A menagerie of graphite morphologies in the Acapulco meteorite with diverse carbon and nitrogen isotopic signatures: Implications for the evolution history of acapulcoite meteorites     

Ahmed El Goresy  Ernst Zinner  Catherine Caillet 《Geochimica et cosmochimica acta》2005,69(18):4535-4556

Morphologies, petrographic settings and carbon and nitrogen isotopic compositions of graphites in the Acapulco meteorite, the latter determined by secondary ionization mass spectrometry, are reported. Seven different graphite morphologies were recognized, the majority of which occur enclosed exclusively in kamacite. Individual graphite grains also rarely occur in the silicate matrix. Kamacite rims surrounding taenite cores of metal grains are separated from the Ni-rich metal cores by graphite veneers. These graphite veneers impeded or prevented Ni-Fe interdiffusion during cooling. In addition, matrix FeNi metal contains considerable amounts of phosphorous (≈ 700 ppm) and silicon (≈ 300 ppm) (Pack et al., 2005 in preparation) thus indicating that results of laboratory cooling experiments in the Fe-Ni binary system are inapplicable to Acapulco metals. Graphites of different morphologies display a range of carbon and nitrogen isotopic compositions, indicating a diversity of source regions before accretion in the Acapulco parent body. The isotopic compositions point to at least three isotopic reservoirs from which the graphites originated: (1) A reservoir with heavy carbon, represented by graphite in silicates (δ¹³C = 14.3 ± 2.4 ‰ and δ¹⁵N = −103.4 ± 10.9 ‰), (2) A reservoir with isotopically light carbon and nitrogen, characteristic for the metals. Its C- and N-isotopic compositions are probably preserved in the graphite exsolutions that are isotopically light in carbon and lightest in nitrogen (δ¹³C = −17 to −23 ‰ δ¹⁵N = −141 to −159 ‰). (3) A reservoir with an assumed isotopic composition (δ¹³C ∼ −5 ‰; δ¹⁵N ∼ −50 ‰). A detailed three-dimensional tomography in reflected light microscopy of the decorations of metal-troilite spherules in the cores of orthopyroxenes and olivines and metal-troilite veins was conducted to clarify their origin. Metal and troilite veins are present only near the fusion crust. Hence, these veins are not pristine to Acapulco parent body but resulted during passage of Acapulco in Earth’s atmosphere. A thorough search for symplectite-type silicate-troilite liquid quench textures was conducted to determine the extent of closed-system partial silicate melting in Acapulco.Metal-troilite spherules in orthopyroxenes and olivines are not randomly distributed but decorate ferromagnesian silicate restite cores, indicating that the metal-spherule decoration around restite silicates took place in a silicate partial melt. Graphite inclusions in these spherules have C- and N- isotopic compositions (δ¹³C = −2.9 ± 2.5 ‰ and δ¹⁵N = −101.2 ± 32 ‰) close to the average values of graphite in metals and in the silicate matrix, thus strongly suggesting that they originated from a mixture of graphite inclusions in metals and silicate matrix graphite during a closed system crystallization process subsequent to silicate-metal-sulfide partial melting. Troilite-orthopyroxene quench symplectite textures in orthopyroxene rims are clear evidence that silicate-sulfide partial melting took place in Acapulco. Due to petrographic heterogeneity on a centimeter scale, bulk REE abundances of individual samples or of individual minerals provide only limited information and the REE abundances alone are not entirely adequate to unravel the formational processes that prevailed in the acapulcoite-lodranite parent body. The present investigations demonstrate the complexity of the evolutionary stages of acapulcoites from accretion to parent body processes.  相似文献   

Evaluation and validation of landslide-susceptibility maps obtained by a GIS matrix method: examples from the Betic Cordillera (southern Spain)   总被引：3，自引：2，他引：3  

