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1.
Soil samples collected from various places in and around Mysore were analyzed for the total trace elements such as Fe, Mn, Cu, Zn, Pb, and Cd. The results of the analysis indicate that the concentration of lead and cadmium in soils is below 2.5 g ml–1 and 0.2 g ml–1, respectively, which are the minimum detection levels, whereas the concentration of iron, manganese, copper, and zinc in most of the samples is within the global average ranges of 3%, 500–1000 g g–1, 15–40 g g–1, and 50–100 g g–1, respectively. The investigated area has the presence of gneisses and schists, in which partly there are igneous intrusions and pegmatitic intrusions. There are amphibolite enclaves in gneisses that account for the higher concentration of trace elements. The lower concentration may be attributed to the presence of silicic type of rock.  相似文献   

2.
Twenty-eight samples of groundwater from bedrock boreholes in three distinct Norwegian geological provinces have been taken and analyzed for content of Rn, U, and Th, together with a wide variety of minor and major species. Median values of 290 Bq/1, 7.6 g/1, and 0.02 g/1 were obtained for Rn, U, and Th respectively, while maximum values were 8500 Bq/1, 170 g/1, and 2.2 g/1. Commonly suggested drinking water limits range from 8 to 1000 Bq/1 for radon and 14 to 160 g/1 for uranium. Radioelement content was closely related to lithology, the lowest concentrations being derived from the largely Caledonian rocks of the Trøndelag area, and the highest from the Precambrian Iddefjord Granite of southeast Norway (11 boreholes) where median values of 2500 Bq/1, 15 g/1 and 0.38 g/1, respectively, were obtained. The Iddefjord Granite is not believed to be unique in Norway in yielding high dissolved radionuclide contents in groundwaters, and several other granitic aquifers warrant further investigation in this respect.  相似文献   

3.
The distribution of some trace metals (Cu, Zn, Ni, Co,Fe, Mn) and of DOC over a particulate (> 1 m),a colloidal (size < 0.45 m and molecular weight > 10 kD) and an ultrafiltered fraction (< 10 kD)was determined at several sites on the Thur River,Switzerland, at various times of the year. Thecomplexation of Cu by strong ligands in theultrafiltrate and in the conventional filtrate (<0.45 m) was compared using a ligand-exchange/CSV method.The <0.45 m concentrations of Cu (from anaverage of 7 nM to 24 nM), Zn (<5–23 nM), Ni (5–13 nM),Co (1.5–3 nM) and Mn (7–92 nM)increased downstream. The major part of Cu, Zn, Niand Co usually occurred in the ultrafiltratefraction at all sites, whereas Fe and Mn were mostlyin the particulate fraction, under conditions of lowsuspended matter content (< 10 mg L-1) in theriver. The percentage of metal in the colloidalfraction, with respect to the 0.45-m filtrate,decreased in the order: Cu (median 11%) > Zn Ni(median 5–6%) > Mn Co (median < 5%). DOCalso consisted mostly of molecules in the < 10 kDrange.Cu was strongly complexed by natural organic ligandsin all filtrate and ultrafiltrate samples. A largepart of the strong Cu binding ligands consisted ofcompounds in the < 10 kD range, but colloidalligands with similar properties also occurred. Cu wasdistributed among the dissolved and the colloidalligands, roughly in proportion to organic carbon.The colloidal fraction (as defined here) did notincrease in its proportional amount downstream and wasonly of limited significance in transporting traceelements in the Thur River under low discharge conditions.  相似文献   

4.
The Oso Bay, Texas, sediments from nine sites were analyzed by GC-MS for organics to measure contamination in the bay. In most of the sites sediments contained tetrachloroethene (87–1433 g/kg), bis (2-ethylhexyl)phthalate (40–193 g/kg), and aliphatic hydrocarbons, C8-C13 (720–2491 g/kg). Sources of these contaminants include a landfill, military facilities, and municipal and industrial discharges. Size analysis of the sediments indicates they contain a high percentage of muddy sand (50–75 percent), which suggests that Oso Bay consists of common bay margin sediments.  相似文献   

