时间延迟对劈裂试验条件下岩石凯塞效应的影响   总被引：1，自引：0，他引：1  

谢强  余贤斌 《岩土力学》2010,31(1):46-50

验证了粗晶花岗岩在劈裂试验条件下凯塞效应的存在性。进行了循环加卸载时间间隔分别为2、15d和45d时岩石的声发射试验,讨论了时间延迟对花岗岩凯塞效应的影响。研究结果表明,前期荷载越接近极限强度,岩石的凯塞效应越不明显;凯塞效应随再次加载时间延迟的增加而削弱,在对花岗岩的声发射试验中观察到15d以后岩石的凯塞效应仍然很显著,45d后凯塞效应基本消失。文中同时对试件与加载设备之间的接触状态对声发射试验结果的影响作了初步的定性分析。  相似文献   

Geochemistry and Sm–Nd isotopic systematics of Ediacaran–Ordovician,sedimentary and bimodal igneous rocks in the western Acatlán Complex,southern Mexico: Evidence for rifting on the southern margin of the Rheic Ocean     

Carlos Ortega-Obregon  J. Brendan Murphy  J. Duncan Keppie 《Lithos》2010,114(1-2):155-167

Ordovician igneous rocks in the western Acatlán Complex (Olinalá area) of southern Mexico include a bimodal igneous suite that intrudes quartzites and gneisses of the Zacango Unit, and all these rocks were polydeformed and metamorphosed in the amphibolite facies during the Devono-Carboniferous. The Ordovician igneous rocks consist of the penecontemporaneous amphibolites, megacrystic granitoids and leucogranite, the latter dated at ca. 464 Ma. Geochemical and Sm–Nd data indicate that the amphibolites have a differentiated tholeiitic signature, and that its mafic protoliths formed in an extensional setting transitional between within-plate and ocean floor. The amphibolites are variably contaminated by a Mesoproterozoic crustal source, inferred to be the Oaxacan basement exposed in the adjacent terrane. The most primitive samples have εNdt (t = 465 Ma) values significantly below that of the contemporary depleted mantle and were probably derived from the sub-continental lithospheric mantle. The megacrystic granites were most probably derived by partial melting of an arc crustal source (similar to the Oaxacan Complex) and triggered by the ascent of mafic magma from the lithospheric mantle. Sm–Nd isotopic signatures suggest that metasedimentary rocks from Zacango Unit were derived from adjacent Oaxacan Complex. Trace elements relationships (e.g. La/Th vs. Hf) and REE patterns suggest provenance in felsic-intermediate igneous rocks with a calc-alkaline signature. The Ordovician bimodal magmatism is inferred to have resulted from rifting on the southern flank of the Rheic Ocean and is an expression of a major rifting event that occurred along much of the northern Gondwanan margin in the Ordovician.  相似文献   

The Response of Estuarine Macrobenthic Communities to Natural- and Human-Induced Changes: Dynamics and Ecological Quality     

João Magalhães Neto  Heliana Teixeira  Joana Patrício  Alexandra Baeta  Helena Veríssimo  Rute Pinto  João Carlos Marques 《Estuaries and Coasts》2010,33(6):1327-1339

Anthropogenic activities are a disturbance factor of coastal systems and can be widely recognized as a major threat to the health of coastal systems. However, natural events cannot be disregarded from management issues because of their significant influence on the communities living in these areas. Based on long-term subtidal data from the Mondego Estuary (Portugal), the effects of natural events (e.g., floods and droughts) on macrobenthic communities were compared with the anthropogenic events. Sampling stations were grouped into characteristic zones (mouth, north arm, south arm) so the community dynamics of each of these estuarine areas could be followed over time. Environmental assessment was performed for stations using the Benthic Assessment Tool (BAT), and compared with the existing pressures. Human impacts persist over a number of years and gradually reduce ecosystem health, as discussed in the European Water Framework Directive. Paradoxically, natural events cause stronger impacts but are of a shorter duration, which allows for a faster recovery of macrobenthic communities. The study showed that caution should be taken when developing and implementing water policies so as not to disregard the importance of the different events (natural and human-caused) on the ecosystem health (e.g., community degradation and water quality and ecological quality status assessment).  相似文献   

