Evaluation of fisheries-management systems with respect to sustainable development   总被引：1，自引：0，他引：1  

Chesson  J.; Clayton  H.; Whitworth  B. 《ICES Journal of Marine Science》1999,56(6):980-984

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Martian meteorite Dhofar 019: A new shergottite     

L. A. Taylor  M. A. Nazarov  C. K. Shearer  H. Y. McSween  J. Cahill  C. R. Neal  M. A. Ivanova  L. D. Barsukova  R. C. Lentz  R. N. Clayton  T. K. Mayeda 《Meteoritics & planetary science》2002,37(8):1107-1128

Abstract— Dhofar 019 is a new martian meteorite found in the desert of Oman. In texture, mineralogy, and major and trace element chemistry, this meteorite is classified as a basaltic shergottite. Olivine megacrysts are set within a groundmass composed of finer grained olivine, pyroxene (pigeonite and augite), and maskelynite. Minor phases are chromite‐ulvöspinel, ilmenite, silica, K‐rich feldspar, merrillite, chlorapatite, and pyrrhotite. Secondary phases of terrestrial origin include calcite, gypsum, celestite, Fe hydroxides, and smectite. Dhofar 019 is most similar to the Elephant Moraine (EETA) 79001 lithology A and Dar al Gani (DaG) 476/489 shergottites. The main features that distinguish Dhofar 019 from other shergottites are lack of orthopyroxene; lower Ni contents of olivine; the heaviest oxygen‐isotopic bulk composition; and larger compositional ranges for olivine, maskelynite, and spinel, as well as a wide range for pyroxenes. The large compositional ranges of the minerals are indicative of relatively rapid crystallization. Modeling of olivine chemical zonations yield minimum cooling rates of 0.5‐0.8 °C/h. Spinel chemistry suggests that crystallization took place under one of the most reduced conditions for martian meteorites, at an fO₂ 3 log units below the quartz‐fayalite‐magnetite (QFM) buffer. The olivine megacrysts are heterogeneously distributed in the rock. Crystal size distribution analysis suggests that they constitute a population formed under steady‐state conditions of nucleation and growth, although a few grains may be cumulates. The parent melt is thought to have been derived from partial melting of a light rare earth element‐ and platinum group element‐depleted mantle source. Shergottites, EETA79001 lithology A, DaG 476/489, and Dhofar 019, although of different ages, comprise a particular type of martian rocks. Such rocks could have formed from chemically similar source(s) and parent melt(s), with their bulk compositions affected by olivine accumulation.  相似文献   

Silica-rich orthopyroxenite in the Bovedy chondrite     

Alex Ruzicka  David A. Kring  Dolores H. Hill  William V. Boynton  Robert N. Clayton  Toshiko K. Mayeda 《Meteoritics & planetary science》1995,30(1):57-70

Abstract— A large (≥4.5 × 7 × 4 mm), igneous-textured clast in the Bovedy (L3) chondrite is notable for its high bulk SiO₂ content (57.5 wt%). The clast consists of normally zoned orthopyroxene (83.8 vol%), tridymite (6.2 %), an intergrowth of feldspar (5.8 %) and sodic glass (3.1 %), pigeonite (1.0 %), and small amounts of chromite (0.2 %), augite, and Fe, Ni-metal; it is best described as a silica-rich orthopyroxenite. The oxygen-isotopic composition of the clast is similar, but not identical, to Bovedy and other ordinary chondrites. The clast has a superchondritic Si/Mg ratio, but has Mg/(Mg + Fe) and Fe/Mn ratios that are similar to ordinary chondrite silicate. The closest chemical analogues to the clast are radial-pyroxene chondrules, diogenites, pyroxene-silica objects in ordinary chondrites, and silicates in the IIE iron meteorite Weekeroo Station. The clast crystallized from a siliceous melt that cooled fast enough to prevent complete attainment of equilibrium but slow enough to allow nearly complete crystallization. The texture, form, size and composition of the clast suggest that it is an igneous differentiate from an asteroid or planetesimal that formed in the vicinity of ordinary chondrites. The melt probably cooled in the near-surface region of the parent object. It appears that in the source region of the clast, metallic and silicate partial melt were largely-to-completely lost during a relatively low degree of melting, and that during a higher degree of melting, olivine and low-Ca pyroxene separated from the remaining liquid, which ultimately solidified to form the clast. While these fractionation steps could not have all occurred at the same temperature, they could have been accomplished in a single melting episode, possibly as a result of heating by radionuclides or by electromagnetic induction. Fractionated magmas can also account for other Si-rich objects in chondrites.  相似文献   

