Rare earth element variations resulting from inversion of pigeonite and subsolidus reequilibration in lunar ferroan anorthosites   总被引：1，自引：0，他引：1  

Odette B. James  Christine FlossJames J. McGee 《Geochimica et cosmochimica acta》2002,66(7):1269-1284

We present results of a secondary ion mass spectrometry study of the rare earth elements (REEs) in the minerals of two samples of lunar ferroan anorthosite, and the results are applicable to studies of REEs in all igneous rocks, no matter what their planet of origin. Our pyroxene analyses are used to determine solid-solid REE distribution coefficients (D = C_REE in low-Ca pyroxene/C_REE in augite) in orthopyroxene-augite pairs derived by inversion of pigeonite. Our data and predictions from crystal-chemical considerations indicate that as primary pigeonite inverts to orthopyroxene plus augite and subsolidus reequilibration proceeds, the solid-solid Ds for orthopyroxene-augite pairs progressively decrease for all REEs; the decrease is greatest for the LREEs. The REE pattern of solid-solid Ds for inversion-derived pyroxene pairs is close to a straight line for Sm-Lu and turns upward for REEs lighter than Sm; the shape of this pattern is predicted by the shapes of the REE patterns for the individual minerals.Equilibrium liquids calculated for one sample from the compositions of primary phases, using measured or experimentally determined solid-liquid Ds, have chondrite-normalized REE patterns that are very slightly enriched in LREEs. The plagioclase equilibrium liquid is overall less rich in REEs than pyroxene equilibrium liquids, and the discrepancy probably arises because the calculated plagioclase equilibrium liquid represents a liquid earlier in the fractionation sequence than the pyroxene equilibrium liquids. “Equilibrium” liquids calculated from the compositions of inversion-derived pyroxenes or orthopyroxene derived by reaction of olivine are LREE depleted (in some cases substantially) in comparison with equilibrium liquids calculated from the compositions of primary phases. These discrepancies arise because the inversion-derived and reaction-derived pyroxenes did not crystallize directly from liquid, and the use of solid-liquid Ds is inappropriate. The LREE depletion of the calculated liquids is a relic of formation of these phases from primary LREE-depleted minerals. Thus, if one attempts to calculate the compositions of equilibrium liquids from pyroxene compositions, it is important to establish that the pyroxenes are primary. In addition, our data suggest that experimental studies have underestimated solid-liquid Ds for REEs in pigeonite and that REE contents of liquids calculated using these Ds are overestimates.Our results have implications for Sm-Nd age studies. Our work shows that if pigeonite inversion and/or subsolidus reequilibration between augite and orthopyroxene occurred significantly after crystallization, and if pyroxene separates isolated for Sm-Nd studies do not have the bulk composition of the primary pyroxenes, then the Sm-Nd isochron age and ε_Nd will be in error.  相似文献   

Community Stories: Explaining Resistance to Street Tree-Planting Programs in Detroit,Michigan, USA     

Christine E. Carmichael  Maureen H. McDonough 《社会与自然资源》2019,32(5):588-605

Non-profit organizations are key actors in urban and community forestry (UCF) initiatives, and sometimes city residents resist their efforts. Between 2011-2014, 24 percent of residents offered a street tree in Detroit, Michigan, USA submitted a “no-tree request.” Differing views on decision-making emerged as a main reason for resistance to tree planting. This study used interviews with city residents, and those within a non-profit organization, between 2014-2016 to understand reasons for conflict over decision-making between these groups. Heritage narratives, or selective representations of the city’s history and character, helped explain conflict over tree planting. Residents who wanted greater decision-making power in tree planting assumed they would be responsible for stewardship, reflecting their historical experiences within the city. The organization’s dominant heritage narrative emphasized that residents held misperceptions of trees based on negative past experiences, and required education on benefits of trees. Recommendations for integrating heritage narratives into UCF efforts are provided.  相似文献   

Teaching Geographical Information Handling Skills for Lower-income Countries   总被引：1，自引：0，他引：1  

Christine E. Dunne  Peter J. Atkins  Michael J. Blakemore  & Janet G. Townsend 《Transactions in GIS》1999,3(4):319-332

Geographical Information Systems are seen by many as a quick 'fix' for the problems of lower-income countries and people in those countries have been encouraged to adopt this perception, along with the technology. As teachers of students from LICs, we seek to avoid reproducing a contextless transfer of technical skills and rather aim to promote an education based on the limitations of the technology and on the nature and construction of information. While identifying GIS as one of many components of 'geographical information', we emphasise the importance of including 'non-GIS' staff in the education process. We advocate a 'problem-posing' approach to the teaching of 'Geographical Information for Development' and discuss some of the challenges which this raises, both for teachers and students.  相似文献   

