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  • Articles  (8)
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  • petrology  (8)
  • 2020-2024
  • 1975-1979  (8)
  • Geosciences  (8)
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  • 1
    ISSN: 1573-8868
    Keywords: regression analysis ; trend analysis ; geochemistry ; petrology
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Mathematics
    Notes: Abstract The Barth Island layered structure is an oval, 6 by 9 km body, consisting of rhythmically layered adamellitic rock in the center which grades outward through jotunite into troctolite. Farther outward the sequence repeats itself in reversed order, strongly reduced in magnitude and finer grained; the adamellitic zone is followed by jotunite which grades into coarse-grained leuconorite and into anorthosite of the Nain complex. The Barth Island structure, having an inverted conical base topped by a hemispherical depression, seems to represent a distorted sequence of rock layers with troctolite at the bottom, grading upward into adamellitic rocks which grade into anorthosite at the top. Trend-surface analysis demonstrates the regional variation of plagioclase and orthopyroxene compositions in the troctolite—adamellite sequence of the central part of the structure. The fits for the second- and third-degree surfaces are good and significant at the 99 percent level. The regression line for compositional variation in coexisting plagioclase and orthopyroxene in all analyzed rocks has a correlation coefficient of r2 = 0.78. The difference between the trends in the troctolite—adamellite sequence and the anorthosite—adamellite sequence is insignificant. The regression curve for compositional variation in coexisting orthopyroxene and olivine has a correlation coefficient of r2 = 0.98. The curve shows good correlation with the experimentally established partitioning curve of Medaris, which indicates that equilibrium conditions prevailed during formation of the olivine—ortho-pyroxene pairs. The results suggest that the troctolite—adamellite sequence and the anorthosite—adamellite sequence are products of fractional crystallization, possibly from the same parental magma.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Mathematical geology 7 (1975), S. 363-371 
    ISSN: 1573-8868
    Keywords: data processing ; geochemistry ; petrology
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Mathematics
    Notes: Abstract An information system is needed to restore access to published information, now so voluminous that suitable levels of familiarity with it cannot be maintained by conventional nonelectronic scholarly devices. The services of the system should be available to petrologists via mail or remote terminal, and should provide, as requested, either retrieval or reduction of data contained in its base. The base should contain chemical, geological, mineralogical, and petrographic information about specimens for which full descriptions have been published. Provisional plans for construction of such a base are briefly reviewed.
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Mathematical geology 8 (1976), S. 25-36 
    ISSN: 1573-8868
    Keywords: principal components analysis ; closure correlations ; geochemistry ; petrology
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Mathematics
    Notes: Abstract The application of R-mode principal components analysis to a set of closed chemical data is described using previously published chemical analyses of rocks from Gough Island. Different measures of similarity have been used and the results compared by calculating the correlation coefficients between each of the elements of the extracted eigenvectors and each of the original variables. These correlations provide a convenient measure of the contribution of each variable to each of the principal components. The choice of similarity measure (variance-covariance or correlation coefficient)should reflect the nature of the data and the view of the investigator as to which is the proper weighting of the variables—according to their sample variance or equally. If the data are appropriate for principal components analysis, then the Chayes and Kruskal concept of the hypothetical open and closed arrays and the expected closure correlations would seem to be useful in defining the structure to be expected in the absence of significant departures from randomness. If the data are not multivariate normally distributed, then it is possible that the principal components will not be independent. This may result in significant nonzero covariances between various pairs of principal components.
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    Mathematical geology 10 (1978), S. 301-310 
    ISSN: 1573-8868
    Keywords: Layered intrusions ; petrology ; thermal histories
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Mathematics
    Notes: Abstract The complete description of the cooling of a layered intrusive sheet is mathematically complex since even the simplest conceivable model involves a moving boundary—the floor or base of the convecting portion of the intrusion for which the boundary conditions are second-order equations including partial derivatives. Numerical solutions for reasonable thermal parameters and initial conditions demonstrate that for most situations between 90 and 100% of the heat loss of the liquid region is through the roof. In certain circumstances the layered series—the crystallized position of the intrusion—actually supplies heat to the convecting region in the late stages of cooling.
