Discordant Silurian paleolatitudes for central Newfoundland: New paleomagnetic evidence from the Springdale Group

Abstract

Ancient remanences are retained by the Early Silurian (429 + 6/-5 Ma) mafic volcanics of the Springdale Caldera (five sites) and the overlying red beds (seven sites). Dual polarity magnetizations are obtained by thermal demagnetization of samples from the red beds, whereas single polarity directions are observed in the volcanics. High unblocking temperatures indicate hematite as the remanence carrier in both the volcanics and sediments. These high-temperature, characteristic remanences are easily isolated and pass both the tilt and conglomerate tests; they are likely to be of primary Silurian age. Characteristic declinations are predominantly northerly and northeasterly, and indicate significant structural rotations on a local scale. When the results of the red beds and the volcanics are combined they show characteristic inclinations that are shallower than those of the correlative Botwood Group (ca. 36[deg] vs. 43[deg]) but not nearly as shallow as those reported from the King George IV Lake area (0.5[deg]). Mean inclinations obtained from the Springdale red beds are, however, significantly shallower than those of the Springdale volcanics. The same difference can be seen in other previous Silurian paleomagnetic studies of central Newfoundland. We infer that an inclination error affects the red bed magnetizations of the Springdale Group, Botwood Group (Wigwam Formation) and rocks of the King George IV Lake area. Therefore, the results from Silurian red beds should not be used to determine paleolatitudes for central Newfoundland. The mean paleolatitude of the Springdale Group volcanics is 30[deg]. The mean paleolatitudes for both the Springdale volcanics and Botwood volcanics (Lawrenceton Formation) are indistinguishable within paleomagnetic error limits from the predicted paleolatitude of Newfoundland on the northeast-trending North American margin. Thus, no detectable post-Silurian displacement is shown by the volcanics of the Springdale Group with respect to cratonic North America.