5.
Lake Suwa, located in the center of the largest Japanese island of Honshu was a typical hypertrophic lake with a dense scum Microcystis species in summer during the 1970's. However, due to the introduction of a sewage treatment plant and the awareness of environmental pollution by local residents, a decrease in the concentration of nutrients in lake water since 1981 has been observed (from 1600 g l–1 and 160 g l–1 in 1977 to 990 g l–1 and 110 g l–1 in 1984 for total nitrogen and phosphorus respectively).  相似文献   

6.
White mica bearing fractions ranging in grain size from 0.4 m to 6.3–20 m were separated from metapelites and intercalated metatuffs of the eastern Rheinisches Schiefergebirge (FRG). The stratigraphic age of these rocks is Middle Devonian (Eifelian), and they contain detrital material of northwestern provenance (Old Red Continent, probably mainly derived from the Caledonian Orogen). Folding in the Carboniferous was associated with cleavage formation and an apparently synkinematic anchizonal metamorphism. Apparent K-Ar ages of metapelite fractions display a marked positive correlation with grain size illustrating the detrital influence which is diminished with decreasing grain size and increasing metamorphism (determined by illite crystallinity). Contrasting grain morphologies observed by SEM enable the interpretation of apparent age/ grain size relationship for coarse fractions. The anticipated lack of detrital mica in metatuffs is confirmed by the fairly consistent apparent K-Ar ages determined for the coarser than 0.63 m size fractions which date the anchizonal metamorphism at ca. 330 Ma. Comparison of metatuff and metapelite apparent ages suggests that the extent of rejuvenation in the latter was largely dependent on grain size. Rejuvenation was also somewhat controlled by the degree of anchizonal metamorphism as suggested by differences in K-Ar results of metapelites which were metamorphosed at variable anchizonal conditions. Fractions <0.63 m from upper anchizonal metapelites record ca. 330 Ma ages similar to those of the 0.63–20 m sizes in metatuffs. Together those results confirm the limited applicability of conventional K-Ar dating on bulk clay fractions (<2 m) of very-low grade (anchizonal) metamorphic rocks in dating metamorphic events and concomitant cleavage formation.  相似文献   

7.
Zusammenfassung Der Pleochroismus der OH-Streckfrequenz (=3,16 ±0,02 ) zeigt sowohl für -Zoisit als auch für -Zoisit, daß die OH-Dipole paralel [001] orientiert sind.
Measurement of the infrared-pleochroism in minerals. X. The pleochroism of the OH-stretching frequency in zoisite
Summary The pleochroism of the OH-stretching frequency (=3.16 ±0.02 ) proves for - and -zoisite that the OH-dipoles are oriented parallel [001].

Mit 1 Abbildung  相似文献   

8.
The Brixen Quartzphyllite, basement of the Southern Alps (Italy), consists of metasediments which had suffered progressive deformation and low grade metamorphism (p max4 kbar, T max375±25° C) during the Palaeozoic. It has been excavated by pre-Permian erosion, buried again beneath a pile of Permo-mesozoic to Cainozoic sediments (estimated T max150° C), and is now exposed anew due to late Alpine uplift and erosion. The behavior of the K-Ar system of white micas is investigated, taking advantage of the narrow constraints on their thermal history imposed by the geological/stratigraphic reference systems.The six structurally and petrographically differing samples come from a single outcrop, whose position is roughly two kilometers beneath the Permian land-surface. White mica concentrates from five grain size fractions (<2 , 2–6 , 6–20 , 20–60 , 60–75 ) of each sample have been analyzed by the conventional K-Ar method, four selected concentrates additionally by the 40Ar/39Ar stepwise heating technique; furthermore, Ar content and isotopic composition of vein quartz were determined.The conventional ages of the natural grain size fractions (20–60 , 60–75) are in the range 316±8 Ma, which corresponds to the 40Ar/39Ar plateau age of 319.0±5.5 Ma within the error limits. The finer grain size fractions yield significantly lower ages, down to 233 Ma for fractions <2 . Likewise low apparent ages (down to 83 Ma) are obtained for the low temperature 40Ar/39Ar degassing steps.There is no correlation between microstructural generation of white mica prevailing in the sample and apparent age. This favours an interpretation of the 316±8 Ma values as cooling age; progressive deformation and metamorphism must be respectively older and their timing cannot be resolved by these methods. The data preclude any significant influence of a detrital mica component as well as of excess argon.The lower ages found for the fine grain-size fractions (respectively the low-T degassing steps) correspond to a near-surface period (p-T-minimum); the values are geologically meaningless. The effect is interpreted to result from partial Ar loss due to reheating during Mesozoic-Cainozoic reburial. A model based on diffusion parameters derived from the outgassing experiments and Dodson's (1979) equation yields a closure temperature of 284±40 °C for a cooling rate of 18° C/Ma. Furthermore, this model suggests that the observed argon loss of up to 5% may in fact have been induced by reheating to 150 °C for 50 Ma.  相似文献   

