On the kinetics of volatile loss from chondrites     

Leo Alaerts  Edward Anders 《Geochimica et cosmochimica acta》1979,43(4):547-553

We have re-examined data by Lipschutz and coworkers on thermal release of T1, Bi, In from primitive chondrites, in order to obtain information on the nature and activation energy (E) of the release processes: desorption, volume diffusion, and decomposition of the host phase. Plausible though not definitive choices may be made in some cases. For the Allende C3 chondrite, the main release for Bi and T1 (80 and 86%) between 400 and 700°C appears to be due to desorption of a surface layer, coupled with grain boundary diffusion as the slow step. The main release of In (80%) above 600°C and the small (10–20%) tails of Bi and T1 between 700 and 1000°C probably represent volume diffusion, with activation energies near 30 kcal/mol. The much smaller E's (2–5 kcal/mol) found for this interval by the Purdue group are artifacts, resulting from their failure to correct the initial concentration for the material lost in the preceding peak. Finally, the residual Bi and T1 remaining at 1000°C seem to represent solid solutions in temperature-resistant phases, such as ‘Q’, the principal carrier of planetary noble gases in the meteorite.This distribution—a small amount in solid solution and a large amount in a surface film—qualitatively agrees with that predicted by Larimer (1973, Geochim. Cosmochim. Acta37, 1603–1623) for condensation from the solar nebula, though some of the substrates may have been sulfides rather than metal.Results for Abee and other primitive meteorites are essentially similar, except for a very abrupt 500°C release of T1 from Krymka (81%) and Bi from Tieschitz (70%). This release may represent decomposition of a thermolabile phase in a late condensate, such as organic matter or phyllosilicates. The presence of such a condensate (‘mysterite’) was inferred previously from the apparent overabundance of T1 and Bi in these meteorites.  相似文献   

Chemical fractionations in meteorites—X. Ureilites     

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   

Chemical fractionations in meteorites—IX. C3 chondrites     

Edward Anders  Hideo Higuchi  R. Ganapathy  John W. Morgan 《Geochimica et cosmochimica acta》1976,40(9):1131-1139

Four C3V chondrites (Grosnaja, Kaba, Mokoia, Vigarano) and three C3O chondrites (Felix, Kainsaz, and Lancé) were analyzed by radiochemical neutron activation for 17 trace elements. Both classes show a typical chondritic step pattern, reflecting loss of volatiles during chondrule formation. Elements condensing above 1300 K (U, Re, Ir, Ni) are present in essentially Cl chondrite proportions, while moderately volatile elements condensing between 1300 K and 800 K (Ge, Rb, Ag) are depleted by a factor of 0.44. However, elements condensing below 700 K (S, Cs, Bi, Tl, Br, Se, Te, In, Cd) are depleted to a still greater degree, and more so in the Ornans subclass (factor of 0.24, except Cd 0.007) than in the Vigarano subclass (factor of 0.29). This additional depletion may be due to a slight (less than 3-fold) dust-gas fractionation, by settling of dust to the median plane of the solar nebula. Among other chondrite classes, ordinary chondrites show a similar depletion, but C2 chondrites do not. Possibly the undepleted meteorites formed in one of the convection zones of the nebula predicted by Cameron and Pine, whereas the depleted meteorites formed in a quiescent region.The condensation of chalocophile elements as a function of H₂S partial pressure is discussed, in an attempt to explain the drastic difference in Cd abundance between the two subclasses. It appears that the $\text{H}{}_2\text{S}\text{H}{}_2$ ratio is the key variable. C3O's seem to have condensed in a region where enough metallic Fe was present to buffer the H₂S pressure, while C3V's condensed in a more oxidized region, where H₂S was in excess. Accretion temperatures, for an assumed nebular pressure of 10^?5 atm, were between 415 and 430 K for C3O's and less than 440 K for C3V's.Two slightly volatile elements, Sb and Au, show variable depletion, presumably reflecting variable loss during chondrule formation. Indeed, their depletion correlates with the abundance of iron-poor olivine, a measure of the peak temperature and time during chondrule formation.  相似文献   

Coexisting pyroxenes — a multivariate statistical approach     

Anders Lindh 《Lithos》1974,7(4):197-205

A population of 117 coexisting nonalkaline pyroxene pairs has been studied statistically to evaluate compositional and thermal effects on the element distribution. K_DMg^opx−cpx is influenced by the Fe/Mg-ratio, by the Ca content—especially of clinopyroxene—and by the content of tetrahedral Al. Fe and tetrahedral Al are found to be negatively correlated. A principal component analysis based on the variation of Si, Al^IV, Al^IV, Fe, Mg, Mn, Ca is performed. Dropping of highly correlated variables does not affect the result significantly. The first principal component reflects the major chemical variation in Fe and Mg. When using Ferrous and ferric iron as separate entries of the analysis, either the second or the third component demonstrates a temperature dependence. It is, however, not possible to obtain pure temperature and chemical components due to the composition not being uncorrelated to temperature of formation. From these components a graph reflecting temperature of formation has been constructed.  相似文献   

Distribution of gold and rhenium between nickel-iron and silicate melts: implications for the abundance of siderophile elements on the Earth and Moon     

Kan Kimura  Roy S Lewis  Edward Anders 《Geochimica et cosmochimica acta》1974,38(5):683-701

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: D_Au = 3.3 × 10⁴, D_Re = (2.4?89) × 10⁴. Gorda Ridge basalt—Fe₁₀Ni₉₀: D_Au = (18?75) × 10⁴. Synthetic lunar basalt—Fe₇₀ Ni₃₀: D_Au≥ 2 × 10⁴, D_Re ≥ 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 D_Au, 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   

A flexible hybrid spectrometer for balloon borne and ground based (sub)millimeter wavelength astronomy     

