首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 15 毫秒
1.
Following the recommendation of the “IASPEI Commission on Magnitudes” from 1967, P-wave magnitudes of distant earthquakes are being computed with the aid of the calibration functions of Gutenberg and Richter (1956). With the development of the instrumental seismology, especially in view of the availability of broad-band recordings, the question arises whether the functions are still adequate.In this investigation new calibration functions for P- and S-waves are presented, which are not only dependent on epicentral distance and focal depth, but also on the period of the spectral component of the wave. The determination of calibration functions is based on the currently most plausible global models for the velocity and anelasticity distribution. Taking into account the effective bandwidth of the instruments employed, eventually leads to the so-called spectral magnitudes.From the spectral magnitudes m(T) , the energy density spectrum E(T) of the respective wave can readily be computed. The corresponding formula is E(T) = 102m(T)− 1.4, with E(T) in joules per hertz.  相似文献   

2.
Hard mode Raman Spectroscopy and optical birefringence studies have been used to evaluate the temperature behaviour of order parameters for the cubictetragonal phase transition in leucite. There is a strong temperature-dependence of Raman line frequencies near 498 cm–1 and 529 cm–1, and the optical birefringence decreases towards zero on heating. Above the transition temperature leucite still shows slight birefringence, which correlates with the persistence of the 200 X-ray reflexion at these temperatures, and is not compatible with the ideal cubic symmetry. Quantitative observations of the temperature evolution of Raman line-frequencies and the birefringence are consistent with an order parameter showing T 1g symmetry, and a nearly-tricritical phase transition behaviour. The results of earlier X-ray and DSC studies imply the operation of an additional order parameter, with E g symmetry; this is observed, but its influence on the transition behaviour is significant only at temperatures close to T c. The two order parameters are related via linear-quadratic or biquadratic coupling. We develop the form of the Landau Potential for leucite — including both order parameters and their couplings — to discuss the present observations and previous structural data.  相似文献   

3.
We have made use of the nearly complete linear polarization of synchrotron radiation to study the polarization dependence of X-ray absorption near-edge structure (XANES) and extended fine structure (EXAFS) in oriented single crystals of gillespite (BaFe2+ Si4O10; Fe2 + in square-planar coordination, point symmetry C 4), anatase (TiO2; Ti4+ in octahedral coordination, point symmetry D 2d), and epidote (Ca2(Al, Fe3+)3SiO4)3(OH); Fe3+ in distorted octahedral coordination, point symmetry (C s). For gillespite, the Fe K-XANES spectrum varies strongly with E-vector orientation of the incident X-ray beam. When the E-vector lies in the plane of the FeO4 group (i.e., perpendicular to the c-axis), multiple-scattering features at 7127 and 7131 eV intensify, whereas when the E-vector is perpendicular to the plane of the FeO4 group (i.e., parallel to the c-axis), a strongly-polarized 1s to 4p bound state transition occurs at 7116 eV and a localized continuum resonance occurs at 7122 eV. The Fe-K-EXAFS spectrum of gillespite is also highly polarization dependent. When the E-vector is perpendicular to c, all four nearest-neighbor oxygens around Fe2+ contribute to the EXAFS signal; when E is parallel to c, the EXAFS signal from nearest-neighbors is reduced by at least 86%. The unpolarized Ti K-XANES spectrum of anatase has three relatively strong pre-edge features at 4967.1, 4969.9, and 4972.7 eV which have resisted definitive interpretation in past studies. The lowest energy feature has a strong xy polarization dependence, suggesting a large amount of 4p x,y character, and it is also very sharp, indicating a well-defined transition energy. Both of these observations are consistent with an excitonic state with a binding energy of 2.8 eV. The two higher energy features, which are characteristic of octahedrally-coordinated Ti4+, show little polarization dependence and are probably due to 1s to 3d bound-state transitions, with a small degree of np character in the final state wavefunction. Interpretation of the polarization dependence of Fe K-XANES spectra for epidote is not as straightforward due to the lower space group symmetry (P21/m) relative to gillespite (P4/ncc) and anatase (I41/amd) and the lower point group symmetry (C s) of the M(3) site which contains most of the Fe3+ in the epidote structure. However, the presence of a shoulder at 7121 eV in the E parallel to b spectrum and its absence in the E normal to bc spectrum are consistent with it being a 1s to 4p z bound-state transition. Strong, weakly x, y polarized features near 7126 eV in both spectra are most likely due to localized continuum transitions. Also, the 1s to 3d pre-edge intensity varies in intensity with E-vector orientation which is consistent with displacement of Fe3+ from the center of the M(3) octahedral site. Analysis of EXAFS spectra of epidote in these two polarizations yields bond distances which are within 0.04 Å of previous single-crystal X-ray diffraction analysis. This study demonstrates the utility of polarized X-ray absorption spectroscopy in quantifying the energies and orbital compositions of final state wavefunctions associated with various X-ray induced transitions in transition-metal containing minerals. It also shows that reasonably accurate M-O distances can be obtained for individual bonds oriented in crystallographically non-equivalent directions.  相似文献   

