Pre-folding magnetization reconfirmed for the Late Ordovician-Early Silurian Dunn Point volcanics, Nova Scotia

Abstract

Paleomagnetic results have been obtained for three new sites in steeply inclined subarea1 volcanic flows of the Dunn Point Formation from the Avalon terrane of Nova Scotia. Demagnetization analysis reveals a characteristic magnetization, carried by hematite, which is similar to that reported in previous studies of this unit. A new and improved fold test for the characteristic component, combining paleomagnetic and structural data from the present study with paleomagnetic data for vertically dipping flows (and laterites) studied previously by the authors, is significantly positive. The new fold test reconfirms the prefolding age of the characteristic component. A primary age of magnetization is inferred, based on field evidence for early oxidation of the flows. The overall mean direction for the characteristic component of D = 344O, I = -60°, k = 68.6, ass = 4.1" (paleopole at 2ON, 130'E) corresponds to a Late Ordovician-earliest Silurian paleolatitude for Avalon of 41°S. The latter is much higher than that predicted for the area on the basis of the cratonic North America apparent polar wander path, implying a substantial post-Ordovician displacement (> 1700 km) of Avalon with respect to the craton. The Dunn Point result supports previous paleogeographic reconstructions that show Avalon together with the continental blocks of Hercynian Europe and northwestern Gondwana.

Comment On: ‘Early Silurian Palaeolatitude of the Springdale Group Redbeds of Central Newfoundland: A Palaeomagnetic Determination With A Remanence Anisotropy Test For Inclination Error’ By J. P. Hodych and K. L. Buchan

“…These results are in agreement with palaeomagnetic results from previous studies of the Springdale Group (Potts, van der Pluijm & Van der Voo 1993a) and other Silurian redbeds of Newfoundland (Lapointe 1979;Buchan & Hodych 1989 Pluijm & Van der Voo 1993b) but are significantly different from coeval volcanic rocks from Newfoundland (Potts et al 1993a;Gales, van der Pluijm & Van der Voo 1989;Lapointe 1979) as well as volcanics from Nova Scotia (Van der Voo & Johnson 1985;Johnson & Van der Voo 1990), that indicate much higher southerly palaeolatitudes at this time. Discrepancies in palaeolatitudes determined from coeval sedimentary and volcanic rocks are not unique to Newfoundland.…”

“…When the correct values for bedding are used, the magnetization predates folding. The matter can only be considered controversial if it is shown that the actual bedding attitudes are different from those so carefully measured by Johnson & Van der Voo (1990). To our knowledge such 'errors' have not been demonstrated.…”

“…Johnson & Van der Voo (1990) show that bedding corrections used by Seguin, Rao & Deutsch (1987) to argue for an inconclusive fold test and hence, unconstrained age of magnetization, were incorrect. When the correct values for bedding are used, the magnetization predates folding.…”

A paleogeographical review of the peri-Gondwanan realm of the Appalachian orogen1This article is one of a series of papers published in this CJES Special Issue: In honour of Ward Neale on the theme of Appalachian and Grenvillian geology.

“…It moved to reside at high southerly latitudes (60°-54°) near Gondwana during the Cambrian Hodych and Buchan 1998;Mac Niocaill 2000). During the Floian, Avalonia moved rapidly north to intermediate (41 ± 8°S) latitudes indicating increasing separation from Gondwana concurrent with a decrease in the separation between Avalonia and Laurentia (Johnson and Van der Voo 1990;Hodych et al 2004;Hamilton and Murphy 2004). Comparable faunal assemblages support Gondwanan linkages for Avalonia until the Tremadoc (Cocks et al 1997;Fortey and Cocks 2003); after which, the faunal provinciality indicates changing affinities from Gondwanan to genera with Laurentian ancestors.…”

A plate tectonic scenario for the Iapetus and Rheic oceans

“…w. Johnson and Van der Voo (1985), x Thompson et al (2010),. y Johnson and Van Der Voo (1990),. z Hamilton and Murphy (2004),.…”