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  • 5
    Electronic Resource
    Electronic Resource
    Springer
    Mathematical geology 11 (1979), S. 627-642 
    ISSN: 1573-8868
    Keywords: sampling ; crystal morphology ; petrology
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Mathematics
    Notes: Abstract Compositional data of orthopyroxene crystals obtained by the electron microprobe may be biased unless zoning morphologies are taken into account in the sampling design. Statistical models (predictive or interpretative) based on such data are open to question because the input data, such as correlations, are spurious. In an attempt to propose sampling designs two established crystal zoning morphologies are considered which are (a) the concentric shell-type and (b) sectoral zonations. These zonational types lend themselves well to statistical population modeling and graphical interpretation provided assumptions of chemical invariance hold or are approximated by a stratified sampling design. The statistical designs may be regarded as limiting cases in the sense that relaxations of certain assumptions lead to other population models. Hypersthene crystals from a central portion of the mafic norite formation at the Strathcona Mine, Sudbury irruptive, are examined for zonation. It appears that the trace elements have a different zoning morphology than the major elements of hypersthene.
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  • 6
    Electronic Resource
    Electronic Resource
    Springer
    Mathematical geology 11 (1979), S. 611-626 
    ISSN: 1573-8868
    Keywords: principal components analysis ; factor analysis ; organic geochemistry ; paleoecology ; petrology
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Mathematics
    Notes: Abstract A three-mode principal components method allows visualization of the structural or taxonomic relationships within three-way data tables. The fundamental model includes three sets of eigenvectors and a “core matrix” relating the principal components of each mode. Formal relationships between the method and the usual principal components formulation allow calculation of “loadings” and “scores” for each mode; taken with the core matrix, these provide a number of points of view in graphical analysis of three-mode data. The model compares favorably with alternative formulations in terms of simplicity of computation, generality, and symmetry of operation among the modes. An organic geochemical example illustrates the method.
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  • 7
    Electronic Resource
    Electronic Resource
    Springer
    Mathematical geology 7 (1975), S. 295-321 
    ISSN: 1573-8868
    Keywords: data processing ; data structure ; independent events ; paleontology ; petrology ; regional mapping ; stratigraphy ; structure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Mathematics
    Notes: Abstract Geological events, such as emplacement of granite or growth of slaty cleavage, may be ordered into a sequence by two methods. One is to assign each event a place in a time scale, such as years before the present, which amounts to assigning events an age designation from the set of real numbers. In ordering such a list, the algebra of real numbers applies. A second method is to determine the time relations of events in pairs, such as a fold is of type (S1, S2) or granite intrudes conglomerate. These binary relations between events may be used to order events into a sequence using the transitive properties of the relation “older than.” It is shown, however, that the binary relations between events do not follow the familiar rules for the algebra of real or integral numbers and it is necessary to erect a new system of relations called the “algebra of events.” The fundamental relation is “older than or equivalent to” and this may be used to define the relations “older than”, “younger than”, “equivalent to”, “incomparable to”, and “covers.” The essential difference from the algebra of integers is that the reflexive relation (“equal to”) is replaced by two such relations (“equivalent to” and “incomparable to”) in the algebra of events. A number of binary relations between events may be assembled into an event matrix which is basically a truth table for the relation “older than.” This may be ordered and stacked by operations termed ORDER and STACK. The relationship of each event to every other event may be determined by simple inspection of an ordered, stacked matrix, and from this a geological history may be assembled. If there are contradictions in the field data, ordering into a proper sequence is impossible and may be detected. If there are ambiguities in the field data, there are several different orders that are proper sequences so that the event matrix may be ordered. However, the ambiguities occur as voids in the stacked matrix.
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  • 8
    Electronic Resource
    Electronic Resource
    Springer
    Mathematical geology 8 (1976), S. 669-681 
    ISSN: 1573-8868
    Keywords: classification ; factor analysis ; economic geology ; mineralization ; petrology
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Mathematics
    Notes: Abstract Geological descriptions of unmineralized and mineralized ultrabasic and basic complexes were collected on a world-wide basis from published literature in the framework of the research project “Basimine.”Its aim is the discovery of controls governing the existence of mineralization in certain complexes and subsequently the development of working hypotheses for nickel prospection. Files were created containing geological and petrological data for each complex. In order to gain an understanding into the relationship existing between variables and complexes, correspondence analysis was applied to various data sets taken from the files. The results indicated criteria, either favorable or unfavorable, for the presence of mineralization in the complexes, and pointed out certain unmineralized complexes which could well be mineralized due to their position as regards known ore deposits in the plan of the factorial axes.
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