Partitioning of K, U, and Th between sulfide and silicate liquids: Implications for radioactive heating of planetary cores

The possibility of heating of planetary cores by K radioactivity has been extensively discussed, as well as the possibility that K partitioning into the terrestrial core is the reason for the difference between the terrestrial and chondritic K/U. We had previously suggested that U and Th partitioning into FeFeS liquids was more important than K. Laboratory FeFeS liquid, silicate liquid partition coefficient measurements (D) for K, U, and Th were made to test this suggestion. For a basaltic liquid at 1450°C and 1.5 GPa, D_U is 0.013 and D_K is 0.0026; thus U partitioning into FeFeS liquids is 5 times greater than K partitioning under these conditions. There are problems with 1-atm experiments in that they do not appear to equilibrate or reverse. However, measurable U and Th partitioning into sulfide was nearly always observed, but K partitioning was normally not observed (D_K ≲ 10^(−4)). A typical value for D_U from a granitic silicate liquid at one atmosphere, 1150°C, and low f0_2 is about 0.02; D_(Th) is similar. At low f0_2 and higher temperature, experiments with basaltic liquids produce strong Ca and U partitioning into the sulfide liquid with D_U > 1. D_(Th) is less strongly affected. Because of the consistently low D_K/D_U, pressure effects near the core-mantle boundary would need to increase D_U by factors of ∼10^3 with much smaller increases in DU in order to have the terrestrial K and U abundances at chondritic levels. In addition, if radioactive heating is important for planetary cores, U and Th will be more important than K unless the lower mantle has K/U greater than 10 times chondritic or large changes in partition coefficients with conditions reverse the relative importance of K versus U and Th from our measurements

Extreme Pu-U and Possible Pu-REE Fractionation in Unequilibrated Chondrites

The purpose of this study is to understand actinide chemistry in chondrites and to evaluate unequilibrated chondrites for either Pu/U or Pu/Nd chronology. Using fission track radiography for Nadiabondi (H5/(Murrell and Burnett, 1982), Dhajala (H3,4), Bremervorde (H3), Sharps (H3), and Tieschitz (H3), we find that U is primarily located in chondrule glass (50-500 ppb, average of ~ 100 ppb). Apatite from the unequilibrated chondrites contains 150-200 ppb U while whitlockite contains < 17 ppb [low compared to type-6 chondrites which have 1-6 ppm U in apatite and ~ 200 ppb in whitlockite (Pellas and Storzer, 1975)]. Nadiabondi phosphates are intermediate (Murrell and Burnett, 1982). These observations suggest that the phosphate U content increases with petrologic type (Pellas and Storzer, 1975), with U obtained from chondrule glass during metamorphism

SiO2-rich condrules in ordinary chondrites

The solar system abundances of Mg, Fe, and Si dictate that chondritic meteorites are silica-deficient compared to most terrestrial or lunar igneous rocks; thus olivine-orthopyroxene assemblages are commonly observed in ordinary chondrites. However, in the unequilibrated H-chondrites Sharps, Bremervorde, and Dhajala, we have observed chondrules and fragments which contain either tridymite or cristobalite as a major phase

Antiferromagnetic Exchange Interaction between Electrons on Degenerate LUMOs in Benzene Dianion

We discuss the ground state of Benzene dianion (Bz$^{2-}$) on the basis of the numerical diagonalization method of an effective model of $\pi$ orbitals. It is found that the ground state can be the spin singlet state, and the exchange coupling between LUMOs can be antiferromagnetic.Comment: Accepted for publication in J. Phys. Soc. Jpn., 2 pages, 3 figure

Coexisting Chalcophile and Lithophile Uranium in Qingzhen (EH3) Chondrite

Mineralogical and textural studies of Qingzhen have shown that it is highly unequilibrated and that it contains a population of chondrules and isolated enstatite grains which preserve the record of more oxidizing nebular conditions (Rambaldi et al., 1983, 1984). Even though in the majority of cases these objects have been affected by various degrees of reduction, some still contain silicates with high (up to 10%) FeO contents

Benthic Nutrient Flux in a Small Estuary in Northwestern Florida (USA)

Benthic nutrient fluxes of ammonium (NH4+), nitrite/nitrate (NO2- + NO3-), phosphate (PO4-3), and dissolved silica (DSi) were measured in Escambia Bay, an estuary within the larger Pensacola Bay system of northwestern Florida (USA). Our study occurred during a severe drought which reduced riverine inputs to Escambia Bay. Laboratory incubations of field-collected cores were conducted on 8 dates between June and October 2000 to estimate nutrient flux, and cores were collected from locations exhibiting a range of sediment organic matter content. NH4+ flux ranged from – 48.1 to 110.4 μmol m-2 h-1, but the mean flux was 14.6 μmol m-2 h-1. Dissolved silica (DSi) fluxes were also variable (-109. 3 to 145.3 μmol m-2 h-1), but the mean net flux (9.3 μmol m-2 h-1) was from the sediment to the water column. Bay sediment fluxes for NO2-+ NO3- and PO4-3 were less variable during this period (– 7.93 to 28.73 and – 1.74 to 3.29 μmol m-2 h-1 for NO2-+ NO3- and PO4-3, respectively). Low NH4+ fluxes were similar to published estimates from lagoonal Gulf of Mexico (GOM) estuaries, possibly due to the reduced freshwater input. Diminished regeneration of phosphate relative to inorganic nitrogen observed during the study period was consistent with previous research in Pensacola Bay suggesting phytoplankton phosphorus limitation. Finally, the estimated residence time of Escambia Bay and the mean turnover times for NH4+ and NO2-+ NO3- suggested that benthic flux significantly influenced nitrogen concentrations in overlying water

