An Acetic Acid‐Based Extraction Protocol for the Recovery of U,Th and Pb from Calcium Carbonates for U‐(Th)‐Pb Geochronology     

Andrew J. Mason  Gideon M. Henderson  Anton Vaks 《Geostandards and Geoanalytical Research》2013,37(3):261-275

A new method for the simultaneous recovery of U, Th and Pb from ca. 0.5 g calcium carbonate samples for the purpose of U‐(Th)‐Pb geochronometry is presented. The protocol employs ion‐exchange chromatography. Standard anion exchange resin (AG 1‐X8 100–200 mesh) was used as the static phase, and 90% acetic acid was used as the mobile phase to elute the unwanted matrix components; dilute nitric acid was used to elute the U, Th and Pb. Blanks of 1.8 pg Th, 6.4 pg Pb and 8.4 pg U were obtained. The protocol was evaluated by determining the isotopic composition of U‐Th‐Pb separates obtained from an in‐house reference material (prepared from a natural speleothem) by MC‐ICP‐MS. An independently dated speleothem was also reanalysed. Based on these tests, the extraction protocol had an acceptable blank and produced a Pb separate sufficiently free of matrix‐induced instrumental biases to be appropriate for U‐Th‐Pb chronology.  相似文献   

Trace element geochemistry of CR chondrite metal     

Emmanuel Jacquet  Marine Paulhiac‐Pison  Olivier Alard  Anton T. Kearsley  Matthieu Gounelle 《Meteoritics & planetary science》2013,48(10):1981-1999

We report trace element analyses by laser ablation inductively coupled plasma mass spectrometry (LA‐ICP‐MS) of metal grains from nine different CR chondrites, distinguishing grains from chondrule interior (“interior grains”), chondrule surficial shells (“margin grains”), and the matrix (“isolated grains”). Save for a few anomalous grains, Ni‐normalized trace element patterns are similar for all three petrographic settings, with largely unfractionated refractory siderophile elements and depleted volatile Au, Cu, Ag, S. All three types of grains are interpreted to derive from a common precursor approximated by the least‐melted, fine‐grained objects in CR chondrites. This also excludes recondensation of metal vapor as the origin of the bulk of margin grains. The metal precursors were presumably formed by incomplete condensation, with evidence for high‐temperature isolation of refractory platinum‐group‐element (PGE)‐rich condensates before mixing with lower temperature PGE‐depleted condensates. The rounded shape of the Ni‐rich, interior grains shows that they were molten and that they equilibrated with silicates upon slow cooling (1–100 K h^?1), largely by oxidation/evaporation of Fe, hence their high Pd content, for example. We propose that Ni‐poorer, amoeboid margin grains, often included in the pyroxene‐rich periphery common to type I chondrules, result from less intense processing of a rim accreted onto the chondrule subsequent to the melting event recorded by the interior grains. This means either that there were two separate heating events, which formed olivine/interior grains and pyroxene/margin grains, respectively, between which dust was accreted around the chondrule, or that there was a single high‐temperature event, of which the chondrule margin records a late “quenching phase,” in which case dust accreted onto chondrules while they were molten. In the latter case, high dust concentrations in the chondrule‐forming region (at least three orders of magnitude above minimum mass solar nebula models) are indicated.  相似文献   

Oxygen isotope composition of phenocrysts from Tristan da Cunha and Gough Island lavas: variation with fractional crystallization and evidence for assimilation     

Chris Harris  H. Stuart Smith  Anton P. le Roex 《Contributions to Mineralogy and Petrology》2000,138(2):164-175

We have measured the δ¹⁸O values of the major phenocrysts (olivine, clinopyroxene and plagioclase) present in lavas from Tristan da Cunha and Gough Island. These islands, which result from the same mantle plume, have enriched radiogenic isotope ratios and are, therefore, prime candidates for an oxygen isotope signature that is distinct from that of MORB. Consistent differences between the δ¹⁸O values of olivine, pyroxene and feldspar in the Gough lavas show that the phenocrysts in the mafic Gough Island lavas are in oxygen isotope equilibrium. The olivines in lavas with SiO₂ <50 wt% have a mean δ¹⁸O value of 5.19‰, consistent with crystallization from a magma having the same oxygen isotope composition as MORB. Phenocrysts in all the Gough lavas show a systematic increase in δ¹⁸O value as silica content increases, which is consistent with closed-system fractional crystallization. The lack of enrichment in δ¹⁸O of the Gough magmas suggests that the mantle source contained <2% recycled sediment. In contrast, the Tristan lavas with SiO₂ >48 wt% contain phenocrysts which have δ¹⁸O values that are systematically ∼0.3‰ lower than their counterparts from Gough. We suggest that the parental mafic Tristan magmas were contaminated by material from the volcanic edifice that acquired low δ¹⁸O values by interaction with water at high temperatures. The highly porphyritic SiO₂-poor lavas show a negative correlation between olivine δ¹⁸O value and whole-rock silica content rather than the expected positive correlation. The minimum δ¹⁸O value occurs at an SiO₂ content of about 45 wt%. Below 45 wt% SiO₂, magmas evolved via a combination of assimilation, fractionational crystallization and crystal accumulation; above 45 wt% SiO₂, magmas appeared to have evolved via closed-system fractional crystallization. Received: 23 November 1998 / Accepted: 27 September 1999  相似文献   

