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121.
Some slope instability problems exist in Ankara clay along E90 highway. The purpose of this paper is to determine the mineralogical and geotechnical properties of soils, and to investigate the causes and mechanisms of three rotational landslides along a section of the highway. In order to accomplish these tasks, field studies, laboratory testing, back analyses, and limit equilibrium and finite difference analyses were performed. The landslides are formed within a soil consisting of clay and silt with a little sand and gravel. Slope stability analyses indicate that long-term stability of already failed slopes is critical. The failures are progressive, showing strain softening behavior with full saturation. Broken irrigation pipes existing near the landslides are found to be the main cause of sliding. Maintenance of the pipes, surface drainage, removal and replacement of the failed (slided) material are considered to be economical and practical solutions for the remediation of the slides. 相似文献
122.
A schist sequence of the central Menderes Massif, in which lenses of fossiliferous marbles are found, is observed in the southern flank of the Aydn Mountain, north of Kök (Aydn), around Erikavak village. These rocks have been considered as Permo-Carboniferous in age and are included in the Göktepe Formation of earlier studies. However, some rudist species are described from thickly bedded gray marbles that have a concordant contact with the overlying schist sequence. Although the rudists have been metamorphosed, it is observed that some contain fossils are well enough preserved to determine the following rudist fauna: Hippurites lapeirousei (GOLDFUSS), Hippurites nabresinensis FUTTERER, Hippurites cf. colliciatus WOODWARD. This rudist fauna dates the schist sequence as Santonian–Campanian. The schist sequence is overlain by a thick tectonostratigraphic pile of orthogneiss which has been interpreted as the Pan-African metamorphic core of the Menderes Massif. A widespread cataclastic and mylonitic zone is present between the underlying rudist-bearing marbles and the structurally overlying orthogneiss sequence. The existing kinematic studies in the footwall and hangingwall of this tectonic contact reveal two different phases of deformations, a contractional phase followed by an extensional phase. During the contractional event, which occurred at 36 Ma, the orthogneiss sequence was thrust faulted northwards over the schist sequence. This thrust fault was later reactivated as a low-angle normal fault beneath a supradetachment sedimentary basin of Early-Middle Miocene age. The fossil discoveries of this study and the existing kinematic studies reveal that a new structural model for the central Menderes Massif in which the tectonometamorphic units form a major southward closing recumbent fold needs to be reviewed. 相似文献
123.
The evaluation of the vulnerability of the karst aquifer and the source in the Coteţul Dobreştilor system was performed on
the basis of geological, hydrogeological and pedological data. The methods proposed in the Final Report of COST Action 620
were used. The available field data resulted in assessing the parameters P, I and in characterizing the saturated aquifer karstic network parameter (K). The soil cover over the carbonate deposits is generally shallow and easily bypassed by the superficial flow, the protection
of the karstic aquifer and the source thus being minimal. 相似文献
124.
Jean-Clair Duchesne Jean-Paul Liègeois Viorica Iancu Tudor Berza Dmitry I. Matukov Mihai Tatu Sergei A. Sergeev 《International Journal of Earth Sciences》2008,97(4):705-723
The Sichevita and Poniasca plutons belong to an alignment of granites cutting across the metamorphic basement of the Getic
Nappe in the South Carpathians. The present work provides SHRIMP age data for the zircon population from a Poniasca biotite
diorite and geochemical analyses (major and trace elements, Sr–Nd isotopes) of representative rock types from the two intrusions
grading from biotite diorite to biotite K-feldspar porphyritic monzogranite. U–Pb zircon data yielded 311 ± 2 Ma for the intrusion
of the biotite diorite. Granites are mostly high-K leucogranites, and biotite diorites are magnesian, and calcic to calc-alkaline.
Sr, and Nd isotope and trace element data (REE, Th, Ta, Cr, Ba and Rb) permit distinguishing five different groups of rocks
corresponding to several magma batches: the Poniasca biotite diorite (P1) shows a clear crustal character while the Poniasca granite (P2) is more juvenile. Conversely, Sichevita biotite diorite (S1), and a granite (S2*) are more juvenile than the other Sichevita granites (S2). Geochemical modelling of major elements and REE suggests that fractional crystallization can account for variations within
P1 and S1 groups. Dehydration melting of a number of protoliths may be the source of these magma batches. The Variscan basement, a
subduction accretion wedge, could correspond to such a heterogeneous source. The intrusion of the Sichevita–Poniasca plutons
took place in the final stages of the Variscan orogeny, as is the case for a series of European granites around 310 Ma ago,
especially in Bulgaria and in Iberia, no Alleghenian granitoids (late Carboniferous—early Permian times) being known in the
Getic nappe. The geodynamical environment of Sichevita–Poniasca was typically post-collisional of the Variscan orogenic phase. 相似文献
125.