Regulation of plasmid-encoded isoprene metabolism in Rhodococcus, a representative of an important link in the global isoprene cycle

Emissions of biogenic volatile organic compounds (VOCs) form an important part of the global carbon cycle, comprising a significant proportion of net ecosystem productivity. They impact atmospheric chemistry and contribute directly and indirectly to greenhouse gases. Isoprene, emitted largely from plants, comprises one third of total VOCs, yet in contrast to methane, which is released in similar quantities, we know little of its biodegradation. Here, we report the genome of an isoprene degrading isolate, Rhodococcus sp. AD45, and, using mutagenesis shows that a plasmid-encoded soluble di-iron centre isoprene monooxygenase (IsoMO) is essential for isoprene metabolism. Using RNA sequencing (RNAseq) to analyse cells exposed to isoprene or epoxyisoprene in a substrate-switch time-course experiment, we show that transcripts from 22 contiguous genes, including those encoding IsoMO, were highly upregulated, becoming among the most abundant in the cell and comprising over 25% of the entire transcriptome. Analysis of gene transcription in the wild type and an IsoMO-disrupted mutant strain showed that epoxyisoprene, or a subsequent product of isoprene metabolism, rather than isoprene itself, was the inducing molecule. We provide a foundation of molecular data for future research on the environmental biological consumption of this important, climate-active compound

Th/U Microdistribution in Enstatite Meteorites

We report here our results to date for the mineralogical distribution of Th and U in the enstatite chondrites. By investigating the behavior of Th and U under the reducing conditions for which the enstatite meteorites formed, we hope to evaluate the suitability of these objectives for ^(244)Pu(_(1/2) = 82 m.y .) chronology, as well as gain insight into the origin of the E-chondrites. Induced fission tracks from a double irradiation have been used to map the distribution of Th and U in polished sections. The preliminary results are shown in Table I. The values are the mean contents of oldhamite (CaS) grains, and the uncertainties are the standard deviations from the mean. In enstatite chondrites both Th and U are concentrated in oldhamite. For example, in a section of Daniel's Kuil at least 70% of the total Th and 90% of the U are found in oldhamite. In Khairpur, alabandite (MnS) was also found to contain U but at a lesser concentration (~20 ppb). The smaller oldhamite grain size in St. Mark's and Abee complicates their study; however, Th+U are also found to concentrate in oldhamite in these two meteorites but at a somewhat lower value than seen in the E-6's. The Th-U ratios in oldhamite determined so far appear relatively unfractionated from the typical value of ~4. The whole rock Th/U value forHvittis was reported to be 5.0 (Morgan and Lovering, 1968) which agrees well with the oldhamite result. However, the whole rock Th/U for Khairpur of 2.5 (Morgan and Lovering, 1968) does not agree with the oldhamite value. This discrepancy will be investigated in an upcoming irradiation; in this irradiation we also hope to complete the data set of Table 1, look at Th/U on a grain-by-brain basis and examine the U distribution in a few enstatite achondrites (aubrites). But with the results to date, a good case can be made for a study of ^(244)Pu in the E-6 chondrites. The majority of Th and U is concentrated with little apparent fractionation in a single mineral, and the particular chemistry of oldhamite should enable a selective Pu-Xe measurement to be made

Actinide Chemistry of Allende Components

U and Th in inclusions. Previous reports of high Th/U in Allende Ca,Al-rich inclusions (Boynton, 1978; Chen and Wasserburg, 1981; Stapanian, 1981) may indicate that U was not acting as a refractory element. The apparent ease of Th/U fractionation in the earliest material makes the ubiquity of Th/U = 3.8 in the solar system hard to understand. U-Th fission track radiography offers the possibility of a better understanding of actinide chemistry in Allende Ca,Al-rich inclusions. Volatility and valence differences between Th and U make these elements potentially useful in distinguishing between primary (condensation?) characteristics and those produced later by alteration. A preliminary examination of TS-23 (a type B inclusion provided by L. Grossman, 1975) shows U to be highly enriched in the inclusion rim. This result is qualitatively similar to that found for U and Th in type A inclusions by Stapanian (1981)

A tight binding model for water

We demonstrate for the first time a tight binding model for water incorporating polarizable anions. A novel aspect is that we adopt a "ground up" approach in that properties of the monomer and dimer only are fitted. Subsequently we make predictions of the structure and properties of hexamer clusters, ice-XI and liquid water. A particular feature, missing in current tight binding and semiempirical hamiltonians, is that we reproduce the almost two-fold increase in molecular dipole moment as clusters are built up towards the limit of bulk liquid. We concentrate on properties of liquid water which are very well rendered in comparison with experiment and published density functional calculations. Finally we comment on the question of the contrasting densities of water and ice which is central to an understanding of the subtleties of the hydrogen bond