C. Irigaray  T. Fernández  R. El Hamdouni  J. Chacón 《Natural Hazards》2007,41(1):61-79

This work presents the results of applying the matrix method in a Geographic Information System (GIS) to the drawing of maps of susceptibility to slope movements in different sectors of the Betic Cordillera (southern Spain). In addition, the susceptibility models built by the matrix method were compared with a multivariate statistical method, and the first method gave the best results. The susceptibility maps drawn by the GIS matrix method were validated by calculating the coefficients of association with the degree of fit between recent slope movements registered in 1997 and the different levels of susceptibility of previously drawn maps (1995–1996) in different representative zones of the Betic Cordillera (southern Spain). The first sector studied showed excellent degrees of fit, with an error of less than 10% for all the slope failures and 3% when considering only failures of natural origin. In the second sector, the relative errors were less than 5%. In the third sector, the error hardly exceeded 6%. The results are discussed in the different zones and for each type of slope movement. In any case, these results evidence the predictive capacity of susceptibility maps drawn in GIS by the matrix method, for a great number of slope movements.  相似文献   

Potentialité d'utilisation d'argiles marocaines de Jbel Kharrou dans l'industrie céramique     

Nadia El Yakoubi  M&#x;hamed Aberkan  Mohamed Ouadia 《Comptes Rendus Geoscience》2006,338(10):693-702

The Ordovician clays of Jbel Kharrou (Rehamna, Morocco) have been studied for their use in ceramic industry. The realised studies were carried out on two samples B1 and B2, the most representative, taken from a clay dominated formation that outcrops 25 km east of the Skhour Rehamna city. The chemical analyses, mineralogical studies and advanced technological tests undertaken on the two samples indicate that these clays can be considered as non-refractory material, so they can be used to the manufacturing of ceramic products: soil and wall tiles, sanitary, pottery, etc. The tested briquettes, cooked at 1040?°C, remain flat, without deformation or defects; they are of cream white dye. These briquettes show a high mechanical resistance to the flexion, the loss in weight remains tolerable with cooking, lightly elevated (12% ); it can be corrected by the addition of a grease-remover. To cite this article: N. El Yakoubi et al., C. R. Geoscience 338 (2006).  相似文献   

Expérimentation et modélisation de la lixiviation de l'azote nitrique dans un sol sableux     

M&#x;hammed Ibnoussina  Mohamed El Haroui  Abdellatif Maslouhi 《Comptes Rendus Geoscience》2006,338(11):787-794

We performed two column experiments to study the impact of different levels of irrigation intensity on the leaching of nitric nitrogen. The experiment was run on a soil packed column and using 200 kg?N/ha as fertilization rate for the first column, and none for the second. In parallel, we carried out digital simulations (mechanist model) to study the transfer of nitrogen through the studied columns followed by an application of the model to various amounts of nitrogen. The impact study of successive irrigations showed that these contribute to the transport and the accumulation of nitric nitrogen of the upper layers towards the deeper layers. The quantity of nitric nitrogen N–NO₃ drained by scrubbing was about 191 kg?N/ha for the first column, and 15 kg?N/ha for the second. In addition, the numerical simulations revealed that the precision of the model is satisfactory with an over-estimation of about 20%. To cite this article: M. Ibnoussina et al., C. R. Geoscience 338 (2006).  相似文献   

Artificial neural network application to estimate kinematic soil pile interaction response parameters   总被引：1，自引：0，他引：1  

Irshad Ahmad  M. Hesham El Naggar  Akhtar Naeem Khan   《Soil Dynamics and Earthquake Engineering》2007,27(9):892-905

Six artificial neural network (ANN) models are developed to predict various response parameters of kinematic soil pile interaction. These responses include (1) kinematic response factors for free and fixed head piles in homogenous soil layer to derive foundation input motion (2) normalized bending moment at fixed head of pile in homogenous soil layer (3) normalized kinematic pile moment at the interface of two soil layers of sharply different soil stiffnesses. These ANN models represent simple solutions that can be implemented in a simple calculator capable of matrix operation and bypass the site response analysis and the complex wave diffraction analysis. The data required for ANN training is generated using beam on dynamic Winkler formulation (BDWF). Fifty percent of the data is used to train the ANN models while remaining 50% is used to test the ANN models. The trained ANN models show good agreement with BDWF results.  相似文献   

http://www.sciencedirect.com/science/article/pii/S1674987112001041   总被引：1，自引：0，他引：1  