Insect outbreaks are major disturbances that affect a land area similar to that of forest fires across North America. The recent mountain pine bark beetle (D endroctonus ponderosae) outbreak and its associated blue stain fungi (Grosmannia clavigera) are impacting water partitioning processes of forests in the Rocky Mountain region as the spatially heterogeneous disturbance spreads across the landscape. Water cycling may dramatically change due to increasing spatial heterogeneity from uneven mortality. Water and energy storage within trees and soils may also decrease, due to hydraulic failure and mortality caused by blue stain fungi followed by shifts in the water budget. This forest disturbance was unique in comparison to fire or timber harvesting because water fluxes were altered before significant structural change occurred to the canopy. We investigated the impacts of bark beetles on lodgepole pine (Pinus contorta) stand and ecosystem level hydrologic processes and the resulting vertical and horizontal spatial variability in energy storage. Bark beetle-impacted stands had on average 57 % higher soil moisture, 1.5 °C higher soil temperature, and 0.8 °C higher tree bole temperature over four growing seasons compared to unimpacted stands. Seasonal latent heat flux was highly correlated with soil moisture. Thus, high mortality levels led to an increase in ecosystem level Bowen ratio as sensible heat fluxes increased yearly and latent heat fluxes varied with soil moisture levels. Decline in canopy biomass (leaf, stem, and branch) was not seen, but ground-to-atmosphere longwave radiation flux increased, as the ground surface was a larger component of the longwave radiation. Variability in soil, latent, and sensible heat flux and radiation measurements increased during the disturbance. Accounting for stand level variability in water and energy fluxes will provide a method to quantify potential drivers of ecosystem processes and services as well as lead to greater confidence in measurements for all dynamic disturbances. 相似文献
126.
Ana??akni?-?atovi?Email author William?A.?Gough 《Theoretical and Applied Climatology》2018,132(1-2):41-54
Climatological observing window (COW) is defined as a time frame over which continuous or extreme air temperature measurements are collected. A 24-h time interval, ending at 00UTC or shifted to end at 06UTC, has been associated with difficulties in characterizing daily temperature extrema. A fixed 24-h COW used to obtain the temperature minima leads to potential misidentification due to fragmentation of “nighttime” into two subsequent nighttime periods due to the time discretization interval. The correct identification of air temperature extrema is achievable using a COW that identifies daily minimum over a single nighttime period and maximum over a single daytime period, as determined by sunrise and sunset. Due to a common absence of hourly air temperature observations, the accuracy of the mean temperature estimation is dependent on the accuracy of determination of diurnal air temperature extrema. Qualitative and quantitative criteria were used to examine the impact of the COW on detecting daily air temperature extrema. The timing of the 24-h observing window occasionally affects the determination of daily extrema through a mischaracterization of the diurnal minima and by extension can lead to errors in determining daily mean temperature. Hourly air temperature data for the time period from year 1987 to 2014, obtained from Toronto Buttonville Municipal Airport weather station, were used in analysis of COW impacts on detection of daily temperature extrema and calculation of annual temperature averages based on such extrema. 相似文献
127.
Monazite behaviour during isothermal decompression in pelitic granulites: a case study from Dinggye,Tibetan Himalaya 总被引：1，自引：0，他引：1
Jia-Min?WangEmail authorView author&#;s OrcID profile Fu-Yuan?Wu Daniela?Rubatto Shi-Ran?Liu Jin-Jiang?Zhang Xiao-Chi?Liu Lei?Yang 《Contributions to Mineralogy and Petrology》2017,172(10):81
Monazite is a key accessory mineral for metamorphic geochronology, but interpretation of its complex chemical and age zoning acquired during high-temperature metamorphism and anatexis remains a challenge. We investigate the petrology, pressure–temperature and timing of metamorphism in pelitic and psammitic granulites that contain monazite from the Greater Himalayan Crystalline Complex (GHC) in Dinggye, southern Tibet. These rocks underwent isothermal decompression from pressure of >10 kbar to ~5 kbar at temperatures of 750–830 °C, and recorded three metamorphic stages at kyanite (M1), sillimanite (M2) and cordierite-spinel grade (M3). Monazite and zircon crystals were dated by microbeam techniques either as grain separates or in thin sections. U–Th–Pb ages are linked to specific conditions of mineral growth on the basis of zoning patterns, trace element signatures, index mineral inclusions (melt inclusions, sillimanite and K-feldspar) in dated domains and textural relationships with co-existing minerals. The results show that inherited domains (500–400 Ma) are preserved in monazite even at granulite-facies conditions. Few monazites or zircon yield ages related to the M1-stage (~30–29 Ma), possibly corresponding to prograde melting by muscovite dehydration. During the early stage of isothermal decompression, inherited or prograde monazites in most samples were dissolved in the melt produced by biotite dehydration-melting. Most monazite grains crystallized from melt toward the end of decompression (M3-stage, 21–19 Ma) and are chemically related to garnet breakdown reactions. Another peak of monazite growth occurred at final melt crystallization (~15 Ma), and these monazite grains are unzoned and are homogeneous in composition. In a regional context, our pressure–temperature–time data constrains peak high-pressure metamorphism within the GHC to ~30–29 Ma in Dinggye Himalaya. Our results are in line with a melt-assisted exhumation of the GHC rocks. 相似文献