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1.
The mid-German crystalline rise has its westernmost exposures at the western margin of the Rhine graben in the southern Pfalz
and the northern Alsace. The outcrops are made up of granitoid rocks and minor volcano-sedimentary sequences. Radiometric
ages obtained by U/Pb, Pb/Pb, Sm/Nd and Rb/Sr analyses of the igneous rocks from this area range from ∼433 to ∼325 Ma thus
covering a time span from the Silurian to the end of the lower Carboniferous. Because the investigated rocks are — according
to their chemical composition — largely related to subduction zone environments, the following three geodynamical scenarios
are postulated, always taking subduction of oceanic crust beneath the mid-German crystalline rise into account: (a) subduction
of the Rheic ocean during the Silurian from the north; (b) subduction of the Rhenohercynian ocean during the late Devonian
(∼369 Ma) from the north; (c) subduction of the Saxothuringian ocean during the lower Carboniferous (∼334 Ma) from the south. 相似文献
2.
The 560-km-long Kerala coast is characterised by long barriers with narrow beaches and steep cliffs. Distribution of cliffs
from nine sections measuring a cumulative length of 63.5 km is evaluated in ArcGIS Software using topomaps and field survey
data. The cliff sections in the southern coast comprise both permeable and impermeable rocks, whereas those along northern
coast are comprised of either Precambrian crystalline and/or Tertiary formations. Notches, caves and even small arches are
developed in Cannanore, Dharmadam and Kadalundi cliffs, where only primary laterites are exposed to wave attack. Stacks composed
of laterite and Precambrian crystallines found in nearshore of cliffed coast indicate recession of shoreline. Mass wasting,
mudslide and mudflow type of cliff failures are common in permeable to semi-permeable rocks, whereas rotational sliding, rockfall
and toppling failure are found in hard rock cliffs. Retreat of cliff sections are induced by natural or anthropogenic activities
or both. Rate of recession vary from a few centimetres to one metre/year depending upon the nature of lithology, structures
and recession agents acting upon the cliffs. Various methods of cliff protection for e.g. hard structures—revetments, groins,
seawalls, breakwater and jetties—and soft measures—artificial reefs/marsh creation, floating breakwaters, beach nourishment,
beach scraping and vegetation planting—are suggested. 相似文献
3.
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
4.
In this study, changes in surface area, morphology and leachability of antimony from mechanically activated berthierite—FeSb2S4, boulangerite—Pb5Sb4S11 and franckeite—FePb5Sn3Sb2S14 by a high-energy planetary mill were investigated. It appears that a selective extraction of antimony from these complex
sulphosalts in alkaline solution of sodium sulphide is positively affected by mechanical activation. The influence of milling
on mineral particle size and shape was studied by scanning electron microscopy. The temperature dependencies of berthierite
alkaline leaching were investigated in an interval of 323–363 K. Resulting experimental activation energies E
a were 0.11 and 6.78 kJ mol−1 for mechanically activated berthierite due to a break of Arrhenius plot. The values E
a are characteristic for a process controlled by diffusion as the rate-controlling step of leaching reaction. 相似文献
5.
Possible paths for the formation of Ap/Bp stars—massive main-sequence stars with strong magnetic fields—are analyzed based
on modern theories for the evolution of single and binary stars. Assuming that the strong magnetic fields of these stars are
the main reason for their comparatively slow axial rotation and the observed anomalies in the chemical compositions of their
atmospheres, possible origins for these high magnetic fields are considered. Analysis of several possible scenarios for the
formation of these stars leads to the conclusion that their surface magnetic fields are probably generated in the convective
envelopes of the precursor stars. These precursors may be young, single stars with masses 1.5–3 M
⊙ that formed at the peripheries of forming star clusters and ended their accretion at the Hayashi boundary, or alternatively
close binaries whose components have convective envelopes, whose merger leads to the formation of an Ap/Bp star. Arguments
are presented supporting the view that the merger of close binaries is the main channel for the formation of Ap/Bp stars,
and a detailed analysis of this scenario is presented. The initial major axes of the merging binary systems must be in the
range 6–12 R
⊙, and the masses of their components in the range 0.7–1.5 M
⊙. When the merging components possess developed convective envelopes and fairly strong initial magnetic fields, these can
generate powerful magnetic fields “inherited” by the products of the merger—Ap/Bp stars. The reason the components of the
close binaries merge is a loss of angular momentum via the magnetic stellar winds of the components. 相似文献
6.
