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361.
The proposals for a European policy framework for Geographic Information (GI) recently put forward by Directorate General XIII raise three sets of issues about measures required to facilitate the dissemination of GI in the European Union: (1)'hot topics' such as privacy and the legal protection of databases that apply to information generally; (2) GI issues such as reference data and metadata services that may require action by the European Commission; and (3) perceived barriers to the development of a European GI market. This paper examines the views of 20 experts responsible for the provision and management of GI in key organizations throughout Europe. A Delphi-style strategy was used to identify the relative importance of the issues raised by the proposals and to ascertain the level of agreement as to the importance of these issues between the experts. The results show that issues relating to copyright, the protection of intellectual property rights, data quality, and data access policies were ranked highly by most of the respondents. A lack of awareness, education, and training (as opposed to the lack of public domain data and metadata services) were viewed as the main barriers to the deveiopment of the GI market in Europe. 相似文献
362.
Constant sets for several turbulence closure models,based on data for the atmospheric boundary layer, areproposed. They differ from those currently used inengineering situations but are self-consistent andtuned to represent atmospheric boundary-layerturbulence. The proposed constant sets are tested in a simple,one-dimensional, neutrally-stratified planetaryboundary-layer flow over a horizontally homogeneousand aerodynamically rough flat surface. Comparisons ofmodel results with similarity theory and large-eddysimulation show promise for improving boundary-layerpredictions. 相似文献
363.
The effect of rain on air-water gas exchange 总被引:5,自引:0,他引:5
364.
365.
PETER WIGLEY 《Sedimentology》1973,20(2):295-304
The Sr2+ content of Barbudan limestones is proportional to the aragonite content. The Sr2+ content of calcite which has replaced aragonite varies from 3000 p.p.m. in the youngest limestones to 50 p.p.m., average values are approximately 300 p.p.m. The (mSr2+/mCa2+)L ratios from well waters within the limestone fall within the predicted values assuming KSrC~0·1. The high (mSr2+/mCa)2+L ratios expected by a lower value of KSrC do not occur. The build up of (mSr2+/mCa2+)L ratios seen in waters from Barbados is not seen in the well waters from Barbuda. The Sr2+ content of calcite is generally lower than is seen in Barbados, but similar to that seen in parts of the Miami Oolite. Diagenesis of aragonite in Barbudan limestones is probably occurring in a more open system than in Barbados. 相似文献
366.
Microprobe analyses of the oxide mineral assemblages from monzonitic,granodioritic, and granitic units of the Finnmarka igneous complex,Oslo area, Norway, disclose a remarkable trend of Mn enrichmentin ilmenite with differentiation. Ilmenite-pyrophanite solidsolutions containing up to 63 mole per cent MnTiO3 have developedunder apparently unusually oxidizing conditions, a conclusiondeduced in part from the fact that Fe2+ is more readily oxidizedthan Mn2+ and was thus preferentially extracted. Several differentmineral reactions may have been involved in this process. Geothermometricapplications of oxide Mn contents must be made with caution. Additional mineralogic complexities, e.g. ilmenite lamellaein magnetite, magnetite lamellae in ilmenite, and, in the granite,the breakdown of ilmenite to rutile+hematite, all provide insightinto the conditions of emplacement and cooling history of thecomplex. 相似文献
367.
CLARKE D. BARRIE; MACDONALD MICHAEL A.; REYNOLDS PETER H.; LONGSTAFFE FRED J. 《Journal of Petrology》1993,34(4):653-679
The South Mountain Batholith is a peraluminous granitic complexranging in composition from biotite granodiorite to muscovite-topazleucogranite. Leucogranitic rocks (with generally<2% biotite) form a minor part ({small tilde}15%) ofthe batholith, and are of two types: (1) associated leucogranitesoccurring as relatively small zones in fine-grained leucomonzogranites;and (2) independent leucogranites forming generallylarger bodies having no particular spatial association withother rock types. Mean chemical compositions of these two typesof leucogranite are as follows (associated, independent): Na2O(346,383),K2O(440,409),andP2O5 (026, 045)in wt.%;Li(149, 281), F(1199, 2712),Rb (393, 725), U (74, 44), Nb (128, 234),Ta (29, 71), and Zr (52, 31) in ppm. Rare earthelements also differ between the two types (associated, independent):REE (341 ppm, 199 ppm); and in the degree and variabilityof heavy REE fractionation (GdN/YbN=4622, 2007).In addition, associated leucogranite has REE compositions similarto those of its host rocks. Mean 18O values (associated +ll212,independent +ll405; relative to SMOW) are comparablewith the mean for the entire South Mountain Batholith (+l0807).Radiometric dating (40Ar/39Ar on muscovite) shows that bothtypes of leucogranite have identical ages of 3723 Ma, equivalentto ages determined by other techniques for granodiorite andmonzogranite samples elsewhere in the batholith. Field relationsand geochemistry suggest that the associated leucogranite resultsfrom an open-system interaction between a fluid and its hostleucomonzogranite, whereas the independent leucogranite bodiesare discrete intrusions of highly fractionated melts that underwentclosed-system, late-magmatic to post-magmatic fluid alteration.Where mineralized, the associated leucogranite characteristicallyhosts greisen-type or disseminated polymetallic mineralization,whereas the independent leucogranite hosts pegmatitic or disseminatedpolymetallic mineralization. 相似文献
368.
