Doctoral Dissertations

Date of Award

5-2007

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Geology

Major Professor

Harry Y. McSween, Jr.

Committee Members

Theodore Labotka, Gregory Baker, Jens Gregor

Abstract

This dissertation is an investigation of two processes of fundamental cosmochemical importance: chondrule formation and chondrule sorting. The first two parts address chondrule formation, while the second two address chondrule sorting. The four parts are each self-contained papers that have been or are in the process of being published.

In Part 1, experimental work on the ordinary chondrite QUE97008 is used to develop a set of textural criteria by which a chondrule’s degree of partial melting can be qualitatively determined and to test the validity of quantitative measures of degree of melting.

In Part 2 the textural criteria developed in Part 1 are used to inventory chondrule precursors by finding natural chondrules that have experienced minimal degrees of partial melting. We show that chondrule precursors are similar mineralogically and chemically to the general chondrule population, implying that chondrule recycling was ubiquitous in the presolar nebula.

In Part 3, X-ray computed technology (CT) data are used to develop a dataset of size and shape measurements for chondrules and metal/sulfide grains in ordinary chondrites. We show that chondrules are in general not spherical, and compare size and shape measurements of chondrules and metal grains to those of other authors.

The dataset developed in Part 3 is applied to the study of chondrule sorting in Part 4. We test hypotheses of mass, photophoretic, and aerodynamic sorting in the nebula and assess the relationship between size sorting of chondrules and metal-silicate fractionation, one of the most fundamental fractionations in cosmochemistry.

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