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
7.
Wilhelm Johannes 《Contributions to Mineralogy and Petrology》1984,86(3):264-273
The beginning of melting in the system Qz-Or-Ab-An-H2 O was experimentally reversed in the pressure range
kbar using starting materials made up of mixtures of quartz and synthetic feldspars. With increasing pressure the melting
temperature decreases from 690° C at 2 kbar to 630° C at 17 kbar in the An-free alkalifeldspar granite system Qz-Or-Ab-H2O. In the granite system Qz-Or-Ab-An-H2O the increase of the solidus temperature with increasing An-content is only very small. In comparison to the alkalifeldspar
granite system the solidus temperature increases by 3° C (7° C) if albite is replaced by plagioclase An 20 (An 40). The difference
between the solidus temperatures of the alkalifeldspar granite system and of quartz — anorthite — sanidine assemblages (system
Qz-Or-An-H2O) is approximately 50° C.
With increasing water pressures plagioclase and plagioclase-alkalifeldspar assemblages become unstable and are replaced by
zoisite+kyanite+quartz and zoisite+muscovite-paragonitess +quartz, respectively. The pressure stability limits of these assemblages are found to lie between 6 and 16 kbar at 600°
C. At high water pressures (10–18 kbar) zoisite — muscovite — quartz assemblages are stable up to 700 and 720° C. The solidus
curve of this assemblage is 10–20° C above the beginning of melting of sanidine — zoisite — muscovite — quartz mixtures.
The amount of water necessary to produce sufficient amounts of melt to change a metamorphic rock into a magmatic looking one
is only small. In case of layered migmatites it is shown that 1 % of water (or even less) is sufficient to transform portions
of a gneiss into (magmatic looking) leucosomes. High grade metamorphic rocks were probably relatively dry, and anatectic magmas
of granitic or granodioritic composition are usually not saturated with water. 相似文献
8.
Environmental assessment of Dhaka City (Bangladesh) based on trace metal contents in road dusts 总被引:1,自引:0,他引:1
Geochemical analysis of street dusts was conducted to evaluate the environment of Dhaka City, Bangladesh. Dust samples were
collected from different areas (industrial, commercial, and residential) of Dhaka City, and their major, trace and rare earth
elements (REE) were determined. Samples from the commercial area had Pb concentrations double those of the industrial and
residential areas. Contents of Zn, Cu, Ni, and Cr in the industrial areas were greater than those in the commercial and residential
areas. The REE patterns of all dusts in Dhaka are similar and are comparable to the average upper continental crust. The condition
of the Dhaka environment was compared to that in Japan and other baseline sediments using Zn–Fe2O3 and Pb–Fe2O3 diagrams. Zn–Fe2O3 trends for the dusts show steep inclination compared to the baseline sediment and the Japanese urban sediment trends. Dhaka
lake data show enrichment of Zn over the dusts, suggestive of Zn pollution from poorly controlled industrial sources. In contrast,
on the Pb–Fe2O3 diagram, Dhaka dusts have greater Pb contents than lake sediments, probably due to the higher traffic density in the commercial
area compared to the residential area including the area around the lake. The results suggest that higher levels of Pb and
Zn in street dusts in Dhaka can most likely be attributed to the anthropogenic sources like vehicle emissions to the atmosphere
and a rapid development. 相似文献
9.
N. A. Kharitonova G. A. Chelnokov E. A. Vakh A. A. Karabtsov N. N. Zykin 《Russian Journal of Pacific Geology》2010,4(1):78-90
The geochemical study of bed rocks, underground and surface waters, and associated gases in the Fadeevskoe deposit of carbonated
waters (Sikhote Alin, Primorye region) revealed that the chemical composition of these waters is formed in the zone of active
water exchange in the limited area of the discharge zone, where hydro carbonate calcic waters with mineralization of up to
1 g/1 are formed in largely potassic-sodic rocks. Calculations of the saturation indices show that the mineral waters are
characterized by the early stage of Ca saturation, being undersaturated with carbonates and aluminosilicates. The main factors
that influence the water mineralization are the excess carbon dioxide in water and the circulation time. The oxygen and carbon
isotope ratios indicate the atmospheric genesis of the aqueous component (δ2H = —117; δ18O = —15.4%o) and the carbon isotope content in the CO2 implies the mantle nature of the carbon dioxide (δ13C = -9.9%o). 相似文献
10.
