Chemical alteration and REE mobilization in meteorites from hot and cold deserts     

Ghislaine Crozaz  Christine Floss 《Geochimica et cosmochimica acta》2003,67(24):4727-4741

The effects of terrestrial weathering on REE mobilization are evaluated for a variety of uncommon meteorites found in Antarctica and in hot deserts. The meteorites analyzed include 7 non-cumulate eucrites, 10 shergottites, 3 nakhlites, 2 lunar meteorites, 4 angrites, 10 acapulcoites, 1 winonaite, and 1 brachinite. In-situ concentration measurements of lanthanides and selected other minor and trace elements were made on individual grains by secondary ion mass spectrometry (SIMS). In Antarctic meteorites, oxidation converts Ce³⁺ to Ce⁴⁺, which is less soluble than the trivalent REE, resulting in Ce anomalies. The mineral most affected is low-Ca pyroxene. However, not all grains of a given mineral are, and distinct analyses of a single grain can even yield REE patterns with and without Ce anomalies. The effect is most pronounced for Antarctic eucrites in which Ce anomalies are observed not only in individual minerals but also in whole rock samples. Although Ce anomalies are observed in meteorites from hot deserts as well, the most characteristic signs of chemical alteration in this environment are a LREE enrichment with a typical crustal signature, as well as Sr, Ba and U contaminations. These can modify the whole rock REE patterns and disturb the isotope systematics used to date these objects. The LREE contamination is highly heterogeneous, affecting some grains and not others of a given mineral (mainly olivine and low-Ca pyroxene, the two minerals with the lowest REE concentrations). The major conduit for REE movement is through shock-induced cracks and defects, and the highest levels of contamination are found in altered material filling such veins and cracks. Meteorites that experienced low shock levels and those that are highly recrystallized are the least altered.  相似文献   

Northwest Africa 773: lunar mare breccia with a shallow-formed olivine-cumulate component, inferred very-low-Ti (VLT) heritage, and a KREEP connection     

Bradley L. Jolliff  Randy L. Korotev  Christine Floss 《Geochimica et cosmochimica acta》2003,67(24):4857-4879

Lunar meteorite Northwest Africa 773 (herein referred to as NWA773) is a breccia composed predominantly of mafic volcanic components, including a prominent igneous clast lithology. The clast lithology is an olivine-gabbro cumulate, which, on the basis of mineral and bulk compositions, is a hypabyssal igneous rock related compositionally to volcanic components in the meteorite. The olivine-gabbro lithology exhibits cumulus textures and, in our largest section of it, includes some 48% olivine (Fo₆₄ to Fo₇₀, average Fo₆₇), 27% pigeonite (En₆₀Fs₂₄Wo₁₆ to En₆₇Fs₂₇Wo₆), 11% augite (En₅₀Fs₁₇Wo₃₃ to En₄₇Fs₁₃Wo₄₀), 2% orthopyroxene (En₇₀Fs₂₆Wo₄), 11% plagioclase (An₈₀ to An₉₄), and trace barian K-feldspar, ilmenite, Cr-spinel, RE-merrillite, troilite, and Fe-Ni metal. The Mg/Fe ratios of the mafic silicates indicate equilibration of Fe and Mg; however, the silicates retain compositional variations in minor and trace elements that are consistent with intercumulus crystallization. Accessory mineralogy reflects crystallization of late-stage residual melt. Both lithologies (breccia and olivine cumulate) of the meteorite have very-low-Ti (VLT) major-element compositions, but with an unusual trace-element signature compared to most lunar VLT volcanic compositions, i.e., relative enrichment in light REE and large-ion-lithophile elements, and greater depletion in Eu than almost all other known lunar volcanic rocks. The calculated composition of the melt that was in equilibrium with pyroxene and plagioclase of the cumulate lithology exhibits a KREEP-like REE pattern, but at lower concentrations. Melt of a composition calculated to have been in equilibrium with the cumulate assemblage, plus excess olivine, yields a major-element composition that is similar to known green volcanic glasses. One volcanic glass type from Apollo 14 in particular, green glass B, type 1, has a very low Ti concentration and REE characteristics, including extremely low Eu concentration, that make it a candidate parent melt for the olivine-gabbro cumulate. We infer an origin for the parent melt of NWA773 volcanic components by assimilation of a trace-element-rich partial or residual melt by a magnesian, VLT magma deep in the lunar crust or in the mantle prior to transportation to the near-surface, accumulation of olivine and pyroxene in a shallow chamber, eruption onto a volcanic surface, and incorporation of components into local, predominantly volcanic regolith, prior to impact mixing of the volcanic terrain and related hypabyssal setting, and ejection from the surface of the Moon. Volcanic components such as these probably occur in the Oceanus Procellarum region near the site of origin of the green volcanic glasses found in the Apollo 14 regolith.  相似文献   

MTBE in Drinking Water Production – Occurrence and Efficiency of Treatment Technologies     

Christine Baus  HsuWen Hung  Frank Sacher  Michael Fleig  Heinz‐Jürgen Brauch 《洁净——土壤、空气、水》2005,33(2):118-132