Book reviews     

T. Littmann  Rudolf Brázdil  Manfred Domrös  Mohammed A. Kishk  A. Wallner  Radan Květ  Andreas Grotewold 《GeoJournal》1992,26(4):547-549

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Risk perception and decision-making: do farmers consider risks from climate change?   总被引：2，自引：0，他引：2  

Anton Eitzinger  Claudia R. Binder  Markus A. Meyer 《Climatic change》2018,147(3-4):507-521

This paper provides one of the first empirical studies that examine the impact of climate change adaptation practices on technical efficiency (TE) among smallholder farmers in Nepal. An adaptation index is used to explore the impact of farmers’ adaptation on TE using the stochastic frontier analysis framework. Data for six districts of Nepal representing all three agro-ecological regions (terai, hill, and mountain) were collected from a focus group discussion, a stakeholder workshop and a household survey. The survey shows that about 91% of the farming households have adopted at least one practice to minimize the adverse impacts of climate change. Empirical results reveal that adaptation is an important factor explaining efficiency differentials among farming households. Those adopting a greater number of adaptation practices on a larger scale are, on average, found to be 13% more technically efficient than those adopting fewer practices on smaller scale. The empirical results also show that average TE is only 0.72, indicating that there are opportunities for farming households in Nepal to further improve productive efficiency, on average by 28%. Other important factors that explain variations in the productive efficiency across farming households include farmer’s education level, irrigation facilities, market access, and social capital such as farmer’s participations in relevant agricultural organizations and clubs. This study provides empirical evidence to policy makers that small scale adjustments made by farmers in response to climate change impacts are effective in improving farmers’ efficiency in agriculture production. This indicates a need for farmers’ involvement in climate change adaptation planning.  相似文献   

A prototype earthquake warning system for strike-slip earthquakes     

M. Nafi Toksöz  Anton M. Dainty  John T. Bullitt 《Pure and Applied Geophysics》1990,133(3):475-487

A prototype expert system has been developed to provide rapid warning of earthquakes while they are occurring. Warning times of up to 100 seconds will be possible. In the complete system, several accelerometers are distributed at intervals within a few kilometers of a known fault; data are telemetered to a central computer which implements the expert system. The expert system incorporates specific information about the type of fault to be monitored, and includes simple rules for estimating the fault slip, rupture length, and seismic moment, all in real time. If the seismic moment exceeds a preset value, an alarm may be issued. The prototype is designed for deployment on near-surface strike-slip faults such as the San Andreas and has been successfully tested with data from the 1979 Imperial Valley and 1984 Morgan Hill earthquakes. Crucial concepts have also been tested using synthetic data calculated for a model of the 1857 Fort Tejon earthquake. Parkfield, California, could be used as a test site.  相似文献   

Epiphytic orchids and their ecological niche under anthropogenic influence in central Himalayas,Nepal   总被引：1，自引：1，他引：0  

Yagya Prasad Adhikari  Anton Fischer  Hagen Siegfried Fischer 《山地科学学报》2016,13(5):774-784

The survival chance of epiphytic orchids today not only depends on the natural site conditions required by the orchids but also on anthropogenic changes in site conditions.This study answers two questions:(1) What is the ecological niche of the different epiphytic orchid species?(2) What are the ecological factors that threaten epiphytic orchid's population under anthropogenic disturbances? Our study area was the Kathmandu valley,Nepal,with its subtropical forest.We established 156 systematically selected sampling points in the Kathmandu area covering different types of ecosystems under human impacts such as densely populated area,agricultural land,mixed agricultural and settled area,old tree patches,and a natural forest in a national park.The ecological niche of the orchid species was analyzed with a principal component analysis(PCA).The correlations between the different site factors were statistically significant.Spearman's rank correlation matrices showed that the variables land-use intensities with altitude,and height with diameter in breast height(dbh) of host had the highest significant positive correlation coefficient(0.67 and 0.64 respectively).On the other hand,host bark p H and altitude as well as land use had a significantly strong negative correlation coefficient(-0.80 and-0.61,respectively).Different epiphytic orchid species interact differently with the given set ofenvironmental factors:for occurrence of Vanda cristata there is no single environmental factor of special influence,while for Rhynchostylis retusa high bark p H and high light availability are important.First two axis of the PCA explained more than 50% of the total variance.Most orchid species occupy a specific,narrow niche in this ecological space.The main causes of anthropogenic influence of orchid population in the Kathmandu Valley are loss of adequate host trees(species and size) and increasing air pollution,resulting in increasing host bark p H.  相似文献   

Stresses and Displacements in Steel-Lined Pressure Tunnels and Shafts in Anisotropic Rock Under Quasi-Static Internal Water Pressure   总被引：1，自引：1，他引：0  

Alexandre J. Pachoud  Anton J. Schleiss 《Rock Mechanics and Rock Engineering》2016,49(4):1263-1287

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Calcite and dolomite in intrusive carbonatites. II. Trace-element variations     

Anton R. Chakhmouradian  Ekaterina P. Reguir  Christopher Couëslan  Panseok Yang 《Mineralogy and Petrology》2016,110(2-3):361-377

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The performance of collars on scour reduction at tandem piers aligned with different skew angles     

Sargol Memar  Aliasghar Beheshti  Majid Rahimpour  Giovanni De Cesare  Anton J. Schleiss 《Marine Georesources & Geotechnology》2020,38(8):911-922

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