9.
Argon diffusion domains in K-feldspar I: microstructures in MH-10   总被引：1，自引：1，他引：0  
Samples of MH-10, a K-feldspar thought to contain discrete diffusion domains for argon, have been examined by light and TEM microsopy to search for domain boudaries. We examined both unheated K-feldspar separates and samples heated in vacuum between 750 and 1150°C in order to characterize the initial microstructure as well as any changes resulting from laboratory heating. The MH-10 rock shows almost no evidence of plastic deformation, and the K-feldspar does not possess networks of dislocations which might define a subgrain structure derived from external stresses. Three classes of substructure are present in the K-feldspar, but only the third appears to have been affected by laboratory heating: (1) Cross-hatched extinction in light microscope is common but variably developed. TEM reveals almost no albite/pericline twinning but tweed microstructure is ubiquitous. (2) Turbid zones occur with about 5 volume % abundance. Micropores, <1 to 2m in diameter, characterize these regions, which often also contain bleds of albite, up to 40 m indiameter, TEM shows these turbid zones to be very complex with intricate twin and tweed structures at the sub-micron scale and numerous dislocation and strain features. (3) Albitic exsolution lamellae (<1 m thick, 20 m long and separated by 1 m) are rarely seen in the light microscope but TEM shows that 0.01 m thick by 0.2–1 m long lamellae, separated by 0.1 to 0.5 m, occur in about 20% of the sample. These lamellae are disk-shaped, have a semi-coherent or coherent relationship to the host K-feldspar, and seem to disappear upon heating to 750°C. Extensive diffusion studies have been conducted on HM-10, and the results analyzed in terms of distribution of sizes of diffusion domains. The preferred result of the analyses was a distribution consisting of three distinct sizes. The largest domain size identified in this way is approximately 50 to 100 m, and this corresponds to blocks of K-feldspar defined by the network of fractured/turbid zones. The smallest domain size inferred from diffusion analysis is 0.1 m which corresponds to the spacing between albite exsolution lamellae that may represent fast diffusion pathways. Alternatively, the modulated argon distribution accompanying the lamellar variation in feldspar composition may result in an overestimation of the initial diffusion coefficients. Even though a promising agreement exists between domain analyses based upon diffusional and microstructural analyses, at least two questions remain unanswered. Firstly, no clear candidate has been identified for a domain of intermediate size. Secondly, the diffusion analysis has been formulated with independent gas release from all domains, whereas the observed structures are likely to be nested (i.e., small domains exist inside bigger domains) with the network of semi-coherent lamellar boundaries having connectivity and permeability which can provide only a modest increase in argon diffusivity over bulk values.  相似文献   