A comparative electron microprobe study of “Aeginetan” wares with potential raw material sources from Aegina,Methana, and Poros,Greece     

Michael J. Dorais  Christine M. Shriner 《Geoarchaeology》2002,17(6):555-577

Qualitative stylistic evidence from ceramic vessels and limited petrographic analysis suggested that a distinctive group of ceramics with visible inclusions of biotite (Gold Mica Fabric) was produced on the island of Aegina, Greece, during the Middle Helladic and Late Helladic I periods. To quantitatively evaluate this provenance, we sampled all potential source rocks on Aegina, Methana, and Poros. Electron microprobe analysis of amphibole in these samples revealed that each of these volcanic centers has its own unique mineralogical signature. Comparative analyses of amphibole in Zerner's original stylistic “Gold Mica Fabric” type sample with the reference samples reveal that two sherds are Aeginetan. Three additional sherds from this sample may have a non‐Aeginetan provenance, probably from a back‐arc setting outside the Saronic Gulf. These results suggest that the hypothesis of a single source production site for Aeginetan Ware should be reexamined. © 2002 Wiley Periodicals, Inc.  相似文献   

Mineral fibres and environmental monitoring:A comparison of different analytical strategies in New Caledonia     

Jasmine Rita Petriglieri  Christine Laporte-Magoni  Peggy Gunkel-Grillon  Mario Tribaudino  Danilo Bersani  Orietta Sala  Monika Le Mestre  Ruggero Vigliaturo  Nicola Bursi Gandolfi  Emma Salvioli-Mariani 《地学前缘(英文版)》2020,11(1):189-202

Covered by ultrabasic units for more than a third of its surface,the New Caledonia(South West Pacific)is one of the largest world producers of Ni-ore from lateritic deposits.Almost all outcrops of geological units and open mines contain serpentine and amphibole,also as asbestos varieties.In this geological context,in which weathering processes had a great contribution in the production and dispersion of mineral fibres into the environment,the development of a routinely analytical strategy,able to discriminate an asbestiform fibre from a non-harmful particle,is a pivotal requisite.However,the acquisition of all these parameters is necessary for determining the risk associated to fibres exposition.A multidisciplinary routinely approach,based on the use of complementary simply-to-use but reliable analytical methods is the only possible strategy.In addition,the instrumental apparatus must be easily transportable on the field,directly on the mining site.The employment of specialized tools such as Polarized Light Microscopy associated to Dispersion Staining method(PLM/DS)and portable Raman spectroscopy for identification of environmental asbestos,are proved extremely effective in the improvement of the performance and rapidity of data acquisition and interpretation.Both PLM/DS and handheld Raman devices confirmed to be discriminant in the detection and characterization of asbestos fibres for both serpentine and amphibole.Furthermore,these techniques proved extremely effective even in the presence of strongly fibrous and altered samples.  相似文献   

FIB‐TEM analysis of cometary material in 10 Stardust foil craters     

Brendan A. Haas  Christine Floss  Rhonda M. Stroud  Ryan C. Ogliore 《Meteoritics & planetary science》2020,55(6):1349-1370

Aluminum foils from the Stardust cometary dust collector contain impact craters formed during the spacecraft's encounter with comet 81P/Wild 2 and retain residues that are among the few unambiguously cometary samples available for laboratory study. Our study investigates four micron‐scale (1.8–5.2 μm) and six submicron (220–380 nm) diameter craters to better characterize the fine (<1 μm) component of comet Wild 2. We perform initial crater identification with scanning electron microscopy, prepare the samples for further analysis with a focused ion beam, and analyze the cross sections of the impact craters with transmission electron microscopy (TEM). All of the craters are dominated by combinations of silicate and iron sulfide residues. Two micron‐scale craters had subregions that are consistent with spinel and taenite impactors, indicating that the micron‐scale craters have a refractory component. Four submicron craters contained amorphous residue layers composed of silicate and sulfide impactors. The lack of refractory materials in the submicron craters suggests that refractory material abundances may differentiate Wild 2 dust on the scale of several hundred nanometers from larger particles on the scale of a micron. The submicron craters are enriched in moderately volatile elements (S, Zn) when normalized to Si and CI chondrite abundances, suggesting that, if these craters are representative of the Wild 2 fine component, the Wild 2 fines were not formed by high‐temperature condensation. This distinguishes the comet's fine component from the large terminal particles in Stardust aerogel tracks which mostly formed in high‐temperature events.  相似文献   

Selective uptake of prokaryotic picoplankton by a marine sponge (Callyspongia sp.) within an oligotrophic coastal system     

Christine E. Hanson  M. James McLaughlin  Glenn A. Hyndes  Joanna Strzelecki 《Estuarine, Coastal and Shelf Science》2009

