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  • Other Sources  (4)
  • 1990-1994
  • 1980-1984  (4)
  • 1955-1959
  • 1982  (4)
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  • 1990-1994
  • 1980-1984  (4)
  • 1955-1959
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  • 1
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    The Blue Angel. I - The mineralogy and petrogenesis of a hibonite inclusion from the Murchison meteorite (1982)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: Results are presented of a mineralogical and petrological examination of a relatively large hibonite-containing inclusion in the Murchison chondrite called the Blue Angel. Mechanisms of formation and modification of hibonite-rich inclusions are investigated. Evidence is found that modifying processes occurred before the inclusion was incorporated into its present location, which indicates a sequence of aqueous and metamorphic alteration followed by disruption and relithification of the protometeoritic material. The mineral chemistry and petrography of the Blue Angel is consistent with a three stage formation history, and extensive alteration of Ca-Al-rich inclusions may have occurred by aqueous alteration and thermal metamorphism followed by explosive mixing processes on a parent body.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Geochimica et Cosmochimica Acta; 46; Apr. 198
    Format: text
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    NASA TECHNICAL REPORTS
  • 2
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    Microchrons - The Rb-87/Sr-87 dating of microscopic samples (1982)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: The present investigation is concerned with the extension of the Rb-Sr dating technique to microscopic samples of individual mineral grains as small as approximately 30 micrometers in size. The measurement of the isotopic composition and the relative number of atoms of Rb and Sr has presented difficulties because of the need to separate Rb from Sr due to the isobaric interference at mass 87. This separation is critical since the changes in Sr-87/Sr-86 are directly related to the age of the sample. The approach used in the considered investigation is a modified version of the direct loading technique reported by Wasserburg et al. (1977). It is shown that measurements can be conducted of the Rb and Sr isotopic compositions and Rb/Sr atom ratios in microsamples containing 10 to the 11th to 10 to the 12th atoms of Sr. Rb-Sr model ages may prove to be of considerable importance in identifying and studying interplanetary dust particles.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Lunar and Planetary Science Conference; Mar 16, 1981 - Mar 20, 1981; Houston, TX
    Format: text
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    NASA TECHNICAL REPORTS
  • 3
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    Age and provenance of the target materials for tektites and possible impactites as inferred from Sm-Nd and Rb-Sr systematics (1982)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: Chemical, trace element, and isotopic compositions of tektites are consistent with production by melting of sediments derived from the old terrestrial continental crust. Each tektite group is characterized by a uniform Nd model age, interpreted as the time of formation of the crustal segment which weathered to form the parent sediment for the tektites. Sr model ages are variable within each group, reflecting Rb-Sr fractionation, and, in the favorable limit of very high Rb/Sr ratios, approach the time of sedimentation of the parent material which melted to form the tektites. Unlike tektites, which are dense homogeneous objects, sanidine spherules are porous, fine grained inhomogeneous objects. The leaching experiment employed by the present study shows that the sanidine spherules could have been formed by an oceanic impact involving basaltic crust and overlying sediments or seawater.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Earth and Planetary Science Letters; 60; 2, Se; Sept
    Format: text
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    NASA TECHNICAL REPORTS
  • 4
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    Chemical composition of HAL, an isotopically-unusual Allende inclusion (1982)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: Samples of hibonite, black rim, and portions of friable rim from an unusual Allende inclusion, named HAL, were analyzed by INAA and RNAA for 37 major, minor, and trace elements. An unusually low amount of Ce was found in HAL, although it otherwise was highly enriched in REE compared to C1 chondrites. HAL is also depleted in Sr, Ba, U, V, Ru, Os, and Ir relative to other refractory elements. It is concluded that the distribution of REE between hibonite and rims was established when hibonite and other refractory minerals were removed at slightly different temperatures from a hot, oxidizing gas in which they previously coexisted as separate grains. Possible locations for the chemical and mass dependent isotopic fractionation are considered to be in ejecta from the low temperature helium-burning zone of a supernova and in the locally oxidizing environment generated by evaporation of interstellar grains of near-chondritic chemical composition.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Geochimica et Cosmochimica Acta; 46; Sept
    Format: text
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    NASA TECHNICAL REPORTS
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