title: Prototyping the next generation of versatile paleomagnetic laboratory
Creators: name: Grappone, Joseph
Publisher: name: University of Liverpool Repository
Year: 2021

description: Investigating the Earth’s magnetic field provides a unique window into the history of Earth’s outer core, where the field is generated. Rocks gain a magnetization that is in the direction of and proportional to the Earth’s magnetic field at the time of their formation, such as when magma erupts from a volcano and cools below its Curie temperature. The gained magnetization has a relaxation time that is frequently longer than the age of the universe, but unfortunately, rocks are subject to the whims of the Earth over geologic time. Given the ages of rocks commonly studied (millions to billions of years old), some paleomagnetic data is noisy and complex. Paleomagnetic intensity data in particular have long been plagued by large and poorly quantified uncertainties. Extracting accurate magnetic measurements relies on having the most advanced equipment and best experimental techniques. This thesis approaches these goals from two directions: prototyping new equipment, which also introduces novel methodology, and fine-tuning existing methods. Contained herein is the development of the world’s first automated high-temperature SQUID (Superconducting Quantum Interference Device) thermomagnetometer. This system can automatically measure the remanent magnetic field of a specimen at an elevated temperature without needing to cool the specimen to ambient temperature. Without repeated heating/cooling cycles, thermochemical alteration is minimized, and the rate of data collection is greatly increased. SQUID sensors improve the sensitivity of the magnetometer system, avoid low blocking temperature components, and provide precise temperature control and minimal alteration. While the original design called for an instrument that could provide continuous magnetization measurements, this proved to be untenable due to technical constraints with the SQUID sensors. Thus, a stepwise version was produced that measures each specimen in (up to) 10 °C increments, instead of continuously. Introducing new equipment by itself is futile if the experiments performed on them are not well calibrated and optimized. To address this problem, this thesis investigates differences in paleomagnetic intensity results produced by different variants of Thellier-style paleointensity protocols using established instruments. The most modern protocol, the IZZI protocol, was found to be broadly accurate but sometimes imprecise. This thesis further attempts to ascertain the cause of differences observed in paleointensity data when the demagnetization mechanism or paleointensity protocol is changed, as nearly a dozen methods are in use throughout the world. Finally, a series of tests evaluates whether the addition of alternating field or liquid nitrogen demagnetization cleansing steps can improve data fidelity. The additional cleansing steps can, in some cases, improve the linearity of paleointensity data sufficiently to pass selection criteria, but cannot affect, for example, other complications like thermochemical alteration. With the ever-growing pressure to provide tangible impacts to the broader scientific community, expanding the versatility of magnetic techniques to new applications is paramount. This thesis broadly applies magnetic techniques to the energy sector, through Magnetic Flux Leakage experiments on Coiled Tubing, in conjunction with Schlumberger as an industrial partner. The future paleomagnetic laboratory is a versatile one, capable of running large batches of specimens (both paleomagnetic and metallic) quickly and accurately, through a combination of improved methods and equipment. This thesis has successfully introduced a new prototype magnetometer design and found that for non-ideal (i.e. real) rocks, the interactions between the rocks and methods are complex. Going forward, the new magnetometer brings high temperature remanence measurements to more rock types and potentially further partnerships with external, industrial partners, like Schlumberger.