4.
  相似文献   

5.
The elucidation of thermal histories by geochronological and isotopic means is based fundamentally on solid-state diffusion and the concept of closure temperatures. Because diffusion is thermally activated, an analytical solution of the closure temperature (T c *) can only be obtained if the diffusion coefficient D of the diffusion process is measured at two or more different temperatures. If the diffusion coefficient is known at only one temperature, however, the true closure temperature (T c *) cannot be calculated analytically because there exist an infinite number of possible (apparent) closure temperatures (Tˉ c ) which can be generated by this single datum. By introducing further empirical constraints to limit the range of possible closure temperatures, however, mathematical analysis of a modified form of the closure temperature equation shows that it is possible to make both qualitative and quantitative estimates of T c * given knowledge of only one diffusion coefficient D M measured at one temperature T M . Qualitative constraints of the true closure temperature T c * are obtained from the shapes of curves on a graph of the apparent T c (Tˉ c ) vs. activation energy E, in which each curve is based on a single diffusion coefficient measurement D M at temperature T M . Using a realistic range of E, the concavity of the curve shows whether T M is less than, approximately equal to, or greater than T c *. Quantitative estimates are obtained by considering two dimensionless parameters [ln êRT^ c vs. T c */T M ] derived from these curves. When these parameters are plotted for known argon diffusion data and for a given diffusion size and cooling rate, it is found that the resultant curves are almost identical for all of the commonly dated K–Ar minerals – biotite, phlogopite, muscovite, hornblende and orthoclase – in spite of differences in their diffusion parameters. A common curve for Ar diffusion can be derived by least-squares fitting of all the Ar diffusion data and provides a way of predicting a “model” closure temperature T cm from a single diffusion coefficient D M at temperature T M . Preliminary diffusion data for a labradorite lead to a T cm of 507 ± 17 °C and a corresponding activation energy of about 65 kcal/mol, given a grain size of 200 μm and a cooling rate of 5 °C/Ma. Curves for He diffusion in silicates (augite, quartz and sanidine) also overlap to a significant degree, both among themselves and with the Ar model curve, suggesting that a single model curve may be a good representation of noble gas closure temperatures in silicates. An analogous model curve for a selection of 18O data can also be constructed, but this curve differs from the Ar model curve. A single model curve for cationic species does not appear to exist, however, suggesting that chemical bonding relationships between the ionic size/charge and crystal structure may influence the closure temperatures of diffusing cations. An indication of the degree of overlap among the various curves for Ar, He, 18O and cations is also obtained by considering the dimensionless parameter E/RT c *; for the noble gases and 18O, E/RT c * values for the respective minerals are very similar, whereas for cations, there is significant dispersion. Given these constraints, this may be a potential method of estimating closure temperatures for certain diffusing species when there are limited diffusion data. Received: 1 July 1999 / Accepted: 24 March 2000  相似文献   

