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41.
Hideo Higuchi John W Morgan R Ganapathy Edward Anders 《Geochimica et cosmochimica acta》1976,40(12):1563-1571
Four ureilites (Dyalpur, Goalpara, Haverö, and Novo Urei) were analyzed by radiochemical neutron activation analysis for Ag, Au, Bi, Br, Cd, Cs, Ge, In, Ir, Ni, Rb, Re, Sb, Se, Te, Tl, and U. An attempt has been made to resolve the data into contributions from the parent ultramafic rock and the injected, carbon- and gas-rich vein material. Interelement correlations, supported by analyses of separated vein material (WANKE et al, 1972), suggest that the vein material is enriched about 10-fold in refractory Ir and Re over moderately volatile Ni and Au, and is low in volatiles except Ge, C, and noble gases. It appears to be a refractory-rich nebular condensate that precipitated carbon by surface catalytic reactions at ˜500K and trapped noble gases but few other volatiles. The closest known analogue is a Cr- and C-rich fraction from the Allende meteorite, highly enriched in heavy noble gases and noble metals. By analogy with Allende, the gas-bearing phase in ureilites may have been an Fe, Cr-sulfide.
The ultramafic rock contains siderophiles and chalcophiles (Ni, Au, Ge, S, Se) at ˜0.05 of Cl chondrite level, and highly volatile elements (Rb, Cs, Bi, Tl, Br, Te, In, Cd) at ˜0.01 Cl level. It probably represents the residue from partial melting of a C3V-like chondrite body, under conditions where phase separation was incomplete so that some liquid was retained. The vein material was injected into this rock at some later time. 相似文献
42.
Dmytro Siergieiev Anders Widerlund Angela Lundberg Lisbeth Almqvist Magali Collomp Johan Ingri Björn Öhlander 《Aquatic Geochemistry》2014,20(1):59-80
Using hydrogeochemical analysis of two large boreal rivers (pristine Kalix and hydropower regulated Lule) discharging into the Gulf of Bothnia, the major impacts of regulation on water discharge, element transport and their seasonal redistribution have been assessed. The pre-regulation hydrogeochemical features were assumed to be similar for the two rivers. For the Lule River, the average maximum runoff was almost halved, while the average minimum was tripled as a result of the regulation. The fraction of winter transport of total organic carbon (TOC), Fe, Si, suspended Mn and P in the Lule River was, according to a conservative estimate, two to three times higher than in the pristine river. Longer residence time in the Lule River delayed arrival of the suspended Mn peak and dissolved Si decline to the river mouth. During summer, the suspended C/N ratio in the regulated river was 10–20 compared to <10 for the pristine, suggesting presence of predominantly old organic material. This was supported by a virtually constant suspended P/Fe ratio throughout the year in the Lule River, indicating low abundance of phytoplankton. TOC varied irregularly in the Lule River suggesting temporal disconnection between the river and the upper riparian zone. The disappearance of the spring flow maximum, a shift of element transport from spring to winter and supply of mainly old organic material during the vegetation growth season may have a pronounced impact on the ecosystem of the Gulf of Bothnia and the river itself. 相似文献
43.
John W. Morgan Marie-Josée Janssens H. Takahashi Jan Hertogen Edward Anders 《Geochimica et cosmochimica acta》1985,49(1):247-259
We have analyzed 10 H-chondrites for 20 trace elements, using RNAA. The meteorites included 4 of petrologic type 4 and 2 each of types 3, 5 and 6.The data show that H-chondrites are not isochemical. H3's are depleted by some 10% not only in Fe (Dodd, 1976), but also in the siderophiles Os, Re, Ir, Ni, Pd, Au, and Ge. Moreover, the abundance pattern of siderophiles varies systematically with petrologic type. As similar fractionations of REE have been observed by Nakamura (1974), it appears that both the proportions and compositions of the main nebular condensates varied slightly during accretion of the H-chondrites. Thus the higher petrologic types are independent nebular products, not metamorphosed descendants of lower petrologic types.Abundances of highly volatile elements (Cs, Br, Bi, Tl, In, Cd, Ar36) correlate with petrologic type, declining by ≤ 10?3 from Type 3 to Type 6. The trends differ from those for artificially heated Type 3's (Ikramuddinet al., 1977b; Herzoget al., 1979), but agree passably with theoretical curves for nebular condensation. Apparently the low volatile contents of higher petrologic types are a primary feature, not the result of metamorphic loss.The mineralogy of chondrites suggests that they accreted between 405 K (absence of Fe3O4) and 560 K (presence of FeS), and the abundances of Tl, Bi, and In further restrict this interval to 420–500 K. Accretion at 1070 ± 100 K, as proposed by Hutchisonet al. (1979, 1980), leads to some extraordinary problems. Volatiles must be injected into the parent body after cooling, which requires permeation of the body by 1011 times its volume of nebular gas. This process must also achieve a uniform distribution of the less volatile elements (Rb, Cu, Ag, Zn, Ga, Ge, Sn, Sb, Se, F), without freezeout in the colder outer layers.Factor analysis of our data shows 3 groupings: siderophiles (Os, Re, Ir, Ni, Pd, Au, and Ge), volatiles (Ag, Br, In, Cd, Bi, and Tl) and alkalis (Rb and Cs). The remaining 5 elements (U, Zn, Te, Se, and Sb) remain unassociated. 相似文献
44.
