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1.
Memory Effects in Rock Salt Under Triaxial Stress State and Their Use for Stress Measurement in a Rock Mass 总被引:3,自引:0,他引:3
Y. L. Filimonov A. V. Lavrov Y. M. Shafarenko V. L. Shkuratnik 《Rock Mechanics and Rock Engineering》2001,34(4):275-291
Summary
Regularities of memory effects in rock salt specimens under triaxial stress state were investigated. Each specimen was subjected
to two loading cycles. The first cycle was axisymmetric triaxial compression (σ1 >σ2=σ3). The second cycle was uniaxial compression in the direction of σ1 of the first cycle. Distinct acoustic emission (AE) and deformation memory effects were observed in the second cycle at the
stress value equal to a linear combination of the first cycle principal stresses given by σ1− (k + 1) σ3, where k is about 0.5–0.6 for rock salt. Anomalies in deformation curves were found to be more reliable than the AE methods in distinguishing
memory symptoms. The necessary pre-requisite for memory formation in the first cycle was that σ1 exceeded the elastic limit, corresponding to the given confining stress σ3. Inflections in uniaxial stress versus axial strain and lateral strain curves, in the second cycle, were observed at equal
stress values if in the first cycle σ1 exceeded the elastic limit and memory-forming damage was induced. If there was no memory-forming damage, those inflections
were seen at different stress values. This characteristic was used to distinguish between true memory effects and natural
characteristic points in deformation curves derived from rock salt testing. A new memory symptom was established, namely a
turn point in curve “uniaxial stress versus differential coefficient of lateral strains”. The results form a basis for application
of the memory effects for stress measurement in rock salt masses. 相似文献
2.
Tae-Gew Ham Yukio Nakata Rolando Orense Masayuki Hyodo 《Geotechnical and Geological Engineering》2012,30(1):119-127
In order to investigate the strength and deformation anisotropy of compacted decomposed granite soils, a series of drained
triaxial compression tests was performed on unsaturated and saturated decomposed granite soils. The specimens were subjected
to compression tests such that the angle δ of the direction of the major principal stress, σ
1, during triaxial compression relative to the compaction plane (bedding plane) varies, with δ = 0°, 45° and 90°. Test results indicated that the compressive strain of the specimens subjected to isotropic consolidation
was influenced strongly by the angle δ. In addition, the effect of the angle δ on the triaxial compressive strength and deformation was more evident in unsaturated specimens than in saturated specimens.
Based on the test results, a procedure which can be used to estimate the shear strength of unsaturated soils taking into account
various angles δ was proposed. 相似文献
3.
On the Ratios between Elastic Modulus and Uniaxial Compressive Strength of Heterogeneous Carbonate Rocks 总被引:3,自引:3,他引:0
V. Palchik 《Rock Mechanics and Rock Engineering》2011,44(1):121-128
The ratios M
R = E/σ
c for 11 heterogeneous carbonate (dolomites, limestones and chalks) rock formations collected from different regions of Israel
were examined. Sixty-eight uniaxial compressive tests were conducted on weak-to-strong (5 MPa < σ
c < 100 MPa) and very strong (σ
c > 100 MPa) rock samples exhibiting wide ranges of elastic modulus (E = 6100–82300 MPa), uniaxial compressive strength (σ
c = 14–273.9 MPa), Poisson's ratio (ν = 0.13–0.49), and dry bulk density (ρ = 1.7–2.7 g/cm3). The observed range of M
R = 60.9–1011.4 and mean value of M
R = 380.5 are compared with the results obtained by Deere (Rock mechanics in engineering practice, Wiley, London, pp 1–20,
1968) for limestones and dolomites, and the statistical analysis of M
R distribution is performed. Mutual relations between E, σ
c, ρ, M
R for all studied rocks, and separately for concrete rock formations are revealed. Linear multiple correlations between E on the one hand and σ
c and ρ on the other for Nekorot and Bina limestone and Aminadav dolomite are obtained. It is established that the elastic modulus
and M
R in very strong carbonate samples are more correlated with ρ−σ
c combination and ε
a max, respectively, than in weak to strong samples. The relation between M
R and maximum axial strain (ε
a max) for all studied rock samples (weak-to-strong and very strong) is discussed. 相似文献
4.
