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971.
《Comptes Rendus Geoscience》2014,346(5-6):130-139
The Earth's core is constituted of iron and nickel alloyed with lighter elements. In view of their affinity with the metallic phase, their relative high abundance in the solar system and their moderate volatility, a list of potential light elements have been established, including sulfur, silicon and oxygen. We will review the effects of these elements on different aspects of Fe–X high pressure phase diagrams under Earth's core conditions, such as melting temperature depression, solid–liquid partitioning during crystallization, and crystalline structure of the solid phases. Once extrapolated to the inner–outer core boundary, these petrological properties can be used to constrain the Earth's core properties. 相似文献
972.
Experimental study of poromechanical behavior of saturated claystone under triaxial compression 总被引:1,自引:1,他引:0
This paper presents experimental results of drained and undrained triaxial compression tests of saturated Meuse–Haute/Marne claystone. The emphasis is to study the evolution of pore pressure with growth of microcracks and the effect of pore pressure on mechanical behavior. Basic mechanical responses are first investigated through drained triaxial compression tests, showing nonlinear stress strain relations, volumetric dilatancy and pressure sensitivity. In undrained triaxial compression tests, the pore pressure exhibits a transition from increase to decrease due to the transition from volumetric compressibility to dilatancy caused by the growth of microcracks. The failure surfaces, determined by total stress and Terzaghi’s effective stress under undrained condition, are compared with the one under drained condition. 相似文献
973.
This study aims to provide knowledge on the thermo-mechanical behaviour of heat exchanger piles, through a laboratory scale model. The model pile (20 mm in external diameter) was embedded in dry sand. The behaviour of the axially loaded pile under thermal cycles was investigated. After applying the axial load on the pile head, the pile temperature was varied between 5 and 30 °C. Seven tests, corresponding to various axial loads ranging from 0 to 70 % of the pile estimated bearing capacity, were performed. The results on pile head displacement show that heating under low axial load induced heave and cooling induced settlement; the pile temperature-displacement curve was found to be reversible and compatible with the thermal expansion curve of the pile. However, at higher axial loads, irreversible settlement of the pile head was observed after a few thermal cycles. The axial load profile measured by the strain gauges evidenced that the pile head load was mainly transferred to the pile toe. Nevertheless, thermal cycles modified significantly the mobilised skin friction along the pile. The total pressure measured at various locations in the soil mass was also slightly influenced by the thermal cycles. 相似文献
974.
Soil treatment with organic non-traditional additives for the improvement of earthworks 总被引:2,自引:0,他引:2
The aim of this study was to characterise the technical and environmental implications of non-traditional treatments of a low-plasticity compacted silt (PI = 14) and to investigate their actions both at the micro- and macro-structural scales. Three non-traditional additives derived from industrial vegetal by-products were studied. These additives are classified as an acid solution, an enzymatic solution (ES) and calcium lignosulfonate (LS). The first step was to characterise the effects of these treatments on Proctor compaction, bearing capacity, unconfined compressive strength and stiffness. The index properties of the treated samples were also measured to assess changes in the interaction between soil minerals and the additives. These experimental results showed that the 0.002 % ES and 2.0 % LS treatments were the most effective at improving the soil dry density and allowing the soil to reach optimum density using 3 % less water or 25 % less compaction energy. In a second step, the mechanisms involved in the treatment were investigated. A microscopic study was conducted including scanning electron microscopy and mercury injection porosity tests; measurements of the surface tension of non-traditional additives mixed with water completed the study and demonstrated that the ES treatment has the same surfactant properties as sodium dodecyl sulphate, a common surfactant. Compaction tests confirmed that the behaviours of the soil after ES and sodium dodecyl sulphate treatments were similar. 相似文献
975.
