Earth and Planetary Sciences ETDs
Publication Date
6-9-1975
Abstract
The chemical compositions of coexisting olivine, orthopyroxene, and clinopyroxene from 50 ordinary chondritic meteorites are presented. The elements, determined by the electron microprobe x-ray analyzer, are Fe, Ca, Mg, Cr and Mn in olivine, and Fe, Ca, Mg, Cr, Mn, Ti and Al in orthopyroxene and clinopyroxene. A method was developed to determine minor elements as low as 50 ppm with a calculated relative error of only +-5% of the amounts present. These data and the calculated Kd2 values were run through the social sciences multivariate analysis program to obtain correlations that would be useful in the classification of meteorites. Using the data generated by multivariate analysis for the minor elements, it is possible to group the ordinary chondrites into the petrologic subgroups 4, 5, and 6 of Van Schmus and Wood (1967). Fe and Mg from coexisting olivine and clinopyroxene can be used to separate chemical groups H, L, and LL in the same fashion as these elements have been used by Keil and Fredriksson (1964). Equilibration temperatures determined by using the curve of Kretz (1963) give 819°C for Hand L group chondrites and 9OO°C for LL group. In addition, when only petrologic subgroups are considered, H-4 chondrites equilibrated at 78O°C, H-S chondrites at 826°C, and H-6 at 826°C. The same relationship does not appear for the Land LL groups. Plots of atomic percent Al versus atomic percent Si, atomic percent Ti versus atomic percent Si, and atomic percent Al versus atomic percent Ti for the clinopyroxenes studied indicate that all the Ti is in 6 fold coordination and is not substituting for Si in the 4 fold coordination site of clinopyroxene. Ti was found to be in excess of what would be compensated for by Al in pyroxene probably because of the reducing conditions present during formation. In addition, when average Ti contents for the subgroup 4, S, and 6 meteorites are plotted on this graph, the subgroup Sand 6 meteorites have higher Ti contents than the subgroup 4 meteorites. Ti is more soluble in the pyroxene structure at higher temperatures which would indicate that the subgroup Sand 6 meteorites equilibrated at a higher temperature than the subgroup 4 meteorites. An Al2O3 versus SiO2 plot for the pyroxenes indicates a close relationship between chondritic pyroxenes and terrestrial metamorphic pyroxenes. Plots of inter-and intragrain variability indicate that variability within and between grains decreases with increasing petrologic subgroup. When Ca from orthopyroxene is plotted against the chemical groups H, L, and LL, an increase in Ca is seen from group 4 to 5 to 6. According to Dodd (1972), this would indicate that group 6 equilibrated at a higher temperature than group 5, and group 5 equilibrated at a higher temperature than group 4 or was held at a certain temperature for a longer period of time. The following geologic history may be suggested from investigation of the coexisting Fe-Mg silicates. After condensation from the solar nebula, i1pact may have produced a nuee ardente or regional metamorphism may have taken place. Therefore, the closer to the base of the tuff a particular meteorite was located, the higher would be its equilibration temperature or, the closer a particular meteorite was to the center of regional metamorphism, the higher would be its equilibration temperature. Thus, either progressive metamorphism or autometamorphism created the petrologic subgroups of Van Schmus and Wood (1967) for the ordinary chondrites.
Degree Name
Earth and Planetary Sciences
Level of Degree
Doctoral
Department Name
Department of Earth and Planetary Sciences
First Committee Member (Chair)
Klaus Keil
Second Committee Member
Douglas Gridley Brookins
Third Committee Member
Wolfgang Eugene Elston
Fourth Committee Member
Albert Masakiyo Kudo
Language
English
Document Type
Dissertation
Recommended Citation
Busche, Frederick D.. "Major And Minor Element Contents Of Coexisting Olivine, Orthopyroxene, And Clinopyroxene In Ordinary Chondritic Meteorites." (1975). https://digitalrepository.unm.edu/eps_etds/422
