Renne This study will clarify the origin of uniquely stable magnetizations associated with crystallographically oriented inclusions of magnetite in silicates (COMIS). These feature are common in several minerals in various igneous and metamorphic rock types, and previous work shows that they preserve exceptionally robust information about Earth's ancient magnetic field. This work will combine submicroscopic mineralogical techniques, including scanning and transmission electron microscopy, electron backscattered diffraction, atomic and magnetic force microscopy, to determine how COMIS form. Rock magnetic analyses combined with magnetic force microscopy will be used to determine the specific mechanisms by which these features acquire their magnetizations. These studies will focus on samples from many different geologic ages and environments. A suite of samples drilled from the sea-floor will be used to evaluate the outstanding question of whether COMIS could be responsible for oceanic magnetic anomalies, whose recognition led to the theory of plate tectonics. A significant goal of the project is to perfect methods for rock-magnetic analysis of individual silicate crystals, including development of methods for determining the intensity and orientation of Earth's magnetic field in the geologic past. Information about the evolution of the magnetic field has implications for the evolution of Earth's core, where the magnetic field originates. The study is also expected to yield an improved basis for deducing plate tectonic movements of the lithosphere for times prior to 200 million years ago when the sea-floor record is nonexistent. The project will involve a PhD student and collaboration with National Labs, National Facilities, and colleagues at other academic institutions.
