共查询到20条相似文献,搜索用时 93 毫秒
1.
The dependence of the partitioning of iron and europium between plagioclase and hydrous tonalitic melt on oxygen fugacity 总被引:1,自引:0,他引:1
The dependence of iron and europium partitioning between plagioclase and melt on oxygen fugacity was studied in the system
SiO2(Qz)—NaAlSi3O8(Ab)—CaAl2Si2O8(An)—H2O. Experiments were performed at 500 MPa and 850 °C/750 °C under water saturated conditions. The oxygen fugacity was varied
in the log f
O2-range from −7.27 to −15.78. To work at the most reducing conditions the classical double-capsule technique was modified.
The sample and a C—O—H bearing sensor capsule were placed next to each other within a BN jacket to minimise loss of hydrogen
to the vessel atmosphere. By this setup redox conditions slightly more reducing than the FeO—Fe3O4 buffer could be maintained even in 96 h runs. Raman spectra showed that the BN was modified by reaction with hydrogen resulting
in a low hydrogen permeability. The partition coefficients determined for Eu at 850 °C and 500 MPa vary from 0.095 at conditions
of the Cu—Cu2O buffer to 1.81 at the most reducing conditions (C—O—H sensor). In the same f
O2 interval the partition coefficient for Fe varies from 0.55 at oxidising conditions to 0.08 at the most reducing conditions.
The partitioning of Sm, which was added as a reference for a trivalent REE, does not vary with the oxygen fugacity, yielding
an average value for D = 0.07. Lowering the temperature to 750 °C for a given f
O2 decreases the partition coefficient of Eu and increases that of Fe. Comparison with published data at 1 atm and at higher
temperatures shows that both temperature and composition of the melt have strong effects on the partitioning behaviour. As
the change of the partition coefficients in the geologically relevant f
O2 range is quite strong, element partitioning of Eu and Fe might be used to estimate redox conditions for the genesis of igneous
rocks. Furthermore, by modelling the partitioning data it is possible to extract information about the redox state of the
melt. Resulting ferric-ferrous ratios show significant differences from those predicted by empirical models.
Received: 14 October 1998 / Received: 5 March 1999 相似文献
2.
Phase relations have been determined at 20 kbar and primarily under suprasolidus conditions in the Fe−Ti-free F-bearing K-richterite—phlogopite
and K-richterite—apatite systems in order to assess the partitioning of F among phlogopite, K-richterite, apatite, and melt
under upper-mantle conditions. Both systems are pseudoternary because they contain forsterite, enstatite and a diopside-rich
clinopyroxene from the breakdown of the mica and K-richterite. The F-bearing K-richterite systems have lower minimum melting
temperatures than the F-bearing phlogopite —apatite system at the same pressure. However in the systems studied, F in phlogopite
appears the most effective component in altering minimum liquid compositions whereas comparison between the present study
and previous systems suggests that the presence of P2O5 during melting may result in more K-enriched melts. Variations in the compositions of the F-bearing phases are primarily
controlled by the bulk compositions of the end-member minerals and by temperature, although buffering by non-F bearing minerals
(e.g. clinopyroxene) may be effective. Distribution coefficients (as wt% ratios) between F-bearing minerals and coexisting
liquids have been determined as functions of bulk composition and temperature for products of experiments. Distribution coefficients
between K-richterite—liquid, apatite—liquid, and phlogopite—liquid are ≥1 to slightly <1 for most bulk compositions, indicating
thatF is generally a compatible element. This conclusion is in agreement with the sequence ofF distribution for similar phases in ultrapotassic rocks. These results preclude F-bearing mineral reservoirs in the mantle,
at depths corresponding to 20 kbar, being capable of producing F-enrichment in ultrapotassic magmas, or being effective in
redox melting processes.
Editorial responsibility: K. Hodges 相似文献
3.
Distribution of arsenic and mercury in subtropical coastal beachrock,Gulf of Mannar,India 总被引:1,自引:0,他引:1
J Dajkumar Sahayam N Chandrasekar S Krishna Kumar G Victor Rajamanickam 《Journal of Earth System Science》2010,119(1):129-135
An assessment of coastal pollution was made on the basis of trace element concentrations (arsenic — As, mercury — Hg) in the
Gulf of Mannar. The beachrock samples were collected along the coastal tracts between Rameswaram and Kanyakumari. The samples
were dried and digested to determine the As and Hg using atomic absorption spectrophotometer (AAS-air-acetylene and nitrous
oxide method). The As and Hg accumulation status of the beachrock was assessed using geo-accumulation index values (I
geo). The accumulation of As and Hg in the beachrock ranges from 2.75 to 20.72 μg g−1 and from 0.06 to 0.31 μg g−1, respectively. The As and Hg concentrations in the beachrocks are compared with crustal average values and average of other
region sediments. The possible source of the contamination is from atmospheric deposition and anthropogenic activities. 相似文献
4.
