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411.
Marghaleray Amini Anton Eisenhauer Florian Böhm Chris Holmden Katharina Kreissig Folkmar Hauff Klaus Peter Jochum 《Geostandards and Geoanalytical Research》2009,33(2):231-247
We report δ44/40Ca(SRM 915a) values for eight fused MPI‐DING glasses and the respective original powders, six USGS igneous rock reference materials, the U‐Th disequilibria reference material TML, IAEA‐CO1 (Carrara marble) and several igneous rocks (komatiites and carbonatites). Sample selection was guided by three considerations: (1) to address the need for information values on reference materials that are widely available in support of interlaboratory comparison studies; (2) support the development of in situ laser ablation and ion microprobe techniques, which require isotopically homogenous reference samples for ablation; and (3) provide Ca isotope values on a wider range of igneous and metamorphic rock types than is currently available in the scientific literature. Calcium isotope ratios were measured by thermal ionisation mass spectrometry in two laboratories (IFM‐GEOMAR and Saskatchewan Isotope Laboratory) using 43Ca/48Ca‐ and 42Ca/43Ca‐double spike techniques and reported relative to the calcium carbonate reference material NIST SRM 915a. The measurement uncertainty in both laboratories was better than 0.2‰ at the 95% confidence level. The impact of different preparation methods on the δ44/40Ca(SRM 915a) values was found to be negligible. Except for ML3‐B, the original powders and the respective MPI‐DING glasses showed identical δ44/40Ca(SRM 915a) values; therefore, possible variations in the Ca isotope compositions resulting from the fusion process are excluded. Individual analyses of different glass fragments indicated that the glasses are well homogenised on the mm scale with respect to Ca. The range of δ44/40Ca(SRM 915a) values in the igneous rocks studied was larger than previously observed, mostly owing to the inclusion of ultramafic rocks from ophiolite sections. In particular, the dunite DTS‐1 (1.49 ± 0.06‰) and the peridotite PCC‐1 (1.14 ± 0.07‰) are enriched in 44Ca relative to volcanic rocks (0.8 ± 0.1‰). The Carrara marble (1.32 ± 0.06‰) was also found to be enriched in 44Ca relative to the values of assumed precursor carbonates (< 0.8‰). These findings suggest that the isotopes of Ca are susceptible to fractionation at high temperatures by, as yet, unidentified igneous and metamorphic processes. 相似文献
412.
Friedrich Lucassen Sven Lewerenz Gerhard Franz José Viramonte Klaus Mezger 《Contributions to Mineralogy and Petrology》1999,134(4):325-341
Crustal xenoliths from basanitic dikes and necks that intruded into continental sediments of the Cretaceous Salta Rift at
Quebrada de Las Conchas, Provincia Salta, Argentina were investigated to get information about the age and the chemical composition
of the lower crust. Most of the xenoliths have a granitoid composition with quartz-plagioclase-garnet-rutile ± K-feldspar
as major minerals. The exceedingly rare mafic xenoliths consist of plagioclase-clinopyroxene-garnet ± hornblende. All xenoliths
show a well equilibrated granoblastic fabric and the minerals are compositionally unzoned. Thermobarometric calculations indicate
equilibration of the mafic xenoliths in the granulite facies at temperatures of ca. 900 °C and pressures of ca. 10 kbar. The
Sm-Nd mineral isochron ages are 95.1 ± 10.4 Ma, 91.5 ± 13.0 Ma, 89.0 ± 4.2 Ma (granitoid xenoliths), and 110.7 ± 23.6 Ma (mafic
xenolith). These ages are in agreement with the age of basanitic volcanism (ca. 130–100 and 80–75 Ma) and are interpreted
as minimum ages of metamorphism. Lower crustal temperature at the time given by the isochrons was above the closure temperature
of the Sm-Nd system (>600–700 °C). The Sm-Nd and Rb-Sr isotopic signatures (147Sm/144Nd = 0.1225–0.1608; 143Nd/144Ndt
0 = 0.512000–0.512324; 87Rb/86Sr = 0.099–0.172; 87Sr/86Srt
0 = 0.708188–0.7143161) and common lead isotopic signatures (206Pb/204Pb = 18.43–18.48; 207Pb/204Pb = 15.62–15.70; 208Pb/204Pb = 38.22 –38.97) of the granitoid xenoliths are indistinguishable from the isotopic composition of the Early Paleozoic metamorphic
basement from NW Argentina, apart from the lower 208Pb/204Pb ratio of the basement. The Sm-Nd depleted mantle model ages of ca. 1.8 Ga from granitoid xenoliths and Early Paleozoic
basement point to a similar Proterozoic protolith. Time constraints, the well equilibrated granulite fabric, P-T conditions and lack of chemical zoning of minerals point to a high temperature in a crust of nearly normal thickness at ca.
