Ordovician paleomagnetic results from the St. George and Table Head carbonates of western Newfoundland

Abstract

We have studied 85 limestone and dolostone samples from 21 sites of the St. George and Table Head groups (Lower and Middle Ordovician) on Port au Port Peninsula (Humber Zone). Their gentle (~15°) tilt is probably Devonian. A steep viscous component dominant in the natural remanence is removed by thermal and (less efficiently) alternating-field demagnetization. In about 60% of all samples, the thermal treatment yielded a southeasterly reverse component ("A"), which typically remained blocked to 450–500 °C and then decayed to noise. Mean A component directions calculated from Zijderveld plots and referred to bedding are D, I = 148.5°, +33.6 °for N = 9 St. George sites and D, I = 150.0°, I = +40.7 °for N = 5 Table Head sites. Corresponding antipoles are 17.5°N, 152.3°E, dp, dm = 2.8°, 4.9 °and 13.4°N, 149.2°E, dp, dm = 2.9°, 4.7°, respectively. We interpret these results as representative of the geomagnetic field in the Early and mid-Ordovician. In 14 samples, mainly from the older St. George strata, thermal treatment yielded a reverse ("B") component with mean direction D, I = 167.9°, −9.2°, corresponding to an antipole at 44.9°N, 138.2°E, dp, dm = 3.6°, 7.1°. We interpret this as a late Paleozoic overprint in diagenetic hematite. The 30° anticlockwise rotation of Newfoundland proposed by Wegener is not supported by our data.

Arcs and backarc basins in the Early Paleozoic lapetus Ocean

“…The APWP for Laurentia is well defined back to the late Precambrian, but is relatively poorly defined for the late Precambrian itself (Deutsch & Prasad 1987;. The APWP used in this paper shows that the orientation of the eastern edge (present-day) of Laurentia from the southern Appalachians to Newfoundland changed remarkably little throughout the 560-390 Ma period.…”

The Occurrence and Origin of Remagnetization in the Sedimentary Rocks of North America

“…Other Late Paleozoic remagnetizations residing in hematite, interpreted to be chemical in origin and perhaps related to orogeny, have been reported from Ordovician carbonates in Newfoundland [Deutsch and Prasad, 1987; Beaubouef et al, 1990] and the Cambrian Peerless Formation in Colorado [Peck et al, 1986].…”

New palaeomagnetic, petrographic and 40Ar/39Ar data to test palaeogeographic reconstructions of Caledonide Svalbard

“…VGP of the Scottish Peterhead granite (Torsvik, 1985) and it also overlaps the 455-415 Ma Laurentia VGPs derived from Scotland, Newfoundland and Indiana, USA (Hodych, 1989;Hall & Evans, 1988;Deutsch & Prasad, 1987;Torsvik, 1984;McCabe et al 1985;Turnell, 1985). The close fit of HORNM VGP with the 455-415 Ma sectors of the two APWPs coincides in time with the 432 ± 7 Ma 40 Ar-39 Ar age obtained by Manecki et al (1998) from the adjacent Proterozoic Sofiebogen Group, which is interpreted as recording the timing of the syntectonic (D 1 -F 1 -S 1 ) Caledonian greenschist-facies metamorphism in the Hornsund region.…”