Abstract

Paleomagnetic results from 61 sites on diabase dikes and sills in Connecticut and Maryland yield a mean pole of position of 100.9 °E. 68.6 °N, α95 = 1.6°. These results combined with those from 7S sites on four diabase sills in the Gettysburg Basin of Pennsylvania produce a mean pole position of 101, 6 °E. 65.4 °N, α95 = 1.3 °from 139 VGPs. These rocks arc probably of Early to early Middle Jurassic age by stratigraphic and inferred stratigraphic position. The paleomagnetic results indicate that the Gettysburg and Hartford Basins did not subside simultaneously.The dispersion of virtual geomagnetic poles about the mean pole of the Connecticut, Pennsylvania, and Maryland intrusive rocks is probably the result of 'homogenization' of magnetic directions during low-temperature oxidation of titanomagnetite to titanomaghemite over a period long enough to erase a considerable amount of dispersion due to secular variation.Rotation of Europe against North America in the prerifting configuration causes good convergence of European Jurassic mean poles and the pole of the Connecticut. Maryland, and Pennsylvania intrusive rocks. This is evidence that separation of the two continents had not begun by Early to early Middle Jurassic time, which is in agreement with earlier findings based on sea-floor magnetic anomalies and faunal assemblages.

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