Paleomagnetism of Eocambrian Long Range dykes and Double Mer Formation from Labrador, Canada

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Abstract
A paleomagnetic study was carried out on two post-Grenvillian units in the Grenville Province of southeast Labrador. These are (i) a swarm of northeast-trending mafic dykes inferred to be part of the Long Range suite and (ii) the Double Mer Formation, which is an undated rift-related red-bed sequence. Three of six mafic dykes investigated, including two having K–Ar (minimum) ages of 514 ± 8 and 553 ± 22 Ma, carry an interpreted primary remanence of declination (D) = 124.8°, inclination (I) = 55.5° (k = 48, α95 = 18.0°), with the corresponding paleopole at 10.8°S, 164.3°E. Three dykes, including one previously dated at 615 ± 2 Ma (U–Pb), yielded anomalous results. Nevertheless, because all six dykes show similar field, petrographic, and chemical characteristics, we consider that they belong to a single swarm. The anomalous directions are interpreted as disturbed paleomagnetic signatures, and the 615 Ma age is extrapolated as dating the primary remanence in the undisturbed dykes. The Double Mer Formation yields a mean direction for five sites at D = 110.8°, I = 50.1° (k = 24.6, α95 = 15.7°), with a corresponding paleopole at 13.0°S, 178.6°E. The similarity of this direction with that for mafic dykes is the first quantitative indication of its previously suspected Eocambrian age. Combining the Long Range dyke and Double Mer data, the paleolatitude of Eocambrian southeast Labrador is estimated to be 26 ± 5°S.

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