6.
In-situ synchrotron X-ray diffraction (XRD) experiments of a natural apatite with the formula of Ca5(PO4)3F0.94Cl0.06 were carried out using a diamond anvil cell and angle-dispersive technique at Photon Factory (PF), Japan. Pressure–volume data were collected up to 7.12 GPa at 300 K. The pressures were determined from the ruby fluorescence spectra shift. The unit-cell parameters and volume decreased systematically with increasing pressure, and a reliable isothermal bulk modulus and its pressure derivative were obtained in this study. The third-order Birch–Murnaghan equation of state yielded the isothermal bulk modulus of KT=91.5(38) GPa, its pressure derivative KT= 4.0(11), and the zero-pressure volume V0=524.2(3) Å3.  相似文献   

7.
This paper is an extension of the earlier one dealing with kyanite in which the best fitting value of the oxygen ligand distance for Cr3+ is adopted to study the spectroscopic properties of Cr3+ ions doped at the two possible Al sites in the other two polymorphs of the aluminosilicate group (Al2O3 · SiO2), namely, andalusite and sillimanite. The superposition model and the crystal field analysis package recently developed for 3d ions doped at arbitrary low symmetry sites in crystals are used to predict energy levels and statevectors within the whole 3d 3 configuration. Then the values of the ground state zerofield splitting for Cr3+ ions at each Al sites in the two crystals are obtained. The splittings of the lower excited states 2 E and 4 T 2 as well as the admixture of 4 T 2 into 2 E have also been predicted. Comparison of our results with the available experimental data enable us to correlate the optical and EPR Spectroscopic properties with the substitutional Cr3+ sites. The conclusion is that in andalusite and sillimanite only the Al sites with nearly-octahedral six-fold coordination seem to be occupied by Cr3+ ions.  相似文献   

8.
Small grains of Ru–Os–Ir sulfides or alloys that formed in the early stages of the crystallization of basaltic magmas occur as inclusions in chromitites from many ophiolite complexes, Ural/Alaskan-type and layered intrusions. The nature of platinum-group elements is debated, i.e., whether they originally occurred in a metallic state or bonded with sulfur or other ligands. The application of kinetics and suggestions regarding the mechanisms of PGE formation may contribute to a better understanding of the genetic processes for platinum-group mineral (PGM) formation. The aim of the present study is to investigate the type of mechanism (associative, dissociative or interchange) and the possibility of direct formation of PGM from the reaction of free metals with sulfur, defining also the structure of possible intermediate species.The literature on the grain sizes (r) of platinum-group minerals (PGM) and their formation temperatures (range between 700 and 1100 °C) reveals an Arrhenius temperature dependence. The activation energy was estimated to be 450 ± 45 kJ mol−1. Applying the Eyring equation to the same data, a linear relationship between 2.5ln(r) + ln(T) versus 1/T was obtained, leading to an estimation of the free energy of activation, ΔG≠ = 440 ± 43 kJ mol−1. The thermodynamic relation ΔG≠ = ΔH≠ − TΔS≠, used together with the relation ΔΗ≠ = Eact − RT leads to the calculation of ΔS≠ at various temperatures. The estimated entropy of activation at various temperatures being almost zero, we suggest an interchange mechanism for PGM formation.The possibility of PGM formation from the direct reaction of free metals with sulfur would be inconsistent with the estimated entropy of activation values (ΔS≠  0) at various temperatures. In the cases of PGMs of known r, the formation temperatures can be estimated, and then the free energy of activation obtained, applying 2.5ln(r) + ln(T) versus 1/T (straight line). From that value, the entropy of activation can be calculated [ΔS≠ = −R + (Eact − ΔG≠)/T], and an interchange mechanism is proposed. Furthermore, applying the relation of 2.5ln(r) + ln(T) versus 1/T on PGM grains of known r and T, an interchange mechanism for their formation can be suggested if they fit the above line.  相似文献   