Y. Sadhuram 《Journal of Earth System Science》1987,96(1):59-67
Variability in the standard deviation of surface wind direction (σθ), under different Pasquill stability regimes on diurnal, seasonal and interannual scales has been investigated making use
of a 10-year data set collected at Visakhapatnam (17°42′ N., 82° 18′ E) during January, April, August and October for winter,
pre-monsoon, monsoon and post-monsoon seasons respectively. The diurnal scale variability in σθ is more pronounced during day time than in night. The seasonal variability in σθ is only moderate around noon while relatively large fluctuations are noticed on inter-annual scale only during day time in
January and August. The seasonal dispersion in σθ decreased from most unstable regime to most stable regime. 相似文献
5.
Marek Kwaśniewski 《Rock Mechanics and Rock Engineering》2011,44(1):103-111
Based on the hypothesis that shearing stresses and normal tensile stresses both play a decisive role in fracturing and brittle
failure of rock material, a novel strength criterion was developed in one of the earlier works of the author. In the criterion,
a certain parameter ν′ occurs which depends on the structure of the material. Originally, the parameter was treated as a constant, which resulted
in a linear form of the strength function F
σ
1 = f(σ
3), where σ
3 = σ
2. Although the linear strength criterion is sometimes found to be applicable to various particular rock materials, it is not,
in general, of a universal character. Analysis of the triaxial test results for 75 different sandstones revealed that parameter
ν′ usually increases in an exponential or linear manner as confining pressure increases, and only in isolated cases does it
seem to be independent of the confining pressure. For these three types of function ν′ = f(p) appropriate strength criteria F
σ
1 = f(σ
3) are given in the present paper. These criteria were used to fit all of the collected empirical data sets. In general, a
very good fit to the data was obtained. 相似文献
6.
Discrete element method modeling of inherently anisotropic rocks under uniaxial compression loading 下载免费PDF全文
A new numerical approach is proposed in this study to model the mechanical behaviors of inherently anisotropic rocks in which the rock matrix is represented as bonded particle model, and the intrinsic anisotropy is imposed by replacing any parallel bonds dipping within a certain angle range with smooth‐joint contacts. A series of numerical models with β = 0°, 15°, 30°, 45°, 60°, 75°, and 90° are constructed and tested (β is defined as the angle between the normal of weak layers and the maximum principal stress direction). The effect of smooth‐joint parameters on the uniaxial compression strength and Young's modulus is investigated systematically. The simulation results reveal that the normal strength of smooth‐joint mainly affects the behaviors at high anisotropy angles (β > 45°), while the shear strength plays an important role at medium anisotropy angles (30°–75°). The normal stiffness controls the mechanical behaviors at low anisotropy angles. The angle range of parallel bonds being replaced plays an important role on defining the degree of anisotropy. Step‐by‐step procedures for the calibration of micro parameters are recommended. The numerical model is calibrated to reproduce the behaviors of different anisotropic rocks. Detailed analyses are conducted to investigate the brittle failure process by looking at stress‐strain behaviors, increment of micro cracks, initiation and propagation of fractures. Most of these responses agree well with previous experimental findings and can provide new insights into the micro mechanisms related to the anisotropic deformation and failure behaviors. The numerical approach is then applied to simulate the stress‐induced borehole breakouts in anisotropic rock formations at reduced scale. The effect of rock anisotropy and stress anisotropy can be captured. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
7.
Analysis of Critical Excavation Depth for a Jointed Rock Slope Using a Face-to-Face Discrete Element Method 总被引:1,自引:0,他引:1
Summary The critical excavation depth of a jointed rock slope is an important problem in rock engineering. This paper studies the
critical excavation depth for two idealized jointed rock slopes by employing a face-to-face discrete element method (DEM).