Uncovering spatiotemporal micromobility patterns through the lens of space–time cubes and GIS tools     

Arias-Molinares  Daniela  García-Palomares  Juan Carlos  Romanillos  Gustavo  Gutiérrez  Javier 《Journal of Geographical Systems》2023,25(3):403-427

Journal of Geographical Systems - In the past ten years, cities have experienced a burst of micromobility services as they offer a flexible transport option that allows users to cover short trips...  相似文献   

Comparison of statistically downscaled precipitation in terms of future climate indices and daily variability for southern Ontario and Quebec,Canada     

Carlos F. Gaitan  William W. Hsieh  Alex J. Cannon 《Climate Dynamics》2014,43(12):3201-3217

Given the coarse resolution of global climate models, downscaling techniques are often needed to generate finer scale projections of variables affected by local-scale processes such as precipitation. However, classical statistical downscaling experiments for future climate rely on the time-invariance assumption as one cannot know the true change in the variable of interest, nor validate the models with data not yet observed. Our experimental setup involves using the Canadian regional climate model (CRCM) outputs as pseudo-observations to estimate model performance in the context of future climate projections by replacing historical and future observations with model simulations from the CRCM, nested within the domain of the Canadian global climate model (CGCM). In particular, we evaluated statistically downscaled daily precipitation time series in terms of the Peirce skill score, mean absolute errors, and climate indices. Specifically, we used a variety of linear and nonlinear methods such as artificial neural networks (ANN), decision trees and ensembles, multiple linear regression, and k-nearest neighbors to generate present and future daily precipitation occurrences and amounts. We obtained the predictors from the CGCM 3.1 20C3M (1971–2000) and A2 (2041–2070) simulations, and precipitation outputs from the CRCM 4.2 (forced with the CGCM 3.1 boundary conditions) as predictands. Overall, ANN models and tree ensembles outscored the linear models and simple nonlinear models in terms of precipitation occurrences, without performance deteriorating in future climate. In contrast, for the precipitation amounts and related climate indices, the performance of downscaling models deteriorated in future climate.  相似文献   

Influence of the spatial resolution of satellite-derived vegetation parameters on the biogenic Volatile Organic Compounds (VOC) emission modeling     

Carlos M. S. Silveira  Oxana A. Tchepel 《Central European Journal of Geosciences》2014,6(1):104-111

Vegetation is a natural source of Volatile Organic Compounds (VOC) that plays an important role in atmospheric chemistry. The main objective of the current study is to implement a model to quantify process-based VOC emissions from plants that focuses on the relationship between the sensitivity of VOC emission estimates to spatial resolution data, based on scientific knowledge and vegetation dynamics derived from satellite observations. The Normalized Difference Vegetation Index (NDVI) and Leaf Area Index (LAI) were elected to examine this issue using different resolutions of satellite-derived products: 22m from the DEIMOS-1 satellite, and 250m and 1000m provided by MODIS. The study is focused on an area of 80×80km² in Portugal for 2011. Detailed land cover and meteorological data are also included in the emission quantification algorithm. The primary outcomes were determined using a multi-scale analysis showing spatial and temporal variations in the vegetation parameters and modeling results. The results confirm that the emissions model is highly sensitive to the spatial resolution of the satellite-derived data, resulting in about a 30% difference in total isoprene emissions for the study area.  相似文献   

Significance of ancient sulfide PGE and Re–Os signatures in the mantle beneath Calatrava,Central Spain     

José María González-Jiménez  Carlos Villaseca  William L. Griffin  Suzanne Y. O’Reilly  Elena Belousova  Eumenio Ancochea  Norman J. Pearson 《Contributions to Mineralogy and Petrology》2014,168(2):1-24

