Graduate Thesis Or Dissertation
 

Paleomagnetism and secular variation of Easter Island basalts

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  • The paleomagnetic history of the volcanic rocks of Easter Island was investigated using standard paleomagnetic techniques. The remanent magnetization of 673 specimens from the three volcanic episodes recognized on the island were measured using a spinner magnetometer. Inclinations, declinations and virtual geomagnetic poles were calculated for each flow. The majority of the samples were collected from the youngest episode, the Terevaka volcanics, which represents activity from the last 200, 000 years. The 65 flows from the Terevaka episode were used to study the Brunhes epoch on Easter Island. A mean geomagnetic pole was located at 87.4°N latitude and 204.2°E longitude. With its oval of 95% confidence, this includes the present geographic pole, as expected for such young rocks. Secular variation, expressed by the angular deviation of the mean virtual geomagnetic pole, was obtained for the Terevaka samples, This value, 12.8° with 95% confidence limits of 14.9° and 11.2°, is compared to other values for Brunhes age rocks. It appears to fit well onto a calculated model for the variation of angular dispersion with site latitude. It also can be related to an anomalously low region of secular variation found in the central Pacific.
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