90 Ma and to a prominent thermal anomaly in the lithosphere. The composition of the xenoliths is similar to the composition
of the Early Paleozoic basement in the Andes of NW Argentina and northern Chile. A thick mafic lower crust seems unlikely
considering low abundance of mafic xenoliths and the predominance of granitoid xenoliths.
Received: 21 July 1998 / Accepted: 27 October 1998 相似文献
413.
Ewa Słaby Michał Śmigielski Tomasz Śmigielski Andrzej Domonik Klaus Simon Andreas Kronz 《Contributions to Mineralogy and Petrology》2011,162(5):909-927
As has been demonstrated in recent years, the heterogeneities of coeval magmas can be more successfully revealed by zoned
megacrysts rather than by analysis of the whole rocks hosting them. Here, the geochemical heterogeneities of feldspar megacrysts
from the Karkonosze granite, Poland, are investigated by LA-ICP-MS. The crystals are the product of migration and growth in
regions of poorly mixed magmas. 3D-modeling of the Ba, Sr, and Rb distributions emphasizes the importance of micro-domain
growth morphologies. Two models of element behavior—a relative concentration model and a composition gradient model—provide
a potentially effective tool for tracking the mixing process on a microscale. Measured concentrations of elements of different
mobilities do not agree with what might be expected from the mixing of two end-member magmas. If mixing was the only process
occurring, linear correlations between the concentrations of any two elements should be observed; this, however, is not the
case. For combinations of any two of the three elements, modeling reveals differing non-linear correlations between concentrations.
The megacryst heterogeneities provide an insight into how mixing magmas are chaotically advected to growing crystals and the
degree of inter-magma element exchange between the magmas. 相似文献
414.
Michels Klaus H. Rogenhagen Johannes Kuhn Gerhard 《Marine Geophysical Researches》2001,22(5-6):465-485
Sedimentary processes and structures across the continental rise in the western Weddell Sea have been investigated using sediment acoustic and multichannel seismic data, integrated with multibeam depth sounding and core investigations. The results show that a network of channels with associated along-channel ridges covers the upper continental slope. The seismic profiles reveal that the channels initially developed as erosive turbidite channels with associated levees on their northern side due to Coriolis force. Later they were partly or fully infilled, probably as a result of decreasing turbidite activity. Now the larger ones exist as erosive turbidite channels of reduced size, whereas the smaller ones are non-erosive channels, their shape being maintained by contour current activity. Drift bodies only developed where slumps caused a distinctive break in slope inclination on the upper continental rise, which served to initiate the growth of a drift body fed by contour currents or by the combined action of turbidites and contourites. The history of sedimentation can be reconstructed tentatively by correlation of seismo-stratigraphic units with the stages of evolution of the drifts on the western side of the Antarctic Peninsula. Three stages can be distinguished in the western Weddell Sea after a pre-drift stage, which is delimited by an erosional unconformity at the top: (1) a growth stage, dominated by turbidites, with occasional occurrence of slumps during its initial phase; (2) during a maintenance stage turbiditiy-current intensity (and presumably sedimentation rate also) decreased, probably as a result of the ice masses retreating from the shelf edge, and sedimentation became increasingly dominated by contour current activity; and (3) a phase of sheeted-sequence formation. A southward decrease in sediment thickness shows that the Larsen Ice Shelf plays an important role in sediment delivery to the western Weddell Sea. This study shows that the western Weddell Sea has some characteristics in common with the southern as well as the northwestern Weddell Sea: contour currents off the Larsen Ice Shelf have been present for a long time, probably since the late Miocene, but during times of high sediment input from the shelves as a result of advancing ice masses a channel-levee system developed and dominated over the contour-current transport of sediment. At times of relatively low sediment input the contour-current transport dominated, leading to the formation of drift deposits on the upper continental rise. Seaward of areas without shelf ice masses the continental rise mainly shows a rough topography with small channels and underdeveloped levees. The results demonstrate that sediment supply is an important, maybe the controlling factor of drift development on the Antarctic continental rise. 相似文献
415.
