Knowing the past intensity of Earth's magnetic field is essential for understanding the geodynamo. Unfortunately, accurate and precise data are limited because of experimental alteration. The investigators have developed a new approach that uses plagioclase crystals separated from mafic rocks. They have shown that these crystals contain minute magnetic inclusions (50-250 nm in size) that are less susceptible to alteration. In this work, the investigators will (i.) gain an increased understanding of the basic rock magnetic carriers in plagioclase through rock magnetism and high resolution scanning transmission electron microscopy; (ii.) constrain the nature of the field during a time when geomagnetic reversal frequency was at a minimum (the Cretaceous Normal Polarity Superchron) using Thellier paleointensity analyses of plagioclase crystals separated from mafic rocks formed at low latitude sites and (iii.) test further the general relationship of reversal frequency and intensity by Thellier analyses of plagioclase crystals from lavas formed during a time of high reversal frequency. Importantly, sites with existing paleointensity results of high technical quality based on analyses of whole rock basalt and submarine basaltic glass will be studied, affording the opportunity to compare results derived from different geologic recorders. Broader impacts of the study include support for a Research Scientist and a graduate student (the latter contributing to Ph.D. thesis studies). In addition, the investigators will involve several undergraduate students in the work, contributing toward undergraduate research and undergraduate Senior thesis studies at the University of Rochester.
