Date of Award

2026

Document Type

Open Access Dissertation

Degree Name

Doctor of Philosophy in Geophysics (PhD)

Administrative Home Department

Department of Geological and Mining Engineering and Sciences

Advisor 1

Aleksey Smirnov

Committee Member 1

James DeGraff

Committee Member 2

Gregory Waite

Committee Member 3

Sarah Green

Abstract

Rock-magnetic and paleomagnetic methods, complemented by electron microscopy and geochemical analyses, are used to investigate three problems in meteorite science, Paleoproterozoic paleoenvironments, and Precambrian magmatism in North America.

Chapter One reviews the methods, terminology, and principles of rock magnetism and paleomagnetism.

Chapter Two tests whether tetrataenite, an equiatomic Fe-Ni alloy, can survive collision-induced shock in ordinary chondrites. Contrary to the accepted view, trace tetrataenite persists in moderately to strongly shocked (S4–S6) chondrites, indicating substantial heterogeneity in impact-generated pressure-temperature conditions. Paleomagnetic records from shocked asteroids may therefore retain primary information, including records of impact-generated magnetic fields.

Chapter Three combines magnetic and geochemical data from the Paleoproterozoic Vulcan Iron Formation in Michigan’s central Upper Peninsula to reconstruct environmental changes during evolution of the Animikie Basin. Its stratigraphic members are genetically distinct and record a progression from euxinic, hydrothermally influenced deep-water deposition of the Traders Member, through siliciclastic sedimentation and shallowing represented by the Brier Slate, to higher-energy, more oxygenated shelf conditions during deposition of the Curry Member. The succession culminated in renewed volcanism and tectonism, marine transgression, and silica-rich deposition of the Loretto Slate as the Marshfield terrane approached and collided with the Superior Craton during the early Penokean Orogeny.

Chapter Four presents paleomagnetic and geochemical studies of mafic and ultramafic intrusions in Michigan’s central Upper Peninsula. These include newly recognized north–south-, northeast–southwest-, and east–west-trending dikes within and around the Carney Lake Gneiss (CLG) complex and near Ralph in Dickinson County, north–south-trending mafic dikes in the Huron Mountain Wilderness Area (HMWA), and the $\sim$1.1 Ga Baraga–Marquette dike swarm. With the exception of the Baraga–Marquette swarm, these intrusions are investigated paleomagnetically for the first time. The results indicate that the CLG and HMWA dikes were emplaced during the Paleoproterozoic, well before initiation of the Midcontinent Rift. Their paleomagnetic and geochemical characteristics are consistent with a possible relationship to the >2.0 Ga Marathon and Fort Frances dike swarms north of Lake Superior. The results also provide evidence that the Baraga–Marquette dike swarm was emplaced during three magmatic pulses rather than a single intrusive event.

Creative Commons License

Creative Commons Attribution-Noncommercial 4.0 License
This work is licensed under a Creative Commons Attribution-Noncommercial 4.0 License

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