Vesiculation and vesicle loss in mid-ocean ridge basalt glasses: He, Ne, Ar elemental fractionation and pressure influence     

Philippe Sarda  Manuel Moreira 《Geochimica et cosmochimica acta》2002,66(8):1449-1458

Sarda and Graham (1990) proposed that in mid-ocean ridge basalts (MORBs), degassing occurs through equilibrium vesiculation followed by various extents of vesicle loss. This model predicts that in a bulk sample of MORB glass with vesicles, the rare gases represent a binary mixture between a vesicle component and a component dissolved in the melt. As vesiculation is expected to produce very different rare gas concentrations and elemental ratios in gas and melt, binary mixing systematics should be recorded in the MORB rare gas abundance data. Indeed, a large range of ⁴He/⁴⁰Ar∗ ratios was known to exist, but these binary mixing systematics remained elusive because helium was used as a proxy for rare gas abundance because helium is not affected by air addition. Here we show that using Ar instead of He, the ⁴He/⁴⁰Ar∗ ratio is higher where the Ar concentration is lower, as expected from simple binary mixing systematics.Taking advantage of the growing Ne database, we further show that the predicted binary mixing is recorded by the He-Ar and He-Ne couples, provided He concentration is not used to trace vesicle abundance. This is because a significant part of helium remains in the melt due to its higher solubility. In contrast, Ar or Ne concentrations, which can both be corrected for air addition, clearly trace vesicles and yield binary mixing patterns that hold for ridges worldwide. The model of vesiculation and vesicle loss thereby finds geochemical support in the rare gas abundance data.The He-Ne-Ar concentration data is best explained by assuming the ratio of helium to neon or argon solubility is about 5 to 15 times higher than values measured in 1 bar laboratory experiments, due to higher He and lower Ne and Ar solubilities. We propose that this is a pressure effect, and vesiculation mainly occurs during magma ascent in the mantle after melting.  相似文献   

Water organisation at the solid–aqueous solution interfaceOrganisation de l'eau à l'interface solide–solution aqueuse     

Laurent J. Michot  Frédéric Villiéras  Michèle François  Isabelle Bihannic  Manuel Pelletier  Jean-Maurice Cases 《Comptes Rendus Geoscience》2002,334(9):611-631

The aim of this review is to examine the present knowledge about water structure close to an interface or confined in porous spaces. First, the structure of liquid water is briefly described. Though its understanding remains incomplete, it appears that it is largely dominated by the hydrogen bond network and its dynamical evolution. The presence of any ‘foreign’ substance in water perturbs such a structure by changing at least locally the hydrogen bond network. For this reason, the presence of a solid interface significantly modifies the structure of the first adsorbed layers. Whatever the support, it is now clearly evidenced that structural perturbations are limited to distances lower than 10–15 Å from the interface. The nature, energetic heterogeneity and hydrophilicility/hydrophobicity of the solid surface influence the arrangement of water molecules. This surface organisation must definitely be considered when studying adsorption phenomena at the solid–aqueous solution interface. The relevance of such problems to geosciences is illustrated by a few situations in which water structure plays a prominent role. To cite this article: L.J. Michot et al., C. R. Geoscience 334 (2002) 611–631.  相似文献   

Cathodoluminescence petrography and isotope geochemistry of KT impact ejecta deposited 360 km from the Chicxulub crater, at Albion Island, Belize     

Bruce W. Fouke  Aubrey L. Zerkle  Walter Alvarez†  Kevin O. Pope‡  Adriana C. OcampO§  Richard J. Wachtman  Jose Manuel Grajales Nishimura¶  Phillipe Claeys  & Alfred G. Fischer†† 《Sedimentology》2002,49(1):117-138

The depositional and diagenetic history of Cretaceous–Tertiary (KT) impact ejecta deposited 360 km from the Chicxulub crater, at Albion Island, Belize, has been investigated using integrated cathodoluminescence and isotopic analyses. A quarry exposes 26 m of Upper Cretaceous Barton Creek Formation dolomitized marine limestone overlain by 16 m of dolomitized Albion Formation impact ejecta. The Albion Formation consists of a lower fine‐grained ≈1‐m‐thick spheroid bed and an upper 15‐m‐thick coarse conglomeratic diamictite bed. A 14‐event paragenetic sequence has been documented and used as a temporal framework to interpret chemostratigraphic trends in bulk rock δ¹⁸O, δ¹³C and ⁸⁷Sr/⁸⁶Sr. The uppermost surface of the Barton Creek Formation was subaerially exposed before the KT impact, as indicated by a brecciated palaeosol that caps upsection decreases in δ¹³C and δ¹⁸O. Small 1‐cm‐diameter spheroids in the spheroid bed exhibit vermicular crystalline textures but lack the concentric zonations common to accretionary lapilli. These spheroids are hypothesized originally to have been impact glass or reactive Ca and Mg oxide dusts that adhered to water vapour particles condensing from the cooling impact vapour cloud. The spheroids were dolomitized soon after deposition. The earliest dolomitization in the matrix sediments of the Albion Formation was also post‐depositional, replacing clays formed by devitrification of impact glass. Dolomite and clay ⁸⁷Sr/⁸⁶Sr exhibit a distinct symmetrical distribution in the spheroid bed ranging from 0·707745 to 0·707872. Although unproven, this may represent primary changes in the chemical composition of the impact glass. The limestone clasts in the diamictite bed were dolomitized before the KT impact and exhibit upsection decreases in bulk rock ⁸⁷Sr/⁸⁶Sr. This suggests that the clasts were excavated from strata equivalent in age or older than the Barton Creek Formation at locations closer to, or in, the Chicxulub crater.  相似文献   