In Germany, the gasoline additive methyl tert‐butyl ether (MTBE) is almost constantly detected in measurable concentrations in surface waters and is not significantly removed during riverbank filtration. The removal of MTBE from water has been the focus of many studies that mostly were performed at high concentration levels and centred in understanding the mechanisms of elimination. In order to assess the performance of conventional and advanced water treatment technologies for MTBE removal in the low concentration range further studies were undertaken. Laboratory experiments included aeration, granulated activated carbon (GAC) adsorption, ozonation and advanced oxidation processes (AOP). The results show that the removal of MTBE by conventional technologies is not easily achieved. MTBE is only removed by aeration at high expense. Ozonation at neutral pH values did not prove to be effective in eliminating MTBE at all. The use of ozone/H₂O₂ (AOP) may lead to a partly elimination of MTBE. However, the ozone/H₂O₂ concentrations required for a complete removal of MTBE from natural waters is much higher than the ozone levels applied nowadays in waterworks. MTBE is only poorly adsorbed on activated carbon, thus GAC filtration is not efficient in eliminating MTBE. A comparison with real‐life data from German waterworks reveals that if MTBE is detected in the raw water it is most often found in the corresponding drinking water as well due to the poor removal efficiency of conventional treatment steps.  相似文献   

Signatures in flowing fluid electric conductivity logs   总被引：1，自引：0，他引：1  

Christine Doughty  Chin-Fu Tsang 《Journal of Hydrology》2005,310(1-4):157-180

Flowing fluid electric conductivity logging provides a means to determine hydrologic properties of fractures, fracture zones, or other permeable layers intersecting a borehole in saturated rock. The method involves analyzing the time-evolution of fluid electric conductivity (FEC) logs obtained while the well is being pumped and yields information on the location, hydraulic transmissivity, and salinity of permeable layers. The original analysis method was restricted to the case in which flows from the permeable layers or fractures were directed into the borehole (inflow). Recently, the method was adapted to permit treatment of both inflow and outflow, including analysis of natural regional flow in the permeable layer. A numerical model simulates flow and transport in the wellbore during flowing FEC logging, and fracture properties are determined by optimizing the match between simulation results and observed FEC logs. This can be a laborious trial-and-error procedure, especially when both inflow and outflow points are present. Improved analyses methods are needed. One possible tactic would be to develop an automated inverse method, but this paper takes a more elementary approach and focuses on identifying the signatures that various inflow and outflow features create in flowing FEC logs. The physical insight obtained provides a basis for more efficient analysis of these logs, both for the present trial and error approach and for a potential future automated inverse approach. Inflow points produce distinctive signatures in the FEC logs themselves, enabling the determination of location, inflow rate, and ion concentration. Identifying outflow locations and flow rates typically requires a more complicated integral method, which is also presented in this paper.  相似文献   

Temporal and spatial cyclicity of accretion at slow-spreading ridges—evidence from the Reykjanes Ridge     

Christine Peirce  Alex Gardiner  Martin Sinha 《Geophysical Journal International》2005,163(1):56-78

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Role of the Kazerun fault system in active deformation of the Zagros fold-and-thrust belt (Iran)     

Christine Authemayou  Olivier Bellier  Dominique Chardon  Zaman Malekzade  Mohammad Abassi 《Comptes Rendus Geoscience》2005,337(5):539-545

Field structural and SPOT image analyses document the kinematic framework enhancing transfer of strike-slip partitioned motion from along the backstop to the interior of the Zagros fold-and-thrust belt in a context of plate convergence slight obliquity. Transfer occurs by slip on the north-trending right-lateral Kazerun Fault System (KFS) that connects to the Main Recent Fault, a major northwest-trending dextral fault partitioning oblique convergence at the rear of the belt. The KFS formed by three fault zones ended by bent orogen-parallel thrusts allows slip from along the Main Recent Fault to become distributed by transfer to longitudinal thrusts and folds. To cite this article: C. Authemayou et al., C. R. Geoscience 337 (2005).  相似文献   

The presolar grain inventory of fine‐grained chondrule rims in the Mighei‐type (CM) chondrites     

Jan Leitner  Knut Metzler  Christian Vollmer  Christine Floss  Pierre Haenecour  Jnos Kodolnyi  Dennis Harries  Peter Hoppe 《Meteoritics & planetary science》2020,55(6):1176-1206

