Multivariate Geostatistïcal Analysis of Ground-Water Contamination: A Case History     

Jonathan D. Istok  Jeffrey D. Smyth  Alan L. Flint 《Ground water》1993,31(1):63-74

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The stress release hypothesis of magma formation     

Robert J. Uffen  Alan M. Jessop 《Bulletin of Volcanology》1963,26(1):57-66

The possibility of magma formation due to the release of stresses in the Crust and Upper Mantle of the Earth is examined for both tensile and compressive failure. The correlation of volcanic activity with shallow and intermediate focus earthquakes is examined in the light of new experimental data on the strength of rocks, and recent theories of the thermal history of the Earth. It is found that in association with earthquakes, granitic magmas may be generated between depths of approximately 15 and 50 kilometers; basaltic magmas between 50 and 100 kilometers; while duntic magmas are unlikely to be generated in this manner.  相似文献   

The opacity of some local Martian dust storms observed by the Viking IRTM     

Garry E. Hunt  Elizabeth A. Mitchell  Alan R. Peterfreund 《Icarus》1980,41(3):389-399

In this paper we analyze some Viking infrared thermal mapping (IRTM) measurements of local Martian dust storms observed in the southern tropical region of the planet between L_s=225 and 262°. The derived opacities of these storms show that in the most opaque regions of the cloud, the optical thickness may be ≈6. Away from the individual clouds, the opacity is ≈2, which is still about four times the background level of dustiness in the Martian atmosphere. We find considerable structure in the derived opacity which will create corresponding variations in the atmospheric heating, which in turn may have an important feedback upon the local winds.  相似文献   

Measurements of solar magnetic fields by Fourier transform techniques     

Theodore D. Tarbell  Alan M. Title 《Solar physics》1976,47(2):563-573

The Fourier techniques of Paper I have been exhaustively calibrated using Unno's results for the absorption profile of a simple Zeeman triplet. If a simple transformation is applied to the normalized line depths, then magnetic field strengths and inclination angles can be measured very accurately from noisy, saturated line profiles. Systematic errors caused by saturation effects can be estimated and reduced by varying one parameter. When a significant fraction of the line profile is unsplit and unpolarized, large errors may be made in measurements of low fields, unless the line is sufficiently weak. For a weak line, a vertical field of 1600 gauss can be measured to 10% accuracy even when 70% of the line profile is stray light. These stray light errors are troublesome in measuring fields of gaps and pores but not sunspots. Numerical results of our error analysis are presented graphically.  相似文献   

Composite synvolcanic intrusions associated with Precambrian VMS-related hydrothermal systems   总被引：2，自引：0，他引：2  

Alan?G.?GalleyEmail author 《Mineralium Deposita》2003,38(4):443-473

Large subvolcanic intrusions are recognized within most Precambrian VMS camps. Of these, 80% are quartz diorite–tonalite–trondhjemite composite intrusions. The VMS camps spatially associated with composite intrusions account for >90% of the aggregate sulfide tonnage of all the Precambrian, intrusion-related VMS camps. These low-alumina, low-K, and high-Na composite intrusions contain early phases of quartz diorite and tonalite, followed by more voluminous trondhjemite. They have a high proportion of high silica (>74% SiO ₂) trondhjemite which is compositionally similar to the VMS-hosting rhyolites within the volcanic host-rock successions. The quartz-diorite and possibly tonalite phases follow tholeiitic fractionation trends whereas the trondhjemites fall within the composition field for primitive crustal melts. These transitional M-I-type primitive intrusive suites are associated with extensional regimes within oceanic-arc environments. Subvolcanic composite intrusions related to the Archean Sturgeon Lake and Noranda, and Paleoproterozoic Snow Lake VMS camps range in volume from 300 to 1,000 km ³. Three have a sill morphology with strike lengths between 15 and 22 km and an average thickness between 1,500 and 2,000 m. The fourth has a gross stock-like shape. The VMS deposits are principally restricted to the volcanic strata above the strike length of the intrusions, as are areally extensive, thin exhalite units. The composite intrusions contain numerous internal phases which are commonly clustered within certain parts of the composite intrusion. These clusters underlie eruptive centers surrounded by areas of hydrothermal alteration and which contain most of the VMS deposits. Early quartz-diorite and tonalite phases appear to have intruded in rapid succession. Evidence includes gradational contacts, magma mixing and disequilibrium textures. They appear to have been emplaced as sill-dike swarms. These early phases are present as pendants and xenoliths within later trondhjemite phases. The trondhjemite phases contain numerous internal contacts indicating emplacement as composite sills. Common structural features of the composite intrusions include early xenolith phases, abundant small comagmatic dikes, fractures and veins and, in places, columnar jointing. Internal phases may differ greatly in texture from fine- to coarse-grained, aphyric and granophyric through seriate to porphyritic. Mineralogical and isotopic evidence indicates that early phases of each composite intrusion are affected by pervasive to fracture-controlled high-temperature (350–450 °C) alteration reflecting seawater-rock interaction. Trondhjemite phases contain hydrothermal-magmatic alteration assemblages within miarolitic cavities, hydrothermal breccias and veins. This hydrothermal-magmatic alteration may, in part, be inherited from previously altered wall rocks. Two of the four intrusions are host to Cu-Mo-rich intrusive breccias and porphyry-type mineralization which formed as much as 14 Ma after the main subvolcanic magmatic activity. The recognition of these Precambrian, subvolcanic composite intrusions is important for greenfields VMS exploration, as they define the location of thermal corridors within extensional oceanic-arc regimes which have the greatest potential for significant VMS mineralization. The VMS mineralization may occur for 2,000 m above the intrusions. In some cases, VMS mineralization has been truncated or enveloped by late trondhjemite phases of the composite intrusions. Evidence that much of the trondhjemitic magmatism postdates the principal VMS activity is a critical factor when developing heat and fluid flow models for these subseafloor magmatic-hydrothermal systems.  相似文献   

