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Document Type

Open Access Dissertation

Degree Name

Doctor of Philosophy (PhD)

Degree Program

Geosciences

Year Degree Awarded

2016

Month Degree Awarded

September

First Advisor

Laurie L. Brown

Second Advisor

Michael L. Williams

Third Advisor

Michael J. Jercinovic

Fourth Advisor

Tobias Baskin

Subject Categories

Geochemistry | Geology | Tectonics and Structure

Abstract

The linking of geophysical information to tectonometamorphic processes holds great potential for the surveying of vast remote areas of the planet and may allow for the transcendence of observational scales. Investigations concerning magnetic properties of the lower continental crust can reveal an incredible wealth of information concerning the conditions of metamorphism, regional extent of deformation, and controls on the magnetic architecture of the lithosphere. This dissertation presents three contributions aimed at the integration of petrology, structural geology, and rock magnetism in order to investigate the magnetic nature of the lower continental crust, constrain tectonometamorphic processes at the regional scale in a remote portion of the Canadian Shield, and develop a new instrument and procedure for magnetic imaging at the hand sample scale. The results of these contributions indicate that the lower continental crust is not particularly magnetic and does not support the hypothesis that the lower continental crust is sufficiently magnetic to account for satellite based long-wavelength anomalies. However, retrograde reactions may produce substantial quantities of magnetite within the middle crust, which may account for these anomalies. Aeromagnetic anomalies across the east Athabasca mylonite triangle are controlled by the mode of magnetite, which in the western Chipman domain was produced upon exhumation through middle crustal conditions. Syn-tectonic retrograde metamorphic reactions in this region produced magnetite in association with the influx of fluids, which was facilitated by a releasing bend geometry of the Cora Lake shear zone. Thermodynamic modeling of retrograde metamorphism suggests magnetite was produced at temperatures of 524--617 C and pressures of 599--740 MPa during an interval of time spanning from 1,882 Ma to 1,870 Ma. These data suggest an increase of oxygen fugacity relative to the magnetite-hematite buffer during exhumation into the middle crust aided in the production of magnetite. The ability to image the heterogeneous distribution of magnetite in samples with the new magnetic imaging device has provided much detail on the textural context of magnetite growth. Ultimately, the scale invariance of magnetism is a powerful tool for the transcendence of observational scale applied to geologic investigations.

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