A geophysical and geochemical approach for seawater intrusion assessment in the Acquedolci coastal aquifer (Northern Sicily) 总被引:2,自引:0,他引:2
Vertical electrical sounding (VES’) surveys and chemical analyses of groundwater have been executed in the coastal plain of
Acquedolci (Northern Sicily), with the aim to circumscribe seawater intrusion phenomena. This urbanized area is representative
of a more general problem interesting most of Mediterranean littoral areas, where intensive overdraft favors a heavy seawater
intrusion through the coastline. Aquifer resistivity seems decisively to be conditioned by the chlorine and magnesium content
in the main aquifer of the region. Schlumberger VES’, together with piezometric and chemical–physical information of groundwater,
allowed us to perform hydrogeological and geophysical elaborations, to propose the occurrence of a relatively narrow belt
marked by fresh–salt water mixing. In the considered plain, pollution risk studies have been already realized by authors with
the proposal to identify—by parametric and synthetic zoning of significant hydrogeological elements—the most vulnerable sectors.
In detail, an intrinsic vulnerability mapping has been already performed, applying the well-known SINTACS system. This paper
intends to give—in this sector of Sicily—an example of integration of different methodologies, showing the role of geophysics
to describe the degradation of aquifers on the whole as well as to assess their pollution risk better. 相似文献
5.
Rahul Mohan Sunil Kumar Shukla Shramik M. Patil Suhas S. Shetye Karima K. Kerkar 《Journal of the Geological Society of India》2011,78(1):36-44
Diatoms from surface sediment samples collected from Enderby Basin of Indian Sector of Southern Ocean were analyzed to determine
the relative abundance and distribution of seven key indicator diatom species viz. Sea ice related species Fragilariopsis rhombica, F. separanda, F. curta, F. ritscheri, Thalassiosira tumida and Actinocyclus actinochilus and Open Ocean species F. kerguelensis on the basis of modern physico-chemical parameters. The relative abundances of different species observed viz. F. rhombica — 6.25%; F. separanda — 12.5%; F. curta — 10.53–13.33%; F. ritscheri — 4.55–12.5%; F. kerguelensis — 6.25–63.64%; T. tumida — 3.13% and A. actinochilus — 9.38–13.33%. The increasing abundance of F. kerguelensis consecutively suggests the effect of Antarctic bottom water in the study area which is further substantiated by the presence
and increasing abundance of F. ritscheri. The gradual decrease in abundance or absence of sea ice related species from the sampled stations indicates the summer and
winter sea ice extent concentration in the study area. The nutrient concentration correlates with the distribution and abundances
of diatom species. 相似文献
6.
Total mass-to-light ratio M/L
B
for S0 — Irr galaxies, whereM is the dynamical mass within the optical radius R
25 (corresponding to 25
m
/sq. arcsec in the B band), increases systematically with (B-V)0 color, but slower than that is predicted by stellar population evolution models without dark halo. It shows that the mean
ratio between dark halo and stellar masses is higher for more “blue“ galaxies. However some galaxies don’t follow this general
trend. The properties of galaxies with extremely high and extremely low values of M/L
B
ratios are compared, and different factors, accounting for the extremes, are analyzed. The conclusion is that in some cases
too high or too low M/L
B
ratios are associated with observational errors, in other cases—with non-typical dark halo mass fraction, and in some cases
— with peculiarities of disc stellar population. Particularly, discs of some galaxies with low M/L
B
ratios turn out to be unusually “light” for their luminosity and colors, which indicates a substantial deficit of low mass
stars as the most probable cause of low M/L
B
. 相似文献
7.
8.