10.
Concentration levels of the trace elements Al, As, B, Ba, Be, Cd, Co, Cr, Cu, Li, Mo, Ni, Pb, Sr, V, Y, and Zn in the shallow Dutch ground water were studied. Data were extracted from the data base of the Dutch National Ground Water Quality Monitoring Network, a network set up to monitor the diffuse contamination. The network contains over 350 sites at a low density of about 1 per 100 km2. The sites are sampled once a year at two depths (approx. 10 and 25 m below surface). A two-step multivariate statistical approach was used, in which the major element chemistry was used to define water types. Within each water type, trace element behavior could be coupled to distinct geochemical processes: dilution, acidification and weathering, carbonate dissolution, oxidation/reduction, and ion exchange. In recently infiltrated acid rain water in low buffering capacity sands, the anthropogenic influence indirectly caused mobilization of Al (median 430 g/l), Cd (0.6 g/l), Co (14 g/l), Cu (2.7 g/l), Ni (16 g/l), Y (11 g/l), and Zn (50 mg/l). In carbonate bearing sediments the acidification is neutralized, and the mentioned trace elements remain immobile. Arsenic and Cr have higher concentrations levels in ground waters with a slightly reducing character and are possibly governed by the dissolution of iron-manganese hydroxides. Boron, Li, and Sr have high concentrations (respectively 875, 80, 2700 g/l) in the water type related to a seawater source. Strontium is related to carbonate dissolution in all other water types (medians ranging from 100 to 1000 g/l). Barium shows a complex behaviour. It is concluded that the high Al, Cd, Co, Cr, Ni, and Zn concentrations are anthropogenically induced. High Ba and Cr concentrations are inferred to be due to natural processes.  相似文献   

11.
Water samples were collected from the Truckee River-Pyramid Lake system, the Walker River-Walker Lake system, and the Carson River, all located in eastern California and western Nevada, U.S.A., at three different times (i.e., summer 1991, spring 1992, and autumn 1992) over a two year period. The concentrations of As, Na, Cl, PO4, and pH were measured in these river samples and the associated terminal lakes. Arsenic values ranged from below 13 nmol/kg near Truckee, California to 160 nmol/kg at Nixon, Nevada in the Truckee River, from 40 nmol/kg in the headwaters of both West and East Walker Rivers to 270 nmol/kg below Weber Reservoir on the main branch of the Walker River, and from <27 nmol/kg to 234 nmol/kg for the lower Carson River system. Arsenic concentrations in Steamboat Creek (0.91 mol/kg–1.80 mol/kg) in the Truckee River catchment are above the U.S. EPA drinking water maximum contaminant level of 0.67 mol/kg, as are the As concentrations in both Pyramid Lake (1.33 mol/kg–1.57 mol/kg ) and Walker Lake (13.7 mol/kg–18.7 mol/kg). Sources of As for all three rivers include weathering of As-rich rocks and/or regolith and input of high-As geothermal spring waters, both processes primarily, although not exclusively, adding As to the headwater regions of these rivers. Steamboat Hot Springs (29 mol/kg As 54.5 mol/kg), for example, is identified as a source of As to the Truckee River via Steamboat Creek. The high As concentrations in Pyramid and Walker Lakes are likely due to (1) desorption of arsenate from aquatic particulate matter in these high pH waters (9.0 pH 9.5), (2) limited biologic uptake of arsenate, and (3) evaporative concentration of the lake waters. Evaluation of molar PO4}/As ratios of river waters and geothermal spring waters (e.g., Steamboat Hot Springs), indicates that phosphate is substantially enriched in Steamboat Creek as well as the mid to lower reaches of the Walker and Carson Rivers. These regions of each river are dominated by agricultural interests and, additionally, in the case of Steamboat Creek, residential areas and golf courses. Our data strongly imply that phosphate-rich agricultural return flow has likely added P to these streams and, consequently, increased their respective P:As ratios.  相似文献   

