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131.
Thermal expansion during the first heating cycle at atmospheric pressure was measured in several directions in seven igneous rocks between 25° and 400°C at slow heating rates. The coefficient of thermal expansion measured under these conditions increases more rapidly as temperature is increased than the average thermal expansion coefficient of the constituent minerals. The “extra” expansion is attributed to the formation of cracks by differential expansion of mineral grains. The presence of such cracks in the rocks during the cooling part of the cycle and during any subsequent heating and cooling cycles will result in a substantial decrease in the coefficient of thermal expansion as compared to that measured during the first heating cycles. The effect of cracks initially present in a rock was studied by measuring the full tensor of the coefficient of thermal expansion on two rocks with anisotropic crack distributions. In these two rocks the coefficient of thermal expansion is least in the direction perpendicular to the plane of greatest crack concentration. The implication of our data is that thermal expansion depends greatly on the fracture state of the rock. Both the fractures in the rock and the boundary conditions on the rock are significant for the interpretation of thermal expansion measurements and for their application to other problems. 相似文献
132.
Michael W. Ovenden Terry Feagin Otis Graf 《Celestial Mechanics and Dynamical Astronomy》1974,8(4):455-471
The Principle of Least Interaction Action, which explains the observed preference in the Solar System for two-satellite resonant configurations, is shown to apply also to the Laplacean satellites of Jupiter and Uranus, in the sense that these triplet resonant structures lie close to configurations for which the time-mean of the action associated with the mutual interaction of the satellites is an overall minimum. Far from the minimum configuration, significant changes take place in the major semi-axes on time-scales ~106-107y. Both systems require times ~108 y to come close to the minimum configuration; to approach resonance to the observed precision of the Laplace relationship (3×10?4 for the Uranian case, 2×10?7 for the Jovian case) requires, for both systems, a time closely comparable with the age of the solar system. 相似文献
133.
W. Edwin Sharp 《Mathematical Geology》2007,39(8):785-786
134.
F. Moseley J.C. Cuttell E.W. Lange D. Stevens J.R. Warbrick 《Journal of Structural Geology》1981,3(3):237-251
The Pre-Betic is the most northerly of the Alpine zones forming the Betic Cordilleras of southern Spain. It consists of strongly folded and faulted Mesozoic and Tertiary rocks, the oldest of which are ferruginous and gypsiferous Triassic mudstones, followed by a predominantly carbonate facies of Cretaceous, Palaeogene and Miocene age. Although this sequence is interrupted by a number of minor unconformities, the major structures were formed during the middle or late Miocene. The highly incompetent Triassic rocks are the most strongly deformed, and form diapiric intrusions discordant to regional structural trends in the younger rocks. The latter are essentially of two facies: massive competent limestones which are deformed by relatively simple folds of large wavelength, and highly incompetent marl-limestone interbeds with complex disharmonic folds and crush belts. Faults include low-angle and high-angle thrusts, gravity slides and wrench faults. The regional tectonic strike is ENE to NE, but the diapiric intrusions mostly follow WNW and N directions. These intrusions have pushed the younger rocks aside, the result being polyphase structures of several trends.Less intense post-Miocene tectonics are mostly associated with continued diapirism and have resulted in the folding and tilting of the late Miocene to Quaternary elastic sediments. 相似文献
135.
136.
The Lyα forest absorption lines in the spectra of quasars are interpreted as caused by the crossings of the light beam with the walls of a bubble structure (expanding with the Hubble flow only). Then, the typical separation between the absorption lines is proportional to the mean size of the bubbles. The variable factor is the expansion rate H[z]. The Friedmann regression analysis of the observed line separations determines the density parameter ω0 and the normalized cosmological term λ0 = λc2/3H20 of the appropriate cosmological model: ω0 = 0.014 ± 0.002, λ0 = 1.080 ± 0.006. Depending on the Hubble parameter this method reveals the values of the present mean matter density pm,0 = 2.6 h2 · 10−28 kg m−3 and of the cosmological constant Λ = 3.77 h2 · 10−52 m−2 (with h = H0/(100 km/s·Mpc)). According to our analysis all models with Λ = 0 must be excluded. The curvature of space is positive. The curvature radius R0 is 3.3 times the Hubble radius (c/H0). The age t0 is 2.8 times the Hubble age (H0−1). 相似文献
137.
Selected-area measurements of lead-isotope ratios in zircons have been made at high mass resolution using a modified A.E.I. IM20 ion-microprobe. At a working resolution of 3200 it is shown that the important interfering molecular peaks generated from the zircon matrix may be separated from atomic lead peaks. Corrections for overlapping peaks, which are necessary in measurements of lead isotopes at low mass resolution, are then only required for 208Pb.Measurements on N.B.S. standards show no isotope discrimination within counting statistics. Determination of 207Pb/206Pb on 29 single zircon grains from a tonalite gneiss and a granite from Lac Seul, northwestern Ontario, give very variable ratios with mean values close to those of bulk separates. Peaks in the distribution of 207/206 ratios obtained from the tonalite gneiss may be interpreted as evidence for two stages of lead loss. High 207/206 ratios are shown to be significant for at least two zircons and probably record a minimum age of formation of 3.3 ± 0.1 b.y. for the gneiss. 相似文献
138.
