Date of Award

Spring 1-1-2018

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

First Advisor

Rebecca M. Flowers

Second Advisor

James R. Metcalf

Third Advisor

Robert S. Anderson

Fourth Advisor

Kevin H. Mahan

Fifth Advisor

Christine Siddoway

Abstract

Cratons are the oldest and most stable portions of continents, but the degree to which they are affected by post-cratonization tectonic and magmatic processes is unclear. Mid-temperature (300-110°C) thermal histories are important for addressing this problem, but these are difficult to resolve due to the paucity of well-developed chronometers sensitive to that temperature window. For example, in the Kaapvaal craton of southern Africa, high temperature (>300°C) geo- and thermochronology constrains Archean craton stabilization, while low temperature (<110°C) thermochronology constrains the Paleozoic-Mesozoic history of craton burial and exhumation, leaving an almost 3 billion year gap in Kaapvaal’s thermal history. The goals of my dissertation are to 1) better resolve titanite He diffusion kinetics to assess its utility as a mid-temperature thermochronometer, and 2) apply titanite and zircon (U-Th)/He (THe, ZHe) thermochronology to decipher the deep-time thermal history of the Kaapvaal craton.

Prior work showed that radiation damage influences the He retentivity and closure temperature (Tc) of apatite and zircon, but this effect was not documented in titanite. I acquired THe dates, Raman spectra, and He diffusion data for a suite of Kaapvaal craton titanite that show at low radiation damage the titanite Tc is ~210-150°C, but at higher damage the Tc drops to <50°C. This damage-diffusivity pattern is similar to zircon, but because titanite typically has substantially lower U and Th, the data imply that for the same protracted thermal history titanite will accumulate less damage and record older dates than zircon.

I applied THe and ZHe dating in a focused study of the Phalaborwa carbonatite, as well as to a broad suite of samples across the craton from both on- and off- the southern African Plateau. THe dates are older than ZHe dates and reach a maximum of 1.0-1.2 Ga from all regions. These data and geologic constraints require a significant, previously undetected heating (≥150°C) event at this time, most simply explained by burial (>4 km) coincident with Namaqua-Natal orogenesis. The inferred basin has been removed from the geologic record, demonstrating the utility of THe and ZHe for detecting such events.

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