12.
Summary We report results of a combined SHRIMP ion microprobe and Raman microprobe study of the correlation between metamictization and U-Pb isotopic discordance of zircon. The spatial resolution of the SHRIMP and Raman probe used are about 200 m3 and 80 m3, respectively. This allows a direct comparison of U-Pb isotopic discordance and metamictization of small areas within zircon crystals. We show that the impact of the oxygen ion beam on the zircon during the SHRIMP analysis does not cause significant amorphization or recrystallization in the remaining zircon on a scale of 1 m. Consequently, it is possible to determine the initial degree of metamictization of zircon within and adjacent to a SHRIMP analytical spot by Raman microprobe measurements after performing SHRIMP analyses. A combination of the two microprobe techniques gives information on the concentration and distribution of radionuclides as well as the degree of metamictization and its heterogeneity and the lateral age distribution within the grain. We found that the degree of U-Pb isotopic discordance correlates closely with the degree of metamictization within single zircon grains, on a scale of 15 m, which is consistent with previous results on the scale of single and multiple zircon grains showing that metamictization enhances the relative potential for secondary loss of radiogenic lead in zircon.
Metamiktisierung und U-Pb-Isotopendiskordanz in Einzelzirkonen: eine komplexe Untersuchung mittels Ramanmikrosonde und SHRIMP Ionensonde
Zusammenfassung Wir präsentieren die Ergebnisse einer Untersuchung des Zussammenhangs von Metamiktisierung und U-Pb Isotopendiskordanz in Zirkonen mittles kombinierter SHRIMP-Ionenmikrosonden- und Ramanmikrosondenanalysen. Die räumliche Auflösung der verwendeten Analysensysteme, experimentell mit 200 m3 (SHRIMP) und 80 m3 (Ramansonde) bestimmt, gestattet den direkten Vergleich der in Mikrobereichen innerhalb von Zirkon-Einkristallen gemessenen Isotopendiskordanzen und Metamiktisierungsgrade. Wir zeigen, daß der während der SHRIMP-Analyse auf den Zirkon einwirkende Sauerstoffionenstrahl weder signifikante Amorphisierung noch Rekristallisation des benachbarten Zirkonmaterials im 1 m-Bereich hervorruft. Es ist deshalb möglich, den Grad der Metamiktisierung eines Zirkon-Mikrobereiches auch in den SHRIMP-Analysengrübchen, d.h. erst nach dem Analysieren dieses Bereiches mit der Ionensonde, mittels hochauflösender Ramanmessungen unverfälscht zu bestimmen. Der Einsatz beider Mikromethoden liefert kombinierte Informationen zu den Gehalten und Verteilungen radioaktiver Elemente, zum Grad der Metamiktisierung und seiner Heterogenität und zur lateralen Altersverteilung innerhalb von Einzelkörnern. Wir weisen eine deutliche Korrelation des Grades der U-Pb-Isotopendiskordanz mit dem Grad der Metamiktisierung im Mikrobereich (15 m Auflösung) nach. Dies stimmt mit früheren, an Einzelzirkonen und Populationen getätigten Beobachtungen überein, daß die Metamiktisierung von Zirkon dessen Potential zu sekundären Bleiverlusten erhöht.
  相似文献   

13.
Captive whitetip reef sharks, Triaenodon obesus,at Sea Life Park (SLP) Hawaii, Waimanalo, Hawaii develop goitre, whereas, T. obesus at the Waikiki Aquarium (WAQ), Honolulu,Hawaii do not develop goitre. To determine theeffects of natural concentrations of iodine on thereduction of goitre, two sharks from SLP with goitrewere placed in an enclosed coastal lagoon with naturalseawater. Using ultrasound measurements the twogoitres were initially 11.4 cm and 14.6 cm in depthand after 3 months decreased to 4.7 cm and 5.7 cm. Radioimmunoassay analysis of the thyroid hormoneT3 sera concentrations were initially 0.22 ng/mland 0.33 ng/ml and increased to 1.84 ng/ml after beingplaced in the lagoon. Sera T4 were initially0.93 ng/ml and 0.99 ng/ml and increased dramaticallyto 17 ng/ml and 56 ng/ml. Over the six month samplingperiod, two resident sharks in the lagoon with normalthyroids had sera T3 concentrations from 0.89ng/ml to 1.1 ng/ml, and sera T4 concentrationsfrom 3.1 ng/ml to 7.9 ng/ml. The hypothyroidcondition in the SLP goitred-sharks is likely linkedto the low environmental iodide (<0.005 M), andhigh nitrate (111 M) of SLP water. The WAQwell-water facility was characterized by anoxic waterwith high iodide (0.60 M), total iodine (1.90M), and typical nitrate (24.6 M)concentrations of interstitial groundwater. Thedifference of iodide concentration of SLP and WAQ tankwater (<0.005 M versus 0.60 M) wasdirectly related to the hydrogeology of the well-watersources. To avoid goitre in marine aquarium systems,we recommend maintaining iodide concentrations of atleast 0.15 M.  相似文献   