To simulate trapping of noble gases by meteorites, we reacted 15 FeCr or FeCrNi alloy samples with CO, H2O or H2S at 350–720 K, in the presence of noble gases. The reaction products, including (Fe,Cr)2O3, FeCr2S4, FeS, C, and Fe3C, were analyzed by mass spectrometry, usually after chemical separation by selective solvents. Three carbon samples were prepared by catalytic decomposition of CO or by dehydration of carbohydrates with H2SO4.The spinel and carbon samples were similar to those of earlier studies (Yang et al., 1982 and Yang and Anders, 1982), with only minor effects attributable to the presence of Ni. All samples sorted substantial amounts of noble gases, with distribution coefficients of 10?1–10?2 cm3 STP/g atm for Xe. On the basis of release temperature three gas components were distinguished: a generally dominant physisorbed component (20–80% of total), and two more strongly bound, chemisorbed and trapped components. Judging from the elemental pattern, the adsorbed components were acquired at the highest noble gas partial pressure encountered by the sample—atmosphere or synthesis vessel.Sulfides, particularly daubréelite, showed three distinctive trends relative to chromite or magnetite: the high-T component was larger, 30–70% of the total; ratios were higher, by up to 102, possibly due to preferential diffusion of Ne during synthesis. In one synthesis, at relatively high P, the gases were sorbed with only minimal elemental fractionation, presumably by occlusion.Most of the features of primordial noble gases can be explained in terms of the data and concepts presented in the three papers of this series. The elemental fractionation pattern of Ar, Kr, Xe in meteorites, terrestrial rocks, and planets resembles the adsorption pattern on the solids studied: carbon, spinels, Sulfides, etc. The variation in ratio may be explained by preferential diffusion of Ne. The high release temperature of meteoritic noble gases may be explained by transformation of physisorbed to chemisorbed gas, as observed in some experiments. The ready loss of meteoritic heavy gases on surficial oxidation (“Phase Q”) is consistent with adsorption, as is the high abundance. Extrapolation of the limited laboratory data suggests that the observed amounts of noble gases could have been adsorbed from a solar gas at 160–170 K and 10?6–10?5 atm, i.e. in the early contraction stages of the solar nebula. The principal unsolved problem is the origin of isotopically anomalous, apparently mass-fractionated noble gases in the Earth's atmosphere and in meteoritic carbon and chromite. 相似文献
45.
46.
The distribution equilibrium of Au and Re between nickel-iron and basaltic melts was studied at 1400–1600°C, using radioactive tracers. Metal/silicate distribution coefficients were 1–3 orders of magnitude higher than earlier estimates, as follows. Mauna Loa basalt—Fe10Ni90: DAu = 3.3 × 104, DRe = (2.4?89) × 104. Gorda Ridge basalt—Fe10Ni90: DAu = (18?75) × 104. Synthetic lunar basalt—Fe70 Ni30: DAu≥ 2 × 104, DRe ≥ 2 × 103. The experimental ΔG1800° for the distribution of Au between nickel-iron and Mauna Loa basalt is ?40 kcal/mole, compared to a calculated value of about ?110 kcal/mole for a reaction involving simple Au3+ ions. Presumably the difference represents stabilization of Au(III) by complex formation with ligands such as Cl?, H2O, etc.Gold abundances in lunar basalts are roughly consistent with the measured DAu, but those in terrestrial basalts are two orders of magnitude too high. This discrepancy may reflect complexing by volatiles in the Earth's upper lithosphere, as well as oxidative destruction of metal in the final stages of accretion. In the absence of a metal phase, siderophile trace elements would remain trapped in the upper mantle and crust. 相似文献
47.
Interpretation of CPTU testing in silt is non-trivial because of the partially drained conditions that are likely to occur during penetration. A better understanding of the pore pressure generation/dissipation is needed in order to obtain reliable design parameters. Following a previous study using X-ray computed tomography (micro-CT) with volumetric digital image correlation (3D-DIC) that clearly showed the formation of distinct dilation and compression areas around the cone; the present work takes a closer look at those areas in order to link volumetric behavior to changes in soil fabric. High-resolution 2D backscattered electron images of polished thin sections prepared from frozen samples at the end of penetration are used. The images have a spatial resolution of 0.4 µm/pixel that allow a clear identification of grains and pore spaces. Image processing techniques are developed to quantify local porosity and obtain the statistical distribution of the particle orientation for the zones around the cone tip and shaft. It is shown that the formation of compaction regions is related to the ability of the grains to rearrange and align along a well-defined preferred orientation forming a more closed-fabric characterized by high anisotropy values, while zones of dilation are associated with a more open packing with grains randomly oriented and with large voids within. These observations suggested that for a saturated soil, water will move from a compressive zone to a neighboring dilative zone, creating a short drainage path. By shedding light on the link between soil fabric and drainage patterns, this study contributes toward a better understanding of the measured macro-response during CPTU tests on silt. 相似文献
48.
