Earth and Planetary Sciences ETDs

Publication Date

2021

Abstract

PROJECT 1: Chondrites are the most primitive objects in the solar system, aggregates of the material that formed in the solar protoplanetary disk during the first 1-5 million years of its formation. However, petrographic observations indicate that most chondrites have been modified by secondary processes, including aqueous alteration, thermal metamorphism, and shock. Fortunately, a few chondrites largely escaped these processes and are considered pristine, such as the CR carbonaceous chondrite Queen Alexandra Range (QUE) 99177. QUE 99177 is an excellent sample for deciphering information about the reactions that took place between unaltered anhydrous solar nebular components and water under highly disequilibrium conditions, as well as primary processes in the solar nebula. The goal of this work is to constrain the earliest interactions between anhydrous chondrules in QUE 99177 with their associated fine-grained, hydrated matrix material.

Models to characterize the aqueous alteration degree of a given chondrite are contentious. Therefore, Chapter 1 proposes a new proxy for assessing the degree of aqueous alteration in weakly altered CR chondrites based on the presence and characteristics of a recently discovered type of rim around chondrules called smooth rims. Smooth rims have been observed surrounding type I chondrules in a few weakly altered CR chondrites, but their nature and formation mechanisms remained unknown. We unravel the origin of these rims and their importance to understanding the earliest fluid-chondrule interactions. Chapter 2 focuses on characterizing the different occurrences of phosphates present in and around type II (mainly) and type I chondrules in QUE 99177. Calcium phosphates are generally considered secondary products, but work has been limited. This study provides evidence of both solar nebular and parent body processes in the formation of Ca phosphates and acquires new insights into the behavior of P during the earliest stages of aqueous alteration in the CR chondrite parent body.

PROJECT 2: The Martian meteorites (Shergottites-Nakhlites-Chassignites and several unique lithologies) represent a direct sampling of igneous processes on Mars, covering a range of different Martian mantle sources and emplacement environments. Although models account for many of their observations, the detailed magmatic processes have not been fully elucidated yet. In Chapter 3, we examine the micro- and nano- structures of apatites using transmission electron microscopy in the two nakhlites NWA 998 and Nakhla. Such microstructural data are currently essentially lacking for samples of planetary or even terrestrial apatite, yet apatite is widely used as an important tracer for reconstructing petrogenetic processes in different planetary environments. In particular, Martian apatite is used for constraining potential volatile reservoirs (the mantle and/or the crust), therefore, understanding apatite microstructures is of fundamental importance for providing robust interpretations of the geochemical data obtained from apatite. In Chapter 3, we show evidence of late igneous and subsolidus reactions that support a model based on crustal assimilation and is inconsistent with the presence of fluids. We discuss the limitations of using apatite to constrain volatile abundances and their sources.

PROJECT 3: High-pressure phases resulting from impacts between asteroids provide excellent opportunities to study phase transitions of the constituent minerals of the Earth’s mantle as well as the dynamics of shock-induced solid-state processes. In Chapter 4, we examine the high-pressure phases enclosed in an exceptionally large shock-induced melt vein in the L6 ordinary chondrite Villalbeto de la Peña. The high-pressure phases identified include: ringwoodite, Ca-rich majorite, Ca-poor majorite, maskelynite, lingunite, pyroxene glass, magnesiowüstite, and ferropericlase. We focus on the behavior of Ca-rich pyroxene because there are only a few occurrences of its high-pressure transformations reported in the literature. Several of our observations represent the first time specific phenomena have been described, such as diopside undergoing direct melting without transforming into its high-pressure polymorph (majorite) and fine-scale zonation in majorite-pyrope grains in the matrix. We discuss implications for the thermal histories and cooling rates in the shock event.

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

Steven B. Simon

Fourth Committee Member

Jin S. Zhang

Fifth Committee Member

Hope A. Ishii

Language

English

Keywords

Meteorites, Asteroids, Solar System, Mars, Apatite

Document Type

Dissertation

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