14.
Zusammenfassung Mikroskopisch Einschluß-freie Andalusite aus Brasilien zeigen im UR-Absorptionsspektrum ein Doppelmaximum bei zirka 2,9 und ein deutlich schwächeres einfaches Maximum bei 3,04 , die OH-Valenzschwingungen zugeordnet werden. Diese Maxima verschwinden nach mehrtägigem Glühen bei 1000° C. In Platten parallel (110) zeigt das Doppelmaximum bei zirka 2,9 einen extrem starken Pleochroismus, wobei die Bande praktisch völlig verschwindet, wenn der elektrische Vektor parallel [001] schwingt. Damit müssen zumindest die OH-Gruppen, die für diese Bande verantwortlich sind, in die Struktur eingebaut sein. Für beide Arten von OH-Gruppen werden die plausiblen Anordnungen diskutiert.
Measurement of the infrared-pleochroism in minerals. VIII. The pleochroism of the OH-stretching frequency in andalusite
Summary Inclusion-free andalusites from Brazil show in the IR absorption spectrum a double maximum at ca. 2.9 and a much weaker single maximum at 3.04 which are interpreted as belonging to OH-stretching frequencies. The maxima disappear after annealing the specimen at 1000°C for several days. Plates parallel to (110) show a very strong pleochroism for the 2.9 -band, the peak being practically of zero height if the electric vector vibrates parallel [001]. This proves that at least the OH-groups which are responsible for this absorption band are constituents of the crystal structure. For both kinds of OH-groups the probable distributions are discussed.

Mit 3 Abbildungen  相似文献   

15.
Measurements of O2, Fe(II), Mn(II)and HS5 in salt marshsediments in the Tagus Estuary, Portugal, made with a voltammetric microelectrode, reveal strong seasonal differences in pore water composition within the 20~cm deep root zone. In spring, oxygen was below detection limit except close to the sediment surface. Fe(II) was present below 5 cm in concentrations ranging from detection limit to 1700 M. In summer, oxygen was present in the pore water almost to the bottom of the root zone in concentrations ranging from detection limit to more than 100 M. The spatial variability was intense: O2 concentrations as high as 78 M and as low as 25 M existed within 2~mm of each other. Fe(II) was below detection limit except towards the bottom of the root zone. In late fall, oxygen was found to 8 cm depth, but in concentrations lower than in summer, and Fe(II) was present below 9 cm. Mn(II) was found at levels declining from typical values of 200 M in spring to less than 20 M in late fall. With one exception, sulfide was below the detection limit in all measurements. During periods when dissolved Fe(II) is available in the pore water at the same time as 2 is delivered by roots, iron-rich concretions can form on roots. These conditions, which lead to precipitation of iron oxide in the sediment adjacent to roots, exist in spring, when new roots infiltrate anoxic Fe(II) containing sediment. They do not exist in summer, when dissolved Fe(II) is unavailable, or in winter, when oxygen is unavailable. The seasonal redox pattern revealed by the pore water chemistry is driven by the annual cycle of growth and decay of roots.  相似文献   

