Paleomagnetic and K-Ar dating studies of Late Cretaceous basaltic dykes intruding Late Permian sediments of Newcastle Coal Measures,Newcastle, Australia-Relationship to the opening of the Tasman Sea

摘要

Paleomagnetic studies of Late Cretaceous basaltic dykes (K-Ar age of ca. 80Ma) and associated sediments reveal the presence of both normal and reverse polarity magnetizations. Correlation with the geomagnetic polarity time scale shows that the normal polarity magnetization could have been acquired in the geomagnetic polarity chron (C33n) and the reversed polarity magnetization may have been acquired in the C33r or C32r polarity chron, respectively. This indicates that pulses of magmatism occurred in the region over a substantial period. The normal and reverse magnetic directions show a clockwise deflection from the north-south direction of 40-50°, which may be related to block rotation associated with deformation events that have occurred subsequent to dyke emplacement or to the opening of the Tasman Sea.