Marcos A. E. Chaparro Ana M. Sinito V. Ramasamy Claudia Marinelli Mauro A. E. Chaparro S. Mullainathan S. Murugesan 《Environmental Geology》2008,56(2):425-437
Rock-magnetic techniques have become a useful tool in environmental issues; in particular, magnetic studies constitute an
alternative way to study pollution in different media. The present contribution focuses on magnetic parameters as pollution
indicators, especially from their relationship with contents of heavy metals. The work was carried out in two Indian rivers
located in Tamil Nadu, southern India. Several sediment samples were collected and studied in the laboratory using magnetic
techniques, magnetic susceptibility, anhysteric remanent magnetization, isothermal remanent magnetization, and chemical techniques
to determine contents of heavy metals. Magnetic mineralogy indicates the predominance of ferrimagnetic minerals; although
magnetite-like minerals are the main magnetic carriers, antiferromagnetic minerals can be present as subordinate carriers.
Concentration-dependent magnetic parameters revealed noticeable differences between both rivers, e.g. magnetic susceptibility
is four times higher in Cauvery than in Palaru River. Moreover, such increase can be interpreted as “magnetic enhancement”
and therefore related to the pollution status. This magnetic enhancement indicated a different pollutant contribution in both
rivers, and also, a different spatial distribution along these rivers, where critical (or more polluted) sites were identified.
On the other hand, univariate and multivariate statistical analyses—e.g. PCoordA, Multifactorial Analysis of distance, PCA
and RDA—were examined, revealing a link between magnetic and chemical variables. Among magnetic parameters, the concentration-dependent
magnetic parameters (e.g. magnetic susceptibility) seem to be the most relevant for this study. 相似文献
9.
Constraints on graphite crystallinity in some Spanish fluid-deposited occurrences from different geologic settings 总被引:1,自引:0,他引:1
Epigenetic, vein-type graphite mineralization originates by deposition from C—O—H fluids in high-temperature environments.
Consequently, fluid-deposited graphite is uniformly highly crystalline in volumetrically large occurrences. This work examines
the factors controlling graphite crystallinity in fluid-deposited occurrences with reference to some case studies from southern
Spain where vein-type graphite is associated with a variety of host rocks. Possible causes influencing high crystallinity
of graphite in these occurrences include: (1) large graphite occurrences are generated from large volumes of fluids that maintain
their temperatures for long periods of time, which is easier at higher temperatures; (2) high temperature conditions are required
for a fluid to precipitate a major part of its dissolved carbon during a small temperature decrease; (3) carbon is incorporated
into C—O—H fluids mainly through devolatilization reactions which also require high temperatures; (4) highly crystalline graphite
generated at high-T/high-P conditions is less susceptible to resorption as P decreases or by subsequent fluid flow; (5) graphite precipitation involves high activation energy that can be overcome only
if the temperature is high enough. These causes can be extrapolated to most vein-type graphite deposits worldwide.
Received: 23 February 1998 / Accepted: 28 April 1998 相似文献
10.
The Late Permian Dalong Formation in Hubei, Hunan, Guizhou and Guangxi in South China could be subdivided into several sedimentary
types according to the lithology, indicative of the great spatial variations of both the lithology and sedimentary facies.
The Dalong Formation deposited during the highest transgression of Late Permian, in particular under the anaerobic and suboxic
conditions, which shows a strong linkage with the hydrocarbon source rocks. The Dalong Formation has some favorable properties
such as hydrocarbon source rocks, including the sediments deposited in highest transgression sea level, the deep slope sedimentary
environments and the low sedimentary rate, which raises the importance of the investigations on the sedimentary features,
the geochemical properties and their relationship with the oil potential.
__________
Translated from Earth Science—Journal of China University of Geosciences, 2007, 32(6): 774–780 [译自: 地球科学—中国地质大学学报] 相似文献
11.
Patterns of Mangrove Wood and Litter Production Within a Beach Ridge-Fringing Reef Embayment,Northern Great Barrier Reef Coast 总被引:1,自引:0,他引:1
Daniel M. Alongi 《Estuaries and Coasts》2011,34(1):32-44
Mortality, litter fall, and patterns of stem growth were examined in Rhizophora- and Ceriops-dominated forests located upstream and downstream in four tidally dominated creeks within a beach reef embayment on the northern
Great Barrier Reef coast. Although patterns of stem densities, basal area, and diameter-at-breast height (DBH) between upstream–downstream
sites and creeks were inconsistent, aboveground biomass, wood production, litter fall, and aboveground net primary productivity
(ANPP) were greater in the Rhizophora-dominated forests. Incremental growth of stems (SI, cm year−1) was slow compared to other mangroves, declining among species as follows: Rhizophora stylosa (mean = 0.080) > Bruguiera exaristata (0.066) = Xylocarpus australasicus (0.064) = Ceriops australis (0.056); SI was greater upstream than downstream, possibly due to nutrient inputs from upland sugarcane cultivation. The
DBH of dead trees were less than the DBH of live trees, suggesting natural mortality, which was greatest for X. australasicus (annual rate = 3.27%), followed by B. exaristata (0.84%), C. australis (0.48%), and R. stylosa (0.33%). Rates of litter fall were seasonal and equivalent to those measured in other mangroves, but rates of ANPP were,
on average, low in most plots. Salinity was likely the main factor limiting growth as correlations of salinity with tree growth
and production were negative. Nutrients may have also played a key regulatory role, with positive correlations between mangrove
production and N and P content of soils and leaves and the comparatively low nutrient content of these sandy soils. The low
ratio of wood to litter production suggests that these forests are in a mature stage of development. 相似文献
12.