Le passage Ordovicien–Silurien et la partie inférieure du Silurien (Sud-Est du Massif armoricain, France)The Ordovician–Silurian transition and the lower part of the Silurian (southeastern Armorican Massif, France)     

Jos Manuel Piarra  Michel Robardet  Ahmed Bourahrouh  Florentin Paris  Zlia Pereira  Jean Le Menn  Rmy Gourvennec  Toms Oliveira  Hubert Lardeux 《Comptes Rendus Geoscience》2002,334(16)

A new section in the Silurian graptolitic ‘phtanites’ (black cherts) of Les Fresnaies at Chalonnes-sur-Loire (SE Armorican Massif) shows for the first time that these rocks (1) succeed conformably to Uppermost Ordovician (Hirnantian) glaciomarine deposits and (2) contain successive graptolite assemblages that characterise the base of the Silurian, the whole Rhuddanian and Aeronian stages and the lower part of the Telychian. To cite this article: J.M. Piçarra et al., C. R. Geoscience 334 (2002) 1177–1183.  相似文献   

Comment on G. Wansard and F. Mezquita, The response of ostracode shell chemistry to seasonal change in a Mediterranean freshwater spring environment     

David L. Dettman  Manuel Palacios-Fest  Andrew S. Cohen 《Journal of Paleolimnology》2002,27(4):487-491

In a study of the minor element chemistry of ostracode shells, Wansard and Mezquita (2001) concluded that the Mg/Ca and Sr/Ca of the ambient water controlled the respective ratios in ostracode calcite. Contrary to their conclusion that minor element chemistry is not influenced by temperature, we find a very strong statistical correlation (r = 0.97) between temperature and shell chemistry in their data. This discrepancy apparently arises due to their use of a partition coefficient model of shell chemistry that masks a number of strong correlations in their data. We argue here that the partition coefficient model is not appropriate for this biologically-mediated carbonate, and that a broader range of possible controls on shell chemistry needs to be tested.  相似文献   

Improving the Abel transform inversion using bending angles from FORMOSAT-3/COSMIC   总被引：2，自引：1，他引：1  

Angela Aragon-Angel  Manuel Hernandez-Pajares  J. Miguel Juan Zornoza  Jaume Sanz Subirana 《GPS Solutions》2010,14(1):23-33

The FORMOSAT-3/COSMIC satellite constellation has become an important tool toward providing global remote sensing data for sounding of the atmosphere of the earth and the ionosphere in particular. In this study, the electron density profiles are derived using the Abel transform inversion. Some drawbacks of this transform in LEO GPS sounding can be overcome by considering the separability concept: horizontal gradients of vertical total electron content (VTEC) information are incorporated by the inversion method, providing more accurate electron density determinations. The novelty presented in this paper with respect to previous works is the use of the phase change between the GPS transmitter and the LEO receiver as the main observable instead of the ionospheric combination of carrier phase observables for the implementation of separability in the inversion process. Some of the characteristics of the method when applied to the excess phase are discussed. The results obtained show the equivalence of both approaches but the method exposed in this work has the potentiality to be applied to the neutral atmosphere. Recent FORMOSAT-3/COSMIC data have been processed with both the classical Abel inversion and the separability approach and evaluated versus colocated ionosonde data.  相似文献   

Holocene glacial history and sea-level changes on James Ross Island,Antarctic Peninsula     

Christian Hjort   lafur Inglfsson  Per Mller  Juan Manuel Lirio 《第四纪科学杂志》1997,12(4):259-273

A reconstruction of deglaciation and associated sea-level changes on northern James Ross Island, Antarctic Peninsula, based on lithostratigraphical and geomorphological studies, shows that the initial deglaciation of presently ice-free areas occurred slightly before 7400 ¹⁴C yr BP. Sea-level in connection with the deglaciation was around 30 m a.s.l. A glacier readvance in Brandy Bay, of at least 7 km, with the initial 3 km over land, reached a position off the present coast at ca. 4600 yr BP. The culmination of the advance was of short duration, and by 4300 yr BP the coastal lowlands again were ice-free. A distinct marine level at 16–18 m a.s.l. was contemporaneous with or slightly post-dates the Brandy Bay advance, thus indicating the relative sea-level around 4600–4500 yr BP. Our results from James Ross Island confirm that over large areas in this part of Antarctica the last deglaciation occurred late. © 1997 John Wiley & Sons, Ltd.  相似文献   