Shojaeddin Niroomand Richard J. Goldfarb Farid Moore Mohammad Mohajjel Erin E. Marsh 《Mineralium Deposita》2011,46(4):409-428
The Kharapeh gold deposit is located along the northwestern margin of the Sanandaj–Sirjan Zone (SSZ) in the West Azerbaijan
province, Iran. It is an epizonal orogenic gold deposit formed within the deformed zone between central Iran and the Arabian
plate during the Cretaceous–Tertiary Zagros orogeny. The deposit area is underlain by Cretaceous schist and marble, as well
as altered andesite and dacite dikes. Structural analysis indicates that the rocks underwent tight to isoclinal recumbent
folding and were subsequently co-axially refolded to upright open folds during a second deformation. Late- to post-tectonic
Cenozoic granites and granodiorites occur northeast of the deposit area. Mineralization mainly is recognized within NW-trending
extensional structures as veins and breccia zones. Normal faults, intermediate dikes, and quartz veins, oriented subparallel
to the axial surface of the Kharapeh antiform, indicate synchronous extension perpendicular to the fold axis during the second
folding event. The gold-bearing quartz veins are >1 km in length and average about 6 m in width; breccia zones are 10–50 m
in length and ≤1 m in width. Hydrothermal alteration mainly consists of silicification, sulfidation, chloritization, sericitization,
and carbonatization. Paragenetic relationships indicate three distinct stages—replacement and silicification, brecciation
and fracture filling, and cataclastic brecciation—with the latter two being gold-rich. Fluid inclusion data suggest mineral
deposition at temperatures of at least 220–255°C and depths of at least 1.4–1.8 km, from a H2O–CO2±CH4 fluid of relatively high salinity (12–14 wt.% NaCl equiv.), which may reflect metamorphism of passive margin carbonate sequences.
Ore fluid δ18O values between about 7‰ and 9‰ suggest no significant meteoric water input, despite gold deposition in a relatively shallow
epizonal environment. Similarities to other deposits in the SSZ suggest that the deposit formed as part of a diachronous gold
event during the middle to late Tertiary throughout the SSZ and during the final stages of the Zagros orogeny. The proximity
of Kharapeh to the main tectonic suture of the orogen, well-developed regional fold systems with superimposed complex fracture
geometries, and recognition of nearby volcanogenic massive sulfide systems that suggest a region characterized by sulfur-
and metal-rich crustal rocks, collectively indicate an area of the SSZ with high favorability for undiscovered gold resources. 相似文献
11.
Minerals of olivine–melilite and olivine–monticellite rocks from the Krestovskiy massif contain primary silicate-salt, carbonate-salt,
and salt melt inclusions. Silicate-salt inclusions are present in perovskite I and melilite. Thermometric experiments conducted
on these inclusions at 1,230–1,250°C showed silicate–carbonate liquid immiscibility. Globules of composite carbonate-salt
melt rich in alkalies, P, S, and Cl separated in silicate melt. Carbonate salt globules in some inclusions from perovskite
II at 1,190–1,200°C separated into immiscible liquid phases of simpler composition. Carbonate-salt and salt inclusions occur
in monticellite, melilite, and garnet and homogenize at close temperatures (980–780°C). They contain alkalies, Ca, P, SO3, Cl, and CO2. According to the ratio of these components and predominance of one of them, melt inclusions are divided into 6 types: I—hyperalkaline
(CaO/(Na2O+K2O)≤1) carbonate melts; II—moderately alkaline (CaO/(Na2O+K2O)>1) carbonate melts; III—sulfate-alkaline melts; IV—phosphate-alkaline melts; V—alkali-chloridic melts, and VI—calc-carbonate
melts. Joint occurrence of all the above types and their syngenetic character were established. Some inclusions demonstrated
carbonate-salt immiscibility phenomena at 840–800°C. A conclusion in made that the origin of carbonate melts during the formation
of intrusion rocks is related to silicate–carbonate immiscibility in parental alkali-ultrabasic magma. The separated carbonate
melt had a complex alkaline composition. Under unstable conditions the melt began to decompose into simpler immiscible fractions.