Nephrite specimens from Longxi,sichuan,prepared by ion-thinning and dispersion techniques have been studied using TEM and SAED.A series of sub-microscopic textures such as (010)multiple-chain faults and related fault terminations.(001)mechanical twinning,sub-grain boundaries or fault walls,tremolite fibrous pseudoform of talc and intergrowth of tremolite and talc with (010)as interface are revealed .By analogy of metallographic textures,characteristics and mechanisms of the process of “deformation-recovery-recrystallization“ are discussed in detail,Topotactic reaction mechanism by which tremolite retrogresses to talc was studied and a retrogressive metamorphic origin of Longxi nephrite is proposed. 相似文献
13.
14.
Laser ablation ICP-MS analysis of tree rings provides a rapid and sensitive method for investigating element concentrations
and fluctuations in trees along time profiles. Time profiles obtained from pine and birch trees from a strongly polluted area
in northwest Russia and a slightly polluted area at the Norwegian-Russian border show that single trees behave rather individualistically
in terms of heavy metal contents as observed in the yearly growth rings. The obtained profiles can not be linked to the pollution
history of the area. No correlation between pollution levels of the soils and observed metal content in tree rings can be
established.
Received: 6 September 1996 / Accepted: 18 November 1996 相似文献
15.
Ron Johnston 《GeoJournal》2009,74(4):347-362
English-language geographical magazines present very different geographical imaginations to their readers than those portrayed
by academic geographers, with whom the editors and publishers of those magazines have very little contact. There is a mutual
lack of appreciation—which could have substantial consequences for the academic discipline. To increase academic geographers’
appreciation of the popular geographies being portrayed, the contents of recent volumes of three magazines—National Geographic, Geographical, and New Zealand Geographic—are distilled, with their major themes identified. One clear conclusion is that there is virtually no contact between the
two imaginations: popular geographical magazines almost entirely ignore the work of academic geographers. 相似文献
16.
Since its introduction in the early part of this century,Rhizophora mangle L. has spread extensively through most of the main islands of the Hawaiian Archipelago. We investigated the structural properties
and estimated productivity of aR. mangle population at Nuupia Ponds Wildlife Management Area (NPWMA), on windward Oahu, where the mangroves were being controlled
due to their propensity to overgrow archaeological sites and the habitat of endangered Hawaiian waterbirds. Mangroves within
NPWMA were very dense (>24,000 trees ha−1) and most were relatively small (only 3.3% of the trees were ≥10 cm DBH). Mean basal area, aboveground biomass, and number
of seedlings were all high, at 37.2 m2 ha−1, 279 t (dry wt) ha−1, and 121 m−2, respectively. The seedling, density may be particularly unusual and appears to be due to extremely high rates of propagule,
production coupled with low rates of propagule predation. Stand productivity was estimated by stem growth (allometry), litterfall,
and a light attenuation approach to determining net canopy photosynthetic production. All three methods yielded estimates
that are higher than previously, reported forR. mangle and comparable with estimates of highly productiveRhizophora spp.-dominated stands in Australia and Asia. The high density, biomass, and productivity of this stand relative to stands
within the species' native range may be due to a combination of favorable site conditions, lack of competition from other
woody plants, and very low rates of herbivory and propagule predation. 相似文献
17.
