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1.
The variation of chemical element compositions in two pyroclastic sequences (Astroni 6 and Averno 2, Phlegrean Fields, Italy) is studied. Both sequences are compositionally zoned indicating a variability of melt compositions in the magma chamber prior to eruption. A clear dichotomy between the behaviour of major vs. trace elements is also observed in both sequences, with major elements displaying nearly linear inter-elemental trends and trace elements showing a variable scattered behaviour. Together with previous petrological investigations these observations are consistent with the hypothesis that magma mixing processes played a key role in the evolution of these two magmatic systems. Recently it has been suggested that mixing processes in igneous systems may strongly influence the mobility of trace elements inducing a ‘diffusive fractionation’ phenomenon, whose extent depends on the mixing time-scale. Here we merge information from 1) numerical simulations of magma mixing, and 2) magma mixing experiments (using as end-members natural compositions from Phlegrean Fields) to derive a relationship relating the degree of ‘diffusive fractionation’ to the mixing time-scales. Application of the ‘diffusive fractionation’ model to the two studied pyroclastic sequences allowed us to apply the relationship derived by numerical simulations and experiments to estimate the mixing time-scales for these two magmatic systems. Results indicate that mixing processes in Astroni 6 and Averno 2 systems lasted for approximately 2 and 9 days, respectively, prior to eruption.  相似文献   

2.
Pollution resulting from terrestrial and aquatic trace elements has become a severe problem across the world. Organic carbon(OC) content has a high affinity for metallic contaminants and it acts as a significant sink for trace elements. The decomposition of OC content directly influences the bioavailability of trace elements. The decomposition of OC content and OC distribution vary spatially, these processes affect the release of trace elements and need further research. In the current study, se...  相似文献   

3.
X-ray diffraction (XRD) of the fine matrix component of four alluvial units and modern channel sediments in the Voidomatis River Basin of northwest Greece shows that fine sediment sources have changed considerably during the late Quaternary. The matrix fraction of the modern channel sediments is derived predominantly from erosion of local flysch rocks and soils. During the last glaciation, however, the fine sediment load of the Voidomatis River was dominated by glacially-ground, finely comminuted limestone materials. Limestone-derived fine sediment is not produced in significant amounts under modern climatic conditions. By combining this XRD work with a detailed programme of clast lithologic 1 analysis we have reconstructed former bedload and fine sediment load composition. The lithological properties of both the coarse (8-256 mm) and fine (< 63 μm) elements of the sediment load have varied markedly during the late Quaternary. A simple, semiquantitative assessment of fine sediment mineralogy, using diffractogram peak-height data, has provided a valuable complement to the information gathered from more traditional clast lithological techniques. Together, in favourable geological settings, fine fraction mineralogy and clast lithological analysis can provide a valuable tool for the reconstruction of late Quaternary alluvial environments.  相似文献   

4.
Chung-Ho  Wang  Chi-Yuen  Wang  Ching-Huei  Kuo  Wen-Fu  Chen 《Island Arc》2005,14(1):37-54
Abstract   The changes in the isotopic composition of, and the groundwater level in, the Choshui River alluvial fan near the ruptured Chelungpu Fault during and following the 1999 ( M w = 7.5) Chi-Chi earthquake in Taiwan are reported. Three aspects of the hydrological changes are noticed. First, following the Chi-Chi earthquake, the lower aquifers beneath the Choshui River fan showed a significant shift in isotopic composition towards that of the surface water in the Choshui River, suggesting enhanced exchanges of water between the river and the groundwater. Second, in some wells, water levels and isotopic compositions in different aquifers converged to the same respective values during the Chi-Chi earthquake, suggesting coseismic exchanges of water between the different aquifers, which implies enhanced permeability due perhaps to the fracturing and breaching of aquitards between the aquifers. Third, the pattern of the coseismic water-level response is distinctly different from that of the shift in the isotopic composition, suggesting that they were produced by different mechanisms.  相似文献   