Different types of carbonate-salt and salt inclusions seem to reflect the composition of these spatially isolated immiscible
fractions. Liquid carbonate-salt immiscibility took place in a wide temperature range from 1,200–1,190°C to 800°C. The occurrence
of this kind of processes under macroconditions might, most likely, cause the appearance of different types of immiscible
carbonate-salt melts and lead to the formation of different types of carbonatites: alkali-phosphatic, alkali-sulfatic, alkali-chloridic,
and, most widespread, calcitic ones. 相似文献
12.
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
13.
Effects of process parameters such as concentrations of FeCl2, NaOH, and drying temperature on the formation mechanism and chemical characteristics of ferrihydrite-modified diatomite
are studied by using X-ray absorption near-edge structure spectroscopy. The spectra were recorded in total electron yield
mode and/or fluorescence yield mode to investigate the chemical nature of Fe and Si on the surface and/or in the bulk of ferrihydrite-modified
diatomite, respectively. It was found that only the surface SiO2 was partially dissolved in the NaOH solution with stirring and heating, whereas the bulk of diatomite seemed to be preserved.
The dissolved Si was incorporated into the structure of ferrihydrite to form the 2-line Si-containing ferrihydrite on the
surface of diatomite. The crystalline degree of ferrihydrite increased with the increasing FeCl2 concentration and the Brunauer–Emmett–Teller specific surface area of ferrihydrite-modified diatomite decreased with the
increasing FeCl2 concentration. The crystalline degree of ferrihydrite decreased with the increase of NaOH concentration. The high temperature
calcination caused an energy shift in the Si L-edge spectra to the high energy side and a transformation of Si-containing
ferrihydrite to crystallized hematite might occur when ferrihydrite-modified diatomite is calcined at 900°C. In this study,
the optimal synthesis conditions for the ferrihydrite-modified diatomite with the least crystalline Si-containing ferrihydrite
and the highest surface area were found to be as the follows: 0.5 M FeCl2 solution, 6 M NaOH solution and drying temperature of 50°C. 相似文献
14.
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
15.
于荣炳 《中国地球化学学报》1989,8(3):283-291
Glauconite is widely distributed in space and time.In China glauconite-bearing strata are extensive occurrence ranging from Late Cretaceous to Middle Proterozoic in age.X-ray powder analysis,X-ray diffracition analysis and differential thermal analysis revealed that glauconite has a mica-type structure between dioctahedron and trioctahedron.Its chemical composition is:Al2O310.6%,SiO249.23%,MgO3.24%,Fe2O317.40%,FeO1.8%,and K2O7.92%,Its crystal form and thermal properties are very similar to those of mica-like clay minerls.According to isotopic age determinations of glauconite in modern oceans (including the East China Sea,the South China Sea and the Yellow Sea),we consider that in the extreme case glauconite is an authigenic mineral.It is generally formed in sedimentary rocks.Is has further proved that glauconite can be used to determine the ages of sedimentary rocks. 相似文献
16.
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
17.
The layer of water-bearing sandstone (PR2 V kt1) named Lower-Kotlin aquifer is widespread in the northwestern part of the Russian platform, within the Moscow Artesian Basin.
It is mostly confined. The aquifer lies directly on the surface of the crystalline basement throughout the basin. The water
mineralization rises from north to south together with the depth of the aquifer. The mineralization growth is mainly caused
by the increase of sodium and chloride contents. Three consequent vertical zones can be marked out: fresh-water zones (<1 g/dm3), brackish-water zone (1–35 g/dm3) and brine zone (>35 g/dm3). Each of these zones has specific regularities of variation of chemical composition. The role of each component is different
for waters of each zone. The aquifer is actively exploited—for public water supply and bottling in the north and for mineral
water treatment in the south. Within St. Petersburg, this water is used for technical purposes of industry. There are some
health resorts and spas in St. Petersburg Region, such as Sestroretsk, Peterhof, Luga, which use the mineral water of the
Lower-Kotlin aquifer. A number of bottling plants produce bottled mineral water. Wide regional location and peculiarities
of chemical composition of the Lower-Kotlin aquifer cause the possibility of the organization of many other spas and health
resorts near St. Petersburg. 相似文献
18.
