Earth and Planetary Sciences ETDs

Publication Date

Fall 12-13-2020

Abstract

The petrology and mineralogy of calcium-aluminum-rich inclusions (CAIs) from CV3 carbonaceous chondrites have been investigated using transmission electron microscopy (TEM). The goal of this dissertation is twofold: (1) to gain new insights into the nebular processes, such as vapor-solid reactions, accretion, transport, that are responsible for the formation of non-igneous CAIs, and (2) to better understand the role of fluid in the secondary alteration of CAIs on the CV3 chondrite parent body. This work represents the first systematic microstructural study of CAIs from CV3 chondrites.

Chapter 2 presents the microstructural observations of primary mineralogies of fine-grained, spinel-rich inclusions (FGIs) from the Leoville and Efremovka meteorites. We observe microscale heterogeneities that have not been reported in previous studies and suggest that these FGIs have recorded an evolutionary condensation sequence in the solar nebula. In Chapter 3, we report microstructures of an enstatite-bearing FGI from Leoville. Investigations of this FGI and several other fine-grained CAIs from Leoville and Efremovka suggest that enstatite is a common, fine-grained condensation phase in CAIs, and it could have recorded a rapid cooling rate in the CAI-forming region. Chapter 4 presents three forsterite-bearing FGIs with a zoning structure from Leoville. The different occurrences of forsterite in the zones may have formed at successively lower pressure conditions and thus their formation may be caused by transport along a negative nebular pressure gradient. In Chapter 5, we study the secondary alteration features of melilite-rich CAIs from Allende. We show that the secondary mineral sequence of melilite can be explained by formation of different phases on a μCaO-μSiO2 gradient in the fluid. The Wark-Lovering rims surrounding these CAIs also show complex alteration microstructures, which are likely to be products of microchemical environments. Finally, in Chapter 6, we study a unique, forsterite-bearing Type C CAI from Allende. Based on the SEM and TEM observations, the observed iron-alkali-halogen zonal sequence can be best explained by a two-stage fluid alteration process on the Allende parent body.

Degree Name

Earth and Planetary Sciences

Level of Degree

Doctoral

Department Name

Department of Earth and Planetary Sciences

First Committee Member (Chair)

Adrian J. Brearley

Second Committee Member

Charles K. Shearer

Third Committee Member

Zachary D. Sharp

Fourth Committee Member

Steven B. Simon

Fifth Committee Member

Karen Ziegler

Project Sponsors

NASA Cosmochemistry grants NNX15AD28G to A. J. Brearley (PI)

Language

English

Keywords

Calcium-aluminum-rich inclusions, CV3 chondrites, Transmission electron microscopy

Document Type

Dissertation

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