Lithospheric and upper mantle structure of central Chile and Argentina   总被引：1，自引：0，他引：1  

Hersh Gilbert  Susan Beck  George Zandt 《Geophysical Journal International》2006,165(1):383-398

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Datation Ar/Ar de la province magmatique de l’Atlantique central dans le Sud-Ouest algérien     

Moulley Charaf Chabou  Amar Sebai  Gilbert Fraud  Herv Bertrand 《Comptes Rendus Geoscience》2007,339(16):970-978

⁴⁰Ar/³⁹Ar step-heating analyses performed on plagioclase separates from seven doleritic basalts (four sills, one dyke and two lava flows) from southwestern Algeria display disturbed age spectra, reflecting various contributions of alteration by sericite and/or excess argon. Weighted mean ages corresponding to the less altered plagioclase fractions yielded minimum ages ranging from 192.7 ± 3.0 to 197.9 ± 2.0 Ma and a minimum date of 198.9 ± 1.8 Ma was obtained on a saddle-shaped age spectrum (excess argon). These ages are in accordance with those previously obtained on the CAMP province and partly in agreement with the peak activity of the CAMP at 198 Ma, highlighted in the neighbouring Taoudenni basin (Mali). In Algeria, the eastern boundary of the CAMP seems to coincide with the Pan-African suture zone.  相似文献   

Capital and Empire: Geographies of Imperial London     

David Gilbert  Felix Driver 《GeoJournal》2000,51(1-2):23-32

The notion of empire has often been regarded in Europe as a matter of diffusion and expansion; something which happened over there rather than close to home. Yet the form, use and representation of modern European cities have been shaped by the global history of imperialism in ways that continue to matter even in an apparently post-imperial age. The signs of empire were prominently displayed within the built environments of all the major cities of late-nineteenth century Europe, as they came (in different ways) to play the role of regional, national and imperial capitals. In what was evidently a pan-European discourse on the imperial city between the mid-nineteenth century and the mid-twentieth, national models were defined in relation to other national models, in a spirit of competition as much as emulation. This paper examines the case of London. British architects and planners frequently complained that London lagged behind its rivals in the struggle for imperial primacy, given the absence of state-sponsored projects to parallel Haussmann's rebuilding of Paris or Leopold's grand plans for Brussels. At the intra-urban scale, the imperial city had a geography which mattered: in the case of London, different parts of the city were associated with different aspects of empire. More generally, it is clear that national debates over imperial urbanism were conditioned not simply by understandings of the global reach of European empires, but also by attitudes towards social, cultural and political change within Europe itself.  相似文献   

Quartz diorites derived by partial melting of eclogite or amphibolite at mantle depths   总被引：4，自引：0，他引：4  

Joseph G. Arth  Gilbert N. Hanson 《Contributions to Mineralogy and Petrology》1972,37(2):161-174

Rare earth elements, Rb, Sr, Ba and K have been determined in tonalite, trondhjemite, dacite, tholeiite and graywacke from the 2700 m.y. old Early Precambrian greenstone-granite terrane of northeastern Minnesota-northwestern Ontario, and also in trondhjemite from the 3550 m.y. old Morton Gneiss, southwestern Minnesota; and the Mesozoic Craggy Peak Pluton, Klamath Mountains, California.The Early Precambrian tholeiites have trace element compositions similar to modern oceanic tholeiites, while the quartz dioritic rocks, regardless of age, have total rare earth contents lower than that of tholeiitic basalts, with near chondritic heavy rare earth contents. Rb, Sr, Ba and K contents of the quartz diorites are about five times that of oceanic tholeiites, with similar alkali and alkaline earth ratios. The Early Precambrian graywacke has a rare earth content intermediate between greenstone and quartz diorite, reflecting its provenance.It is proposed that the analyzed quartz dioritic rocks, whether plutonic tonalite, dacite porphyry, gneissic or plutonic trondhjemite, or trondhjemite dikes had similar modes of origin, and were derived by partial melting of amphibolite or eclogite of basaltic or gabbroic composition at depths greater than thirty kilometers, leaving a residue consisting predominantly of garnet and clinopyroxene.  相似文献   

Fehler der Eisen-Konstantan-Thermoelemente bei Feuchtemessungen mit dem thermoelektrischen Psychrometer     