416.
Previous field and laboratory studies showed that organically bound nutrients can contribute largely to the export of N, P, and S from soil into aquatic systems. One possible determinant for the losses of dissolved organic nutrients leaving the soil environment could be their distribution between dissolved organic matter (DOM) fractions of different mobility in soil. To elucidate the potential influence of DOM fractions under varying flow conditions on the vertical translocation of organically bound nutrients, we determined the concentrations and fluxes of dissolved organic C (DOC) and nutrients (DON, DOP, DOS) in soil water under a Scots pine (Pinus sylvestris L.) and a European beech (Fagus sylvatica L.) forest. We sampled seepage water from the organic forest floor layer and the mineral subsoil using zero‐tension lysimeters and soil pore water using tension lysimeters and suction cups. DOM in soil water was fractionated into hydrophilic and hydrophobic compounds by XAD‐8 at pH 2. We found that the organic forest floor layers were large sources for DOC, DON, DOP, and DOS. The dissolved organic nutrients were mainly concentrated in the hydrophilic DOM fraction which proved to be more mobile in mineral soil pore water than the hydrophobic one. Consequently, the concentrations and fluxes of dissolved organic nutrients decreased less with depth than those of DOC. Concentrations as well as fluxes in subsoil pore water of DOC and dissolved organic nutrients in the studied weakly developed soils were high as compared with literature data on deeply developed forest soils. Under conditions of rapid water flow through the strongly structured mineral soil at the beech site, almost no retention of DOM took place and thus the influence of the distribution of organically bound nutrients between the DOM fractions on the export of DON, DOP, and DOS was negligible. 相似文献
417.
The surface nuclear magnetic resonance (SNMR) method has been tested at a site in Haldensleben, northern Germany, to assess the suitability of this new method for groundwater exploration and environmental investigations. More information is obtained by SNMR, particularly with respect to aquifer parameters, than with other geophysical techniques. SNMR measurements were carried out at three borehole locations, together with 2D and 1D direct current geoelectrics, as well as ground-penetrating radar, and well logging (induction log, gamma-ray log and pulsed neutron-gamma log). Permeabilities were calculated from the grain-size distributions of core material determined in the laboratory. It is demonstrated that the SNMR method is able to detect groundwater and the results are in good agreement with other geophysical and hydrogeological data. Using the SNMR method, the water content of the unsaturated and saturated zones (i.e. porosity of an aquifer) can be reliably determined. This information and resistivity data permit in situ determination of other aquifer parameters. Comparison of the SNMR results with borehole data clearly shows that the water content determined by SNMR is the free or mobile water in the pores. The permeabilities estimated from the SNMR decay times are similar to those derived from sieve analysis of core material. Thus, the combination of SNMR with geoelectric methods promises to be a powerful tool for studying aquifer properties. 相似文献
418.
