George M. Dineen

B. Sc. Honours Thesis

Magnetic Properties of a Bermudian Pillowed Lava Flow

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This study is concerned with the description and interpretation of the opaque mineralogy and paleomagnetic properties of a 3.0 m core interval which is comprised of a pillowed lava flow and basal intrusive sheet taken from a depth of 776 m in an 802 m core drilled on the Bermuda Seamount. Results indicate that the observed magnetic properties are controlled by inter-related and generally non-separable effects of grain size, magnetic phase volume and alteration. Secondary mineralization and inclination of polarity within the flow unit indicate that the flow has been megneticly overprinted by a normal polarity magnetic event and hydrothermal alteration associated with mid-Tertiary sheet intrusion. The remanence of the sheet and flow is of low intensity and is primarily carried by secondary magnetite formed at sub-Curie point temperatures. Shallow reverse and steep normal inclinations are interpreted as the resultant magnetic vectors of a frequently reversing geomagnetic field and a secondary shallow chemical remanent magnetization.

The flow and sheet units are characterized by type 2 and type 1 titanomagnetite, respectively. The opaque phases display extensive alteration ranging from grain cracking to complete granulation and titanohematite replacement.

High temperature and tectonic adjustment within the lava sequence at the depth of the core interval may contribute to the high degree of alteration and dipolar inclination dispersion observed.

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Pages: 112
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