T. Gilbert 《Theoretical and Applied Climatology》1955,6(3):280-291

Zusammenfassung Drei verschiedene Eisen-Konstantan Thermoelemente wurden in Petroleum und in Wasser geeicht, wobei die passive Lötstelle einmal auf 0° und einmal auf 50° C lag. Die beiden Eichkurven in Wasser zeigen bei dem extremsten Thermoelement eine maximale Temperaturdifferenz von 1,1°C. Die Eichung in Petroleum ergibt gegenüber Wasser eine etwas geringere Temperaturdifferenz, die aber mit ausreichender Genauigkeit vernachlässigt werden kann. Auffallend ist das Auseinanderlaufen der Eichkurven der einzelnen Thermoelemente. Der Unterschied hierbei ist direkt proportional zur Temperaturdifferenz (t _akt.–t _pass.) und ist wohl auf die Vorgeschichte der Materialien zurückzuführen.

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Summary Three different iron-constantan thermocouples were gauged in both petroleum and water, the passive soldered joint lying at 0°C and subsequently at 50°C. The two gauging curves in water show, for the extremest thermocouple, a highest temperature difference of 1,1°C. Gauging in petroleum yields, with regard to water, a somewhat smaller temperature difference which can be neglected with sufficient accuracy. There is an obvious divergence of the gauging curves of the three thermocouples. The difference is directly proportional to the temperature difference (t _active–t _passive) and may be accounted for by the previous state and treatment of the material in question.

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Résumé On a étalonné trois thermoéléments différents de ferro-constantan dans du pétrole et dans de l'eau, les soudures passives étant une fois à 0° et une autre fois à 50° C. Les deux courbes d'étalonnage dans l'eau accusent pour le thermoélément le plus extrême une différence de température n'excédant pas 1,1°, tandis que dans le pétrole cette différence est un peu plus faible, mais peut être pratiquement négligée. La divergence des courbes d'étalonnage de chaque thermoélément est remarquable; l'écart est proportionnel à la différence de température des soudures et s'explique probablement par l'état antérieur des matériaux.

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Mit 5 Textabbildungen.  相似文献   

Attenuation and Biodegradation of Chlorophenols in Ground Water at a Former Wood Treating Facility     

Andy Davis  Jim Campbell  Craig Gilbert  Michael V. Ruby  Meridan Bennett  Susan Tobin 《Ground water》1994,32(2):248-257

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A Synthetic Haematite Reference Material for LA‐ICP‐MS U‐Pb Geochronology and Application to Iron Oxide‐Cu‐Au Systems     

Liam Courtney‐Davies  Sarah E. Gilbert  Cristiana L. Ciobanu  Simon R. Tapster  Marcus W. Richardson  Nigel J. Cook  Benjamin P. Wade  Max R. Verdugo‐Ihl  Kathy Ehrig  Daniel J. Condon 《Geostandards and Geoanalytical Research》2021,45(1):143-159

In both nature and synthetic experiments, the common iron oxide haematite (α‐Fe₂O₃) can incorporate significant amounts of U into its crystal structure and retain radiogenic Pb over geological time. Haematite is a ubiquitous component of many ore deposit types and, therefore, represents a valuable hydrothermal mineral geochronometer, allowing direct constraints to be placed on the timing of ore formation and upgrading. However, to date, no suitable natural haematite reference material has been identified. Here, a synthetic haematite U‐Pb reference material (MR‐HFO) is characterised using LA‐ICP‐MS and ID‐TIMS. Centimetre‐scale ‘chips’ of synthesised α‐Fe₂O₃ were randomly microsampled via laser ablation‐extraction and analysed using ID‐TIMS. Reproducible U/Pb and Pb/Pb measurements were obtained across four separate chips (n = 13). Subsequently, an evaluation of the suitability MR‐HFO in constraining U‐Pb data via LA‐ICP‐MS is presented using a selection of natural samples ranging from Cenozoic to Proterozoic in age. The MR‐HFO normalised U‐Pb ratios are more concordant and ages more accurate versus the same LA‐ICP‐MS spot analyses normalised to zircon reference material, when compared with independently acquired ID‐TIMS data from the same natural haematite grains. Results establish MR‐HFO as a suitable reference material for LA‐ICP‐MS haematite U‐Pb geochronology.  相似文献   

Projections of Future Trends in Biogeochemical Conditions in the Northwest Atlantic Using CMIP5 Earth System Models     