9.
The distribution of rare earth elements (REE) between clinopyroxene (cpx) and basaltic melt is important in deciphering the processes of mantle melting. REE and Y partition coefficients from a given cpx-melt partitioning experiment can be quantitatively described by the lattice strain model. We analyzed published REE and Y partitioning data between cpx and basaltic melts using the nonlinear regression method and parameterized key partitioning parameters in the lattice strain model (D 0, r 0 and E) as functions of pressure, temperature, and compositions of cpx and melt. D 0 is found to positively correlate with Al in tetrahedral site (Al T ) and Mg in the M2 site (MgM2) of cpx and negatively correlate with temperature and water content in the melt. r 0 is negatively correlated with Al in M1 site (AlM1) and MgM2 in cpx. And E is positively correlated with r 0. During adiabatic melting of spinel lherzolite, temperature, Al T , and MgM2 in cpx all decrease systematically as a function of pressure or degree of melting. The competing effects between temperature and cpx composition result in very small variations in REE partition coefficients along a mantle adiabat. A higher potential temperature (1,400°C) gives rise to REE partition coefficients slightly lower than those at a lower potential temperature (1,300°C) because the temperature effect overwhelms the compositional effect. A set of constant REE partition coefficients therefore may be used to accurately model REE fractionation during partial melting of spinel lherzolite along a mantle adiabat. As cpx has low Al and Mg abundances at high temperature during melting in the garnet stability field, REE are more incompatible in cpx. Heavy REE depletion in the melt may imply deep melting of a hydrous garnet lherzolite. Water-dependent cpx partition coefficients need to be considered for modeling low-degree hydrous melting.  相似文献   

10.
依据烃源岩地球化学实验手段和油气地化理论,对辽东湾地区辽中凹陷东营组东二下段(Ed2-1)和东三段(Ed3)地层进行了有机地化分析。在实验获取总有机碳(TOC)、生烃潜量(S1+S2)、氢指数(IH)、氢碳比(H/C)、氧碳比(O/C)、最大热解峰温(Tmax)、镜质体反射率(Ro)等有机地化参数的基础上,对有机质丰度、类型、成熟度等进行了系统分析,同时对东营组烃源岩进行了综合评价。研究表明,东二下段S1+S2集中在0~3 mg/g,TOC集中在0%~1.5%;东三段S1+S2集中分布在4~9 mg/g之间,TOC集中分布在1%~1.25%。东二下段有机质类型主要是III型,东三段有机质类型为II1、II2型。东二下段Ro0.5,东三段Ro0.5,并且随着深度的增加东三段烃源岩Ro相应的增加。Tmax随着深度的增加呈现出先增加后减少的异常现象,该种异常现象出现的原因与烃源岩有机质类型和有机质丰度之间存在很大关联。  相似文献   

11.
Isobaric volume measurements for MgO were carried out at 2.6, 5.4, and 8.2 GPa in the temperature range 300–1073 K using a DIA-type, large-volume apparatus in conjunction with synchrotron X-ray powder diffraction. Linear fit of the thermal expansion data over the experimental pressure range yields the pressure derivative, (∂α/∂P) T , of −1.04(8) × 10−6 GPa−1 K−1 and the mean zero-pressure thermal expansion α0, T  = 4.09(6) × 10−5 K−1. The α0, T value is in good agreement with results of Suzuki (1975) and Utsumi et al. (1998) over the same temperature range, whereas (∂α/∂P) T is determined for the first time on MgO by direct measurements. The cross-derivative (∂α2/∂P∂T) cannot be resolved because of large uncertainties associated with the temperature derivative of α at all pressures. The temperature derivative of the bulk modulus, (∂K T/∂T) P , of −0.025(3) GPa K−1, obtained from the measured (∂α/∂P) T value, is in accord with previous findings. Received: 2 April 1999 / Revised, accepted: 22 June 1999  相似文献   

