Sodium and manganese homogeneity in chondritic meteorites Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/1831cn367

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  • Four to six one-gram specimens separated by a distance of several inches were obtained from each of 23 large chondritic meteorites (approximately 1 kg each) representing the olivine bronzite (H5), olivine hypersthene (L6) and enstatite (E5) classifications. Each specimen was analyzed for Na and Mn via instrumental neutron activation analysis to a precision of about 1.5% using the 2.75 Mev and 0.84 Mev photopeaks for Na and Mn, respectively. The olivine bronzite (H5) falls were found to exhibit a Mn homogeneity dispersion range of 3.9% to 1.7% for the large individual meteorites; Na dispersion range was 5.2% to 4.9%. One group of olivine bronzite (H5) finds consisting of five large meteorite fragments exhibited a Mn dispersion range of 0.8% to 2.7%; Na dispersion range was 1.8% to 4.7%. Another group of olivine bronzite (H5) finds consisting of four large pieces showed a Mn dispersion range from 3.8% to 17% ; Na dispersion range, 3.8% to 31%. The olivine hypersthene (L6) falls showed a Mn dispersion of 1.4% to 3.4%; Na dispersion, 2.0% to 7.1%. The olivine hypersthene finds showed a Mn dispersion range of 2.5% to 5.3%; Na dispersion range, 1.5% to 7.6%. The single enstatite find showed a. relative dispersion of 45% for Mn and 28% for Na. It was found that the olivine bronzite (H5) group may be divided into two subgroups on the basis of abundances and the homogeneity of Mn. No significant correlation between the lithophilic elements Mn and Ha was established. It was found that terrestrial fractionation presumably by leaching, may occur causing a significant depletion in Na. Manganese does not exhibit large depletion factors. The relative dispersion of both sodium and manganese are shown to increase by a factor of about two for finds compared to falls. It is suggested that for some of olivine-hypersthene falls an Mn concentration gradient may be present. Assuming chondrites represent the initial accretion products from the primitive solar nebula in the asteroidal volume of the solar system, the dispersion of Mn and Na suggest that the nebula was homogeneous within 1 to 4 percent.
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