Diane Lavoie  Nicolas Lambert  Denis Gilbert 《大气与海洋》2019,57(1):18-40

We use the results from eight of the Earth System Models (ESMs) made available for the Fifth Assessment Report of the Intergovernmental Panel on Climate Change to analyze the projected changes in biogeochemical conditions over the next 50 years in the northwest Atlantic. We looked at the projected changes using the Representative Concentration Pathway 8.5 scenario in the 100–400?m depth range over a large region and at more specific locations to assess the relevance of using these outputs to force a regional climate downscaling model of the Gulf of St. Lawrence. The projected trends for dissolved oxygen (decrease), pH (decrease), and nitrate (variable although negative in general) represent a continuation of the recently observed trends in the area. For primary production, no firm conclusions can be drawn because of large differences in the trends from one model to another. The consistency of the trends near the regional model lateral boundaries leads us to conclude that the ESM trends can be used to set up future boundary conditions to evaluate regional impacts of climate change although the uncertainty of the results for the Scotian Shelf will be greater than for the Gulf of St. Lawrence.  相似文献   

Intermobility of barium,strontium, and lead in chloride and sulfate leach solutions     

Rollog  Mark  Cook  Nigel J.  Guagliardo  Paul  Ehrig  Kathy  Gilbert  Sarah E.  Kilburn  Matt 《Geochemical transactions》2019,20(1):1-12

Iron(III)-precipitates formed by the oxidation of dissolved Fe(II) are important sorbents for major and trace elements in aquatic and terrestrial systems. Their reductive dissolution in turn may result in the release of associated elements. We examined the reductive dissolution kinetics of an environmentally relevant set of Fe(II)-derived arsenate-containing Fe(III)-precipitates whose structure as function of phosphate (P) and silicate (Si) content varied between poorly-crystalline lepidocrocite, amorphous Fe(III)-phosphate, and Si-containing ferrihydrite. The experiments were performed with 0.2–0.5 mM precipitate-Fe(III) using 10 mM Na-ascorbate as reductant, 5 mM bipyridine as Fe(II)-complexing ligand, and 10 mM MOPS/5 mM NaOH as pH 7.0 buffer. Times required for the dissolution of half of the precipitate (t_50%) ranged from 1.5 to 39 h; spanning a factor 25 range. At loadings up to ~ 0.2 P/Fe (molar ratio), phosphate decreased the t_50% of Si-free precipitates, probably by reducing the crystallinity of lepidocrocite. The reductive dissolution of Fe(III)-phosphates formed at higher P/Fe ratios was again slower, possibly due to P-inhibited ascorbate binding to precipitate-Fe(III). The slowest reductive dissolution was observed for P-free Si-ferrihydrite with ~ 0.1 Si/Fe, suggesting that silicate binding and polymerization may reduce surface accessibility. The inhibiting effect of Si was reduced by phosphate. Dried-resuspended precipitates dissolved 1.0 to 1.8-times more slowly than precipitates that were kept wet after synthesis, most probably because drying enhanced nanoparticle aggregation. Variations in the reductive dissolution kinetics of Fe(II) oxidation products as reported from this study should be taken into account when addressing the impact of such precipitates on the environmental cycling of co-transformed nutrients and contaminants.

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Offshore pile system model biases and reliability     

Jinbo Chen  Robert B. Gilbert 《Georisk: Assessment and Management of Risk for Engineered Systems and Geohazards》2017,11(1):55-69

ABSTRACT

Recent hurricanes between 2004 and 2008 in the Gulf of Mexico provide valuable new information about design model biases and uncertainties because multiple offshore platforms were loaded beyond the predicted capacity of their pile systems and because there was a failure of a pile system. A Bayesian calibration of model bias factors based on predicted versus observed performance of pile systems in hurricanes indicates that the conventional American Petroleum Institute design method for pile capacity is slightly conservative by about 10% for base shear (i.e. lateral) failures of pile systems in clay, unbiased for overturning (i.e. axial) failures of pile systems in clay, and conservative by more than 50% for overturning failures of piles systems in sand. The epistemic uncertainty in the updated bias factors is represented by coefficient of variation values of about 0.25 for base shear and overturning failures of pile systems in clay and 0.35 for overturning failures of pile systems in sand. A reliability assessment with the calibrated model bias factors shows that the current design practice produces lower reliability for a pile system with three piles versus one with eight piles and lower reliability for a pile system failing in overturning versus one failing in base shear. Therefore, the current design practice could potentially be improved by taking into account the mode of failure and the redundancy in the pile system to provide for a more uniform level of reliability.  相似文献