Comprehensive Study of the Mid-Cenozoic Liverpool, Australia, Reversal: Construction of a Highly Detailed, Full-Vector Paleomagnetic Record From Southern Hemisphere Lavas

University Of Wisconsin-Madison, Madison WI

Investigators

Abstract

It is well-established that Earth's magnetic field arises from motion within its electrically conducting liquid outer core by way of a dynamo process; however, a complete understanding of field generation remains enigmatic. In particular, the problem of polarity reversal remains elusive. Observation of field behavior (variations in direction and intensity) during reversals comes from laboratory analysis of the magnetic information "fossilized" in rocks at the time of their formation. The bulk of our knowledge about the structure of reversing fields has come from drilled core samples at locations in the Northern Hemisphere. Hence, a complete understanding of transitional field behavior on a global scale, and the dynamo process responsible, requires considerably more input from the Southern Hemisphere. Such is the focus of our study of an extensive sequence of Tertiary lavas from the Liverpool Volcano in eastern Australia, which is known to contain the record of an ancient field reversal at about 40 million years ago. Our goal is to obtain the most complete paleomagnetic documentation of polarity reversal recorded in the Southern Hemisphere, both with regard to the progression of directional swings, as well as the changes in field strength. In addition, we are using isotopic dating techniques to date the lavas in order to determine the precise age and duration of the reversal. Results from the project will be used to develop improved global models of dynamo reversal and to supply needed constraints for sophisticated computer simulation. Studies of the geomagnetic field are important because it shields the Earth from harmful cosmic rays and provides the means for human and animal navigation. The field is decaying in strength at a rate that, if it were to continue, would vanish in less than 2000 years. If this occurred, it could signal the onset of an attempt by the dynamo to reverse polarity. Through our study of the Liverpool Australia Reversal we hope to better understand the nature of transitional magnetic field behavior, which has important implications for our understanding of the processes in the deep Earth's interior that give rise to the geomagnetic field. In addition to the scientific goals of the project, the research is supporting the training of undergraduate students at California State Polytechnic University, and is contributing to research infrastructure at the University of Wisconsin.