Nitrogen in peridotite xenoliths: Lithophile behavior and magmatic isotope fractionation     

Reika Yokochi  Bernard Marty  Pete Burnard 《Geochimica et cosmochimica acta》2009,73(16):4843-7521

In order to document the origin and speciation of nitrogen in mantle-derived rocks and minerals, the N and Ar contents and isotopic compositions were investigated for hydrous and anhydrous peridotite xenoliths from Ataq, Yemen, from Eifel, Germany, and from Massif Central, France. Nitrogen and Ar were extracted by stepwise combustion with a fine temperature resolution, followed by fusion in a platinum crucible. A large isotopic disequilibrium of up to 25.4‰ is observed within single peridotite xenoliths, with δ¹⁵N values as low as −17.3‰ in phlogopite whereas clinopyroxene and olivine show positive δ¹⁵N values. Identical Sr isotopic ratios of phlogopite, clinopyroxene and whole rock in this wehrlite sample are consistent with crystallization from a common reservoir, suggesting that the light N signature of phlogopite might be the result of isotopic fractionation during N uptake from the host magma. The nitrogen concentration is systematically high in phlogopite, (7.6-25.7 ppm), whereas that of bulk peridotite xenoliths is between 0.1 and 0.8 ppm. The high N content of phlogopite is at least partly due to host magma-mineral interaction, and may also suggest the occurrence of N as that substituted for K⁺ during mineral growth in mafic magmas. Such speciation is consistent with the fact that N and Rb contents correlate well for a set of samples from mantle regions that were affected by subduction-related metasomatism and magmatism. The N/Rb ratios of these samples are comparable with values estimated for subduction zone magmas, but are one order of magnitude lower than the N/Rb ratios characterizing subducting slabs. This difference suggests preferential release of N relative to alkalis in the forearc region. N/⁴⁰Ar^∗ ratios of minerals from analyzed mantle xenoliths are much higher than those of vesicles in MORBs and OIBs, requiring either the occurrence of nitrogen speciation in the mantle more compatible than Ar, significant loss of fluid phase during entrainment, or long residence time of volatile elements in the mantle source(s) of fluids to increase drastically the ⁴⁰Ar^∗ budget of the latter.  相似文献   

Organochlorine and mecury concetrations in eggs of grey plovers (Pluvialis squatarola) breeding in the Lena Dlta, north-east Sibveria, 1997     

Klaus-Michael Exo  Pete H. Becker  Ute Sommer 《Polar research》2000,19(2):261-265

Seven eggs from four clutches of grey plovers ( Pluvialis squatarola ) breeding in the Lena Delta, Sakha Republic, Yakutia, in 1997 were analysed for persistent organochlorines and mercury. Contamination levels were low and within the same range as found in eggs from waders (Charadriiformes) breeding in north-west Europe. One exception was ∑HCH, averaging 99.2 ng g⁻¹ fresh egg mass, a level about ten times higher than in wader eggs from north-west Europe. β-HCH accounted for 98% of the total HCH concentration. There are indications that the pesticide levels may reflect former local use. ∑PCB level (57.0 ng g⁻¹, 62 congeners) and mercury concentration (68.7 ng g⁻¹) can be considered low.  相似文献   