The DEM is based on the discontinuity analysis which can consider anisotropic and discontinuous deformations due to joints
and their orientations. It uses four lump-points at each surface of rock blocks to describe their interactions. The relationship
between the critical excavation depth D
s
and the natural slope angle α, the joint inclination angle θ as well as the strength parameters of the joints c
r
,φ
r
is analyzed, and the critical excavation depth obtained with this DEM and the limit equilibrium method (LEM) is compared.
Furthermore, effects of joints on the failure modes are compared between DEM simulations and experimental observations. It
is found that the DEM predicts a lower critical excavation depth than the LEM if the joint structures in the rock mass are
not ignored. 相似文献
8.
S. Merkel A. P. Jephcoat J. Shu H.-K. Mao P. Gillet R. J. Hemley 《Physics and Chemistry of Minerals》2002,29(1):1-9
Physical properties including the equation of state, elasticity, and shear strength of pyrite have been measured by a series
of X-ray diffraction in diamond-anvil cells at pressures up to 50 GPa. A Birch–Murnaghan equation of state fit to the quasihydrostatic
pressure–volume data obtained from laboratory X-ray source/film techniques yields a quasihydrostatic bulk modulus K
0T
=133.5 (±5.2) GPa and bulk modulus first pressure derivative K
′
0T
=5.73 (±0.58). The apparent equation of state is found to be strongly dependent on the stress conditions in the sample. The
stress dependency of the high-pressure properties is examined with anisotropic elasticity theory from subsequent measurements
of energy-dispersive radial diffraction experiments in the diamond-anvil cell. The calculated values of K
0T
depend largely upon the angle ψ between the diffracting plane normal and the maximum stress axis. The uniaxial stress component
in the sample, t=σ3−σ1, varies with pressure as t=−3.11+0.43P between 10 and 30 GPa. The pressure derivatives of the elastic moduli dC
11/dP=5.76 (±0.15), dC
12/dP=1.41 (±0.11) and dC
44/dP=1.92 (±0.06) are obtained from the diffraction data assuming previously reported zero-pressure ultrasonic data (C
11=382 GPa, C
12=31 GPa, and C
44=109 GPa).
Received: 21 December 2000 / Accepted: 11 July 2001 相似文献
9.
10.
Well-formed, texturally-early fluid inclusions in garnets from the Archean Pikwitonei granulite domain, Manitoba, Canada,
have been analyzed using microthermometric methods. The mean CO2 homogenization temperature (to liquid) for inclusions in 12 of 13 samples from the Cauchon Lake-Nelson River area is +15.2°
C (n=125, 2σ=8.2° C), corresponding to a CO2 density of 0.82 g/cm3. Inclusions in the remaining sample have somewhat lower CO2 homogenization temperatures (mean=+5.4° C, n=24). The studied inclusions contain an estimated 10 to 20 vol. percent H2O, with minor amounts of other fluid species such as CH4, N2, and/or H2S. The fluid inclusions were probably trapped during early garnet growth at relatively low pressures (≤5 kbar if at 750° C),
and appear to have undergone only limited or possibly no subsequent re-equilibration. This interpretation is consistent with
the “anti-clock-wise” P-T-t path (heating before loading) determined for the Pikwitonei region by other workers. For such a prograde path, inclusions
entrapped early, at high temperatures but at relatively low pressures, would experience internal underpressures during most
of the subsequent prograde and retrograde phases of metamorphism. The texturally-early fluid inclusions in garnets from the
Pikwitonei region therefore cannot be used to provide direct information about the highest metamorphic temperature and pressure conditions (750° C and 7 kbar). However, the results obtained in this study suggest that texturally-early fluid
inclusions in garnets may, in some cases, retain evidence of the prograde metamorphic path. 相似文献
11.
