A paleomagnetic investigation of early Paleozoic rocks in western Newfoundland

The results of paleomagnetic studies on carbonate rocks of Cambrian and Ordovician age from the Western Platform of Newfoundland are presented. The study includes tectonically transported Middle Ordovician strata. All the rocks studied are weakly magnetic and so all remanence measurements were made with a cryogenic magnetometer. -- Two characteristic components, "A" and "B", both of reverse polarity, were isolated by thermal demagnetization from each of the Port au Port Group (mid-to Upper Cambrian) and St. George Group (Lower Ordovician) on the Port au Port Peninsula. It was concluded that the "A" component represents a primary or early diagenetic magnetization, corresponding to a Cambrian pole at 3.4°N, 145.6°E and a Lower Ordovician pole at 17.5°N, 152.3°E. The respective "B" component poles seem to be Late Paleozoic (Kiaman) overprints. Magnetic mineralogy studies show that the "A" component is carried by magnetite and the "B" component by diagenetic hematite. -- In the Port au Choix area, the St. George Group did not show evidence of Late Paleozoic overprinting, but yielded a characteristic direction 40° misaligned in declination with the age-equivalent rocks on the Port au Port Peninsula. The remanence, which resides in magnetite, corresponds to a pole at 2O.5°N, 113.3°E and may be a thermoviscous remagnetization related to the Acadian orogeny. -- A single characteristic component with pole at 15.9 N, 153.6°E was isolated from the Middle Ordovician Table Head Group on the Port au Port Peninsula. This component predates the probable Acadian deformation. A polarity change between the uppermost Table Head and the lowermost Long Point Group was identified, though the Long Point rocks mostly yielded unstable magnetizations. -- A magnetization predating the Acadian(?) folding was isolated from the Middle Ordovician strata of the allochthonous Cow Head Group. The corresponding pole position falls close to the poles from the platformal Ordovician rocks, suggesting that these rocks were not transported far. -- The hypothesis of a rotation of western Newfoundland relative to mainland North America is not supported. However, a relative rotation between the Port au Port area and part of the Great Northern Peninsula (north of Cow Head) is possible. -- Key Words: Paleomagnetism; Lower Paleozoic; carbonates; western Newfoundland; primary remanence; Kiaman overprints