Anders Emrich 《Experimental Astronomy》1990,1(4):227-235

This paper describes a flexible spectrometer architecture consisting of standard units that can be configured to meet different requirements. The spectrometer is a hybrid between an analog filterbank and digital autocorrelator. Two applications are given, one for balloon borne submillimeter radio astronomy employing a compact and low power design, and one for millimeter imaging with a much more powerful and flexible system. The basic hardware and software units are described as well as the overall architecture. Thanks to the modularized approach the spectrometer can easily be modified for other application areas, such as plasma physics or molecular spectroscopy.  相似文献   

Foreword     

Anders Lindroth 《Tellus. Series B, Chemical and physical meteorology》2007,59(5):787-787

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The young star cluster system in the Antennae: evidence for a turnover in the luminosity function     

P. Anders  N. Bissantz  L. Boysen  R. de Grijs  U. Fritze-v.Alvensleben 《Monthly notices of the Royal Astronomical Society》2007,377(1):91-106

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Transports of Nordic Seas water masses and excess SF₆ through Fram Strait to the Arctic Ocean     

Marika Marnela  Bert Rudels  K. Anders Olsson  Leif G. Anderson  Daniel J. Torres  James H. Swift 《Progress in Oceanography》2008,78(1):1-11

To determine the exchanges between the Nordic Seas and the Arctic Ocean through Fram Strait is one of the most important aspects, and one of the major challenges, in describing the circulation in the Arctic Mediterranean Sea. Especially the northward transport of Arctic Intermediate Water (AIW) from the Nordic Seas into the Arctic Ocean is little known. In the two-ship study of the circulation in the Nordic Seas, Arctic Ocean - 2002, the Swedish icebreaker Oden operated in the ice-covered areas in and north of Fram Strait and in the western margins of Greenland and Iceland seas, while RV Knorr of Woods Hole worked in the ice free part of the Nordic Seas. Here two hydrographic sections obtained by Oden, augmented by tracer and velocity measurements with Lowered Acoustic Doppler Current Profiler (LADCP), are examined. The first section, reaching from the Svalbard shelf across the Yermak Plateau, covers the region north of Svalbard where inflow to the Arctic Ocean takes place. The second, western, section spans the outflow area extending from west of the Yermak Plateau onto the Greenland shelf. Geostrophic and LADCP derived velocities are both used to estimate the exchanges of water masses between the Nordic Seas and the Arctic Ocean. The geostrophic computations indicate a total flow of 3.6 Sv entering the Arctic on the eastern section. The southward flow on the western section is found to be 5.1 Sv. The total inflow to the Arctic Ocean obtained using the LADCP derived velocities is much larger, 13.6 Sv, and the southward transport on the western section is 13.7 Sv, equal to the northward transport north of Svalbard. Sulphur hexafluoride (SF₆) originating from a tracer release experiment in the Greenland Sea in 1996 has become a marker for the circulation of AIW. From the geostrophic velocities we obtain 0.5 Sv and from the LADCP derived velocities 2.8 Sv of AIW flowing into the Arctic. The annual transport of SF₆ into the Arctic Ocean derived from geostrophy is 5 kg/year, which is of the same magnitude as the observed total annual transport into the North Atlantic, while the LADCP measurements (19 kg/year) imply that it is substantially larger. Little SF₆ was found on the western section, confirming the dominance of the Arctic Ocean water masses and indicating that the major recirculation in Fram Strait takes place farther to the south.  相似文献   

Extraterrestrial chromite distribution across the mid-Ordovician Puxi River section, central China: Evidence for a global major spike in flux of L-chondritic matter     

Anders Cronholm  Birger Schmitz 《Icarus》2010,208(1):36-155

Previous studies of mid-Ordovician limestone in Sweden have shown that over a stratigraphic interval representing a few million years there is a two orders-of-magnitude enrichment in fossil L-chondritic meteorites (Ø = 1-21 cm) and sediment-dispersed extraterrestrial chromite (EC) grains (>63 μm). This has been interpreted as a dramatic increase in the flux of L-chondritic matter to Earth following the breakup of the L-chondrite parent body, which based on Ar-Ar gas retention ages (470 ± 6 Ma) of recently fallen meteorites occurred at about this time. Here we show that the general trend in the distribution of sediment-dispersed EC grains can be reproduced in the Puxi River section in central China. A total of 288 kg of limestone was searched for chrome spinels. In samples spanning the lower 8 m of the section, representing the Paroistodus originalis and Lenodus antivariabilis conodont zones, a total of 110 kg of limestone yielded only one EC grain. Similarly to the Swedish sections, EC grains begin to be common in the overlying L. variabilis Zone and remain common throughout the upper 9 m of the section, representing the L. variabilis, Yangtzeplacognathus crassus and L. pseudoplanus zones. In this part of the section 178 kg of limestone yielded 290 EC grains, with an average chemical composition very similar to chromite from recent L chondrites. In most of the beds over this interval one finds 1-4 EC grains per kilogram rock, a clear two orders-of-magnitude enrichment relative to the lower part of the section. Small bed-by-bed variations in the EC content over the upper interval most likely reflect small variations in sedimentation rates. The Puxi River section contains only very rare terrestrial chrome spinel grains, which can be distinguished already by their rounded, abraded appearance compared to the angular, pristine extraterrestrial spinels. In the mid-Ordovician, based on paleoplate reconstructions, the Puxi River site was positioned at mid-latitudes on the southern hemisphere a couple of thousand kilometers east of the Swedish sites. The prominent enrichment of EC grains over the same stratigraphic interval in China and Sweden is supporting evidence for a dramatic increase in the flux of L-chondritic matter to Earth shortly after the disruption of the L-chondrite parent body in the asteroid belt.  相似文献