16.
Divariant oxide plus metal assemblages potentially make useful redox sensors for use in hydrothermal and other high pressure experiments. Here we report the calibration of the (Ni, Mn)O/Ni redox sensor in which the Ni/NiO (NNO) oxygen buffer is displaced to lower oxygen chemical potentials (O2), by the solid solution of MnO in the oxide phase. This assemblage was chosen because: (1) it covers a useful range of O2; (2) the system can be calibrated very accurately. Values of O2 defined by the (Ni, Mn)O/Ni assemblage were determined electrochemically, from 900 to 1300 K, using calcia-stabilized zirconia solid electrolytes. The oxide compositions (8 in total, ranging from 0.1X NiO0.8) were analysed afterwards by electron microprobe, and were checked for internal consistency by measuring the lattice parameters (a0), using powder XRD. The accuracies of the measurements, both assessed theoretically and established empirically, are (1): ±80J/mol in O2, ±0.0002 Å in a0 and ±0.002 to 0.005 in X NiO. Activity-composition relations were fitted to the Redlich-Kister formalism. There is a slight asymmetry (corresponding to a subregular model) across the solution with A 0 G =9577(±45) J/mol, and A 1 G =–477(±80) J/mol. The experimental data were also used to derive the parameters Vex, Hex and Sex. There is no obvious relationship between excess volumes and enthalpies of mixing, nor between excess volumes and excess entropies. The experimental data from this study have been used to formulate the (Ni, Mn)O/Ni redox sensor expression: O2 = 2(NNO) + 2RTlnX NiO + 2(1 – X NiO)2[11483 – 1.697T] – 477(4X NiO – 1)(900 < T(K) < 1300) where O2(NNO)=–478967+248.514T–9.7961 T In T, from O'Neill and Pownceby(1993a).  相似文献   

17.
Zusammenfassung Der primare klastische Anteil des mittleren Muschelkalks besitzt ein Maximum in den Korngrößen von 6–20, Ø , das über weite Strecken konstant bleibt. Der Mineralgehalt besteht aus Quarz, Feldspat, Glimmer und vielleieht Kaolinit.Bei der Diagenese warden Quarz und Feldspat teils korrodiert, teils wurden Quarz und Albit neu gebildet. In Randgebieten entstand Glaukonit vermutlich aus Glimmern.Durch Grundwassereinwirkung bildete rich ein zweites Maximum zwischen 0–2 Ø aus. Dabei ist in diesen Korngrößen eine Zunahme an Illit und Kaolinit und das Neuauftreten von Montmorillonit zu verzeichnen.Bei der Verwitterung verschwand das Maximum zwischen 6–20 Ø zugunsten eines Maximums zwischen 0–2 Ø . Damit verschwand auch der primäre Mineralgehalt fast völlig. Die Fraktionen unter 2 Ø setzen sich aus einem illitähnlichen Mineral zusammen.Durch Grundwassertätigkeit und Oberflächenverwitterung wurde also nicht nur der lösliche Anteil des mm ausgelaugt, sondern es sind auch deutliche Veränderungen des klastischen Anteils wahrzunehmen.Herrn Professor Dr.Carl W. Correns zum 60. Geburtstag gewidmet.  相似文献   

18.
It has recently been shown thatnitrogen contained in humic substances can be releasedas low molecular weight species through photochemicalprocesses or reactions. Nitrogen released in thismanner may then become available for biological useand chemical reactivity. This report providesadditional kinetic data for nitrogen photochemistry oforganic matter in natural waters from Louisiana andfor Suwannee River humic and fulvic acids. Naturalwater samples were fractionated into colloidal(>0.2 m, <1000 Dalton) and dissolved (>1000Dalton) fractions and the kinetics of these fractionsas well as 0.2 m filtered water samples weremeasured. For irradiations of less than 10 hours ofsimulated noon-time sun, samples showed linearproduction of ammonium and first-order fading at350 nm. Ammonium photoproduction was enhanced asmuch as three-fold by lowering pH, but linear kineticswere maintained. Light-dark cycling showed continuedrelease of ammonium immediately after irradiation,followed by uptake at longer post irradiation times.A two step mechanism was proposed to explain theobserved kinetics. Calculated net daytime release ofammonium from natural surface waters ranged from 0.33to 1.9 M h-1 in the samples studied,corresponding to a photic zone conversion rate of9–20% of the total organic nitrogen per day intoammonium.  相似文献   

