| Popis: |
To obtain an early Ordovician paleomagnetic pole position for North America, and to determine the paleolatitude of its margin of the lapetus Ocean prior to the Taconic orogeny, a study of the lower St. George Group (Tremadocian-Arenigian) of western Newfoundland was undertaken. Analysis of 84 oriented core samples from six localities on Port au Port Peninsula indicates that the NRM of the St. George rocks is the resultant of three distinct paleomagnetic directions. The first is a steep downward component commonly observed in the low temperature range of demagnetization (room temperature 250°C) in virtually all samples, that roughly corresponds to the present day axial dipole field direction in situ ( D = 350° , I = 68° ). The second is a stable component with southerly declinations and shallow-intermediate negative inclinations ( D , I in situ = 176° , −20°; D , I tilt corrected = 173° , −5°, respectively) usually seen in the range of 450–600°C and found in approximately 46% of the specimens. The third is a stable southeasterly, shallow-intermediate positive component ( D , I insitu = 161° , 16°; D , I tilt correcied = 163° , 34°, respectively) generally unblocked within the 350–550°C or 450–600°C range which was observed in 40% of the specimens. These components of remanence are herein referred to as the Type 1, Type 2, and Type 3 components, respectively. The remaining 14% of the specimens were found to be either directionally unstable to thermal demagnetization or totally overprinted by the Type 1 component. The Type 2 component is interpreted to represent a post-folding, Late Paleozoic remagnetization possibly associated with the Alleghanian Orogeny. On the other hand, the Type 3 component is interpreted as an Early Ordovician, possibly pre-Taconic remanence and, in tilt corrected coordinates, yields a paleolatitude for this region of the North American craton of 19° S ± 6° . |