Finite difference modeling of contaminant transport using analytic element flow solutions     

James R. Craig  Alan J. Rabideau 《Advances in water resources》2006

The two-dimensional implementation of the analytic element method (AEM) is commonly used to simulate steady-state saturated groundwater flow phenomena at regional and local scales. However, unlike alternative groundwater flow simulation methods, AEM results are not ordinarily used as the basis for simulation of reactive solute transport. The use of AEM-simulated flow fields is impeded by the discrepancy between a continuous representation of flow and a typically discrete representation of transport, and requires translation of the flow solution to a discrete analog. This paper presents a variety of methods for analytically calculating conservative discrete water fluxes and integrated components of the dispersion tensor across cell interfaces. An Eulerian finite difference method based on these AEM-derived parameters is implemented for use in simulation of 2D (vertically averaged) solute transport. This implementation is first benchmarked against existing methods that use standard finite difference flow solutions, then used to investigate the effects of an inaccurate discrete water balance. It is shown that improper translation of AEM fluxes leads to significant water balance errors and inaccurate simulation of contaminant transport.  相似文献   

Water clarity modeling in Lake Tahoe: Linking suspended matter characteristics to Secchi depth     

Theodore J. Swift  Joaquim Perez-Losada  S. Geoffrey Schladow  John E. Reuter  Alan D. Jassby  Charles R. Goldman 《Aquatic Sciences - Research Across Boundaries》2006,68(1):1-15

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Simulation of a Stably Stratified Atmospheric Boundary Layer Using One-Dimensional Turbulence     

Alan R. Kerstein  Scott Wunsch 《Boundary-Layer Meteorology》2006,118(2):325-356

One-dimensional turbulence (ODT) is a single-column simulation in which vertical motions are represented by an unsteady advective process, rather than their customary representation by a diffusive process. No space or time averaging of mesh-resolved motions is invoked. Molecular-transport scales can be resolved in ODT simulations of laboratory-scale flows, but this resolution of these scales is prohibitively expensive in ODT simulations of the atmospheric boundary layer (ABL), except possibly in small subregions of a non-uniform mesh.Here, two methods for ODT simulation of the ABL on uniform meshes are described and applied to the GABLS (GEWEX Atmospheric Boundary Layer Study; GEWEX is the Global Energy and Water Cycle Experiment) stable boundary-layer intercomparison case. One method involves resolution of the roughness scale using a fixed eddy viscosity to represent subgrid motions. The other method, which is implemented at lower spatial resolution, involves a variable eddy viscosity determined by the local mesh-resolved flow, as in multi-dimensional large-eddy simulation (LES). When run at typical LES resolution, it reproduces some of the key high-resolution results, but its fidelity is lower in some important respects. It is concluded that a more elaborate empirically based representation of the subgrid physics, closely analogous to closures currently employed in LES of the ABL, might improve its performance substantially, yielding a cost-effective ABL simulation tool. Prospects for further application of ODT to the ABL, including possible use of ODT as a near-surface subgrid closure framework for general circulation modeling, are assessed.  相似文献   

Progressive aqueous alteration of CM carbonaceous chondrites     

Alan E. Rubin  Josep M. Trigo-Rodríguez  Heinz Huber 《Geochimica et cosmochimica acta》2007,71(9):2361-2382