Spinel lherzolite and wehrlite xenoliths from the Cenozoic Calatrava volcanic field carry the geochemical imprint of metasomatic agents that have affected the subcontinental lithospheric mantle beneath Central Iberia. Some xenoliths (mainly wehrlites) were enriched in REE, Sr, P, and CO₂ by silicic-carbonate-rich metasomatic melts/fluids, while others record the effects of subduction-related hydrous silicate fluids that have precipitated amphibole and induced high Ti/Eu in primary clinopyroxene. The petrographic observations and geochemical data suggest that interstitial glass in the xenoliths represent the quenched products of Si-rich melts that infiltrated the mantle peridotite shortly before the entrainment of the xenoliths in the host magmas that erupted ca 2 million years ago. During their infiltration, the metasomatic melts reacted with peridotite, resulting in silica enrichment, while remobilizing grains of iron-rich monosulfide solid solution (Fe-rich Mss) initially enclosed in, or intergranular to, primary olivine and pyroxenes. In situ laser ablation inductively coupled plasma-mass spectrometry analysis of single sulfide grains reveals that the Fe-rich Mss in glass shows platinum-group element (PGE) patterns and ¹⁸⁷Os/¹⁸⁸Os compositions identical to the Fe-rich Mss occurring as inclusions in, or at grain boundaries of primary silicates. Moreover, independent of its microstructural position, Fe-rich Mss exhibits PGE and ¹⁸⁷Os/¹⁸⁸Os signatures typical of Mss either residual after partial melting or crystallized directly from sulfide melts. Our findings reveal that young metasomatic melt(s)/fluid(s) may carry remobilized sulfides with PGE and Os-isotopic signatures identical to those of texturally older sulfides in the peridotite xenolith. These sulfides thus still provide useful information about the timing and nature of older magmatic events in the subcontinental mantle.  相似文献   

A Middle Miocene carbonate embankment on an active volcanic slope: Ilhéu de Baixo,Madeira Archipelago,Eastern Atlantic     

B. Gudveig Baarli  Mrio Cacho  Carlos M. da Silva  Markes E. Johnson  Eduardo J. Mayoral  Ana Santos 《Geological Journal》2014,49(1):90-106

Carbonate factories on insular oceanic islands in active volcanic settings are poorly explored. This case study illuminates marginal limestone deposits on a steep volcanic flank and their recurring interruption by deposits linked to volcaniclastic processes. Historically known as Ilhéu da Cal (Lime Island), Ilhéu de Baixo was separated from Porto Santo, in the Madeira Archipelago, during the course of the Quaternary. Here, extensive mines were tunnelled in the Miocene carbonate strata for the production of slaked lime. Approximately 10 000 m³ of calcarenite (−1 to 1ø) was removed by hand labour from the Blandy Brothers mine at the south end of the islet. Investigations of two stratigraphic sections at opposite ends of the mine reveal that the quarried material represents an incipient carbonate ramp developed from east to west and embanked against the flank of a volcanic island. A petrographic analysis of limestones from the mine shows that coralline red algae from crushed rhodoliths account for 51% of all identifiable bioclasts. This material was transported shoreward and deposited on the ramp between normal wave base and storm wave base at moderate depths. The mine's roof rocks are formed by Surtseyan deposits from a subsequent volcanic eruption. Volcaniclastic density flows also are a prevalent factor interrupting renewed carbonate deposition. These flows arrived downslope from the north and gradually steepened the debris apron westwards. Slope instability is further shown by a coral rudstone density flow that followed from growth of a coral reef dominated by Pocillopora madreporacea (Lamarck), partial reef collapse, and transport from a more easterly direction into a fore‐reef setting. The uppermost facies represents a soft bottom at moderate depths in a quiet, but shore‐proximal setting. Application of this study to a broader understanding of the relationship between carbonate and volcaniclastic deposition on oceanic islands emphasizes the susceptibility of carbonates to dilution and complete removal by density flows of various kinds, in contrast to the potential for preservation beneath less‐disruptive Surtseyan deposits. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献