《Geomechanics and Geoengineering》2013,8(2):149-158
The objective of the paper is to derive the strength and modulus properties of rockmass as a function of intact rock strength and joint factor. The joint factor reflects the combined effect of joint frequency, joint inclination and joint strength. A study for the strength and deformation characteristics of jointed rock is done by conducting standard laboratory tests on cylindrical specimens of plaster of Paris after introducing artificial joints. The specimens having one to four joints at different inclinations which vary from 0° to 90° were tested at different confining conditions. The test results were examined to understand the effect of joint frequency and joint inclination on the strength and deformation behaviour of rock mass. Empirical correlations were developed for prediction of the uniaxial compressive strength and elastic modulus of jointed rocks. Results are compared with the earlier work on jointed specimens covering a wide variety of rocks. So, knowing the intact rock properties and the joint factor, the jointed rock properties can be estimated. These relations can be used for developing an equivalent continuum model for rock mass for handling boundary value problems. A failure criterion as proposed by Ramamurthy (1993) has been validated from these experimental results. 相似文献
12.
Previous research revealed that the cross-bedding related anisotropy in Jurassic aeolian Aztec Sandstone cropping out in the Valley of Fire State Park, Nevada, affects the orientation of compaction bands, also known as anti-cracks or closing mode structures. We hypothesize that cross-bedding should have a similar influence on the orientation of the opening mode joints within the same rock at the same location. To test this hypothesis, we investigated the relationship between the orientation of cross-beds and the orientation of different categories of joint sets including cross-bed package confined joints and joint zones in the Aztec Sandstone. The field data show that the cross-bed package confined joints occur at high-angle to bedding and trend roughly parallel to the dip direction of the cross-beds. In comparison, the roughly N–S trending joint zones appear not to be influenced by the cross-beds in any significant way but frequently truncate against the dune boundaries.To characterize the anisotropy due to cross-bedding in the Aztec Sandstone, we measured the P-wave velocities parallel and perpendicular to bedding from 11 samples and determined an average P-wave anisotropy to be slightly larger than 13%. From these results, a model based on the generalized Hooke's law for anisotropic materials is used to analyze deformation of cross-bedded sandstone as a transversely isotropic material. In the analysis, the dip angle of cross-beds is assumed to be constant and the strike orientation varying from 0° to 359° in the east (x), north (y), and up (z) coordinate system. We find qualitative agreement between most of the model results and the observed field relations between cross-beds and the corresponding joint sets. The results also suggest that uniaxial extension (εzz > εxx = εyy = 0) and axisymmetric extension (εxx = εyy < εzz and εxx = εyy > εzz) would amplify the influence of cross-bedding associated anisotropy on the joint orientation whereas a triaxial extension (εxx > εyy > εzz) would mitigate this influence. We suggest that the potential implication of different categories of joint sets (i.e., cross-bed package confined joints and joint zones) forming in response to the variation of the boundary conditions (axisymmetric extension and triaxial extension, respectively) and the interplay with the rock anisotropy is significant. These results have important implications for fluid flow through aeolian sandstones in reservoirs and aquifers. 相似文献
13.
Field and Laboratory Tests Investigating Settlements of Foundations on Weathered Keuper Marl 总被引:1,自引:1,他引:0
Ernst-Dieter Hornig 《Geotechnical and Geological Engineering》2010,28(3):233-240
Measured settlements of buildings on the weathered Keuper Marl appeared to be much smaller than calculated settlements, which
were based on stiffness modulus from standard oedometer tests. Therefore, both special triaxial K
0-tests and oedometer tests were carried out for an accurate determination of stiffness moduli. Modulus obtained in the triaxial
K
0-tests were at least two to three times the values obtained in the oedometer tests. To verify observations from the laboratory
tests, the loads and the settlements of two single footings on weathered Keuper mudstone have been measured during construction
of a building over 1 year. Also, a large scale footing load test with measurements of deformations were conducted on the weathered
Keuper mudstone. The measured settlements of the two single footings and the tested foundation were compared with the settlements
based on conventional calculations with moduli from oedometer tests and triaxial K
0-tests. Up to a foundation pressure of σv = 500 kN/m2 the calculated settlement based on E
S-modulus obtained from triaxial K
0-tests was found to correspond well to the measured deformation. For foundation pressure beyond 500 kN/m2, the foundation
response was highly non-linear and it could not be described any more with the linear-elastic model. Therefore the footing
load test was also simulated by FEM analyses. 相似文献
14.
