Earth and Planetary Sciences ETDs

Publication Date

5-1979

Abstract

The matrices of fourteen unequilibrated (type 3 and 3, 4) ordinary chondrites (all witnessed falls) were analyzed using transmitted and reflected light microscopy, electron microprobe analysis, and instrumental neutron activation analysis. The matrix is defined as the fine-grained silicate material between chondrules, chondrule fragments, other distinct silicate grains, and Fe-Ni and troilite grains. It makes up about 13 percent of each meteorite. Although all meteorites in this study have been altered to some extent since their formation, those with least alteration indicate that the unaltered matrix had submicron grain size, a clastic texture, and was friable even though interstitial pore space was partially filled with amorphous material. Principle minerals were Olivine, Fe-Ni, troilite, and possibly magnetite. The primitive matrix was richer in Fe0, Na20, and K2, and depleted in Cr203 and Si02 compared to the whole-rock silicate fraction. These trends hold regardless of the compositional classification of the meteorite.

Magnetite-pentlandite assemblages in Semarkona and Ngawi indicate that hydrothermal solutions may have affected the matrix in these meteorites at or near the time of agglomeration.

Recrystallization of the matrix included grain growth, loss of porosity and friability, nucleation of new phases (apatite, plagioclase, low-Ca pyroxene), and chemical equilibration within the matrix and between matrix and whole rock. All of the meteorites have experienced this recrystallization to some degree, and they can be roughly ordered in a sequence from least to most altered. The matrix in the most altered meteorites is very similar to the matrix in some type 4 chondrites.

Textural and compositional evidence suggests that the recrystallization of unequilibrated chondrites resulted from a combination of shock metamorphism and some form of steady state heating.

Degree Name

Earth and Planetary Sciences

Level of Degree

Masters

Department Name

Department of Earth and Planetary Sciences

First Committee Member (Chair)

Klaus Keil

Second Committee Member

Douglas Gridley Brookins

Third Committee Member

Rodney Charles Ewing

Language

English

Document Type

Thesis

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