Melt/harzburgite reaction in the petrogenesis of tholeiitic magma from Kilauea volcano, Hawaii     

T. P. Wagner  T. L. Grove 《Contributions to Mineralogy and Petrology》1998,131(1):1-12

We use the results of elevated pressure melting experiments to constrain the role of melt/mantle reaction in the formation of tholeiitic magma from Kilauea volcano, Hawaii. Trace element abundance data is commonly interpreted as evidence that Kilauea tholeiite is produced by partial melting of garnet lherzolite. We experimentally determine the liquidus relations of a tightly constrained estimate of primary tholeiite composition, and find that it is not in equilibrium on its liquidus with a garnet lherzolite assemblage at any pressure. The composition is, however, cosaturated on its liquidus with olivine and orthopyroxene at 1.4 GPa and 1425 °C, from which we infer that primary tholeiite is in equilibrium with harzburgite at lithospheric depths beneath Kilauea. These results are consistent with our observation that tholeiite primary magmas have higher normative silica contents than experimentally produced melts of garnet lherzolite. A model is presented whereby primary tholeiite forms via a two-stage process. In the first stage, magmas are generated by melting of garnet lherzolite in a mantle plume. In the second stage, the ascent and decompression of magmas causes them to react with harzburgite in the mantle by assimilating orthopyroxene and crystallizing olivine. This reaction can produce typical tholeiite primary magmas from significantly less siliceous garnet lherzolite melts, and is consistent with the shift in liquidus boundaries that accompanies decompression of an ascending magma. We determine the proportion of reactants by major element mass balance. The ratio of mass assimilated to mass crystallized (M_a/M_c) varies from 2.7 to 1.4, depending on the primary magma composition. We use an AFC calculation to model the effect of melt/harzburgite reaction on melt rare earth and high field strength element abundances, and find that reaction dilutes, but does not significantly fractionate, the abundances of these elements. Assuming olivine and orthopyroxene have similar heats of fusion, the M_a/M_c ratio indicates that reaction is endothermic. The additional thermal energy is supplied by the melt, which becomes superheated during adiabatic ascent and can provide more thermal energy than required. Melt/harzburgite reaction likely occurs over a range of depths, and we infer a mean depth of 42 km from our experimental results. This depth is well within the lithosphere beneath Kilauea. Since geochemical evidence indicates that melt/harzburgite reaction likely occurs in the top of the Hawaiian plume, the plume must be able to thin a significant portion of the lithosphere. Received: 4 February 1997 / Accepted: 27 August 1997  相似文献   

The nature of the cometary knots in the Helix planetary nebula (NGC 7293)     

Meaburn  Clayton  Bryce  Walsh  Holloway  & Steffen 《Monthly notices of the Royal Astronomical Society》1998,294(2):201-223

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Time-dependent structure in ultraviolet absorption lines of the rapid rotators HD 64760 (B0 Ib) and HD 93521 (O9.5 V)     

Ian D. Howarth  Townsend  Clayton  Fullerton  Gies  Massa  Prinja  & Reid 《Monthly notices of the Royal Astronomical Society》1998,296(4):949-960

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Mechanisms of hydrothermal crystallization of quartz at 250°C and 15 kbar     

Yukihiro Matsuhisa  Julian R. Goldsmith  Robert N. Clayton 《Geochimica et cosmochimica acta》1978,42(2):173-182

Oxygen isotopic exchange between quartz and water, using a novel technique in which both ¹⁸O/¹⁶O and ¹⁷O/¹⁶O fractionations were measured, yielded an equilibrium fractionation Δ¹⁸ = 9.0 at 250°C and 15 kbar. The reaction proceeds predominantly by solution of fine grains and growth of larger grains. Exchange by solid-state diffusion is immeasurably slow at this temperature. Under the same experimental conditions, cristobalite behaves quite differently, becoming transformed to sub-micron quartz crystals in a few minutes. The phase transformation is accompanied by a kinetic isotope effect yielding quartz in isotopic disequilibrium with water. It is possible that such disequilibrium products are also formed in other experiments involving phase transitions or mineral syntheses.  相似文献   

Multiple parent bodies of polymict brecciated meteorites     

Robert N. Clayton  Toshiko K. Mayeda 《Geochimica et cosmochimica acta》1978,42(3):325-327