12.
Thermal diffusivity (D) of garnets with diverse chemical compositions was measured using the laser-flash technique, which is accurate (±2%) and isolates the lattice component from direct radiative transfer. Temperatures ranged from ~290 to ~1,600 K (unless limited by melting). Seven synthetic (e.g., YAG, GGG) and 15 natural garnets with two types of ionic substitution [Ca3(Fe,Al)2Si3O12 and (Mg,Fe,Ca)3Al2Si3O12] and varying amounts of OH- were examined. Cation substitution or hydroxyl incorporation lowers D from end-member values. Thermal diffusivity is constant once the temperature (T) exceeds a critical value (T sat) of ~1,100 to 1,500 K. From ~290 K to T sat, the measurements are best represented by 1/D=A+BT+CT 2 where A, B, and C are constants. These constants vary little among diverse chemical compositions, suggesting that the oxygen sublattice controls heat transport. Higher order terms are needed only when T sat is low, such as Ant Hill garnet wherein 1/D=0.049403+0.0032299T−2.3992T 2×10−6+6.0168T 3×10−10(1/D in s/mm2; T in K). The mean free path (λ, computed from D and sound velocities) is slightly larger than the lattice parameter above T sat, in accord with phonon–phonon interactions requiring non-localized modes. At most temperatures, λ is nm-sized. Large values of λ are obtained by extrapolation to a few Kelvins, suggesting that boundary scattering can only be important at extremely cold temperatures. The observed behavior with T and chemical composition is consistent with the damped harmonic oscillator model. Phonon transport is best represented by inverse thermal diffusivity wherein 1/D goes as T n where n is between 1 and 3 up to ~200 K, depends on a quadratic or cubic polynomial at moderate T, but is constant above T sat. The predicted and observed temperature response of 1/D mimics the well-known form for heat capacity, in that acoustic modes control heat transport near cryogenic temperatures, optic phonons dominate above ambient temperature, and a limit analogous to that of Dulong and Petit is reached at very high temperature, due to full population of discrete phonon states.  相似文献   

13.
Using a conventional high-T furnace, the solid solutions between magnesiochromite and manganochromite, (Mg1−x Mn x )Cr2O4 with x = 0.00, 0.19, 0.44, 0.61, 0.77 and 1.00, were synthesized at 1,473 K for 48 h in open air. The ambient powder X-ray diffraction data suggest that the V–x relationship of the spinels does not show significant deviation from the Vegard’s law. In situ high-T powder X-ray diffraction measurements were taken up to 1,273 K at ambient pressure. For the investigated temperature range, the unit-cell parameters of the spinels increase smoothly with temperature increment, indicating no sign of cation redistribution between the tetrahedral and octahedral sites. The V–T data were fitted with a polynomial expression for the volumetric thermal expansion coefficient (aT = a0 + a1 T + a2 T - 2 \alpha_{T} = a_{0} + a_{1} T + a_{2} T^{ - 2} ), which yielded insignificant a 2 values. The effect of the composition on a 0 is adequately described by the equation a 0 = [17.7(8) − 2.4(1) × x] 10−6 K−1, whereas that on a 1 by the equation a 1 = [8.6(9) + 2.1(11) × x] 10−9 K−2.  相似文献   

14.
Using powder X-ray diffraction of heated solids to pressures reaching 68 GPa, the pressure-volume-temperature (PVT) data on corundum Al2O3 and ɛ-Fe were determined with the following results: *Corundum,*Iron, *Al2O3*ɛ-Fe Isothermal bulk*258 (2)*164 (3)  modulus K'300, 1 (GPa) Pressure derivative K300, 1*4.88 (4)*5.36 (16) Temperature derivative*–0.020 (2)*–0.043 (3)  (∂K T,1 /∂T) P (GPa/K) Molar volume V300,1*25.59 (2)*6.76 (2)  (cm3/mol) Isobaric thermal expansion at 1 atm (0.101 MPa) is given by (K–1): α T =2.6 (2) 10–5+1.81 (9) 10–9 T–0.67 (6)/T 2 for corundum, and α T =5.7 (4) 10–5+4.2 (4) 10–9 T–0.17 (7)/T 2 for iron ɛ-Fe. Received: 1 March 1997 / Revised, accepted: 21 August 1997  相似文献   