An isotope-geochronological study has been performed to examine the products of Late Cenozoic collision volcanism on the northern
coast of Lake Van, Turkey. We obtained 45 new K—Ar dates, based on which the principal time characteristics of volcanic activity
in the region have been determined. Volcanic activity in the northern coast of Lake Van has lasted ∼15 myr; it has had an
expressed discrete nature, when periods of intense volcanic activity alternated with long-lasting pose periods. Four stages
of Neogene—Quaternary volcanism have been identified: Middle Miocene (15.0—13.5 Ma), Late Miocene (10—9 Ma), Pliocene (5.8—3.7
Ma), and Quaternary (1.0—0.4 Ma). The average duration of the stages was 1—2 myr; the stages were separated from each other
with periods of inactivity of approximately equal lengths (∼3 myr). For each of the Pliocene and Quaternary stages, three
additional phases of volcanism have been identified, which were separated from each other with short time intervals (a few
hundred thousand years). The last burst of volcanic activity in the study area occurred ∼400 ka; similar to Quaternary volcanism
in general, it was not characterized by a high intensity. An important result of the studies performed was to confirm the
existence of a separate Middle Miocene stage of collision volcanism for the Caucasian—Anatolian Segment of the Alpine Fold
Belt. New geochronological data generated presented in this paper indicate that Neogene—Quaternary volcanism in this portion
of the belt started much earlier (∼15 Ma) than assumed by the majority of the previous researchers. 相似文献
18.
Lars Chresten Lund-Hansen Thorbjørn Joest Andersen Morten Holtegaard Nielsen Morten Pejrup 《Estuaries and Coasts》2010,33(6):1442-1451
Optical constituents as suspended particulate matter (SPM), chlorophyll (Chl-a), colored dissolved organic matter (CDOM),
and grain sizes were obtained on a transect in the arctic fjord-type estuary Kangerlussuaq (66°) in August 2007 along with
optical properties. These comprised diffuse attenuation coefficient of downwelling PAR (K
d(PAR)), upwelling PAR (K
u(PAR)), particle beam attenuation coefficient (c
p), and irradiance reflectance R(−0, PAR). PAR is white light between 400 and 700 nm. The estuary receives melt water from the Greenland Inland Ice and stations
covered a transect from the very high turbid melt water outlet to clear marine waters. Results showed a strong spatial variation
with high values as for suspended matter concentrations, CDOM, diffuse attenuation coefficient K
d(PAR), particle beam attenuation coefficients (c
p), and reflectance R(−0, PAR) at the melt water outlet. Values of optical constituents and properties decreased with distance from the melt water
outlet to a more or less constant level in central and outer part of the estuary. There was a strong correlation between inorganic
suspended matter (SPMI) and diffuse attenuation coefficient K
d(PAR) (r
2 = 0.92) and also for particle beam attenuation coefficient (c
p; r
2 = 0.93). The obtained SPMI specific attenuation—K
d*(PAR) = 0.13 m2 g−1 SPMI—and the SPMI specific particle beam attenuation—c
p* = 0.72 m2 g−1—coefficients were about two times higher than average literature values. Irradiance reflectance R(−0, PAR) was comparatively high (0.09−0.20) and showed a high (r
2 = 0.80) correlation with K
u(PAR). Scattering dominated relative to absorption—b(PAR)/a(PAR) = 12.3. Results strongly indicated that the high values in
the optical properties were related to the very fine particle sizes (mean = 2–6 μm) of the suspended sediment. Data and results
are discussed and compared to similar studies from both temperate and tropical estuaries. 相似文献
19.
Recent conversations concerning organic food systems have focused on the conventionalization hypothesis, which posits that
the organic food sector has become increasingly bifurcated between “historical” players in the organic movement on one side,
and on the other by distributors and industrial operators recently arrived in the sector, who practice a more conventionalized
form of organic agriculture which is now on the ascendancy. The most prominent explanations for the growth and dominance of
a conventionalized organic food system have been economic, based in the logics of input costs, especially land rent. We use
the cases of the Belgian Blue commodity system and the Belgian organic beef commodity system to argue that conventionalization
is also cognitive. To understand the role of cognition in the ascendance of the conventional organic food sector, we utilize
concept of “référentiel”—or system of cognitive references—as developed by Muller and Jobert. We believe that comparing organic and conventional practices as two systems of cognitive
references makes a deeper understanding of conventionalization possible in two ways: first because it makes it clear that
the two systems coexist on a cognitive level, understood in a broad sense as tightly knit sets of knowledges, beliefs, standards,
and images. Secondly, the concept of référentiel enables one to understand how the conventional system can become irreversible
(lock-in effect) and thus incompatible with the development of the organic system.
相似文献
Pierre M. StassartEmail: |