W. C. Zhu C. H. Wei J. Liu T. Xu D. Elsworth 《Rock Mechanics and Rock Engineering》2013,46(6):1353-1366
It has been widely reported that coal permeability can change from reduction to enhancement due to gas adsorption even under the constant effective stress condition, which is apparently inconsistent with the classic theoretical solutions. This study addresses this inconsistency through explicit simulations of the dynamic interactions between coal matrix swelling/shrinking induced damage and fracture aperture alteration, and translations of these interactions to permeability evolution under the constant effective stress condition. We develop a coupled coal–gas interaction model that incorporates the material heterogeneity and damage evolution of coal, which allows us to couple the progressive development of damage zone with gas adsorption processes within the coal matrix. For the case of constant effective stress, coal permeability changes from reduction to enhancement while the damage zone within the coal matrix develops from the fracture wall to further inside the matrix. As the peak Langmuir strain is approached, the decrease of permeability halts and permeability increases with pressure. The transition of permeability reduction to permeability enhancement during gas adsorption, which may be closely related to the damage zone development in coal matrix, is controlled by coal heterogeneity, external boundary condition, and adsorption-induced swelling. 相似文献
139.
Atmospheric composition is a key control on climate and the habitability of planetary surfaces. Ablation of infalling micrometeorites has been recognised as one way in which atmospheric chemistry can be changed, especially at times in solar system history when the infall rates of exogenous material were high. Despite its potential to influence climate and habitability, extraterrestrial sulphur dioxide is currently an unquantified contribution to the atmospheres of the terrestrial planets. We have used flash pyrolysis to simulate the atmospheric entry of micrometeorites and Fourier-transform infrared spectroscopy to identify and quantify the sulphur dioxide produced from the carbonaceous meteorites Orgueil (CI1), ALH 88045 (CM1), Cold Bokkeveld (CM2), Murchison (CM2) and Mokoia (CV3). We have used this approach to understand the introduction of sulphur dioxide to the atmospheres of Earth and Mars from infalling micrometeorites. Sulphates, present in carbonaceous chondrites at a few wt.%, are resistant to thermal decomposition, limiting the yields of sulphur dioxide from unmelted micrometeorites. Infalling micrometeorites are a minor source of present-day sulphur dioxide on Earth and Mars, calculated to be up to around 2400 tonnes and about 350 tonnes, respectively. During the Late Heavy Bombardment (LHB), the much greater infall rates of micrometeoritic dust are calculated to be associated with average production rates of sulphur dioxide of around 20 Mt yr−1 for the early Earth and 0.5 Mt yr−1 for early Mars, for a LHB of 100 Myr. These rates of delivery of sulphur dioxide at high altitudes would have reduced the solar energy reaching the surfaces of these planets, via scattering of sunlight by stratospheric sulphate aerosols, and may have had detrimental effects on developing biospheres by promoting cooler climates and reducing the probability of liquid water on planetary surfaces. 相似文献
140.
Richard L. Reynolds Joseph G. Rosenbaum Josh Rapp Michael W. Kerwin J. Platt Bradbury Steven Colman David Adam 《Journal of Paleolimnology》2004,31(2):217-233
Petrological and textural properties of lacustrine sediments from Upper Klamath Lake, Oregon, reflect changing input volumes of glacial flour and thus reveal a detailed glacial history for the southern Cascade Range between about 37 and 15 ka. Magnetic properties vary as a result of mixing different amounts of the highly magnetic, glacially generated detritus with less magnetic, more weathered detritus derived from unglaciated parts of the large catchment. Evidence that the magnetic properties record glacial flour input is based mainly on the strong correlation between bulk sediment particle size and parameters that measure the magnetite content and magnetic mineral freshness. High magnetization corresponds to relatively fine particle size and lower magnetization to coarser particle size. This relation is not found in the Buck Lake core in a nearby, unglaciated catchment. Angular silt-sized volcanic rock fragments containing unaltered magnetite dominate the magnetic fraction in the late Pleistocene sediments but are absent in younger, low magnetization sediments. The finer grained, highly magnetic sediments contain high proportions of planktic diatoms indicative of cold, oligotrophic limnic conditions. Sediment with lower magnetite content contains populations of diatoms indicative of warmer, eutrophic limnic conditions. During the latter part of oxygen isotope stage 3 (about 37–25 ka), the magnetic properties record millennial-scale variations in glacial-flour content. The input of glacial flour was uniformly high during the Last Glacial Maximum, between about 21 and 16 ka. At about 16 ka, magnetite input, both absolute and relative to hematite, decreased abruptly, reflecting a rapid decline in glacially derived detritus. The decrease in magnetite transport into the lake preceded declines in pollen from both grass and sagebrush. A more gradual decrease in heavy mineral content over this interval records sediment starvation with the growth of marshes at the margins of the lake and dilution of detrital material by biogenic silica and other organic matter. 相似文献