N. Peyraube R. Lastennet A. Denis P. Malaurent J. D. Villanueva 《Environmental Earth Sciences》2014,72(10):4207-4215
Saturation index with respect to calcite (SIc) and equilibrium CO2 partial pressure are important parameters to study groundwater in limestone aquifers. Aside from their use in time series, CO2 and SIc are used to estimate the baseline of CO2 in the vadose zone. The objective of this paper is to present conceptual examples on the use of the CO2–SIc relationship to have new information from usual parameters. Case study was considered as an example of use from Cussac site, a limestone aquifer in southwest of France. The result showed that CO2 baseline in unsaturated zone is found close to 25,000 ± 1,000 ppm. 相似文献
976.
Nicolas Hawie Remy Deschamps Fadi H. Nader Christian Gorini Carla Müller Delphine Desmares Ahmed Hoteit Didier Granjeon Lucien Montadert François Baudin 《Arabian Journal of Geosciences》2014,7(4):1323-1349
This paper presents an updated review of the Upper Mesozoic and Cenozoic sedimentological and stratigraphic evolution of the Levant margin with a focus on the northern Lebanon. Facies and microfacies analysis of outcrop sections and onshore well cores (i.e., Kousba and Chekka) supported by nannofossil and planktonic foraminifers biostratigraphy, allowed to constrain the depositional environments prevailing in the Turonian to Late Miocene. The “Senonian” (a historical term used to define the Coniacian to Maastrichtian) source rock interval was subdivided into four sub-units with related outer-shelfal facies: (1) Upper Santonian, (2) Lower, (3) Upper Campanian, and (4) Lower Maastrichtian. This Upper Cretaceous rock unit marks the major drowning of the former Turonian rudist platform. This paper confirms the Late Lutetian to Late Burdigalian hiatus, which appears to be a direct consequence of major geodynamic events affecting the Levant region (i.e., the continued collision of Afro-Arabia with Eurasia), potentially enhanced by regressional cycles (e.g., Rupelian lowstand). The distribution of Late Burdigalian–Serravallian rhodalgal banks identified in northern Lebanon was controlled by pre-existing structures inherited from the pulsating onshore deformation. Reef barriers facies occur around the Qalhat anticline, separating an eastern, restricted back-reef setting from a western, coastal to open marine one. The acme of Mount Lebanon’s uplift and exposure is dated back to the Middle–Late Miocene; it led to important erosion of carbonates that were subsequently deposited in paleo-topographic lows. The Late Cretaceous to Cenozoic facies variations and hiatuses show that the northern Lebanon was in a higher structural position compared to the south since at least the Late Cretaceous. 相似文献
977.
《Geoforum》2014
Concerns with the politics and practices of resource rights and access are integral to contemporary debates over environmental justice. Struggles over identity politics, especially the strategic articulation and deployment of particular identities at diverse geographical scales, have recently emerged as important mediators of justice claims in respect of resources rights, but also of recognition and procedural justice. To date, critical, multi-scalar analyses of identity-based claims for environmental justice have focused largely on the indigenous peoples’ movement. In doing so, they have failed to embrace an emergent dimension of identity-based, trans-scalar justice, namely the fledgling global pastoralists’ movement, the empirical focus for this paper. In the early years of the 21st century mobile pastoralists have begun to carve out new global spaces, through which diverse groups have attempted to negotiate common ground and forge common identities in their struggles for justice. In particular, mobile pastoralists have become increasingly visible in conservation politics and contests over land rights as they lay claim to both discursive and material ground as ‘custodians of the commons’ in an era of global climatic change. This paper draws on empirical work amongst pastoralists, NGOs and activists from Kenya, Mongolia and Spain to explore these identities, their implications for resource rights and access and the multi-scalar chains of accountability and legitimacy between global activists and their local constituents. 相似文献
978.
