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941.
Behavior of epidote at high pressure and high temperature: a powder diffraction study up to 10 GPa and 1,200 K 总被引:1,自引:0,他引:1
G. Diego Gatta Marco Merlini Yongjae Lee Stefano Poli 《Physics and Chemistry of Minerals》2011,38(6):419-428
The thermo-elastic behavior of a natural epidote [Ca1.925 Fe0.745Al2.265Ti0.004Si3.037O12(OH)] has been investigated up to 1,200 K (at 0.0001 GPa) and 10 GPa (at 298 K) by means of in situ synchrotron powder diffraction.
No phase transition has been observed within the temperature and pressure range investigated. P–V data fitted with a third-order Birch–Murnaghan equation of state (BM-EoS) give V
0 = 458.8(1)Å3, K
T0 = 111(3) GPa, and K′ = 7.6(7). The confidence ellipse from the variance–covariance matrix of K
T0 and K′ from the least-square procedure is strongly elongated with negative slope. The evolution of the “Eulerian finite strain”
vs “normalized stress” yields Fe(0) = 114(1) GPa as intercept values, and the slope of the regression line gives K′ = 7.0(4). The evolution of the lattice parameters with pressure is slightly anisotropic. The elastic parameters calculated
with a linearized BM-EoS are: a
0 = 8.8877(7) Å, K
T0(a) = 117(2) GPa, and K′(a) = 3.7(4) for the a-axis; b
0 = 5.6271(7) Å, K
T0(b) = 126(3) GPa, and K′(b) = 12(1) for the b-axis; and c
0 = 10.1527(7) Å, K
T0(c) = 90(1) GPa, and K’(c) = 8.1(4) for the c-axis [K
T0(a):K
T0(b):K
T0(c) = 1.30:1.40:1]. The β angle decreases with pressure, βP(°) = βP0 −0.0286(9)P +0.00134(9)P
2 (P in GPa). The evolution of axial and volume thermal expansion coefficient, α, with T was described by the polynomial function: α(T) = α0 + α1
T
−1/2. The refined parameters for epidote are: α0 = 5.1(2) × 10−5 K−1 and α1 = −5.1(6) × 10−4 K1/2 for the unit-cell volume, α0(a) = 1.21(7) × 10−5 K−1 and α1(a) = −1.2(2) × 10−4 K1/2 for the a-axis, α0(b) = 1.88(7) × 10−5 K−1 and α1(b) = −1.7(2) × 10−4 K1/2 for the b-axis, and α0(c) = 2.14(9) × 10−5 K−1 and α1(c) = −2.0(2) × 10−4 K1/2 for the c-axis. The thermo-elastic anisotropy can be described, at a first approximation, by α0(a): α0(b): α0(c) = 1 : 1.55 : 1.77. The β angle increases continuously with T, with βT(°) = βT0 + 2.5(1) × 10−4
T + 1.3(7) × 10−8
T
2. A comparison between the thermo-elastic parameters of epidote and clinozoisite is carried out. 相似文献
942.
New insights into Late Pleistocene explosive volcanic activity and caldera formation on Ischia (southern Italy) 总被引:1,自引:1,他引:1
A new pyroclastic stratigraphy is presented for the island of Ischia, Italy, for the period ∼75–50 ka BP. The data indicate
that this period bore witness to the largest eruptions recorded on the island and that it was considerably more volcanically
active than previously thought. Numerous vents were probably active during this period. The deposits of at least 10 explosive
phonolite to basaltic-trachyandesite eruptions are described and interpreted. They record a diverse range of explosive volcanic
activity including voluminous fountain-fed ignimbrite eruptions, fallout from sustained eruption columns, block-and-ash flows,
and phreatomagmatic eruptions. Previously unknown eruptions have been recognised for the first time on the island. Several
of the eruptions produced pyroclastic density currents that covered the whole island as well as the neighbouring island of
Procida and parts of the mainland. The morphology of Ischia was significantly different to that seen today, with edifices
to the south and west and a submerged depression in the centre. The largest volcanic event, the Monte Epomeo Green Tuff (MEGT)
resulted in caldera collapse across all or part of the island. It is shown to comprise at least two thick intracaldera ignimbrite
flow-units, separated by volcaniclastic sediments that were deposited during a pause in the eruption. Extracaldera deposits
of the MEGT include a pumice fall deposit emplaced during the opening phases of the eruption, a widespread lithic lag breccia
outcropping across much of Ischia and Procida, and a distal ignimbrite in south-west Campi Flegrei. During this period the
style and magnitude of volcanism was dictated by the dynamics of a large differentiated magma chamber, which was partially
destroyed during the MEGT eruption. This contrasts with the small-volume Holocene and historical effusive and explosive activity
on Ischia, the timing and distribution of which has been controlled by the resurgence of the Monte Epomeo block. The new data
contribute to a clearer understanding of the long-term volcanic and magmatic evolution of Ischia. 相似文献
943.
