Abstract

Paleomagnetic data from isotopically dated Cambrian and Ordovician plutons in central Colorado indicate a Cambrian-Ordovician paleopole close to the late Paleozoic pole position.

Samples were partially demagnetized by both ac and thermal techniques. Magnetic directions were essentially the same regardless of treatment. Polished section and Curie temperature analysis indicate that the principal magnetic phase is low-titanium titanomagnetite. In many samples, titanomagnetite is the only magnetic iron oxide; in some samples, hematite occurs additionally. However, those samples containing hematite show the same remanent directions as those containing only titanomagnetite. All of our studies indicate that the magnetization is thermoremanent magnetization (TRM) acquired during the Cambrian and Ordovician.

Our results suggest that either little polar wandering occurred between the early and late Paleozoic or, if substantial wandering did occur, by late Paleozoic time the paleopole has returned to a position that was nearly coincident with that of the early Paleozoic.

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