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51.
Separated fractions from the Mayo Belwa aubrite have been analysed for the rare earth elements (REE). The data show no ytterbium anomalies but the feldspar and magnetic fractions show complementary europium anomalies. The separated phases together account for the total REE abundances in the bulk meteorite which are about 0.5 times chondritic. The REE content of the feldspar is greater than that of the bulk meteorite. The partition coefficients for the REE between feldspar and orthopyroxene are about 10 times (in favour of the feldspar) those of the nearest equivalent terrestrial feldspar/orthopyroxene pairs, implying that the distribution of the REE which would result from equilibrium co-crystallisation from a single liquid has been disturbed by a later event. This occurred more recently than 4.33 b.y. ago and resulted in a redistribution of the REE between the feldspar and a REE enriched residue. However, the REE patterns of the minerals are very like those of terrestrial equivalents and appear to be the result of igneous cumulus processes on a parent body rather than condensation of dust from a nebular gas. 相似文献
52.
The magmatic oxygen fugacity (fO2) of a thirty foot wide feldspathic peridotite dyke has been determined using the experimental method of Fudali (1965). Determinations were made on samples from both the marginal and central portions of the dyke and a difference of approximately one order of magnitude in fO2 was observed. This difference is attributed to the increase in the H2O content of the liquid as crystallization proceeded and to diffusion of hydrogen out of the dyke. It is concluded that the dyke was emplaced with an fO2 between 10–8 and 10–9 atmospheres. Data on the absorbtion of Fe by the silver/palladium sample containers during the experiments are given in an appendix. 相似文献
53.
S. C. Kohn R. Dupree M. G. Mortuza C. M. B. Henderson 《Physics and Chemistry of Minerals》1991,18(2):144-152
Phases with the composition K2MgSi5O12, belonging to the leucite structure group were synthesised under dry and hydrothermal conditions and studied using 29Si NMR. The 29Si spectrum for the dry-crystallised material (which is cubic) consists of a single broad line, suggesting a high degree of disorder. The hydrothermally crystallised material (which is probably monoclinic, with a distorted leucite lattice) has a 29Si spectrum which consists of ten lines of equal intensity, two of which have small chemical shift anisotropies and are therefore assigned to Q4(4Si) sites. These data have been interpreted in terms of a structure with 12 distinct tetrahedral sites over which 2 Mg atoms and 10 Si atoms are fully ordered. A 2-dimensional COSY spectrum shows correlations between some Q4(3Si) silicon atoms and two other Q4(3Si) silicon atoms. This fully constrains the topology of the unit cell. Two schemes of Si/Mg ordering over the unit cell can give good fits to the COSY spectrum. Using the tetrahedral (T) site notation defined for natural tetragonal leucite, the first of these arrangements involves Mg and Q4(4Si) silicon atoms each occupying one T1-type site and one T3-type site, and Q4(3Si) silicons occupying the remaining sites, i.e. four T2-type sites, two T1-type sites and two T3-type sites. In the second arrangement, the T2-type sites are occupied by Mg atoms and Q4(4Si) silicon atoms and all the T1-and T3-type sites are occupied by Q4(3Si) atoms. 相似文献
54.
Tiny cryptanthe (Cryptantha minima Rydb.) is an endangered annual plant adapted to prairie sand dunes of Canada. Thermal time and hydrothermal time models were used to quantify the effect of temperature and water potential on seed germination and to relate it to field conditions. Tiny cryptanthe seeds had a base temperature of ?3.9 °C for germination. Final germination percentage was highest at temperatures near the freezing point. Seeds required approximately 130.6 °C d to reach 50% germination under optimal water conditions. Seed germination was sensitive to water stress and large seeds had lower germination than small ones especially at reduced water potentials and higher temperatures. The high potential germination and low seed dormancy indicate that tiny cryptanthe lacks a dormancy mechanism, but the unique germination response to temperature enables it to fully utilize water from spring snowmelt before drought in the summer. Future climate change with higher temperatures could reduce regeneration success of this species unless there is an associated increase in winter and spring precipitation. 相似文献
55.
