Construction of partial demagnetization systems and their application to paleomagnetic studies

Abstract

This thesis reviews the basic theory of rock magnetism and the consequent need for partial demagnetization techniques. It also describes the construction of thermal demagnetization systems and their application to the paleomagnetic study of both igneous and sedimentary rocks. As an alternating field (A.C.) demagnetizer became available during the course of this study a comparison is also made between both techniques of demagnetization. Paleomagnetic study of part of a sedimentary sequence at Hinakura Road, Wairarapa has reduced the number of discrepancies between the magnetic reversal stratigraphies previously determined there and those at Mangaopari Stream further south. Investigation of a lahar mound at Bruce Road, Mt Ruapehu showed that the Gothenberg Magnetic Event was not present in this locality. This area had previously been thought to provide the only evidence for the presence of the Gothenberg Event in the Southern Hemisphere. A pilot partial demagnetization study of volcanic samples from the Awatere River, Marlborough provided some evidence for a 50° clockwise rotation of this area since the Cretaceous.