944.
Understanding the fundamental issues related with the effect of shear velocity on frictional characteristics at the interface
of rock surfaces is an important issue. In this paper, strain-rate dependence on friction is investigated in relation to sliding
behaviour under normal load. The phenomenon of stick-slip of granite and shaly sandstone with a tribometer at constant rate
of strain under normal loads was observed. 相似文献
945.
Vulnerability of groundwater in Quaternary aquifers to organic contaminants: a case study in Wuhan City,China 总被引:5,自引:0,他引:5
Yanxin Wang Broder J. Merkel Yilian Li Hui Ye Surong Fu Dana Ihm 《Environmental Geology》2007,53(3):479-484
More than 30 organic contaminants were detected in shallow groundwaters at Wuhan, the largest city in central China. Seriously
contaminated groundwaters were from densely populated, industrial and commercial areas. Abnormal concentrations were found
in groundwater from Hankou, downtown Wuhan: trimethylbenzene up to 29 μg/L, tetramethylbenzene up to 866 μg/L, and trichloroethene
up to 9.5 μg/L. Benzene, Toluene, Ethylene and Xylene (BTEX) contamination of groundwater is serious and widespread at Wuhan,
ranging between 0.14 and 25.0 μg/L. Considering the hydrogeological conditions of most Chinese cities, DRAMIC, a modified
version of the widely used DRASTIC model, was proposed by the authors for assessing vulnerability of groundwater to contamination.
The factors D, R, A and I in DRAMIC model are the same as in DRASTIC. The factor topography is ignored. The factor soil media is substituted by a new factor aquifer thickness (M) and the factor hydraulic conductivity of the aquifer by a new factor impact of contaminant (C). The equation for determining the DRAMIC Index is: DRAMIC = 5D
R + 3R
R + 4A
R + 2M
R + 5I
R + 1C
R. The calculated DRAMIC Index can be used to identify areas that are more likely to be susceptible to groundwater contamination
relative to each other. The higher the DRAMIC Index is, the greater the groundwater pollution potential. Applying DRAMIC,
a GIS-based vulnerability map for Wuhan city was prepared. Interestingly, places such as downtown Hankou, where enhanced concentrations
of BTEX have been detected, correspond quite well with those with higher DRAMIC ratings. 相似文献
946.
The rapid proliferation of Phragmites australis in North America has challenged resource managers to curb its expansion and reduce the loss of functional tidal marsh. We
investigated whether native plant competition could reduce the ability of Phragmites to invade a tidal marsh, and if plant diversity (species richness, evenness, and composition) altered the competitive outcome.
Immature Phragmites shoots and four native halophytes were transplanted to small but dense field plots (~1,200 shoots m−2) comprising three community structure types (Phragmites alone, Phragmites + 1 native species, and Phragmites + 4 native species). Interspecific competition significantly reduced Phragmites aboveground biomass, shoot length production, density, and survival by approximately 60%. Additionally, plots planted with
greater native diversity contained Phragmites with the lowest growth and survival, potentially indicating diversity-enhanced resource competition. Competition consistently
reduced the growth of Phragmites even under favorable conditions: lack of strong tidal flooding stresses as well as elevated nutrient pools. 相似文献
947.