Elastic wave propagation in an irregularly layered medium   总被引：1，自引：0，他引：1  

Rossana Vai  Jos Manuel Castillo-Covarrubias  Francisco J. Snchez-Sesma  Dimitri Komatitsch  Jean-Pierre Vilotte 《Soil Dynamics and Earthquake Engineering》1999,18(1):385

The indirect boundary element method (IBEM) is used to simulate wave propagation in two-dimensional irregularly layered elastic media for internal line sources. The method is based on the integral representation for scattered elastic waves using single layer boundary sources. Fulfillment of the boundary conditions leads to a system of integral equations. Results are obtained in the frequency domain and seismograins are computed through Fourier synthesis. In order to test and validate the method we present various comparisons between our results and the time series obtained analytically for a buried line source in a half-space and by using the recently developed spectral element method (SEM).  相似文献   

Minimizing the impacts of contaminant intrusion in small water distribution networks through booster chlorination optimization     

Nilufar?Islam  Manuel?J.?Rodriguez  Ashraf?Farahat  Rehan?SadiqEmail author 《Stochastic Environmental Research and Risk Assessment (SERRA)》2017,31(7):1759-1775

Contaminant intrusion in a water distribution network (DN) has three basic pre-conditions: source of contaminant (e.g., leaky sewer), a pathway (e.g., water main leaks), and a driving force (e.g., negative pressure). The impact of intrusion can be catastrophic if residual disinfectant (chlorine) is not present. To avoid microbiological water quality failure, higher levels of secondary chlorination doses can be a possible solution, but they can produce disinfectant by-products which lead to taste and odour complaints. This study presents a methodology to identify potential intrusion points in a DN and optimize booster chlorination based on trade-offs among microbiological risk, chemical risk and life-cycle cost for booster chlorination. A point-scoring scheme was developed to identify the potential intrusion points within a DN. It utilized factors such as pollutant source (e.g., sewer characteristics), pollution pathway (water main diameter, length, age, and surrounding soil properties, etc.), consequence of contamination (e.g., population, and land use), and operational factors (e.g., water pressure) integrated through a geographical information system using advanced ArcMap 10 operations. The contaminant intrusion was modelled for E. Coli O156: H7 (a microbiological indicator) using the EPANET-MSX programmer’s toolkit. The quantitative microbial risk assessment and chemical (human health) risk assessment frameworks were adapted to estimate risk potentials. Booster chlorination locations and dosages were selected using a multi-objective genetic algorithm. The methodology was illustrated through a case study on a portion of a municipal DN.  相似文献   

Adjustments in channel morphology due to land‐use changes and check dam installation in mountain torrents of Calabria (southern Italy)          下载免费PDF全文

Diego Fortugno  Carolina Boix‐Fayos  Giuseppe Bombino  Pietro Denisi  Juan Manuel Quiñonero Rubio  Vincenzo Tamburino  Demetrio Antonio Zema 《地球表面变化过程与地形》2017,42(14):2469-2483

In Mediterranean semi‐arid conditions, the availability of studies monitoring channel adjustments as a response to reforestation and check dams over representative observation periods, could help develop new management strategies. This investigation is an integrated approach assessing the adjustments of channel morphology in a typical torrent of southern Italy after land‐use changes and check dam construction across a period of about 60 years. A statistical analysis of historical rainfall records, an analysis of land‐use changes in the catchment area and a geomorphological mapping of channel adjustments were carried out and combined with field surveys of bed surface grain‐size over a 5‐km reach including 14 check dams. The analysis of the historical rainfall records showed a slight decrease in the amount and erosivity of precipitation. Mapping of land‐use changes highlighted a general increase of vegetal coverage on the slopes adjacent to the monitored reaches. Together with the check dam network installation, this increase could have induced a reduction in water and sediment supply. The different erosional and depositional forms and adjustments showed a general narrowing between consecutive check dams together with local modifications detected upstream (bed aggradation and cross‐section expansion together with low‐flow realignments) and downstream (local incision) of the installed check dams. Changes in the torrent bends were also detected as a response to erosional and depositional processes with different intensities. The study highlighted: the efficiency of check dams against the disrupting power of intense floods by stabilizing the active channel and the influence of reforestation in increasing hillslope protection from erosion and disconnectivity of water and sediment flows towards the active channel. Only slight management interventions (for instance, the conversion of the existing check dams into open structures) are suggested, in order to mobilize the residual sediment avoiding further generalized incision of the active channel and coast line erosion. Copyright © 2017 John Wiley & Sons, Ltd.  相似文献