The behaviour of tungsten in granitic melt-vapour systems 总被引:9,自引:0,他引:9
An experimental study has been carried out to determine the effect of solution composition on the partitioning behaviour of
tungsten in granitic melt-vapour systems at 800° C and 1 kbar. With chloride and phosphate solutions, tungsten partitions
strongly into the aqueous phase, whereas with fluoride, carbonate and borate solutions, and water alone, tungsten partitions
in favour of the melt. With chloride solutions, the fluid/melt partition coefficients (K
D) for W show a marked positive correlation with chloride concentration, and suggest that at low chloride concentrations W-Cl
complexes with low Cl∶W ratios (such as associated equivalents of (WO3)2C1−) may be present. In contrast, at higher chloride concentrations complexes with high Cl∶W ratios (such as WOCl4, WCl6 and associated ionic equivalents) may predominate. With phosphate solutions, K
D shows little variation with phosphate concentration, and phosphorus heteropolytungstates (such as H3[PW12O40]) may be present. There is no evidence to suggest that fluoride, carbonate or borate complexes of tungsten are important
under the experimental conditions: the data for these compositions can be interpreted assuming that isopolytungstates (such
as H6[H2W12O40]) are present. Within high temperature hydrothermal solutions tungsten may be transported principally as isopolytungstates
and heteropolytungstates in addition to chloride complexes, and this may, in part, account for the common association of apatite
and arsenopyrite with scheelite and wolframite in tungsten deposits. 相似文献
56.
A portion of the debate about climate reconstructions of the past millennium, and in particular about the well-known Mann-Bradley-Hughes
(“MBH” 1998, 1999) reconstructions, has become disconnected from the goal of understanding natural climate variability. Here,
we reflect on what can be learned from recent scientific exchanges and identify important challenges that remain to be addressed
openly and productively by the community. One challenge arises from the real, underlying trend in temperatures during the
instrumental period. This trend can affect regression-based reconstruction performance in cases where the calibration period
does not appropriately cover the range of conditions encountered during the reconstruction. However, because it is tied to
a unique spatial pattern driven by change in radiative balance, the trend cannot simply be removed in the method of climate
field reconstruction used by MBH on the statistical argument of preserving degrees of freedom. More appropriately, the influence
from the trend can be taken into account in some methods of significance testing. We illustrate these considerations as they
apply to the MBH reconstruction and show that it remains robust back to AD 1450, and given other empirical information also
back to AD 1000. However, there is now a need to move beyond hemispheric average temperatures and to focus instead on resolving
climate variability at the socially more relevant regional scale. 相似文献
57.
R.K. Lowry S.J.B. Reed J. Nolan P. Henderson J.V.P. Long 《Earth and Planetary Science Letters》1981,53(1):36-40
An ion-microprobe-based technique has been used to measure lithium tracer-diffusion coefficients (DLi) in an alkali-basaltic melt at 1300, 1350 and 1400°C. The results can be expressed in the form:DLi=7.5 ×10?2exp(?27,600/RT)cm2S?1The results show significantly faster diffusion rates than those previously recorded for other monovalent, divalent and trivalent cations in a tholeiitic melt. Consequently, diffusive transport of ions acting over a given time in a basaltic melt can produce a wider range of transport distance values than hitherto supposed. Hence, it is concluded that great care should be exercised when applying diffusion data to petrological problems. 相似文献
58.
59.
Surfactants are chemical compounds that can change the contact angle of a water drop on solid surfaces and are commonly used to increase infiltration into water repellent soil. Since production fields with water repellent soil often contain areas of wettable soil, surfactants applied to such fields worldwide will likely be applied to wettable soil, with unknown consequences for irrigation‐induced erosion, runoff, or soil water relations. We evaluated surfactant and simulated sprinkler irrigation effects on these responses for three wettable, Pacific Northwest soils, Latahco and Rad silt loams, and Quincy sand. Along with an untreated control, we studied three surfactants: an alkyl polyglycoside (APG) in solution at a concentration of 18 g active ingredient (AI) kg?1, a block copolymer at 26 g kg?1, and a blend of the two at 43 g kg?1. From 2005 to 2009 in the laboratory, each surfactant was sprayed at a rate of 46·8 l ha?1 onto each soil packed by tamping into 1·2‐ by 1·5‐m steel boxes. Thereafter, each treated soil was irrigated twice at 88 mm h?1 with surfactant‐free well water. After each irrigation, runoff and sediment loss were measured and soil samples were collected. While measured properties differed among soils and irrigations, surfactants had no effect on runoff, sediment loss, splash loss, or tension infiltration, compared to the control. Across all soils, however, the APG increased volumetric water contents by about 3% (significant at p≤0·08) at matric potentials from 0 to ? 20 kPa compared to the control. With a decrease in the liquid–solid contact angle on treated soil surfaces, surfactant‐free water appeared able to enter, and be retained in pores with diameters ≥ 15 µm. All told, surfactants applied at economic rates to these wettable Pacific Northwest soils posed little risk of increasing either runoff or erosion or harming soil water relations. Moreover, by increasing water retention at high potentials, surfactants applied to wettable soils may allow water containing pesticides or other agricultural chemicals to better penetrate soil pores, thereby increasing the efficacy of the co‐applied materials. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
60.