We investigated the inventory of presolar silicate, oxide, and silicon carbide (SiC) grains of fine‐grained chondrule rims in six Mighei‐type (CM) carbonaceous chondrites (Banten, Jbilet Winselwan, Maribo, Murchison, Murray and Yamato 791198), and the CM‐related carbonaceous chondrite Sutter's Mill. Sixteen O‐anomalous grains (nine silicates, six oxides) were detected, corresponding to a combined matrix‐normalized abundance of ~18 ppm, together with 21 presolar SiC grains (~42 ppm). Twelve of the O‐rich grains are enriched in ¹⁷O, and could originate from low‐mass asymptotic giant branch stars. One grain is enriched in ¹⁷O and significantly depleted in ¹⁸O, indicative of additional cool bottom processing or hot bottom burning in its stellar parent, and three grains are of likely core‐collapse supernova origin showing enhanced ¹⁸O/¹⁶O ratios relative to the solar system ratio. We find a presolar silicate/oxide ratio of 1.5, significantly lower than the ratios typically observed for chondritic meteorites. This may indicate a higher degree of aqueous alteration in the studied meteorites, or hint at a heterogeneous distribution of presolar silicates and oxides in the solar nebula. Nevertheless, the low O‐anomalous grain abundance is consistent with aqueous alteration occurring in the protosolar nebula and/or on the respective parent bodies. Six O‐rich presolar grains were studied by Auger Electron Spectroscopy, revealing two Fe‐rich silicates, one forsterite‐like Mg‐rich silicate, two Al‐oxides with spinel‐like compositions, and one Fe‐(Mg‐)oxide. Scanning electron and transmission electron microscopic investigation of a relatively large silicate grain (490 nm × 735 nm) revealed that it was crystalline åkermanite (Ca₂Mg[Si₂O₇]) or a an åkermanite‐diopside (MgCaSi₂O₆) intergrowth.  相似文献   

The role of baseflow in dissolved solids delivery to streams in the Upper Colorado River Basin          下载免费PDF全文

Christine A. Rumsey  Matthew P. Miller  Gregory E. Schwarz  Robert M. Hirsch  David D. Susong 《水文研究》2017,31(26):4705-4718

Salinity has a major effect on water users in the Colorado River Basin, estimated to cause almost $300 million per year in economic damages. The Colorado River Basin Salinity Control Program implements and manages projects to reduce salinity loads, investing millions of dollars per year in irrigation upgrades, canal projects, and other mitigation strategies. To inform and improve mitigation efforts, there is a need to better understand sources of salinity to streams and how salinity has changed over time. This study explores salinity in the baseflow fraction of streamflow, assessing whether groundwater is a significant contributor of dissolved solids to streams in the Upper Colorado River Basin (UCRB). Chemical hydrograph separation was used to estimate baseflow discharge and baseflow dissolved solids loads at stream gages (n = 69) across the UCRB. On average, it is estimated that 89% of dissolved solids loads originate from the baseflow fraction of streamflow, indicating that subsurface transport processes play a dominant role in delivering dissolved solids to streams in the UCRB. A statistical trend analysis using weighted regressions on time, discharge, and season was used to evaluate changes in baseflow dissolved solids loads in streams (n = 27) from 1986 to 2011. Decreasing trends in baseflow dissolved solids loads were observed at 63% of streams. At the three most downstream sites, Green River at Green River, UT, Colorado River at Cisco, UT, and the San Juan River near Bluff, UT, baseflow dissolved solids loads decreased by a combined 823,000 metric tons (mT), which is approximately 69% of projected basin‐scale decreases in total dissolved solids loads as a result of salinity control efforts. Decreasing trends in baseflow dissolved solids loads suggest that salinity mitigation projects, landscape changes, and/or climate are reducing dissolved solids transported to streams through the subsurface. Notably, the pace and extent of decreases in baseflow dissolved solids loads declined during the most recent decade; average decreasing loads during the 2000s (28,200 mT) were only 54% of average decreasing loads in the 1990s (51,700 mT).  相似文献   

Diffusive mass exchange of non‐reactive substances in dual‐porosity porous systems – column experiments under saturated conditions          下载免费PDF全文

Bastian Knorr  Piotr Maloszewski  Florian Krämer  Christine Stumpp 《水文研究》2016,30(6):914-926

Diffusive mass exchange into immobile water regions within heterogeneous porous aquifers influences the fate of solutes. The percentage of immobile water is often unidentified in natural aquifers though. Hence, the mathematical prediction of solute transport in such heterogeneous aquifers remains challenging. The objective of this study was to find a simple analytical model approach that allows quantifying properties of mobile and immobile water regions and the portion of immobile water in a porous system. Therefore, the Single Fissure Dispersion Model (SFDM), which takes into account diffusive mass exchange between mobile and immobile water zones, was applied to model transport in well‐defined saturated dual‐porosity column experiments. Direct and indirect model validation was performed by running experiments at different flow velocities and using conservative tracer with different molecular diffusion coefficients. In another column setup, immobile water regions were randomly distributed to test the model applicability and to determine the portion of immobile water. In all setups, the tracer concentration curves showed differences in normalized maximum peak concentration, tailing and mass recovery according to their diffusion coefficients. These findings were more pronounced at lower flow rates (larger flow times) indicating the dependency of diffusive mass exchange into immobile water regions on tracers' molecular diffusion coefficients. The SFDM simulated all data with high model efficiency. Successful model validation supported the physical meaning of fitted model parameters. This study showed that the SFDM, developed for fissured aquifers, is applicable in porous media and can be used to determine porosity and volume of regions with immobile water. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

Application of an extreme winter storm scenario to identify vulnerabilities,mitigation options,and science needs in the Sierra Nevada mountains,USA     

Christine M. Albano  Michael D. Dettinger  Maureen I. McCarthy  Kevin D. Schaller  Toby L. Welborn  Dale A. Cox 《Natural Hazards》2016,80(2):879-900

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