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

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.

Reply to comment by J. G. Meert and R. Van der Voo on ‘New palaeomagnetic result from Vendian red sediments in Cisbaikalia and the problem of the relationship of Siberia and Laurentia in the Vendian’

“…Meert and Van der Voo suggest that Sept‐Iles ‘A’ is a result of later remagnetization, but it is also possible that the Callander pole is a result of remagnetization: the baked contact test for the Sept‐Iles is more rigorous than for the Callander or Catoctin ‘A’. Meert and Van der Voo agreed with us about a 615 Ma age for the Long Range pole (Murthy et al . 1992; Kamo & Gower 1994).…”

Chapter 7 Neoproterozoic glacial palaeolatitudes: a global update

“…Both data sets contain an unusually large spread of inclinations and hence implied palaeolatitudes of emplacement, confounding simple interpretations (reviewed by Hodych & Cox 2007;McCausland et al 2007). Low to moderate palaeolatitudes for the Long Range dykes (Murthy et al 1992) are supported by subsequent work (McCausland et al 2009, abstract only). For the younger, Grenville Dykes, a positive baked-contact test demonstrates that the steep palaeomagnetic B remanence found in some of the dykes is primary (Murthy 1971;Hyodo & Dunlop 1993).…”

Chapter 35 The Tatonduk inlier, Alaska–Yukon border

“…This pole is consistent with the grand mean pole on the contemporaneous Franklin LIP (Denyszyn et al 2009), and demonstrates that Laurentia straddled the equator during deposition of the Rapitan Group (Macdonald et al 2010b). Although Laurentia remained at low latitudes until 615 Ma according to the controversial Long Range Dyke pole (Murthy et al 1992;Hodych et al 2004), Laurentia appears to have migrated to high latitudes by 590 Ma (Murthy 1971). McCausland et al (2007) provide an excellent review of the Ediacaran palaeomagnetic data from Laurentia.…”