Abstract
In the Central Mobile Belt of Newfoundland, three volcanic groups of early Middle Ordovician age (Robert's Arm, Summerford, and Chanceport) are thought to have formed within the Iapetus Ocean. Demagnetization analyses of 328 samples from these three groups has yielded similar magnetic directions, calculated by combining stable end-point directions and great-circle poles. The three groups yield similar poles located at 6°N, 140°E; 8°N, 140°E; and 10°N, 131°E, corresponding to paleolatitudes of about 30°S. The magnetization of the Robert's Arm Group passes the tilt test, and one site shows normal polarity, antipodal to the directions of the other sites. The paleolatitude of 31°S places the volcanic rocks at the time of their formation in the middle of Iapetus, between the Laurentian margin at about 15°S and the location of the Avalon Terrane at >50°S. Subsequent accretion to Laurentia and the presently adjacent island-arc rocks represented by the Moreton's Harbour Group occurred after northward drift in the later Ordovician/earliest Silurian and before the Middle Silurian.