Diffusive fractionation of noble gases and helium isotopes during mantle melting     

Pete Burnard   《Earth and Planetary Science Letters》2004,220(3-4):287-295

The large differences in He and Ar diffusivities in silicate minerals could result in fractionation of the He/Ar ratio during melting of the mantle, producing He/Ar ratios in the primary mantle melts that are higher than those of the bulk mantle. Modeling noble gas diffusion out of the bulk mantle into fast diffusion pathways (such as fractures or melt channels) suggests that significant (order of magnitude) He/Ar fractionation will occur if the fast diffusion channels are spaced several meters apart and the noble gas residence in these diffusion channels is of the order days to weeks. In addition, the 15% difference in ³He and ⁴He diffusivities could also produce isotopic fractionation between the melt and its solid source. Modeling the behavior of He and Ar during melting shows that small increases (few %) in ³He/⁴He should be correlated with larger variations (factor of 5) in ⁴He/⁴⁰Ar. However, in order to test this hypothesis the effects of subsequent He–Ar fractionation that occur during degassing have to be corrected. I describe a scheme that can separate He/Ar variations in the primary melt from overprinted fractionation during magmatic degassing. Using the degassing-corrected data, there is a correlation between the primary melt’s ⁴He/⁴⁰Ar and ³He/⁴He in mid-ocean ridge basalts (MORBs). The slope of the correlation is consistent with the models of preferential diffusion of ³He relative to ⁴He and of ⁴He relative to ⁴⁰Ar from the solid mantle into the melt. Diffusive fractionation of noble gases during melting of the mantle can also account for low ⁴He/⁴⁰Ar ratios commonly found in residual mantle xenoliths: preferential diffusion of He relative to Ar will produce some regions of the mantle with low ⁴He/⁴⁰Ar, the complement of the high ⁴He/⁴⁰Ar ratios in basalts. Diffusive fractionation cannot, however, account for differences between the He and Ne isotopic compositions of MORBs compared with ocean island basalts (OIBs); not only are the extremely high ³He/⁴He ratios of OIBs (up to 50 Ra) difficult to produce at reasonable mantle time and lengthscales, but also the Ne isotopic compositions of MORBs and OIBs do not lie on a single mass fractionation line, therefore cannot result from diffusive fractionation of a single mantle Ne source. If preferential diffusion of He from the solid mantle into primary melts is a significant process during generation of MORBs, then it is difficult to constrain the He concentration of the mantle: He concentrations in basalts and the He flux to the ocean essentially result from extraction of He from a larger (and unknown) volume of mantle than that that produced the basalts themselves. The He concentration of the mantle cannot be constrained until more accurate estimates of the diffusion contribution are available.  相似文献   

Investigations of subsurface flow constructed wetlands and associated geomaterial resources in the Akumal and Reforma regions,Quintana Roo,Mexico     

Mark P. S. Krekeler  Pete Probst  Misha Samsonov  Cynthia M. Tselepis  William Bates  Lance E. Kearns  J. Barry Maynard 《Environmental Geology》2007,53(4):709-726

Subsurface flow constructed wetlands in the village of Akumal, Quintana Roo, Mexico were surveyed to determine the general status of the wetland systems and provide baseline information for long term monitoring and further study. Twenty subsurface flow wetlands were surveyed and common problems observed in the systems were overloading, poor plant cover, odor, and no secondary containment. Bulk mineral composition of aggregate from two subsurface flow constructed wetlands was determined to consist solely of calcite using bulk powder X-ray diffraction. Some soil structure is developed in the aggregate and aggregate levels in wetlands drop at an estimated rate between 3 and 10 cm/year for overloaded wetlands owing to dissolution. Mineral composition from fresh aggregate samples commonly is a mixture of calcite and aragonite. Trace amounts of Pb, Zn, Co, and Cr were observed in fresh aggregate. Coefficients of permeability (k) varied from 0.006 to 0.027 cm/s with an average values being 0.016 cm/s. Grain size analysis of fresh aggregate samples indicates there are unimodal and multimodal size distributions in the samples with modes in the coarse and fine sand being common. Investigations of other geologic media from the Reforma region indicate that a dolomite with minor amounts of Fe-oxide and palygorskite is abundant and may be a better aggregate source that the current materials used. A Ca-montmorillonite bed was identified in the Reforma region as well and this unit is suitable to serve as a clay liner to prevent leaks for new and existing wetland systems. These newly discovered geologic resources should aid in the improvement of subsurface flow constructed wetlands in the region. Although problems do exist in these wetlands with respect to design, these systems represent a successful implementation of constructed wetlands at a community level in developing regions.  相似文献   

The effects of hardpan layers on the water chemistry from the leaching of pyrrhotite-rich tailings material     

S.?E.?GilbertEmail author  D.?R.?Cooke  P.?Hollings 《Environmental Geology》2003,44(6):687-697

Column leaching experiments were used to determine the effects of an iron-rich hardpan layer, on the rate of tailings oxidation and the composition of leachate waters, from the Renison Bell tailings dams in western Tasmania, Australia. One-meter-long PVC columns, filled with tailings, cover material (Cassiterite Flotation Tailings) and hardpan samples from the tailings dams, were leached over a period of 14 weeks. Under dry cover conditions, when hardpan was present, the solute loads peaked at 21–49 days (Fe at 2,294 ppm and SO ₄ ^2- at 4,700 ppm), and stabilised at much lower concentrations after 9 weeks. In contrast, the solute loads steadily increased over time in the column where hardpan was absent (SO ₄ ^2- from 1,800 to 3,100 ppm, and Fe from 407 to 1,692 ppm). Under saturated cover conditions, the solute concentrations in the leachate also increased with time (SO ₄ ^2-from 1,900 to 17,000 ppm, and Fe from 480 to 8,500 ppm). The presence of a hardpan layer between the reactive tailings and cover material has been found to improve leachate water chemistry and lessen the rate of sulphide oxidation.  相似文献   