CM chondrites are aqueously altered rocks that contain ∼9 wt% H₂O⁺ (i.e., indigenous water) bound in phyllosilicates; also present are clumps of serpentine-tochilinite intergrowths (previously called “poorly characterized phases” or PCP), pentlandite and Ni-bearing pyrrhotite. We studied 11 CM chondrites that span the known range from least altered to most altered. We used various petrologic properties (many previously identified) that provide information regarding the degree of aqueous alteration. There are no known unaltered or slightly altered CM chondrites (e.g., rocks containing numerous chondrules with primary igneous glass). Some CM properties result from processes associated with early and intermediate stages of the alteration sequence (i.e., hydration of matrix, alteration of chondrule glass, and production of large PCP clumps). Other petrologic properties reflect processes active throughout the alteration sequence; these include oxidation of metallic Fe-Ni, alteration of chondrule phenocrysts, changes in PCP composition (reflecting an increase in the phyllosilicate/sulfide ratio), and changes in carbonate mineralogy (reflecting the development of dolomite and complex carbonates at the expense of Ca carbonate).On the basis of these parameters, we propose a numerical alteration sequence for CM chondrites. Because there are no known CM samples that display only incipient alteration, the least altered sample was arbitrarily assigned to subtype 2.6. The most altered CM chondrites, currently classified CM1, are assigned to subtype 2.0. These highly altered rocks have essentially no mafic silicates; they contain chondrule pseudomorphs composed mainly of phyllosilicate. However, their bulk compositions are CM-like, and they are closer in texture to other C2 chondrites than to CI1 chondrites (which lack chondrule pseudomorphs). Using several diagnostic criteria, we assigned petrologic subtypes (±0.1) to every CM chondrite in our study: QUE 97990, CM2.6; Murchison, CM2.5; Kivesvaara, CM2.5; Murray, CM2.4/2.5; Y 791198, CM2.4; QUE 99355, CM2.3; Nogoya, CM2.2; Cold Bokkeveld, CM2.2; QUE 93005, CM2.1; LAP 02277, CM2.0; MET 01070, CM2.0.The proposed CM numerical alteration sequence improves upon the existing scheme of Browning et al. (1996) in that it does not require a complicated algorithm applied to electron-microprobe data to determine the average matrix phyllosilicate composition. The new sequence is more comprehensive and employs petrologic subtypes that are easier to use and remember than mineralogic alteration index values.New neutron-activation analyses of QUE 97990, QUE 93005, MET 01070, Murchison and Crescent, together with literature data, confirm the compositional uniformity of the CM group; different degrees of alteration among CM chondrites do not lead to resolvable bulk compositional differences. This suggests that the textural differences among individual CM chondrites reflect progressive alteration of similar hypothetical CM3.0 starting materials in different regions of the same parent body, with minimal aqueous transport of materials over appreciable (e.g., meters) distances.  相似文献   

Petrogenesis of acapulcoites and lodranites: A shock-melting model     

Alan E. Rubin 《Geochimica et cosmochimica acta》2007,71(9):2383-2401

Acapulcoites are modeled as having formed by shock melting CR-like carbonaceous chondrite precursors; the degree of melting of some acapulcoites was low enough to allow the preservation of 3-6 vol % relict chondrules. Shock effects in acapulcoites include veins of metallic Fe-Ni and troilite, polycrystalline kamacite, fine-grained metal-troilite assemblages, metallic Cu, and irregularly shaped troilite grains within metallic Fe-Ni. While at elevated temperatures, acapulcoites experienced appreciable reduction. Because graphite is present in some acapulcoites and lodranites, it seems likely that carbon was the principal reducing agent. Reduction is responsible for the low contents of olivine Fa (4-14 mol %) and low-Ca pyroxene Fs (3-13 mol %) in the acapulcoites, the observation that, in more than two-thirds of the acapulcoites, the Fa value is lower than the Fs value (in contrast to the case for equilibrated ordinary chondrites), the low FeO/MnO ratios in acapulcoite olivine (16-18, compared to 32-38 in equilibrated H chondrites), the relatively high modal orthopyroxene/olivine ratios (e.g., 1.7 in Monument Draw compared to 0.74 in H chondrites), and reverse zoning in some mafic silicate grains. Lodranites formed in a similar manner to acapulcoites but suffered more extensive heating, loss of plagioclase, and loss of an Fe-Ni-S melt.Acapulcoites and lodranites experienced moderate post-shock annealing, presumably resulting from burial beneath material of low thermal diffusivity. The annealing process repaired damaged olivine crystal lattices, lending acapulcoites and lodranites the appearance of unshocked (i.e., shock-stage S1) rocks. Any high-pressure phases that may have formed during initial shock reverted to their low-pressure polymorphs during annealing. Some samples were subsequently shocked again; several acapulcoites reached shock-stage S2 levels, ALH 84190 reached S3, and the lodranite MAC 88177 reached S5.  相似文献