A palaeomagnetic study of igneous rocks from eastern Australia, with special reference to rock bodies of Mesozoic age

Abstract

Scope of the work - Palaeomagnetism is the study of the direction of ancient or 'fossil' magnetization of rocks. If the measured direction in a rock sample is the direction acquired in the earth's magnetic field at the time of formation, defined as the primary (0) direction, and if the age and orientation of the rock is known, the result may be used to study the magnetic field at that time. To do this it is necessary to provide evidence for supposing that the direction obtained is primary, and therefore reflects the earth's magnetic field at the time of formation. A succession of such directions from rocks of increasing age may then be used to show changes in the magnetic field in previous epochs relative to the sampling area. This thesis is mainly concerned with the observation of 'fossilized' magnetization directions in igneous rocks from eastern Australia formed during the Mezozoic Era, and from which the direction of the magnetic field at that time may be inferred: directions from some Tertiary rocks ere also studied for comparison. During these studies it was found necessary to supplement the apparatus existing in the Department of Geophysics with an oven for thermal demagnetization. I constructed de-gaussing coils for this (chapter 2). (First two paragraphs of introduction.) Show more