15.
Four new types of paramagnetic centers — NH+ 3, N2?, Al-O?, E 1 — have been detected in microcline perthites from pegmatites in the Ukrainian Shield. Values are tabulated for their g and A tensors and limits of thermal stability determined. The NH+ 3 center substitutes the K+ ion. It occurs naturally in potash feldspars but is intensified by gamma or X-ray irradiation. It is regarded as a radiational development of the more general NH+ 4 ? K+ isomorphism. It disappears after heating to temperatures higher than 470 K. The N2? center is an uncommon example of isomorphous substitution of a bridging oxygen, being located on a O D(m) site between T 2(o) and T 1(m) silicon sites. It is stable to 820 K. The hole center, Al-O?, has been detected on an O A(l) oxygen shared by T 1(o) and T 1(m) tetrahedra. It is stable to 590 K. The E 1 center in these alkali feldspars is similar to the E 1 center in quartz, being an electron trapped in an oxygen vacancy in the O B (o) position. It is stable to 420 K. The NH+ 3, Al-O? and E 1 centers can be restored from temperatures above their stability limits by gamma radiation. Concentration of centers varies from sample to sample depending on conditions of formation and subsequent history of the minerals.  相似文献   

16.
 The thermoelastic parameters of natural andradite and grossular have been investigated by high-pressure and -temperature synchrotron X-ray powder diffraction, at ESRF, on the ID30 beamline. The P–V–T data have been fitted by Birch-Murnaghan-like EOSs, using both the approximated and the general form. We have obtained for andradite K 0=158.0(±1.5) GPa, (dK/dT )0=−0.020(3) GPa K−1 and α0=31.6(2) 10−6 K−1, and for grossular K 0=168.2(±1.7) GPa, (dK/dT)0=−0.016(3) GPa K−1 and α0=27.8(2) 10−6 K−1. Comparisons between the present issues and thermoelastic properties of garnets earlier determined are carried out. Received: 7 July 2000 / Accepted: 20 October 2000  相似文献   

17.
The synthetic amphibole Na0.95(Li0.95Mg1.05)Mg5Si8O22(OH)2 was studied in situ at high-T, using IR OH-stretching spectroscopy and synchrotron X-ray powder diffraction. At room-T the sample has P21 /m symmetry, as shown by the FTIR spectrum. It shows in the OH region two well-defined and intense absorptions at 3,748 and 3,712 cm−1, respectively, and two minor bands at 3,667 and 3,687 cm−1. The main bands are assigned to the two independent O–H groups in the primitive structure. The two minor bands evidencing the presence of small amount of vacant A-site (A□0.05). With increasing T, these bands shift continuously and merge into a unique absorption at high temperature. A change as a function of increasing T is revealed by the evolution of the refined unit-cell parameters, whose trend shows a transition to C2/m at about 320–330°C. The spontaneous scalar strain, fitted with a tricritical 2–6 Landau potential, gives a T c of 325(10)°C (β parameter = 0.27). Comparison with the second-order P21 /m ⇔ C2/m phase transition at 255°C for synthetic amphibole ANa0.8B(Na0.8Mg1.2)CMg5Si8O22(OH)2 indicates that the substitution of Na with Li at the B-sites strongly affects the thermodynamic character and the T c of the phase transition. The comparison of LNMSH amphiboles with cummingtonitic ones shows that the high-T thermodynamic behaviour is affected by A-site occupancy.  相似文献   