5.
The chemical composition of riverine suspended sediment is the integration of the weathering crust minerals, soil organic matter and erosion agency within a specific drainage basin, which has been largely disturbed by the human activities. Selected metal elements of the riverine suspended sediment in the Zhujiang River were analysed using inductively coupled plasma–atomic emission spectrometry (ICP–AES) in three different hydrological phases from 1997 to 1998 at Makou and Sanshui hydrographic gauge stations, located at the lower reaches of the two main tributaries of the Zhujiang River, i.e. the Xijiang and the Beijing Rivers respectively. Organic carbon and nitrogen were also analysed using a conventional element analyser. The results demonstrate that the chemical composition of the riverine suspended sediment show obvious variability in different hydrological phases, which closely correlate to the organic matter content in suspended sediment. Intensified erosion in the flood phase results in lower concentration of the organic matter than that in the lower water level phase. The riverine suspended sediment with rich organic matter in the lower water level phase adsorbs some metal elements from the river water. Copyright © 2003 John Wiley & Sons, Ltd.  相似文献   

6.
Forty-two elements have been measured via INAA and RNAA in six samples of five rocks from a 2-m tan-gray boulder-2 breccia (South Massif), in four soils from the South Massif and a valley soil. The chemical composition of the four metaclastic rocks corresponds to “high alumina” (52% Pl) and medium-K KREEP-type rocks. Rock 72335,2 is a medium K anorthositic gabbro (74% Pl). Both the North and South Massifs appear to be medium-K KREEP in composition and thus may represent a single stratigraphic unit of the Serenitatis basin event. Four soils of the South Massif are identical in composition to medium-K KREEP; they are more feldspathic and lower in LIL trace elements relative to the boulder-2 rocks. The valley soil 75081 is like the 10084 soil; both soils are high in TiO2 and both are deficient in KREEP. Th and U give a sharp distinction between the valley and highland soils. The South Massif rocks and soils contain siderophiles at the 2–4% Cl level and show an ancient meteoritic pattern. Five samples of the four rocks have Ir/Au ratios of ± 0.02 which we assign to the Serenitatis basis planetesimal. The valley soil at Camelot Crater has low siderophiles (1% Cl). Our systematic study of four shadowed and exposed soils does not support the labile hypothesis for Cd, In, Tl and Zn. We observe no volatile (atmophile) movement from the South Massif highland soils to the valley soil 75081. The volatiles Cs and Tl appear to have been fractionated in the boulder-2 rocks during cratering, brecciation and metamorphic processes. The uniform ratio of FeO/MnO = 80–85, observed for all previous mare and highland sites, also holds for the Taurus-Littrow site.  相似文献   

7.
We discuss the chemical compositions of rhyolites from three distinct tectonic settings: (i) the continental rift from Ethiopia (both Oligocene–Miocene and Quaternary rhyolites); (ii) the early Miocene continental arc of Japan (the Mt Wasso rhyolites related to the rifting of the Japan Sea); and (iii) the oceanic Izu–Bonin Island Arc. The comparison reveals that the oceanic island arc rhyolites have high contents of CaO, Al2O3, and Sr, and extremely low abundance of trace elements including K2O. In contrast, the Ethiopian continental rift rhyolites are characterized by low contents of CaO, Al2O3, and Sr, and high contents of K2O, and are enriched in the whole range of trace elements. The continental arc Mt Wasso rhyolites are apparently low in Nb content, although they display similar chemical trends to those of the Ethiopian rhyolites. This obvious difference in the chemical signatures of the rhyolites from the three tectonic settings is the consequence of their derivation from different sources. The implication of this result is that fractional crystallization processes were dominant in the rift‐related rhyolites both from continental rift and continental arc regardless of the prevailing tectonic setting and the nature of the crust (age, thickness, composition), whereas the oceanic island arc rhyolites may form through partial melting of young, mafic crust.  相似文献   