Marc?UlrichEmail author Manuel?Mu?oz Stéphane?Guillot Michel?Cathelineau Christian?Picard Benoit?Quesnel Philippe?Boulvais Clément?Couteau 《Contributions to Mineralogy and Petrology》2014,167(1):952
The weathering of mantle peridotite tectonically exposed to the atmosphere leads commonly to natural carbonation processes. Extensive cryptocrystalline magnesite veins and stock-work are widespread in the serpentinite sole of the New Caledonia ophiolite. Silica is systematically associated with magnesite. It is commonly admitted that Mg and Si are released during the laterization of overlying peridotites. Thus, the occurrence of these veins is generally attributed to a per descensum mechanism that involves the infiltration of meteoric waters enriched in dissolved atmospheric CO2. In this study, we investigate serpentinite carbonation processes, and related silicification, based on a detailed petrographic and crystal chemical study of serpentinites. The relationships between serpentine and alteration products are described using an original method for the analysis of micro-X-ray fluorescence images performed at the centimeter scale. Our investigations highlight a carbonation mechanism, together with precipitation of amorphous silica and sepiolite, based on a dissolution–precipitation process. In contrast with the per descensum Mg/Si-enrichment model that is mainly concentrated in rock fractures, dissolution–precipitation process is much more pervasive. Thus, although the texture of rocks remains relatively preserved, this process extends more widely into the rock and may represent a major part of total carbonation of the ophiolite. 相似文献
979.
Saskia?ErdmannEmail author Caroline?Martel Michel?Pichavant Alexandra?Kushnir 《Contributions to Mineralogy and Petrology》2014,167(6):1016
Amphibole is widely employed to calculate crystallization temperature and pressure, although its potential as a geobarometer has always been debated. Recently, Ridolfi et al. (Contrib Mineral Petrol 160:45–66, 2010) and Ridolfi and Renzulli (Contrib Mineral Petrol 163:877–895, 2012) have presented calibrations for calculating temperature, pressure, fO2, melt H2O, and melt major and minor oxide composition from amphibole with a large compositional range. Using their calibrations, we have (i) calculated crystallization conditions for amphibole from eleven published experimental studies to examine the problems and the potential of the new calibrations; and (ii) calculated crystallization conditions for amphibole from basaltic–andesitic pyroclasts erupted during the paroxysmal 2010 eruption of Mount Merapi in Java, Indonesia, to infer pre-eruptive conditions. Our comparison of experimental and calculated values shows that calculated crystallization temperatures are reasonable estimates. Calculated fO2 and melt SiO2 content yields potentially useful estimates at moderately reduced to moderately oxidized conditions and intermediate to felsic melt compositions. However, calculated crystallization pressure and melt H2O content are untenable estimates that largely reflect compositional variation in the crystallizing magmas and crystallization temperature and not the calculated parameters. Amphibole from Merapi’s pyroclasts yields calculated conditions of ~200–800 MPa, ~900–1,050 °C, ~NNO + 0.3–NNO + 1.1, ~3.7–7.2 wt% melt H2O, and ~58–71 wt% melt SiO2. We interpret the variations in calculated temperature, fO2, and melt SiO2 content as reasonable estimates, but conclude that the large calculated pressure variation for amphibole from Merapi and many other arc volcanoes is evidence for thorough mixing of mafic to felsic magmas and not necessarily evidence for crystallization over a large depth range. In contrast, bimodal pressure estimates obtained for other arc magmas reflect amphibole crystallization from mafic and more evolved magmas, respectively, and should not necessarily be taken as evidence for crystallization in two reservoirs at variable depth. 相似文献
980.
Luc G. Bulot Jean-Louis Latil Alex Hairabian Arnaud Fournillon 《Proceedings of the Geologists' Association. Geologists' Association》2014
Nolaniceras nolani ( Seunes, 1887) has been widely quoted in the Upper Aptian literature over the years. Re-examination of the holotype of the species shows that it has always been misidentified and that this taxon is represented by a single specimen, the holotype, of uncertain age. As a consequence, its use as an index species for the Upper Aptian should be reconsidered and abandoned. 相似文献