Wilson Yetoh Fantong Hiroshi Satake Festus T. Aka Samuel N. Ayonghe Kazuyoshi Asai Ajit K. Mandal Andrew A. Ako 《Environmental Earth Sciences》2010,60(1):107-120
Unplanned exploitation of groundwater constitutes emerging water-related threats to MayoTsanaga River Basin. Shallow groundwater
from crystalline and detrital sediment aquifers, together with rain, dams, springs, and rivers were chemically and isotopically
investigated to appraise its evolution, recharge source and mechanisms, flow direction, and age which were used to evaluate
the groundwater susceptibility to contamination and the basin’s stage of salinization. The groundwater which is Ca–Na–HCO3 type is a chemically evolved equivalent of surface waters and rain water with Ca–Mg–Cl–SO4 chemistry. The monsoon rain recharged the groundwater preferentially at an average rate of 74 mm/year, while surface waters
recharge upon evaporation. Altitude effect of rain and springs show a similar variation of −0.4‰ for δ18O/100 m, but the springs which were recharged at 452, 679, and 773 m asl show enrichment of δ18O through evaporation by 0.8‰ corresponding to 3% of water loss during recharge. The groundwater which shows both local and
regional flow regimes gets older towards the basins` margin with coeval enrichment in F− and depletion in NO3
−. Incidentally, younger groundwaters are susceptible to anthropogenic contamination and older groundwaters are sinks of lithologenic
fluoride. The basins salinization is still at an early stage. 相似文献
19.
Predicting riverine dissolved silica fluxes to coastal zones from a hyperactive region and analysis of their first-order controls 总被引:2,自引:1,他引:1
Jens Hartmann Nils Jansen Hans H. Dürr Akira Harashima Kenji Okubo Stephan Kempe 《International Journal of Earth Sciences》2010,99(1):207-230
Silicate weathering and resulting transport of dissolved matter influence the global carbon cycle in two ways. First by the
uptake of atmospheric/soil CO2 and second by providing the oceanic ecosystems via the fluvial systems with the nutrient dissolved silica (DSi). Previous
work suggests that regions dominated by volcanics are hyperactive or even “hot spots” concerning DSi-mobilization. Here, we
present a new approach for predicting DSi-fluxes to coastal zones, emphasizing “first-order” controlling factors (lithology,
runoff, relief, land cover and temperature). This approach is applied to the Japanese Archipelago, a region characterized
by a high percentage of volcanics (29.1% of surface area). The presented DSi-flux model is based on data of 516 catchments,
covering approximately 56.7% of the area of the Japanese Archipelago. The spatial distribution of lithology—one of the most
important first order controls—is taken from a new high resolution map of Japan. Results show that the Japanese Archipelago
is a hyperactive region with a DSi-yield 6.6 times higher than the world average of 3.3 t SiO2 km−2 a−1, but with large regional variations. Approximately 10% of its area exceeds 10 times the world average DSi-yield. Slope constitutes
another important controlling factor on DSi-fluxes besides lithology and runoff, and can exceed the influence of runoff on
DSi-yields. Even though the monitored area on the Japanese Archipelago stretches from about 31° to 46°N, temperature is not
identified as a significant first-order model variable. This may be due to the fact that slope, runoff and lithology are correlated
with temperature due to regional settings of the Archipelago, and temperature information is substituted to a certain extent
by these factors. Land cover data also do not improve the prediction model. This may partly be attributed to misinterpreted
land cover information from satellite images. Implications of results for Earth System and global carbon cycle modeling are
discussed. 相似文献
20.
Compared to most studied kimberlite pipes of the Yakutian province, diamonds from the Poiskovaya, Zapolyarnaya, and Leningrad
pipes (about 100 determinations) are characterized by a decrease in the average δ13C (−4.59, −4.50,−4.04‰) and by relatively low average nitrogen contents (93, 254, 304 ppm, respectively). These pipes also
differ in the relative abundance of alpha-1 group crystals in Galimov’s classification. Based on a stable combination of morphology
and properties, we distinguished diamond populations of the common origin. All of them have significant a negative correlation
between δ13C and the nitrogen content. This correlation is considered to be a result of synchronous and progressive loss of nitrogen
and the light isotope 12C in the medium during the diamond formation. The conclusion is drawn that the alpha-1 crystals were formed in the open fluid
system. The pyrolysis of ethane—C2H6 → CH4 + H2 + Cdiam—is assumed to be a model of diamond precipitation from fluid. The pressure release due to extension deformation of the mantle
under tectonic action might be a factor shifting this reaction toward diamond formation. 相似文献