Morphology, Stability and Paleointensity of the Early Geomagnetic Field as Recorded by 2.9-2.4 Ga Mafic Rocks in Western Australia

Michigan Technological University, Houghton MI

Investigators

Abstract

Data on the long-term history and characteristics of geomagnetic field in the Precambrian are crucial for understanding the origin and nature of the early Earth's geodynamo and as a prerequisite for using paleomagnetism to study the geological processes of the early Earth. In the absence of strict theoretical constraints, study of the direction and strength of the geomagnetic field becomes a principal source of these data. The Archean-Proterozoic boundary interval is of special interest because it may mark the time of initial growth of the solid inner core, which may have affected the energetic and morphological characteristics of the geodynamo. The morphology, stability, and strength of the Late Archean and Early Proterozoic geodynamo are investigated by detailed paleodirectional and paleointensity analyses of three mafic magmatic suites in Western Australia, which contains the world's most pristinely preserved record of such rocks through the time interval under consideration: ~2.42 Ga Widgiemooltha dike swarm in the Yilgarn craton, ~2.78 Ga mafic lava flows and dikes of the Fortescue group of the Pilbara craton, and ~2.92 Ga layered mafic complexes of the western Pilbara craton. This study provides a synoptic view of the Late Archean-Early Proterozoic geodynamo, including time-averaged paleointensity values, estimates of the relative contributions from dipole and non-dipole field components, and paleolatitude-dependent estimates of paleosecular variation. The study generates important constraints on models of the Earth's thermal evolution and age of inner core formation. Broader impacts of this work include educational efforts at Michigan Technological University and Yale University, such as involvement of graduate and undergraduate students in all aspects of the work including both field assistance and laboratory analyses, as well as preparation of a PhD dissertation and senior research projects.