Abstract

One hundred and twenty oriented drill cores were collected from 20 sites in the Karmutsen basalts of Karnian age in the eastern part of Vancouver Island. Alternating field and thermal demagnetization studies reveal stable endpoint directions in 13 sites which fall into the following groups: (1) northwest-up (four sites); (2) north-up (four sites); (3) north-northeast-down (four sites); and (4) easterly-up (one site). The northwest-up direction is observed in the least altered samples with only pure magnetite of high coercive force and blocking temperatures as a carrier. The north-up direction, which shows streaking in a east–west sense, is also observed in (other) least altered specimens, and shows a complex magnetic mineralogy with lower coercivity. The north-northeast-down direction occurs in definitely more altered specimens, and some specimens show a northerly flat magnetization at the end of the blocking temperature range. The easterly-up direction is poorly defined but may correspond to the direction reported for the Nicolai Greenstones in Alaska. The relation between these groups of directions is not clear, and only in a few specimens an indication for the separation of remanence components has been observed. The available evidence indicates that a northerly component is probably the oldest and that the northwest-up magnetization may represent this component. The pole position calculated for this magnetization is 90°E, 21°N which is about 40°S of the Triassic pole position for cratonic North America. The discrepancy would be larger still if the northwest-up direction is a single component secondary direction. The discrepancy can, of course, be explained by a northward shift of the Karmutsen from a source area near 10°N with or without a sinistral rotation.

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