8.
The 1300 km long Narmada River flows along a structural lineament, alternating between constricting rocky gorges and rapids, and meandering wide alluvial reaches. Channel forms and processes were studied in a 120 km long section of an alluvial reach. Channel size, shape and bedforms in the Narmada River are related to very large floods which have occurred three times in this century. During such floods the entire 400 m wide channel is utilized and 10–15 m high cliffs on both sides operate as riverbanks. Normally, even the high flows of the south-western monsoon are insufficient to fill the whole channel, and hence their effects are limited to building of discontinuous floodplains between the cliffs and modifying bedforms and bars. A channel-in-channel topography is thus created. The very large floods are also responsible for erosion of the rocky stretches and building of point bars. The river meanders, but its movement is restricted because of (1) rocky gorges and scablands operating as anchor points at intervals, and (2) the presence of high alluvial cliffs which are topped on extremely rare occasions. In spite of being located in a tectonically active zone in a monsoon setting, it is the exceptional high-magnitude floods at irregular intervals which control the form and behaviour of the Narmada River.  相似文献   

9.
During the summer of 1989 surface sediment samples were collected in Lake Coeur d'Alene, the Coeur d'Alene River and the St Joe River, Idaho, at a density of approximately one sample per square kilometre. Additional samples were collected from the banks of the South Fork of the Coeur d'Alene and the Coeur d'Alene Rivers in 1991. All the samples were collected to determine trace element concentrations, partitioning and distribution patterns, and to relate them to mining, mining related and discharge operations that have occurred in the Coeur d'Alene district since the 1880s, some of which are ongoing. Most of the surface sediments in Lake Coeur d'Alene north of Conkling Point and Carey Bay are substantially enriched in Ag, As, Cu, Cd, Hg, Pb, Sb and Zn relative to unaffected sediments in the southern portion of the lake near the St Joe River. All the trace element enriched sediments are extremely fine grained (mean grain sizes « 63 μm). Most of the enriched trace elements, based on both the chemical analyses of separated heavy and light mineral fractions and a two step sequential extraction procedure, are associated with an operationally defined Fe oxide phase; much smaller percentages are associated either with operationally defined organics/sulphides or refractory phases. The presence, concentration and distribution of the Fe oxides and heavy minerals indicates that a substantial portion of the enriched trace elements are probably coming from the Coeur d'Alene River, which is serving as a point source. Within the lake, this relatively simple point source pattern is complicated by a combination of (1) the formation of trace element rich authigenic Fe oxides that appear to have reprecipitated from material solubilized from anoxic bed sediments and (2) physical remobilization by currents and wind driven waves. The processes that have caused the trace element enrichment in the surface sediments of Lake Coeur d'Alene are likely to continue for the foreseeable future.  相似文献   

10.
Water chemistry, chlorophyll “a” concentration in phytoplankton and periphyton, and the structure of bacterioplankton communities of the Zeya River and its tributaries are assessed in the construction zone of the Nizhne-Zeiskaya HPP. The results of multidisciplinary studies demonstrate the effect of natural and anthropogenic factors on the formation of water quality in the examined part of the Zeya River.  相似文献   

11.
By the example of an area near the active Karymskii Volcano (on the eastern coast of Kamchatka) it is shown that under conditions of regular supply of pyroclastic material on the diurnal surface, organic soil matter transforms very slowly and mobile trace elements of newly fallen volcanic ashes are the major plant nutrition source. Geochemical specialization of the studied area is characterized by lower concentrations of most trace elements relative to their clarkes for soils and by an excess of trace element contents over the clarkes for living matter in plants. Newly fallen ashes are enriched in mobile trace elements, which in dissolved form pass into adjacent media due to hypergene geochemical processes.  相似文献   

