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151.
Relationships between reference mafic dikes and deformations in the Gridino zone, Belomorian province, Fennoscandian Shield, make it possible to subdivide the deformations into three groups: pre-dike, synmagmatic, and post-dike. The Neoarchaean eclogite-bearing mélange was formed by disintegration of large eclogite slices in the course of ductile flow, which was associated with synkinematic granitoid magmatism and metamorphism varying from the granulite to amphibolite facies. Exotic blocks, including those of eclogites, are distributed in the TTG gneisses as layers and lenses, whose thicknesses range from a few to a few hundred metres and which are conformable with the foliation. Ductile flow brought the rock complexes to the depth level where brittle–ductile deformations were possible. As a result, certain parts of the mélange were deformed in a more rigid setting. A number of mafic dike swarms were emplaced into relatively cold rocks in an extensional environment in the earliest Palaeoproterozoic. The dikes cut across all earlier structures and are thus an important benchmark for distinguishing Neoarchaean and Palaeoproterozoic processes. Post-dike (~1.9 Ga) tectonic activity was associated with local deformations and discrete metamorphic retrogression to amphibolite facies. None of them significantly affected the pre-existing regional structure. 相似文献
152.
Mathematical Geosciences - Machine-learning-based proxy models are often used to replace many of the flow simulations required in optimizations of subsurface flow processes. Because the optimizer... 相似文献
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Ulrike Hoff Oleg Dirksen Veronika Dirksen Gerhard Kuhn Hanno Meyer Bernhard Diekmann 《Boreas: An International Journal of Quaternary Research》2014,43(1):22-41
Holocene palaeolimnological conditions were reconstructed by analysing fossil diatom assemblages within a lacustrine sediment core from Lake Sokoch, southern Kamchatka (Russia). Sediments of this proglacial lake cover the past 9400 years and hence represent almost the whole Holocene history. The biosiliceous muddy sample material was analysed for several geochemical and biological parameters, such as the total organic carbon and biogenic silica content, and the diatom community (quantitative and qualitative changes). Based on changes in the relative abundances of the most frequent species Aulacoseira subarctica, Staurosira martyi and Stephanodiscus alpinus and a depth‐constrained cluster analyses (CONISS), five diatom assemblage zones could be identified. The oldest stage recovered lies between 9400 and 9000 cal. a BP and reflects the initial lake stage after the retreat of local glaciers, with a high detrital sediment supply, shallow‐water conditions and a high diatom diversity. The next zone (9000–6200 cal. a BP) shows a more mature lake system with accumulating biogenic remains and higher water levels during climate amelioration. This is followed by the most obvious change in the diatom assemblage, delineated by an occurrence of S. alpinus, between 6200 and 2700 cal. a BP. Wet conditions in spring probably led to an enhanced fluvial runoff and eutrophic to hypertrophic conditions. The end of this period might reflect climate deterioration related to the Neoglacial epoch of the Holocene. Between 2700 and 1600 cal. a BP the sediments of Lake Sokoch reveal oligotrophic water conditions in a windy high‐energy environment. The youngest interval, between 1600 cal. a BP and the Present, indicates shallow‐water conditions and a very short growing season, which might reflect the Little Ice Age. The results may offer a baseline for the interpretation of Holocene palaeoenvironmental changes in Kamchatka and their relation to regional climate change from a palaeoecological perspective. 相似文献
156.