Marine sponges are key players in the transfer of carbon from the pelagic microbial food web into the benthos. Selective uptake of prokaryotic picoplankton (<2 μm) by a demosponge (Callyspongia sp.), and carbon flux through this process, were examined for the first time in the oligotrophic coastal waters of southwestern Australia, where sponge abundance and biodiversity ranks among the highest in the world. Water sampling and flow rate measurements were conducted over five sampling occasions following the InEx method of Yahel et al. (2005), with heterotrophic bacteria and autotrophic Synechococcus cyanobacteria identified and enumerated by flow cytometry. Callyspongia sp. demonstrated high filtration efficiencies, particularly for high DNA (HDNA) bacteria (up to 85.3% in summer 2008) and Synechococcus (up to 91.1% in autumn 2007), however efficiency varied non-uniformly with time and food type (p < 0.01). Overall filtration efficiency for Synechococcus (86.6 ± 6.3%; mean ± s.d.) was always significantly higher (p < 0.05) than for low DNA (LDNA) bacteria (40 ± 17.2%), except during winter 2007 (p = 0.14) when ambient Synechococcus concentrations were lowest. When compared to ambient abundances of the different food types, Callyspongia sp. exhibited consistently negative selectivity for LDNA bacteria and positive selectivity for Synechococcus, while HDNA bacteria was generally a neutral or positive selection. The total carbon removal rate (sum of all prokaryotic picoplankton cells), calculated on a per unit area basis, varied significantly with time (p < 0.01), with lowest rates recorded during the winter (0.5 ± 0.4–0.6 ± 0.8 mg C m⁻² d⁻¹) and highest values recorded in summer (3.5 ± 1.9 mg C m⁻² d⁻¹). These flux estimates quantify the role of a demosponge species in the ultimate fate of prokaryotic picoplankton within the nearshore food webs of southwestern Australia, and support the conclusion that sponges actively select food particles that optimise their nutritional intake.  相似文献   

Feature reduction using a singular value decomposition for the iterative guided spectral class rejection hybrid classifier     

Rhonda D. Phillips  Layne T. Watson  Randolph H. Wynne  Christine E. Blinn 《ISPRS Journal of Photogrammetry and Remote Sensing》2009,64(1):107-116

Feature reduction in a remote sensing dataset is often desirable to decrease the processing time required to perform a classification and improve overall classification accuracy. This paper introduces a feature reduction method based on the singular value decomposition (SVD). This SVD-based feature reduction method reduces the storage and processing requirements of the SVD by utilizing a training dataset. This feature reduction technique was applied to training data from two multitemporal datasets of Landsat TM/ETM+ imagery acquired over a forested area in Virginia, USA and Rondônia, Brazil. Subsequent parallel iterative guided spectral class rejection (pIGSCR) forest/non-forest classifications were performed to determine the quality of the feature reduction. The classifications of the Virginia data were five times faster using SVD-based feature reduction without affecting the classification accuracy. Feature reduction using the SVD was also compared to feature reduction using principal components analysis (PCA). The highest average accuracies for the Virginia dataset (88.34%) and for the Rondônia dataset (93.31%) were achieved using the SVD. The results presented here indicate that SVD-based feature reduction can produce statistically significantly better classifications than PCA.  相似文献   

Comparison of the performance of flow‐routing algorithms used in GIS‐based hydrologic analysis     

John P. Wilson  Christine S. Lam  Yongxin Deng 《水文研究》2007,21(8):1026-1044

Flow direction and specific catchment area were calculated for different flow‐routing algorithms using TAPES‐G and TauDEM. A fuzzy classification was used along with eight topo–climatic attributes to delineate six landscape classes from a 10‐m USGS DEM. A series of maps and tabular outputs were produced to compare flow‐routing predictions in different parts of the study area in the Santa Monica Mountains of southern California. The matched pair t‐test was used to compare the performance of pairs of specific catchment area grids across six user‐defined fuzzy landscape classes. The results show that (1) the ‘source’ cells predicted with the D∞, DEMON, and FD8 algorithms were confined to hilltops; (2) two single flow‐routing algorithms (Rho8, D8) produced poor results; and (3) the choice of flow‐routing algorithm has potentially important consequences for the calculation of upslope contributing areas, sediment transport capacity, topographic wetness, and several other topographic indices. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   

TECHNIQUES OF CONSTRUCTING REGIONAL INPUT-OUTPUT TABLES: ACHIEVEMENTS     

金玉献  Christine MLeigh 《中国地理科学(英文版)》1992,2(4):337-356

The development of any analytical method should have to experience at least four stages: its initial status, growth, mature and declining. However, although the regional input-output analysis has been widely applied for more than forty years, it is still one of the most important approach in regional economic analysis and forecast at present in the world. This is due to the never ended modifications and its great potentials. In this paper, we review the historical development of the regional input-output analysis.  相似文献