12.
Changes in the level of the Yangtze River caused by anthropogenic water regulation have major effects on the hydrological processes and water cycle in surrounding lakes and rivers. In this study, we obtained isotopic evidence of changes in the water cycle of Yangtze River during the two drought years of 2006 and 2013. Isotopic evidence demonstrated that the δ18O and δD levels in Yangtze River exhibited high spatial heterogeneity from the upper to lower reaches, which were controlled by atmospheric precipitation, tributary/lake water mixing, damming regulation, and water temperature. Both the slope and intercept of Yangtze River evaporative line (δD = 7.88 δ18O + 7.96) were slightly higher than those of local meteoric water line of Yangtze River catchment (δD = 7.41 δ18O + 6.01). Most of the river isotopic values were located below the local meteoric water line, thereby implying that the Yangtze River water experienced a certain degree of evaporative enrichment on isotopic compositions of river water. The high fluctuations in the isotopic composition (e.g., deuterium excess [d‐excess]) in the middle to lower reaches during the initial stage of operation for the Three Gorges Dams (2003–2006) were due to heterogeneous isotopic signatures from the upstream water. In contrast to the normal stage (after 2010) characterized by the maximum water level and largest water storage, a relatively small variability in the deuterium excess was found along the middle to lower reaches because of the homogenization of reservoir water with a longer residence time and complete mixing. The effects of water from lakes and tributaries on the isotopic compositions in mainstream water were highlighted because of the high contributions of lakes water (e.g., Dongting Lake and Poyang Lake) efflux to the Yangtze River mainstream, which ranged from 21% to 85% during 2006 and 2013. These findings suggest that the retention and regulation of the Three Gorges Dams has greatly buffered the isotopic variability of the water cycle in the Yangtze catchment, thereby improving our understanding of the complex lake–river interactions along the middle to lower reaches in the future.  相似文献   

13.
The distribution of trace metals in alluvial sediments depends on their natural background concentrations, and on the dynamics of contemporary depositional and erosional (mainly flood‐induced) processes. Geological and geochemical investigations were carried out in the valley of Vistula River near Magnuszew (central Poland). Sediment samples were collected from a depth of 35 cm and comprise sediments of all defined geomorphological features. Identification and geological interpretation of the morphodynamic sediment features was supported by aerial photographs and high‐resolution satellite images. These studies revealed that the distribution of trace metals is closely linked to the morphogenesis of the alluvial floodplain. The highest concentrations of Cu, Co, Zn, V, Cr and Ni were observed in crevasse‐splays deposits. By contrast, Sr, Pb and As were concentrated in deposits which fill oxbow lakes (partly infilled with organic deposits). The lowest concentrations of trace metals were detected in flood sediments deposited within erosional troughs. The geomorphological and sedimentological history of the fluvial features explains the pattern of heavy metal distribution on the current floodplain surface. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

14.
The suspended particulate and fine-grained floodplain sediments were collected from the main stream and tributaries of the Changjiang River for Sr-Nd isotopic measurements. The εNd(0) values gradually decrease downstream from -10.8 on average in the upper reaches to -12.3 in the lower reaches, whereas the 87Sr/86Sr ratios increase correspondingly, averaging 0.721899 and 0.725826 respectively in the upper and middle-lower reaches. The compositional variations primarily reflect the complex con- trols of provenance rocks, chemical weathering, and sediment characters between different catchments, among which the abnormal Sr-Nd isotopic compositions of the Yalong, Fujiang, Tuojiang and Yuanjiang rivers indicate the sediment provenance contributions from the Emeishan Basalt in the upper reaches and the old metamorphic and siliceous rocks in the middle-lower reaches. The Sr-Nd isotopic ratios of the Changjiang sediments can better reflect the average composition of weathered continental crust compared to other major rivers in the world because of the unique source rock types in the Changjiang drainage basin. The recognition of the Sr-Nd isotopic systematics of the Changjiang sediments will contribute to our understanding of the Changjiang evolution history and continental weathering processes during the Cenozoic, and also to reconstructing the paleoenvironmental changes in East China and the marginal seas.  相似文献   