The Shear Behavior of Bedding Planes of Weakness Between Two Different Rock Types with High Strength Difference 总被引:4,自引:2,他引:2
A. H. Ghazvinian A. Taghichian Mahmoud Hashemi S. A. Mar’ashi 《Rock Mechanics and Rock Engineering》2010,43(1):69-87
In this article, the shear behavior of discontinuities caused by bedding planes of weakness between two different rock types
with high strength difference is investigated. The effect of roughness and compressive strength of joint wall in such discontinuities
are studied. The designed profiles consist of two regular and three irregular artificial joints molded by three types of plaster
mortars with different uniaxial compressive strengths. Firstly, it is demonstrated that the shear behavior of discontinuities
with different joint wall compressive strengths (JCS) is different from rock joints with identical wall compressive strengths
by showing that Barton’s empirical criterion is not appropriate for the former discontinuities. After that, some correlation
equations are proposed between the joint roughness coefficient (JRC) parameter and some surface statistical/fractal parameters,
and the normal stress range of Barton’s strength criterion is also modified to be used for such discontinuities. Then, a new
empirical criterion is proposed for these discontinuities in such a way that a rational function is used instead of JRC log10(JCS/σ
n) as i
0(σ
c/σ
n)a/[b + (σ
c/σ
n)
a
] by satisfying the peak dilation angle boundary conditions under zero and very high normal stress (physical infinite normal
stress causing zero peak dilation angle). The proposed criterion has three surface parameters: i
0, a, and b. The reason for separation of i
0 from JRC is indicated and the method of its calculation is mentioned based on the literature. The two remaining coefficients
(a and b) are discussed in detail and it is shown that a shows a power-law relationship with b, introducing the coefficient c through b = c
a
. Then, it is expressed that a is directly related to discontinuity surface topography. Finally, it is shown that the coefficient c has higher values in irregular profiles in comparison with regular profiles and is dominated by intensity of peak dilation
angle reduction (majorly related to the surface irregularity and minorly related to roughness). The coefficient c is to be determined by performing regression analysis on experimental data. 相似文献
15.
Y. L. Chen J. Ni W. Shao Y. C. Zhou A. Javadi R. Azzam 《Rock Mechanics and Rock Engineering》2012,45(2):241-249
In this paper, white Portland cement was used as an experimental material. Prismatic specimens with pre-existing flaws at
different angles of inclination (α) varying through 0°, 30°, 45°, 60°, 75° to 90° and cylindrical specimens with different numbers of pre-existing flaws (n) varying through 0, 1, 2 to 3 were tested under uni-axial compression tests. Crack initiation, propagation, coalescence,
and failure were observed. The corresponding analytical expression for the stress intensity factor under uni-axial compression
was derived, the coefficient of friction and the stress intensity factor of the specimens on the surfaces of the crack were
analysed, and the corrective coefficient for the stress intensity factor was introduced. Fatigue tests with a loading frequency
of f = 100 Hz were carried out on cylindrical specimens with constant amplitude of the cyclic load which is a proportion of the
compressive load at failure (F
f) obtained from the uni-axial compression tests. The fatigue property of the specimens was analysed and the relationship (S
max − lg N
f) between the maximum stress and the number of loading cycles at failure for specimens with pre-existing flaws was proposed.
The effect of pre-existing flaws on the fatigue life (N
f) and dynamic load (S
D) which can be applied was investigated. 相似文献
16.