The use of spectral analysis-based exact solutions to characterize topography-controlled groundwater flow 总被引:1,自引:1,他引:1
Spectral analysis enhances the ability to analyze groundwater flow at a steady state by separating the top boundary condition into its periodic forms. Specifically, spectral analysis enables comparisons of the impact of individual spatial scales on the total flow field. New exact spectral solutions are presented for analyzing 3D groundwater flow with an arbitrarily shaped top boundary. These solutions account for depth-decaying, anisotropic and layered permeability while utilizing groundwater flux or the phreatic surface as a top boundary condition. Under certain conditions, groundwater flow is controlled by topography. In areas where the groundwater flow is controlled by the topography, the unknown water table is often approximated by the topography. This approximation induces a systematic error. Here, the optimal resolution of digital elevation models (DEMs) is assessed for use as a top boundary in groundwater flow models. According to the analysis, the water-table undulation is smoother than the topography; therefore, there is an upper limit to the resolution of DEMs that should be used to represent the groundwater surface. The ability to represent DEMs of various spectral solutions was compared and the results indicate that the fit is strongly dependent on the number of harmonics in the spectral solution. 相似文献
49.
A special kind of magma mixing is extraordinarily well exposed in the Bittersberg subvolcanic complex in the Tertiary volcanic field of the German Westerwald: A trachytic melt has been penetrated by a latitic dyke which has been dispersed within the host magma as small spherical enclaves (globules). Whole rock analyses of the globules show a change in composition that cannot be explained by a simple mechanical mixing between the endmembers. The most evolved globules have a phonolitic composition. Microprobe measurements in the microlithic matrix of the host rock and the guest indicate a diffusive motion of the alkalis from the host into the globules. On the other hand, an opposite trend can be observed for Ca, Mg, Fe and Ti, which are impoverished in the globules. The trace elements and the middle rare earth elements (MREE) has also been involved in the diffusive exchange. The REE-pattern of the most evolved (phonolitic) globules shows a characteristic trough in the area of the MREE which is almost identical to the REE-pattern of many phonolites. The phonolites and the alkali-rich trachytes of the Westerwald show similar globular textures as the Bittersberg volcanics. Therefore, generation of these rocks involving diffusive element exchange during mixing processes in a magma reservoir situated on a deeper crustal level may be possible. 相似文献
50.
Panagiotis Dimakis Bjrn Inge Braathen Jan Inge Faleide Anders Elverhi Steinar T. Gudlaugsson 《Tectonophysics》1998,300(1-4)
The creation of the huge fans observed in the western Barents Sea margin can only be explained by assuming extremely high glacial erosion rates in the Barents Sea area. Glacial processes capable of producing such high erosion rates have been proposed, but require the largest part of the preglacial Barents Sea to be subaerial. To investigate the validity of these proposals we have attempted to reconstruct the western preglacial Barents Sea. Our approach was to combine erosion maps based on prepublished data into a single mean valued erosion map covering the whole western Barents Sea and consequently use it together with a simple Airy isostatic model to obtain a first rough estimate of the preglacial topography and bathymetry of the western Barents Sea margin. The mean valued erosion map presented herein is in good volumetric agreement with the sediments deposited in the western Barents Sea margin areas, and as a direct consequence of the averaging procedures employed in its construction we can safely assume that it is the most reliable erosion map based on the available information. By comparing the preglacial sequences with the glacial sequences in the fans we have concluded that 1/2 to 2/3 of the total Cenozoic erosion was glacial in origin and therefore a rough reconstruction of the preglacial relief of the western Barents Sea could be obtained. The results show a subaerial preglacial Barents Sea. Thus, during interglacials and interstadials the area may have been partly glaciated and intensively eroded up to 1 mm/y, while during relatively brief periods of peak glaciation with grounded ice extending to the shelf edge, sediments have been evacuated and deposited at the margins at high rates. The interplay between erosion and uplift represents a typical chicken and egg problem; initial uplift is followed by intensive glacial erosion, compensated by isostatic uplift, which in turn leads to the maintenance of an elevated, and glaciated, terrain. The information we have on the initial tectonic uplift suggests that the most likely mechanism to cause an uplift of the dimensions and magnitude of the one observed in the Barents Sea is a thermal mechanism. 相似文献