15.
Edwin  Ortiz  Barry P.  Roser 《Island Arc》2006,15(2):223-238
Abstract Basement rocks in the catchment of the Kando River in southwest Japan can be divided into two main groups. Paleogene to Cretaceous felsic granitoids and volcanic rocks dominate in the upstream section, and more mafic, mostly Miocene volcanic and volcaniclastic rocks occur in the downstream reaches. Geochemically distinctive Mount Sambe adakitic volcanic products also crop out in the west. X‐ray fluorescence analyses of major elements and 14 trace elements were made of two size fractions (<180 and 180–2000 µm) from 86 stream sediments collected within the catchment, to examine contrasts in composition between the fractions as a result of sorting and varying source lithotype. The <180 µm fractions are depleted in SiO2 and enriched in most other major and trace elements relative to the 180–2000 µm fractions. Na2O, K2O, Ba, Rb and Sr are either depleted relative to the 180–2000 µm fractions, or show little contrast in abundance. Sediments from granitoid‐dominated catchments are distinguished by greater K2O, Th, Rb, Ba and Nb than those derived from the Miocene volcanic rocks. Granitoid‐derived <180 µm fractions are also enriched in Zr, Ce and Y. Sediments derived from the Miocene volcanic rocks generally contain greater TiO2, Fe2O3*, Sc, V, MgO and P2O5, reflecting their more mafic source. Sediments containing Sambe volcanic rocks in their source are marked by higher Sr, CaO, Na2O and lower Y, reflecting an adakitic signature that persists into the lower main channel, where compositions become less variable as the bedload is homogenized. Normalization against source averages shows that compositions of the 180–2000 µm fractions are less fractionated from their parents than are the <180 µm fractions, which are enriched for some elements. Contrast between the size fractions is greatest for the granitoid‐derived sediments. Weathering indices of the sediments are relatively low, indicating source weathering is moderate, and typical of temperate climates. Some zircon concentration has occurred in granitoid‐derived <180 µm fractions relative to 180–2000 µm counterparts, but Th/Sc and Zr/Sc ratios overall closely reflect both provenance and homogenization in the lower reaches.  相似文献   

16.
This paper reviews the role of alluvial soils in vegetated gravelly river braid plains. When considering decadal timescales of river evolution, we argue that it becomes vital to consider soil development as an emergent property of the developing ecosystem. Soil processes have been relatively overlooked in accounts of the interactions between braided river processes and vegetation, although soils have been observed on vegetated fluvial landforms. We hypothesize that soil development plays a major role in the transition (speed and pathway) from a fresh sediment deposit to a vegetated soil‐covered landform. Disturbance (erosion and/or deposition), vertical sediment structure (process history), vegetation succession, biological activity and water table fluctuation are seen as the main controls on early alluvial soil evolution. Erosion and deposition processes may not only act as soil disturbing agents, but also as suppliers of ecosystem resources, because of their role in delivering and changing access (e.g. through avulsion) to fluxes of water, fine sediments and organic matter. In turn, the associated initial ecosystem may influence further fluvial landform development, such as through the trapping of fine‐grained sediments (e.g. sand) by the engineering action of vegetation and the deposit stabilization by the developing aboveground and belowground biomass. This may create a strong feedback between geomorphological processes, vegetation succession and soil evolution which we summarize in a conceptual model. We illustrate this model by an example from the Allondon River (Switzerland) and identify the research questions that follow. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

17.
Major- and trace-element systematics of the magmas erupted during the recent activity of Vesuvius (1631–1944) show that composition ranges are narrow and identical in each activity cycle except for the 1631 eruption which emitted also more differentiated products. These rocks are the most basic magmas erupted in Vesuvius. The high K and incompatible-element contents of these products are characteristic of the whole Roman-Campanian Province.Lavas and tephra of the 1906 and 1944 eruptions are highly porphyric. Geochemical modelling shows that these products are mechanical mixing of a slightly differentiated melt and various proportions of phenocrysts. Except ratios of highly incompatible trace elements (Th/La, Th/Ta, Th/Ba), no chemical characteristics of primary and differentiated melts can be simply inferred from bulk erupted products. An inverse method for calculating melt and mineral compositions is presented. Calculated weigth fractions are consistent with measured modal compositions. A model of crystal differential accumulation controlled by relative phase densities and eruption rates is proposed.  相似文献   