GIS-based landslide susceptibility mapping using bivariate statistical analysis in Devrek (Zonguldak-Turkey) 总被引:5,自引:10,他引:5
Devrek town with increasing population is located in a hillslope area where some landslides exist. Therefore, landslide susceptibility
map of the area is required. The purpose of this study was to generate a landslide susceptibility map using a bivariate statistical
index and evaluate and compare the results of the statistical analysis conducted with three different approaches in seed cell
concept resulting in different data sets in Geographical Information Systems (GIS) based landslide susceptibility mapping
applied to the Devrek region. The data sets are created from the seed cells of (a) crowns and flanks, (b) only crowns, and
(c) only flanks of the landslides by using ten different causative parameters of the study area. To increase the data dependency
of the analysis, all parameter maps are classified into equal frequency classes based directly on the percentile divisions
of each corresponding seed cell data set. The resultant maps of the landslide susceptibility analysis indicate that all data
sets produce fairly acceptable results. In each data set analysis, elevation, lithology, slope, aspect, and drainage density
parameters are found to be the most contributing factors in landslide occurrences. The results of the three data sets are
compared using Seed Cell Area Indexes (SCAI). This comparison shows that the crown data set produces the most accurate and
successful landslide susceptibility map of the study area. 相似文献
948.
Observed summer (May–October) rainfall in Myanmar for the period 1981–2010 was used to investigate the interannual variability of summer monsoon rainfall over Myanmar. Empirical orthogonal function, the sequential Mann-Kendall test, power spectrum analysis, and singular value decomposition (SVD) were deployed in the study. Results from spectral analysis showed that the variability of rainfall over Myanmar exhibits a 2- to 6-year cycle. An abrupt change in rainfall over the country was noted in 1992. There was a notable increasing rainfall trend from 1989. After the sudden change, the mean rainfall increased by 36.1 mm, compared with the mean rainfall before the sudden change, and was associated with a rise in temperature of about 0.2 °C. An increase in heavy rainfall days was observed from the early 1990s to 2010. IOD and ENSO play an important role in the interannual variability of the summer rainfall over Myanmar. The covariability between rainfall over Myanmar and Indian Ocean SST generally suggests that a positive IOD mode is associated with suppressed rainfall in the central and northern parts of Myanmar. During a negative IOD mode, nearly the whole Myanmar experiences enhanced rainfall, which is associated with devastating socioeconomic impacts. The covariability between the rainfall over Myanmar and the sea surface temperature in the Pacific Ocean in the first and second SVD modes was dominated by warming in the east and central Pacific—an El Niño-like pattern—resulting in dry conditions in central Myanmar. 相似文献
949.
Anne Marie de Grosbois 《Environmental Geology》2008,54(5):1121-1126
950.
Two distinct layers usually exist in the upper ocean. The first has a near-zero vertical gradient in temperature (or density) from the surface and is called the isothermal layer (or mixed layer). Beneath that is a layer with a strong vertical gradient in temperature (or density), called the thermocline (or pycnocline). The isothermal layer depth (ILD) or mixed layer depth (MLD) for the same profile varies depending on the method used to determine it. Also, whether they are subjective or objective, existing methods of determining the ILD do not estimate the thermocline (pycnocline) gradient. Here, we propose a new exponential leap-forward gradient (ELG) method of determining the ILD that retains the strengths of subjective (simplicity) and objective (gradient change) methods and avoids their weaknesses (subjective methods are threshold-sensitive and objective methods are computationally intensive). This new method involves two steps: (1) the estimation of the thermocline gradient G th for an individual temperature profile, and (2) the computation of the vertical gradient by averaging over gradients using exponential leap-forward steps. Such averaging can filter out noise in the profile data. Five existing methods of determining the ILD (difference, gradient, maximum curvature, maximum angle, and optimal linear fitting methods) as well as the proposed ELG method were verified using global expendable bathythermograph (XBT) temperature and conductivity–temperature–depth (CTD) datasets. Among all the methods considered, the ELG method yielded the highest skill score and the lowest Shannon information entropy (i.e., the lowest uncertainty). 相似文献