Field evidence from intrusive and effusive carbonatites supportsthe existence of calciocarbonatite magmas. Published experimentalevidence in the model system Na2OCaOAl2O3SiO2CO2indicated the formation of nearly pure (99%) CaCO3 immiscibleliquids from a carbonated silicate liquid. This evidence hasbeen used to support interpretations of extremely CaCO3-richcalciocarbonatite magmas, and immiscible liquids with compositionsof almost pure CaCO3 in metasomatized mantle peridotite andeclogite. Detailed phase relationships are constructed in themodel system, based on phase fields intersected by the joinNaAlSi3O8CaCO3 (Ab-CC) at 1.0, 1.5, and 2.5 GPa between1100 and 1500C, and analyzed immiscible liquids. The miscibilitygap between silicate-rich liquid and carbonate-rich liquid intersectedby the join Ab-CC contracts considerably with decreasing pressure:2.5 GPa, between Ab10CC90 (by wt%) and Ab65CC35 above 1310C;1.5 GPa, betweenAb23CC77 and Ab43CC57 above 1285C; 1.0 GPa,not intersected. The liquidus piercing point between calciteand silicates becomes enriched in CaCO3 with decreasing pressure,from Ab80CC20 at 2.5 GPa to Ab47CC53 at 1.0 GPa. No immiscibleliquid contains more than 80% dissolved CaCO3, and all containat least 5% Na2CO3. A round CaCO3 phase exhibiting morphologysimilar to that displayed by immiscible liquid globules is determinedto be crystalline calcite under experimental conditions. Thetopology of the phase fields and field boundaries illustratesthe kinds of processes and controls existing in magmatic systems.Calciocarbonatite magmas cannot be produced by equilibrium immiscibilityprocess in the mantle. Carbonated silicate magmas in the crustyield residual calciocarbonatite magmas by fractionation alongthe silicate-calcite field boundary, reached either directlyfrom the silicate liquidus or more commonly via the miscibilitygap. Immiscible carbonaterich magmas when freed from the silicateparent cool down a sleep silicate liquidus until they reacha silicate-carbonate field boundary. There is no experimentalevidence for immiscible calciocarbonatite magmas with > 80%CaCO3, and calcite lapilli cannot be formed from 99% CaCO3 magmas.Sovites are surely cumulates. KEY WORDS: carbonatite; join NaAlSi3O8CaCO3; liquid immiscibility; sovite
* Corresponding author. Telephone: (818)-3956239. Fax: (818)-5680935. e-mail: wjl{at}gpi.caltech.edu 相似文献
369.
New Pb, Sr and Nd isotope data from volcaniclastic sedimentsrecovered from the Tonga forearc and Lau Basin permit the isotopicevolution of a section of this arc system, next to the modernisland of Ata, to be traced through the backarc basin riftingprocess from 7.0 Ma to the present. The new data suggest thatthe isotopic character of the mantle wedge remains constant,and of Pacific mid-ocean ridge basalt (MORB) character, duringthe early rifting phase. The isotopic evidence supports traceelement data in showing an increase in the sediment contributionto arc petrogenesis about 23 m.y. after the start ofLau Basin rifting. Since 0.45 Ma the sediment contribution decreasedto pre-rift values with the initiation of spreading in the adjacentbackarc basin, where the high sediment influence is not seenin the isotopes. The isotopes show a relative increase in thevolcaniclastic compared with pelagic sediment involvement duringrifting. The inferred peak in sediment subduction is probablythe result of a decoupling of the two plates owing to roll-backof the Pacific lithosphere at the time of arc rifting. KEY WORDS: isotopes; Pacific; rifting; subduction; volcanism
*Corresponding author. Telephone: (508) 289 3437. Fax: (508) 457 2187. e-mail: pclift{at}whoi.edu 相似文献
370.
The effects of infiltration, diffusion, and local structureon the contact metamorphism of the Cambrian Weeks Formation,a calcareous argillite located in western Utah, were examinedusing stable isotope systematics and mineral mass-balance considerations.The emplacement of the Jurassic Notch Peak granitic stock resultedin metamorphism characterized with increasing proximity to theintrusion by phlogopite, diopside, and wollastonite isograds.The isograds are generally concentric around the stock, withdiopside and wollastonite isograds {small tilde}600 and 400m from the contact, respectively, but are deflected near a pre-intrusionfault where the wollastonite isograd is 1. 5 km from the contact.Where the isograds are concentric, the wollastonite isogradmarks an isotopic front with whole-rock 18O values approachingthe 9.5% value of the stock. In contrast, the 18O values inthe unmetamorphosed to diopside-grade rocks range from 16.3to 20.2%. Near the fault the isotopic front extends throughthe diopside zone, suggesting that the fault was a major conduitfor magmatic water. Waterrock ratios for the diopside- and wollastonite-gradesamples determined from mineralogic mass balance are nearlyone order of magnitude larger than one-box closed-systemratios determined from shifts in stable isotope ratios. Chromatographicmodels for isotopic exchange and propagation of isograds showthat one-dimensional infiltration of magmatic water throughpore spaces would lead to an isotopic front at 50 m from thestock and the wollastonite isograd would be only 8 km from thestock. These distances are significantly smaller than observed.It is suggested that most of the magmatic water flowed throughfractures or thin permeable layers, with the extent of isotopicexchange between the magmatic water in these conduits and theadjacent rocks being controlled by the extent of reaction progressin the rocks. Considerations of CO2H2O interdiffusivitiesin fluids indicate that removal of CO2 from the reaction frontstoward the intrusion or the fault was sufficiently rapid tocontrol the geometry of the isograds. 相似文献