Andreas Prokoph  Hafida El Bilali  Richard Ernst 《地学前缘(英文版)》2013,4(3):263-276

Large igneous provinces (LIPs) are considered a relevant cause for mass extinctions of marine life throughout Earth’s history. Their flood basalts and associated intrusions can cause significant release of SO₄ and CO₂ and consequently, cause major environmental disruptions. Here, we reconstruct the long-term periodic pattern of LIP emplacement and its impact on ocean chemistry and biodiversity from δ³⁴S_sulfate of the last 520 Ma under particular consideration of the preservation limits of LIP records. A combination of cross-wavelet and other time-series analysis methods has been applied to quantify a potential chain of linkage between LIP emplacement periodicity, geochemical changes and the Phanerozoic marine genera record. We suggest a mantle plume cyclicity represented by LIP volumes (V) of V = ?(350–770) × 10³ km³ sin(2πt/170 Ma) + (300–650) × 10³ km³ sin(2πt/64.5 Ma + 2.3) for t = time in Ma. A shift from the 64.5 Ma to a weaker ～28–35 Ma LIP cyclicity during the Jurassic contributes together with probably independent changes in the marine sulfur cycle to less ocean anoxia, and a general stabilization of ocean chemistry and increasing marine biodiversity throughout the last ～135 Ma. The LIP cycle pattern is coherent with marine biodiversity fluctuations corresponding to a reduction of marine biodiversity of ～120 genera/Ma at ～600 × 10³ km³ LIP eruption volume. The 62–65 Ma LIP cycle pattern as well as excursion in δ³⁴S_sulfate and marine genera reduction suggest a not-yet identified found LIP event at ～440–450 Ma.  相似文献   

Third-order secular Solution of the variational equations of motion of a satellite in orbit around a non-spherical planet     

M. K. Ammar  S. M. El Shaboury  M. R. Amin 《Astrophysics and Space Science》2012,340(1):43-61

We constructed an analytical theory of satellite motion up to the third order relative to the oblateness parameter of the Earth (J ₂). Equations of secular variations was developed for the first three orbital elements (a, e, i) of an artificial satellite. The secular variations are solved in a closed form.  相似文献   

Inverted Barrovian Metamorphic Zones in the Poly-Deformed Domains of the Western Wadi Allaqi Shear Zone (South Eastern Desert,Egypt): Geochemical and Structural Constraints     

Radwan  A.  El Fakharani  A.  Abbas  H.  Younis  M. H.  Emam  A.  Fawzy  Sh. 《Geotectonics》2021,55(1):94-111

Geotectonics - Poly-deformed late-Proterozoic metamorphic domains covering Um Ashira area at the western segment of Wadi Allaqi shear zone, South Eastern Desert of Egypt, show evidences of inverted...  相似文献   

Evaluation of Axial Performance of Hollow Bar Micropiles Constructed with Different Drill Bit to Hollow Bar Diameter Ratio     

Abdlrahem  Maged A.  El Naggar  M. Hesham 《Geotechnical and Geological Engineering》2021,39(5):3669-3688

Geotechnical and Geological Engineering - Hollow bar micropiles (HBMP) have been popular for some time due to their fast installation and efficient load transfer mechanism. In the construction of...  相似文献   

Site response analysis for deep and soft sedimentary deposits of Dhaka City,Bangladesh     

Rahman  Md. Zillur  Siddiqua  Sumi  Kamal  A. S. M. Maksud 《Natural Hazards》2021,106(3):2279-2305

Natural Hazards - The ground motion intensity of an earthquake is significantly changed when seismic waves propagate from the bedrock to the near-surface soft geological materials. The ground where...  相似文献