The high-pressure stability of zoisite and phase relationships of zoisite-bearing assemblages 总被引:5,自引:0,他引:5
The fluid-absent reaction 12 zoisite = 3 lawsonite + 7 grossular + 8 kyanite + 1 coesite was experimentally reversed in the
model system CaO-Al2O3-SiO2-H2O (CASH) using a multi-anvil apparatus. The upper pressure stability limit for zoisite was found to extend to 5.0 GPa at 700 °C
and to 6.6 GPa at 950 °C. Additional experiments both in the H2O-SiO2-saturated and in the H2O-Al2O3-saturated portions of CASH provide further constraints on high pressure phase relationships of lawsonite, zoisite, grossular,
kyanite, coesite, and an aqueous fluid. Consistency of the present experiments with the H2O-saturated breakdown of lawsonite is demonstrated by thermodynamic analysis using linear programming techniques. Two sets
of data consistent with databases of Berman (1988) and Holland and Powell (1990) were retrieved combining experimental phase
relationships, calorimetric constraints, and recently measured elastic properties of solid phases. The best fits result in
G
f
,1,298
∘,zoisite=−6,499,400 J and S
1,298
∘,zoisite=302 J/K, and G
f
,1,298
∘,lawsonite=−4,514,600 J and S
1,298
∘,lawsonite=220 J/K for the dataset of Holland and Powell, and G
f
,1,298
∘,zoisite=−6,492,120 J and S
1,298
∘,zoisite=304 J/K, and G
f
,1,298
∘,lawsonite=−4,513,000 J and S
1,298
∘,lawsonite= 218 J/K for the dataset of Berman. Examples of the usage of zoisite as a geohygrometer and as a geobarometer in rocks metamorphosed
at eclogite facies conditions are worked, profiting from the thermodynamic properties retrieved here.
Received: 23 December 1996 / Accepted: 29 August 1997 相似文献
17.
Mualla Cengiz Çinku 《International Journal of Earth Sciences》2011,100(7):1633-1645
The Jurassic paleogeographic position of the Pontides is not well studied because of insufficient paleomagnetic data. For
this reason, a paleomagnetic study was carried out in order to constrain the paleolatitudinal drift of the Turkish blocks
during the Jurassic period. A total of 32 sites were sampled from volcanic and volcanoclastic rocks of the Lower/Middle Jurassic
Kelkit formation (Eastern Pontides), Mudurnu formation (Sakarya continent) and Upper Jurassic–Lower Cretaceous Ferhatkaya
formation exposed around Amasya region (Eastern Pontides). Rock magnetic experiments demonstrate that the main ferromagnetic
mineral is pseudo-single-domain titanomagnetite in these rocks. Paleomagnetic analysis revealed two main components of the
natural remanent magnetization during stepwise thermal and alternating field demagnetization. The first component is a low-coercivity
(unblocking temperature) component with a direction sometimes similar to that of the earth’s present field or a viscous component.
The second component, which is interpreted as the characteristic remanent magnetization (ChRM) direction, has low to high
coercivity properties between 20 and 100 mT or unblocking temperatures between 300 and 580°C. A positive fold test at the
95% level of confidence proved that the ChRM of the sites is primary. Paleomagnetic directions calculated for the Kelkit formation
in the Eastern Pontides have a mean direction of D = 334.8°, I = 49.7°, α
95 = 7.1° after tilt-correction. A mean direction of D = 332.2°, I = 48.5°, α
95 = 14.6° was obtained from the volcanoclastic rocks of the Mudurnu formation, and D = 324.3°, I = 43.3°, α
95 = 9.5° was calculated for the Upper Jurassic–Lower Cretaceous limestones/Ferhatkaya formation of the Amasya region. The Jurassic
rocks in the Eastern Pontides and Mudurnu region are considered to represent products of the rifted Neo-Tethys ocean, while
the Upper Jurassic–Lower Cretaceous sediments in Amasya are related to basin-filling materials. The data suggest that the
Kelkit formation was formed at 30.5°N paleolatitude and the equivalent Mudurnu formation at 29.5°N paleolatitude. The paleolatitude
of the Eastern Pontides indicates that this rifting block was separated from Eurasia by a marginal basin instead of being
a part of Eurasia. The lower paleolatitude of the Amasya region at 24.8°N in the Upper Jurassic to Lower Cretaceous clearly
indicates southward drift of the Turkish blocks during the Jurassic to Lower Cretaceous period together with the motion of
Eurasia. 相似文献
18.