A coupled hydrology–biogeochemistry model to simulate dissolved organic carbon exports from a permafrost‐influenced catchment          下载免费PDF全文

Jason S. Lessels  Doerthe Tetzlaff  Sean K Carey  Pete Smith  Chris Soulsby 《水文研究》2015,29(26):5383-5396

We outline the development of a simple, coupled hydrology–biogeochemistry model for simulating stream discharge and dissolved organic carbon (DOC) dynamics in data sparse, permafrost‐influenced catchments with large stores of soil organic carbon. The model incorporates the influence of active layer dynamics and slope aspect on hydrological flowpaths and resulting DOC mobilization. Calibration and evaluation of the model was undertaken using observations from Granger Basin within the Wolf Creek research basin, Yukon, northern Canada. Results show that the model was able to capture the dominant hydrological response and DOC dynamics of the catchment reasonably well. Simulated DOC was highly correlated with observed DOC (r² = 0.65) for the study period. During the snowmelt period, the model adequately captured the observed dynamics, with simulations generally reflecting the timing and magnitude of the observed DOC and stream discharge. The model was less successful over the later summer period although this partly reflected a lack of DOC observations for calibration. The developed model offers a valuable framework for investigating the interactions between hydrological and DOC processes in these highly dynamic systems, where data acquisition is often very difficult. © 2015 The Authors Hydrological Processes Published by John Wiley & Sons, Ltd.  相似文献   

Inter-comparison of cosmogenic in-situ He, Ne and Cl at low latitude along an altitude transect on the SE slope of Kilimanjaro volcano (3°S, Tanzania)     

Irene Schimmelpfennig  Alice Williams  Raphaël Pik  Pete Burnard  Samuel Niedermann  Robert Finkel  Björn Schneider  Lucilla Benedetti 《Quaternary Geochronology》2011,6(5):425-436

Because the intensity and energy spectrum of the cosmic ray flux are affected by atmospheric depth and geomagnetic-field strength, cosmogenic nuclide production rates increase considerably with altitude and to a lesser degree with latitude. The scaling methods used to account for spatial variability in production rates assume that all cosmogenic nuclides have the same altitude dependence. In this study we evaluate whether the production rates of cosmogenic ³⁶Cl, ³He and ²¹Ne change differently with altitude, which is plausible due to the different threshold energies of their production reactions. If so, nuclide-specific scaling factors would be required.Concentrations of the three cosmogenic nuclides were determined in mafic phenocrysts over an altitude transect between 1000 and 4300 m at Kilimanjaro volcano (3°S). Altitude dependence of relative production rates was assessed in two ways: by determination of concentration ratios and by calculation of apparent exposure age ratios for all nuclide pairs. The latter accounts for characteristics of ³⁶Cl that the stable nuclides ³He and ²¹Ne do not possess (radioactive decay, high sensitivity to mineral composition and significant contributions from production reactions other than spallation). All ratios overlap within error over the entire transect, and altitudinal variation in relative production rates is not therefore evident. This suggests that nuclide-specific scaling factors are not required for the studied nuclides at this low-latitude location. However, because previous studies have documented anomalous altitude-dependent variations in ³He production at mid-latitude sites, the effect of latitude on cross-calibrations should be further evaluated.We determined cosmogenic ²¹Ne/³He concentration ratios of 0.1864 ± 0.0085 in pyroxenes and 0.377 ± 0.018 in olivines, agreeing with those reported in previous studies.Despite the absence of independently determined ages for the studied lava surfaces, the consistency in the dataset should enable progress to be made in the determination of the production rates of all three nuclides as soon as the production rate of one of the nuclides has been accurately defined.To our knowledge this is the first time that ³⁶Cl has been measured in pyroxene. The Cl extraction method was validated by measuring ³⁶Cl in co-existing plagioclase phenocrysts in one of the samples.  相似文献   

