Linking Rock Magnetic Properties to the Performance of Paleointensity Techniques

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This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).The direction and intensity of the Earth's magnetic field varies in both time and space. As volcanic rocks cool they record a snapshot of the field and through careful laboratory experiments the evolution of the magnetic field during Earth's approximately 4.5 billion year history can be unravelled. Determining the Earth's magnetic field across critical periods of time will allow a greater understanding of convection in the Earth's liquid outer core, the growth of the solid inner core, interactions between the Earth's outer core and solid mantle, and the relationship between the rate of plate-tectonics and heat flow across the core-mantle boundary. Although the direction of the magnetic field is straightforwardly determined experimentally, its magnitude (also called paleointensity) is more problematic. Without accurate paleointensity measurements the Earth's magnetic field cannot be defined fully and the important processes outlined above will never be fully understood.Although progress has been made in the theoretical understanding of paleointensity and the methodologies used to obtain more accurate results, there has not been a comprehensive study linking the success of paleointensity experiments to the specific magnetic properties of the materials being studied. The research outlined in this proposal aims to identify rock magnetic characteristics that when combined with specific paleointensity procedures will lead to more accurate estimates of the strength of the Earth's magnetic field. Most paleointensity techniques are time and labor intensive and have low success rates (25 to 35%). A small number of innovative studies have proposed methods for screening samples to improve the accuracy of the estimates determined using a specific paleointensity technique. We aim to build on this approach by fully characterizing the rock magnetic properties of our samples and then matching their properties with the best suited paleointensity technique. The samples that will be used to address these problems are lavas from the volcanic island of Fogo, Cape Verde, and were erupted during the last sixty years when the intensity of the geomagnetic field is known from observatory data. Samples will be examined using a meticulous suite of rock magnetic analyses and Mossbauer spectroscopy. Electron microscopes will be used to image mineralogic microstructures and determine elemental compositions. Multiple paleointensity methods will be assessed, including variations on the most commonly used techniques as well as newer approaches needing further validation. No previous study has applied this variety of paleointensity techniques on such well-characterized samples. Results of this research will guide future workers in choosing the most appropriate paleointensity technique based on a sample's rock magnetic properties, increasing efficiency and accuracy. This research will ultimately benefit geophysicists and planetary scientists investigating and modeling deep Earth processes. In addition to the research goals of this project, the award is supporting three early career researchers, is broadening the participation of underrepresented groups in the earth sciences, and is providing training for undergraduate students.