N. Al-Shayea 《Rock Mechanics and Rock Engineering》2002,35(4):271-297
Summary
A fracture toughness study was conducted on a limestone rock formation from a petroleum reservoir in Saudi Arabia, and results
were compared with those for outcrop specimens from the same geological formation. The objective was to investigate the possibility
of using outcrop specimens to estimate the fracture toughness behavior of reservoir rock at in-situ conditions of temperature and confining pressure. The study was made on reservoir specimens from a depth of about 3.5 km,
at both ambient and reservoir conditions. Mixed mode I–II fracture toughness at reservoir conditions of high temperature and
confining pressure was studied using straight notched Brazilian disk (SNBD) specimens under diametrical compression. Tests
were conducted at ambient conditions, at an effective confining pressure (σ3) of 28 MPa (4000 psi), and at a temperature of 116°C. The results showed a substantial increase in fracture toughness under confining pressure. Under σ3=28 MPa, the pure mode-I fracture toughness (K
IC), increased by a factor of about 3.2, and the pure mode-II fracture toughness (K
IIC) increased by a factor of 4.4, compared to those under ambient conditions. On the other hand, K
IC at 116°C was only 25% more than that at ambient conditions. These results were compared with recent results for outcrop specimens
from the same geological formation. The results reveal that outcrop specimens can be successfully used to predict the fracture
behavior of reservoir specimens at in-situ conditions, in spite of some differences at ambient conditions. Additionally, fracture toughness envelopes were obtained
for reservoir specimens at ambient and high pressure conditions, in both positive and negative regions.
Received September 14, 2000; accepted February 22, 2002 Published online September 2, 2002 相似文献
19.
The lattice constants of paragonite-2M1, NaAl2(AlSi3)O10(OH)2, were determined to 800 °C by the single-crystal diffraction method. Mean thermal expansion coefficients, in the range 25–600 °C,
were: αa = 1.51(8) × 10−5, αb = 1.94(6) × 10−5, αc = 2.15(7) × 10−5 °C−1, and αV = 5.9(2) × 10−5 °C−1. At T higher than 600 °C, cell parameters showed a change in expansion rate due to a dehydroxylation process. The structural refinements
of natural paragonite, carried out at 25, 210, 450 and 600 °C, before dehydroxylation, showed that the larger thermal expansion
along the c parameter was mainly due to interlayer thickness dilatation. In the 25–600 °C range, Si,Al tetrahedra remained quite unchanged,
whereas the other polyhedra expanded linearly with expansion rate proportional to their volume. The polyhedron around the
interlayer cation Na became more regular with temperature. Tetrahedral rotation angle α changed from 16.2 to 12.9°. The structure
of the new phase, nominally NaAl2 (AlSi3)O11, obtained as a consequence of dehydroxylation, had a cell volume 4.2% larger than that of paragonite. It was refined at room
temperature and its expansion coefficients determined in the range 25–800 °C. The most significant structural difference from
paragonite was the presence of Al in fivefold coordination, according to a distorted trigonal bipyramid. Results confirm the
structural effects of the dehydration mechanism of micas and dioctahedral 2:1 layer silicates. By combining thermal expansion
and compressibility data, the following approximate equation of state in the PTV space was obtained for paragonite: V/V
0 = 1 + 5.9(2) × 10−5
T(°C) − 0.00153(4) P(kbar).
Received: 12 July 1999 / Revised, accepted: 7 December 1999 相似文献
20.
Anil Kumar Y J Bhaskar Rao V M Padma Kumari A M Dayal K Gopalan 《Journal of Earth System Science》1988,97(1):107-114
Palaeomagnetic, geochemical and geochronological studies have been conducted on a set of dolerite dykes intruding the Peninsular
gneisses near Huliyurdurga town, Karnataka, as a reconnaissance survey indicated a Cretaceous age for them. The dykes are
mainly tholeiitic in composition with their 87Sr/86Sr ratios tightly clustered around 0·7045. Their palaeomagnetic data (D
m
=329°,I
m
=−55°) and the corresponding palaeopole coordinates (λ
p
= 34°S,L
p
=108°E) are strikingly close to those of the Deccan Traps to the north. Whole rock K-Ar ages of these dykes ranging between
69 and 84 Ma are also similar to the range of K-Ar ages of the Deccan basalts. The chemical, palaeomagnetic and temporal coherence
between the dykes and the Deccan basalts indicate that they may indeed be tectonically related events. 相似文献