18.
A pressure-volume-temperature data set has been obtained for lawsonite [CaAl2Si2O7(OH)2.H2O], using synchrotron X-ray diffraction and an externally heated diamond anvil cell. Unit-cell volumes were measured to 9.4 GPa and 767 K by angle dispersive X-ray diffraction using imaging plates. Phase changes were not observed within this pressure-temperature range, and lawsonite compressed almost isotropically at constant temperature. The P-V-T data have been analyzed using a Birch- Murnaghan equation of state and a linear equation of state expressed as β=–1/V0 (∂V/∂P) T . At room temperature, the derived equation of state parameters are: K 0=124.1 (18) GPa K'0 set to 4) and β–1=142.0(24) GPa, respectively. Our results are intermediate between previously reported measurements. The high-temperature data show that the incompressibility of lawsonite decreases with increasing temperature to ∼500 K and then increases above. Hence, the second order temperature derivative of the bulk modulus is taken into account in the equation of state; a fit of the volume data yields K 0=123.9(18) GPa, (∂K/∂T)P=–0.111(3) GPa K–1, (∂2 K/∂T 2)P=0.28(6) 10–3 GPa K–2, α0=3.1(2) 10–5 K–1, assuming K'0=4. Received: 2 June 1998 / Revised, accepted: 12 Ocotber 1998  相似文献   

19.
The morphology and sedimentology of glacially influenced fan-deltas on massifs at the margin of the southern Altiplano, Bolivia, suggest a broadly synchronous expansion of glaciers and palaeolake Tauca during the late-glacial interval. This is shown by sedimentary successions of glacigenic, glacifluvial and glacideltaic facies linking palaeoglaciers with palaeolake Tauca on the flanks of Cerro Azanaques and Cerro Tunupa at altitudes of 3770–3720 m. Radiocarbon dates from peat overlain by glacial diamict and glacifluvial outwash indicate that glaciers in this area reached their last glacial maximum extent after ca. 13 300 14 C yr BP. Glacifluvial fan-deltas contiguous with the moraines confirm that the advance coincided with a highstand of palaeolake Tauca radiocarbon dated to the interval ca. 13 500–11 500 yr BP. Modeling of climatic controls on this glacier advance suggests the primary forcing was increased summer (wet season) moisture, possibly amounting to 600 mm above the modern values of 200–400 mm. Greater cloud cover probably depressed local temperatures and reduced the evaporation rate. The consequent rise in effective annual moisture ( P − E ) comfortably accommodates a palaeolake 48–50 × 10 3 km 2 in area and up to 100 m deep in the southern Altiplano. Because the palaeoglacier equilibrium-line altitudes rose toward the south and west, like the gradient of modern precipitation totals, we conclude that the increased late-glacial moisture was brought by weather systems similar to those of the present, but that atmospheric conditions were cloudier and cooler. © 1997 John Wiley & Sons, Ltd.  相似文献   

20.
川西坳陷新场构造带须家河组超压演化与流体的关系   总被引：1，自引：0，他引：1  
沉积盆地超压体系是油气勘探与开发过程中一个不容忽视的问题,不仅影响了地质流体的运移和聚集,更为勘探带来安全隐患。以实测地压和油田水化学数据为基础,对川西坳陷新场构造带须四段和须二段现今地层水矿化度与现今压力系数关系进行比较,结合地层水特征系数和阴阳离子关系,综合前人研究结果,对须四段和须二段压力演化史与地层水演化过程进行分析,考察川西坳陷须家河组超压系统演化与地层水演化的耦合关系。结果表明,须家河组超压发育与地层水具有密切的联系:(1)须家河组储层段压力分布范围较广,在弱超压至超强压之间,须二段属于中超压而须四段属于超高压,平面分布中须二段探测井中矿化度随压力系数增加而减少,须四段则相反;(2)在压实过程中,由于流体排驱受阻导致"欠压实"超压的产生,随着超压的不断积聚,局部出现裂缝,导致地层水更加强烈的混合作用和运移;(3)生烃作用导致自生压力增大,地层水离子水岩作用强烈,造成流体包裹体与现今地层水离子成分分异;(4)构造挤压抬升过程中,须四段裂缝不发育,压力进一步升高,须二段则产生泄压,出现了凝析水和水侵现象,造成须四段和须二段现今地层水特征的差异。  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号