First Advisor

Alexander Ruzicka

Date of Award

6-14-2019

Document Type

Thesis

Department

Geology

Subjects

Chondrules -- Chemical analysis, Chondrules -- Effect of water on, Chondrites (Meteorites), Scanning electron microscopy, Transmission electron microscopy

DOI

10.15760/geohonors.01

Abstract

Aqueous alteration, chemical or petrologic change through the addition of water, is a proposed secondary effect of ordinary chondrites. Some minimally metamorphosed chondrites have been noted to have strong signs of aqueous alteration (Weisberg et al., 2006), but the degree of the effect in other chondrites is not clear. There is a specific chondrule type called “bleached chondrules” in which aqueous alteration is proposed to occur in a widespread fashion for all metamorphic grades (Grossman et al., 2000). Using transmitted optical microscopy (OM) and scanning electron microscopy (SEM) at Portland State University, this report obtained chemical and petrological data of nine select meteoritic bleached chondrules to test if the findings in Grossman et al. (2000) holds true for chondrites NWA 11991 (LL3.5) and Tieschitz (H/L3.6). Chondrules 4, 7, and 8, agreed with Grossman et al. (2000) in optical imagery, porosity, and bulk/subset chemical data. Chondrules 2, 3, and 5, agreed with optical imagery and bulk/subset chemical data but did not agree with the expected porosity. Chondrules 1, 6, and 9, did not agree with Grossman et al. (2000) and deviate from one another. Based on these findings, it is determined that aqueous alterations of the sort described by Grossman et al. does not fully describe bleaching process and that additional processes are necessary for bleaching. There is evidence within the findings that dissolution of the mesostasis occurred but due the inconsistency surrounding the solubility of elements, a physical removal of the mesostasis had to occur.

Rights

© 2019 Robert P. Kostynic

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Comments

An undergraduate honors thesis submitted in partial fulfillment of the requirements for the degree of Bachelor of Science in Geology with Honors.

Persistent Identifier

https://archives.pdx.edu/ds/psu/28946

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