating has occurred. This concurs with the findings of Sugiura and Strangeway (1981) and Bogard et al. (1982).  相似文献   

Fractionation in the solar nebula: condensation of yttrium and the rare earth elements     

William V Boynton 《Geochimica et cosmochimica acta》1975,39(5):569-584

The condensation of Y and the rare earth elements (REE) from the solar nebula may be controlled by thermodynamic equilibrium between gas and condensed solids. Highly fractionated REE patterns may result if condensates are removed from the gas before condensation is complete. It is found that the fractionation is not a smooth function of REE ionic radius but varies in an extremely irregular pattern. Both Yb and Eu are predicted to be extremely depleted in the early condensate without the requirement of condensation in the divalent state. The model is discussed with respect to a highly fractionated pattern observed by Tanaka and Masuda (Icarus19, 523–530 1973), in a pink Ca-Al-rich inclusion from the Allende meteorite and can account for the abundances of each REE determined. According to the model this inclusion represents a condensate from a previously fractionated gas rather than from a gas of solar composition. Before the condensation of this inclusion, an earlier condensate was formed and was removed from equilibrium with the gas.  相似文献   

Martian Case Study of Multivariate Correlation and Regression with Planetary Datasets     

Suniti Karunatillake  Olivier Gasnault  Steven W. Squyres  John M. Keller  Daniel M. Janes  William Boynton  Horton E. Newsom 《Earth, Moon, and Planets》2012,108(3-4):253-273

We synthesize multivariate correlation and regression methods to characterize unique relationships among compositional and physical properties of a planetary surface locally, regionally, and globally. Martian data including elemental mass fractions, areal fractions of mineral types, and thermal inertia constitute our case study. We incorporate techniques to address the effects of spatial autocorrelation and heteroscedasticity. We also utilize method and fit diagnostics. While the Mars Odyssey and Mars Global Surveyor missions provide the exploratory context in our discussion, our approach is applicable whenever the interrelationships of spatially binned data of continuous-valued planetary attributes are sought. For example, our regional-scale case study reinforces the strength of the spatial correlation among K, Th, and the dominant mineralogic type within northern low albedo regions (surface type 2) of Mars. Recent chemical and mineralogic data from the MESSENGER mission at Mercury and Dawn at Vesta may be analyzed effectively with these hierarchical regression methods to constrain geochemical processes. Likewise, our algorithm could be applied locally with the wide variety of compositional data expected from the MSL mission at Gale Crater in general, and the ChemCam sampling grids in particular.  相似文献   

Erratum to: Synthesis in Estuarine and Coastal Ecological Research: What Is It,Why Is It Important,and How Do We Teach It?     

W. Michael Kemp  Walter R. Boynton 《Estuaries and Coasts》2012,35(3):911-912

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