Road density as a proxy for population density in regional-scale risk modeling     

Pete Quinn 《Natural Hazards》2013,65(3):1227-1248

This paper examines the use of road network data as a proxy for interpreting population density, which is of use in regional-scale qualitative risk assessment for natural hazards. Comparison of available road network and population data at various scales in Ontario and Quebec yields a best-fit relationship of D _P  = 28 D _R ² . Analysis of available high-resolution topographic data for the Caribbean island nation of Saint Lucia suggests similar power law trends, with expected population density in Saint Lucia roughly half that of Canada for the same road density. Together, these findings suggest that D _P  ~ 10–30 D _R ² may represent a useful range broadly applicable for a wide variety of geographic, climactic and socioeconomic settings. The Canadian relationship has been used to generate a population density model for the lowlands of eastern Ontario and southern Quebec, and this model has been compared with the spatial distribution of seismic hazard to develop a qualitative seismic risk map. The seismic risk map, presented primarily for illustrative purposes, shows elevated seismic risk in urban centers in the study area, and along a predominantly rural area east of Quebec City on both shores of the Saint Lawrence River.  相似文献   

The protection of Antarctic terrestrial ecosystems from inter- and intra-continental transfer of non-indigenous species by human activities: A review of current systems and practices     

Kevin A. Hughes  Pete Convey 《Global Environmental Change》2010,20(1):96-112

Invasions by non-indigenous species are amongst the greatest threats to global biodiversity, causing substantial disruption to, and sometimes local extinction of, individual species and community assemblages which, in turn, can affect ecosystem structure and function. The terrestrial environment of Antarctica consists of many isolated ‘islands’ of ice-free ground. Prolonged isolation makes Antarctic biodiversity vulnerable to human-mediated impacts, in particular (1) the introduction of non-indigenous species from outside Antarctica, and (2) the redistribution of indigenous Antarctic species between biologically distinct areas within the continent. The Protocol on Environmental Protection to the Antarctic Treaty, the primary instrument through which environmental management is addressed within the Antarctic Treaty System, says little about unintentional introduction of non-indigenous species to Antarctica, and nothing specifically about human-mediated transfer of native species from one area to another. We review the effectiveness of the Antarctic protected area system, the primary means through which area-specific environmental protection is achieved under the Antarctic Treaty System. This reveals that the measures described in most Antarctic Specially Protected Area (ASPA) and Antarctic Specially Managed Area (ASMA) Management Plans, by themselves, may not be sufficient to (1) minimise the possibility of introduction of plants, animals and microbes not native to the protected area or (2) adequately protect the many unusual assemblages of species, type localities or only known habitats of certain species found in Antarctica. We discuss issues that should be considered in the development of a more effective system, including the implementation of appropriate biosecurity measures across different spatial scales and applied to different biological groups.  相似文献   

Low solubility of He and Ar in carbonatitic liquids: Implications for decoupling noble gas and lithophile isotope systems     

Pete Burnard  Michael J. Toplis 《Geochimica et cosmochimica acta》2010,74(5):1672-236

In order to asses the importance of carbonatitic liquids in transporting noble gases in the mantle, the solubilities of He and Ar in carbonatitic liquids were estimated from analyses of calcium-potassium carbonate glasses that had been synthesized at 1 bar and temperatures between 850 and 950 °C under He or Ar enriched atmospheres. Despite poor reproducibility related to difficulties synthesizing carbonatite glass, we have been able to estimate He and Ar solubilities in carbonatite liquids to be 1 × 10⁻⁸ and 2 × 10⁻⁹ mol g⁻¹ at 1 bar respectively (with ?50% uncertainty). Despite the significant uncertainties on these estimates, it is clear that the noble gases are not massively soluble in carbonatite liquids (within error, these solubilities are identical to their equivalent solubilities in tholeiitic melts). Assuming the results of these low pressure experiments can be applied to mantle conditions, it seems unlikely that carbonatite metasomatism per se transports noble gases within the mantle. It is nevertheless possible that partitioning of lithophile trace elements (including the important radioelements, U, K and Th) and noble gases between a carbonatitic melt and a silicate melt could effectively decouple lithophile and noble gas isotope systematics because the carbonatitic melt expressedly does not transport noble gases, yet is known to efficiently transport incompatible trace elements.  相似文献