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At least 361 records · Page 20
All sourcesNASA NTRSDOE OSTI
NASA NTRS1973

Plagioclase mineralogy of olivine alkaline basalt

A geological and mineralogical study of the Potrillo volcanics is reported. The investigation consisted first of field mapping to establish and identify the different rock types and volcanic features in order to determine the geological history. Next, samples were collected and analyzed petrographically to determine suitable rocks from the various stratigraphic units for study of plagioclase. Samples selected for further study were crushed and the plagioclase extracted for the determination of composition and structural state. These results were then related to the petrology and crystallization of the basalt.

Hoffer, J. M.↗
NASA NTRS1978

Shear flow beneath oceanic plates - Local nonsimilarity boundary layers for olivine rheology

The principle of local similarity, which has been used to model the two-dimensional boundary layers in the oceanic upper mantle, permits calculation of the temperature, velocity, and stress fields with essentially analytic techniques. Finite difference numerical methods are hard pressed to resolve the detail required by the large variation of viscosity between the lithosphere and the asthenosphere. In this paper the local similarity approximation has been justified by quantitatively evaluating the effect of nonsimilarity due to viscous heating, nonlinear temperature- and pressure-dependent rheology, buoyancy, adiabatic cooling, etc. Nonsimilar effects produce only small modifications of the locally similar boundary layers; important geophysical observables such as surface heat flux and ocean floor topography are given to better than 10 percent by the locally similar solution. A posteriori evaluations of the terms neglected in the boundary layer simplification of the complete equations have been conducted on the locally similar temperature and velocity profiles close to the spreading ridge. The boundary layer models are valid to depths of 100 km at 3 m.y. and 10 km at 0.3 m.y.

Yuen, D. A.↗
NASA NTRS1983

Nuclear track and compositional studies of olivines in CI and CM chondrites

The CI and CM chondrites, with bulk chemical compositions closely resembling solar values, are important for the study of early solar system processes. Noble gas and particle track studies have revealed that a majority of the CI and CM chondrites contain precompaction solar wind and solar flare irradiation records. A quantitative understanding of these records is important because it would allow constraints to be placed on the environment in which the irradiation occurred, and, therefore, on the mode of evolution of the CI and CM chondrites. The present investigation is concerned primarily with fossil track evidence, taking into account selected specimens of several CI and CM chondrites. In addition, the results are presented of extensive studies of the angular distributions of tracks in irradiated grains from four CM chondrites. The results provide information on the exposure geometry of the grains.

Goswami, J. N.↗
NASA NTRS1983

Use of olivine and plagioclase saturation surfaces for the petrogenetic modeling of recrystallized basic plutonic systems

During petrogenetic studies of basic plutonic rocks, there are at least three major questions to be considered: (1) what were the relative proportions of cumulate crystals and intercumulus melt in a given sample? (2) what is the composition and variation in composition of the melts within the pluton? and (3) what is the original composition of the liquids, their source and evolution prior to the time of emplacement? Use of both saturation surfaces can place strong limits on the compositions of potential cumulate phases and intercumulus melts. Consideration of appropriate trace elements can indicate whether a sample is an orthocumulate, adcumulate or mesocumulate. Thus, when trace element and petrographic data are considered together with the saturation surfaces, it should be possible to begin to answer the three major questions given above, even for strongly recrystallized basic plutons.

Hanson, G. N.↗