In three brecciated meteorites, Bencubbin, Cumberland Falls and Plainview, the oxygen isotopic compositions of different rock types within each meteorite were determined to seek genetic relationships between them. In all cases the isotopic compositions are not consistent with derivation from a single parent body. There is no evidence that chondrites and achondrites could be derived from a common parent body. The chondritic inclusions in Bencubbin and Cumberland Falls cannot be identified with any of the ordinary chondritic meteorites. The carbonaceous chondritic fragments in Bencubbin are smilar to, but not identical with, C2 meteorites. The achondritic portion of Bencubbin has a very unusual isotopic composition, which, along with its close relative Weatherford, sets it in a class distinctly apart from other achondrites. Lithic fragments in brecciated meteorites provide a wider range of rock types than is represented by known macroscopic meteorites. Collisions between some meteorite parent bodies were of sufficiently low velocity that fragments of both are preserved in breccias.  相似文献   

Primordial compositions of refractory inclusions   总被引：1，自引：0，他引：1  

L. Grossman  S.B. Simon  M.H. Thiemens  R.W. Williams  T. Ding  R.N. Clayton  T.K. Mayeda 《Geochimica et cosmochimica acta》2008,72(12):3001-3021

Bulk chemical and O-, Mg- and Si-isotopic compositions were measured for each of 17 Types A and B refractory inclusions from CV3 chondrites. After bulk chemical compositions were corrected for non-representative sampling in the laboratory, the Mg- and Si-isotopic compositions of each inclusion were used to calculate its original chemical composition assuming that the heavy-isotope enrichments of these elements are due to Rayleigh fractionation that accompanied their evaporation from CMAS liquids. The resulting pre-evaporation chemical compositions are consistent with those predicted by equilibrium thermodynamic calculations for high-temperature nebular condensates, but only if different inclusions condensed from nebular regions that ranged in total pressure from 10⁻⁶ to 10⁻¹ bar, regardless of whether they formed in a system of solar composition or in one enriched in dust of ordinary chondrite composition relative to gas by a factor of 10 compared to solar composition. This is similar to the range of total pressures predicted by dynamic models of the solar nebula for regions whose temperatures are in the range of silicate condensation temperatures. Alternatively, if departure from equilibrium condensation and/or non-representative sampling of condensates in the nebula occurred, the inferred range of total pressure could be smaller. Simple kinetic modeling of evaporation successfully reproduces observed chemical compositions of most inclusions from their inferred pre-evaporation compositions, suggesting that closed-system isotopic exchange processes did not have a significant effect on their isotopic compositions. Comparison of pre-evaporation compositions with observed ones indicates that 80% of the enrichment in refractory CaO + Al₂O₃ relative to more volatile MgO + SiO₂ is due to initial condensation and 20% due to subsequent evaporation for both Types A and B inclusions.  相似文献   

Modeling monthly meteorological and agronomic frost days,based on minimum air temperature,in Center-Southern Brazil     

Clayton?Alcarde?AlvaresEmail author  Paulo?César?Sentelhas  José?Luiz?Stape 《Theoretical and Applied Climatology》2018,134(1-2):177-191

Although Brazil is predominantly a tropical country, frosts are observed with relative high frequency in the Center-Southern states of the country, affecting mainly agriculture, forestry, and human activities. Therefore, information about the frost climatology is of high importance for planning of these activities. Based on that, the aims of the present study were to develop monthly meteorological (F _MET) and agronomic (F _AGR) frost day models, based on minimum shelter air temperature (T _MN), in order to characterize the temporal and spatial frost days variability in Center-Southern Brazil. Daily minimum air temperature data from 244 weather stations distributed across the study area were used, being 195 for developing the models and 49 for validating them. Multivariate regression models were obtained to estimate the monthly T _MN, once the frost day models were based on this variable. All T _MN regression models were statistically significant (p < 0.001), presenting adjusted R ² between 0.69 and 0.90. Center-Southern Brazil is mainly hit by frosts from mid-fall (April) to mid-spring (October). The period from November to March is considered as frost-free, being very rare a frost day within that period. Monthly F _MET and F _AGR presented significant sigmoidal relationships with T _MN (p < 0.0001), with adjusted R ² above of 0.82. The residuals of the frost day models were random, which means that the sigmoidal models performed quite well for interpreting the frost day variability throughout the study area. The highlands of Santa Catarina, Rio Grande do Sul, São Paulo, and Minas Gerais had in average more than 25 and 13 frosts per year, respectively, for F _MET and F _AGR. The F _MET and F _AGR maps developed in this study for Center-Southern Brazil is a useful tool for farmers, foresters, and researchers, since they contribute to reduce frost spatial and temporal uncertainty, helping in planning project for strategic purposes. Furthermore, the monthly F _MET and F _AGR maps for this Brazilian region are the first zoning of these variables for the country.  相似文献