Viacheslav G. Makarov Oleg V. Zaytsev Valentina D. Budaeva Felipe Salinas-Gonzalez 《Journal of Oceanography》2008,64(5):675-690
A unified method of approximation, extrapolation, and objective layering is offered for processing vertical oceanographic
profiles. The method is demonstrated using seawater density and consists of adjustable splitting of each individual profile
into N vertical layers based on tentative, piecewise linear homogeneous approximation with specified accuracy and a final fitting
of an N-layered analytical model to data. A set of 3N coefficients of the model includes one density value at the sea surface; N−1 depths of layer interfaces; and N pairs of coefficients that describe a profile shape within the n-th layer—an asymptotic density value (a key parameter for extrapolation) and a vertical scale of maximum density variability
(related to vertical gradient). Several distinctive characteristics of the technique are: (1) It can be used for the analysis
of the vertical structure of individual profiles when N is an unknown parameter, and spatial interpolation when N should be equal for all profiles. (2) A justified downward extrapolation of incomplete data is possible with the model, especially
if historical deepwater profiles are available. (3) Layer interfaces, as well as other coefficients, are derived with only
one fitting to the entire profile. (4) The technique, using its general formulation, can serve as a parent for developing
various types of models. The simpler step-like (with hyperbolic or exponential approximation) and more complicated smooth
(continuous in gradient space) models were designed and tested against a large number of density profiles from the Sea of
Okhotsk and the Gulf of California. Comparison of parametric, z-levels and isopycnal averaging was done for the region off the northeastern coast of Sakhalin. 相似文献
157.
Yuliy A. Dashevsky Semen Petrov Alexandr N. Vasilevskiy Oleg B. Bocharov Gleb V. Dyatlov 《Studia Geophysica et Geodaetica》2017,61(1):69-92
Reliable estimates of the fluid pressure in the pore space of rocks are critical for different aspects of petroleum exploration and production including injection operations and scenarios of water flooding. Numerous approaches are available for formation pore pressure evaluation, however, these measurements become a challenge inside a cased borehole, and a list of possible options is short: either the casing is to be perforated, or the production tubing needs to be disconnected to perform the pressure tests. We present a method for through-casing evaluation of formation pore pressure without shutting down production. We suggest equipping an observation well with a borehole gravimeter and acquiring time variations of the vertical component of the gravity field. Changes in gravity occur during gas production and are related to time variations of formation pore pressure. Gravity changes obtained in the observation well are supposed to be inverted for time-dependent formation pore pressure variations beyond the casing. Our results and recommendations are based on numerical modeling of pore pressure spatial distribution during gas field exploitation and relevant changes in borehole gravity. Benchmark models were elaborated in order to consider a dynamic process of pressure changes in time and space under conditions similar to those in the Medvezhye gas field (Russia). Different modeling scenarios are considered for early and late stages of gas field exploitation. The sensitivity analysis was performed to estimate quantitatively a sensitivity of borehole temporal gravity changes to variations in formation pore pressure behind the casing. Based on resolution analysis we justify the possibility to extract the gravity measurements directly related to changes in pore pressure from the total changes in the gravity field due to reservoir exploitation. The impact of pore pressure on the gravity field measured in boreholes during the water flooding is also evaluated, and obtained results are discussed. 相似文献
158.
This paper is concerned with the hydroelastic responses of a mat-like, rectangular very large floating structure (VLFS) edged with a pair of horizontal/inclined perforated anti-motion plates in the context of the direct coupling method. The updated Lagrangian formulae are applied to establish the equilibrium equations of the VLFS and the total potential formula is employed for fluids in the numerical model including the viscous effect of the perforated plates through the Darcy''s law. The hybrid finite element-boundary element (FE-BE) method is implemented to determine the response reduction of VLFS with attached perforated plates under various oblique incident waves. Also, the numerical solutions are validated against a series of experimental tests. The effectiveness of the attached perforated plates in reducing the deflections of the VLFS can be significantly improved by selecting the proper design parameters such as the porous parameter, submergence depth, plate width and inclination angle for the given sea conditions. 相似文献
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Karibibite (ideally, Fe2As4O9) occurs in vugs in massive loellingite of the Karibib pegmatite area, South West Africa. It is brownish yellow and finely fibrous. The thickness of the soft, single fibers is less than 1 micron, unsuitable for single-crystal X-ray study. Electron diffraction and X-ray powder pattern indicate that the mineral is orthorhombic, with . The space group cannot be given. The mineral is paramagnetic with yellow fluorescence and is pleochroic with γ > 2.10, α = 1.96, 2Vα large, d = 4.07. It is soluble in acids and alkali hydroxide. Decomposition starts around 320 °C. The infra-red absorption spectrum indicates absence of AsO4 groups. The mineral is classified tentatively as an oxide or arsenite. 相似文献