Matthew Coggon Caryl Ann Becerra Klaus Nüsslein Karen Miller Richard Yuretich Sarina J. Ergas 《Geochimica et cosmochimica acta》2012
Biological reduction of iron-sulfate minerals, such as jarosite, has the potential to contribute to the natural attenuation of acid mine drainage (AMD) sites. Previous studies of AMD attenuation at Davis Mine, an abandoned pyrite mine in Rowe Massachusetts, provided evidence of iron and sulfate reduction by indigenous bacteria. Jarosite is a large component of the sediment at Davis Mine and may play a role in AMD attenuation. In this study, microcosms were constructed with groundwater and sediment from Davis Mine and amended with glycerol, nitrogen and phosphorus (GNP) and naturally formed natrojarosite. Over time, higher total iron, sulfate, pH and sodium concentrations and lower oxidation–reduction potentials were observed in microcosms amended with GNP and jarosite, compared with unamended microcosms and killed controls. Geochemical modeling predicted jarosite precipitation under microcosm conditions, suggesting that abiotic processes were unlikely contributors to jarosite dissolution. SEM imaging at the jarosite surface showed microbial attachment. Microbial community composition analysis revealed a shift to higher populations of Clostridia, which are known to reduce both iron and sulfate. The results show that jarosite may be utilized as an electron acceptor by iron and/or sulfate reducing bacteria at Davis Mine and its presence may aid in the attenuation of AMD. 相似文献
419.
Kimmo?T.?TolonenEmail author Klaus?P.?Brodersen Tanya?A.?Kleisborg Kerstin?Holmgren Magnus?Dahlberg Ladislav?Hamerlik Heikki?H?m?l?inen 《Journal of Paleolimnology》2012,47(4):531-547
We sampled living and subfossil phantom midge (Diptera: Chaoboridae) larvae from surface sediments of 21 small lakes in Southern
Sweden to examine the influence of fish and selected abiotic variables on the abundance and species composition of chaoborid
assemblages. We expected total Chaoborus abundance to be inversely correlated with fish abundance and Chaoborus species most sensitive to fish predation to be found only in fishless lakes. We aimed to use the observed relationships to
develop models to reconstruct past fish abundances from chaoborid remains and the abiotic environment. C. flavicans occurred in almost every lake, whereas subfossil C. obscuripes were found in the surface sediments of only one fishless lake. The density of living C. flavicans larvae correlated negatively with fish abundance, lake order and size. The concentration of C. flavicans subfossils was negatively associated with pH, lake size, water transparency and fish abundance. Regression models that included
lake morphometry and landscape position as additional predictors of fish abundance performed better than models that used
only Chaoborus predictors. The explained variance in fish abundance varied from 52 to 86%. Leave-one-out cross-validation indicated moderate
performance of the two best models. These models explained 51 and 56% of the observed untransformed fish density and biomass,
respectively. In addition, all Chaoborus models were unbiased in closely following the 1:1 reference line in plots of observed versus predicted values. These results
are a promising step in developing midge-based paleolimnological reconstructions of past fish abundance, and the approach
might be improved by including chironomid remains in the models. 相似文献
420.
Soil moisture from operational meteorological satellites 总被引:2,自引:0,他引:2
Wolfgang Wagner Vahid Naeimi Klaus Scipal Richard de Jeu José Martínez-Fernández 《Hydrogeology Journal》2007,15(1):121-131
In recent years, unforeseen advances in monitoring soil moisture from operational satellite platforms have been made, mainly due to improved geophysical retrieval methods. In this study, four recently published soil-moisture datasets are compared with in-situ observations from the REMEDHUS monitoring network located in the semi-arid part of the Duero basin in Spain. The remotely sensed soil-moisture products are retrieved from (1) the Advanced Microwave Scanning Radiometer (AMSR-E), which is a passive microwave sensor on-board NASA’s Aqua satellite, (2) European Remote Sensing satellite (ERS) scatterometer, which is an active microwave sensor on-board the two ERS satellites and (3) visible and thermal images from the METEOSAT satellite. Statistical analysis indicates that three satellite datasets contribute effectively to the monitoring of trends in surface soil-moisture conditions, but not to the estimation of absolute soil-moisture values. These sensors, or rather their successors, will be flown on operational meteorological satellites in the near future. With further improvements in processing techniques, operational meteorological satellites will increasingly deliver high-quality soil-moisture data. This may be of particular interest for hydrogeological studies that investigate long-term processes such as groundwater recharge. 相似文献