18.
An in-situ microanalysis of Pb isotopic compositions in sulfide minerals is carried out by using femtosecond laser-ablation multi-collector inductively coupled plasma mass spectrometry(fs LA-MC-ICP-MS).High-temperature-activated carbon was used to filter Hg contained in the carrier gas,which reduced the Hg background signal by 48%and also lowered the detection limit of the analysis.Fractionation and mass discrimination effects existing in the ICP-MS analytical processes were corrected using an internal reference Tl in conjunction with an external reference NIST SRM 610.The proposed method was used to analyze the Pb isotopic compositions of chalcopyrite,pyrite,and sphalerite from the Dulong Sn-Zn-In polymetallic ore district.The results showed that in this ore district,the sulfide minerals and different grains of the same sulfide mineral show a large variation in Pb content up to 1000-fold.The studied pyrites show relatively higher Pb contents and homogeneous Pb isotopic compositions,whereas the sphalerites have low Pb contents but most variable Pb isotopic compositions.It is suggested that the large variation of Pb isotopic composition may reflect a late hydrothermal superimposition on the primary sulfide formation.In addition,radiogenic Pb accumulated by radioactive decay of trace amounts of U over time in the host minerals may also be one of the causes for the large variation range of Pb content and Pb isotopic composition of those low-Pb sphalerites.Chalcopyrite and sphalerite grains with Pb content greater than 10 ppm presented a consistent Pb isotopic distribution,whereas all the sulfide grains with Pb content greater than 100 ppm had consistent Pb isotopic composition within 2s measurement uncertainties.The in-situ analysis of Pb isotopic composition agreed well with the results obtained by conventional chemical methods within2s measurement uncertainties,indicating that the data obtained by fs LA-MC-ICP-MS are reliable.Additionally,this study indicates that the Pb isotopic composition could truthfully record the source of ore-forming minerals only for sulfide minerals with high Pb content.On the contrary,the Pb isotopic composition of low-Pb sulfide minerals may be affected by trace amounts of U in the host minerals that may lead to a highly radiogenic Pb isotope ratio.Alternatively,it is also possible that late fluid metasomatic overprinting may alter the Pb isotopic compositions.  相似文献   

19.
长江中下游浅水湖泊沉积物腐殖质组分赋存特征   总被引：9，自引：3，他引：6  
应用化学方法,对长江中下游浅水湖泊表层沉积物有机质含量、腐殖质组成及结合形态进行了研究.结果表明:①长江中下游浅水湖泊11个沉积物的有机质含量变化较大.在0.98%-11.0%之问波动.污染程度重的沉积物中有机质含量均较污染程度轻的高.其有机质的分布特征与沉积物污染程度和湖泊周边的人类活动有关.②腐殖质组成中,胡敏酸(...  相似文献   

20.
Coal combustion processes lead to release of gases and particulate matter (PM) into the atmosphere that are often harmful to human health. These airborne pollutants seem to be dispersed and deposited in soils mainly according to the prevailing atmospheric conditions. Several trace elements can be found attached to PM as well as Fe-rich magnetic particles that can produce magnetic enhancement in the uppermost soil horizons. In the present work, we use a simple Gaussian Dispersion Model (GDM) for modelling the distribution of fine PM emission coming from a small coal (coke) burning factory in order to evaluate the relationship between such modelled data (PM distribution) and measured data (soil magnetic properties and trace metal contents). Our results show a strong spatial variation of concentration-dependent magnetic parameters based on a uniform magnetomineralogy in the overall study area. In addition, these results were analysed using multivariate statistics for 13 magnetic and chemical variables and the GDM results for two different atmospheric stability classes, and hence the in-situ magnetic susceptibility, anhysteretic and saturation remanent magnetization showed positive and statistically significant correlation with the GDM results (R = 0.70). Therefore, these results demonstrate the usefulness of magnetic properties in monitoring the PM distribution in soils or other environmental PM collectors.  相似文献   

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