19.
Fission-track ages in apatite are generally accepted as giving a measure of the time over which a sample has been exposed to temperatures below approximately 100° C. A compilation of the lengths of confined fission tracks in a wide variety of apatites from different geological environments has shown that the distribution of confined track lengths can provide unique thermal history information in the temperature range below about 150° C over times of the order of 106 to 109 years. The distribution of confined lengths of freshly produced induced tracks is characterised by a narrow, symmetrical distribution with a mean length of around 16.3 m and a standard deviation of the distribution of approximately 0.9 m. In volcanic and related rocks which have cooled very rapidly, and never been reheated above about 50° C, the distribution is also narrow and symmetric, but with a shorter mean of 14.5 to 15 m, and a standard deviation of the distribution of approximately 1.0 m. In granitic basement terrains which are thought never to have been significantly disturbed thermally, since their original post-emplacement cooling, the distribution becomes negatively skewed, with a mean around 12 or 13 m and a standard deviation between 1.2 and 2 m.This distribution is thought to characterise slow continuous cooling from temperatures in excess of 120° C, to ambient surface temperatures. More complex thermal histories produce correspondingly complex distributions of confined tracks. The continuous production of tracks through time, coupled with the fact that the length of each track shrinks to a value characteristic of the maximum temperature it has experienced, gives a final length distribution which directly reflects the nature of the variation of temperature with time. Most distinctive of the myriad possible forms of the final distribution are the bimodal distributions, which give clear evidence of a two-stage history, including high and low temperature phases. The study of confined length distributions therefore offers invaluable evidence on the meaning of any fission-track age, and bears the potential of providing rigorous constraints on thermal history in the temperature regime below about 150° C. The results of this study strongly suggest that any apatite fission-track age determination should be supported by a confined track length distribution.  相似文献   

20.
Isothermal, hydrothermal experiments were performed on two compositionally contrasting hornblendes from amphibolites in order to examine Ar diffusion behavior in metamorphic hornblendes. Ten experiments on sample RF were performed at temperatures of 750°C, 800°C, and 850°C and pressures of 1 kbar using measured grain radii of 158, 101, and 34 m. Eight experiments on sample 118576 were performed under the same conditions using measured grain radii of 145, 77, and 25 m. Minor (<5%) alteration was observed in high temperature runs. Diffusion coefficients were calculated from measured radiogenic 40Ar loss following treatment assuming a spherical geometry for the mineral aggregate. Diffusivities calculated for different grain sizes vary by up to an order of magnitude for a given temperature indicating that the effective diffusion radius was less than the measured grain radius. Diffusivities for RF and 118576 calculated for grain radii of 101 and 145 m, respectively, form a linear array on an Arrhenius diagram with slopes indicating activation energies of 60 kcal/mol. No correlation between Mg number (100 Mg/(Mg+Fe)) and activation energy was observed. Diffusivities calculated for these experiments are higher than previously reported results from similar experiments performed on hornblendes. A comparison of results for 34 m splits from these two studies indicates higher apparent diffusivities (by a factor of 5), which probably result from observed phyllosilicate inter-growths (chlorite) and/or exsolution lamellae that partition the metamorphic hornblendes into smaller subdomains. Diffusivities calculated for experiments performed on 65 m and 34 m splits of 40Ar/39Ar standard MMhb-1 at 800°C and 1 kbar are consistent with a previously reported activation energy of 65 kcal/mol. Arrhenius parameters which emerge from the empirical model of Fortier and Giletti (1989) agree with experimental results to within analytical uncertainty. Although results of these experiments support previously reported estimates of the activation energy of 40Ar in hornblende (60 kcal/mol), phyllosilicate intergrowths and/or microstructures such as exsolution lamellae within the two metamorphic hornblendes result in extremely small diffusion domains, which may lead to lower Ar retentivities and lower closure temperatures. The effective diffusion dimension for 40Ar in hornblende is not likely to be defined by dislocations but rather by some larger structure within the crystal. TEM and SEM studies may provide some insight into the effective diffusion dimension for 40Ar in amphiboles, thereby enabling better estimates of closure temperatures and more precise temperature-time reconstructions.  相似文献   

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