Palaeomagnetism of theca.440 Ma Cape St Mary’s sills of the Avalon Peninsula of Newfoundland: implications for Iapetus Ocean closure

Abstract

We report on the palaeomagnetism of the gabbroic Cape St Mary’s sills of the Avalon Peninsula of Newfoundland, which have previously yielded a 441±2 Ma U–Pb baddeleyite age (latest Ordovician or earliest Silurian). At 12 of 19 sites, stepwise alternating‐field or thermal demagnetization isolated a stable characteristic remanence carried by magnetite. This remanence is shown to pre‐date Early Devonian folding of the sills. Although a baked‐contact test was inconclusive, the positive fold test and the low grade of metamorphism of the sills (prehnite–pumpellyite facies) make it likely that the characteristic remanence is primary. The tilt‐corrected site‐mean characteristic remanence has a declination of 343° and an inclination of −51° (k=25, α95=9°), yielding a ∼440 Ma palaeopole at 10°N, 140°E (dm=12°, dp=8°) for West (North American) Avalonia. The corresponding ∼440 Ma palaeolatitude for the Avalon Peninsula is 32°S±8°. The only other West Avalonian palaeolatitude determination from rocks that could be of similar age is from the Dunn Point volcanics of Nova Scotia; their more southerly palaeolatitude of 41°S±5° suggests that they are significantly older than 440 Ma, a possibility that we recommend testing with U–Pb dating. Although no ∼440 Ma palaeolatitude determinations are available for East Avalonia (parts of southern Britain and Ireland), interpolating between mid‐Ordovician and mid‐Silurian determinations gives an estimate of ∼25°S. This is consistent with our Cape St Mary’s result and, if the Iapetus Ocean closed orthogonally, with a narrow (∼1000 km) Iapetus Ocean of approximately east–west orientation between Avalonia and Laurentia by 440 Ma.

Late Neoproterozoic to Early Palaeozoic palaeogeography of Avalonia: some palaeomagnetic constraints from Nuneaton, central England

“…In order to eliminate the potential ambiguities of such data, the field sampling has been conducted on a wide agerange of rocks that have been the subject of recent detailed geological study (Bridge et al 1998). With this chronological framework in place, we were able to calculate late Neoproterozoic and Late Ordovician palaeolatitudes which are consistent with those obtained from rocks of similar ages in Newfoundland (Hodych & Buchan, 1998;McNamara et al 2001). 1), and their ages have been either determined radiometrically, or can be reasonably constrained biostratigraphically.…”

Early Ordovician rifting of Avalonia and birth of the Rheic Ocean: U–Pb detrital zircon constraints from Newfoundland

“…Separation during the Early Ordovician is supported by subsidence analysis (Prigmore et al 1997), comparable faunal assemblages until the Tremadoc (Cocks et al 1997;Fortey & Cocks 2003) and palaeomagnetic data that indicate that Avalonia resided at high southerly latitude near Gondwana from the Middle Cambrian to the end of the Early Ordovician (van der Voo & Johnson 1985;Hodych & Buchan 1998;MacNiocaill, 2000;Hamilton & Murphy 2004). The zircon data presented herein are compatible with a younger timing of separation of Avalonia from Gondwana that occurred in the Early Ordovician (Fig.…”

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.

“…Paleomagnetic data from Ediacaran rocks of the Musgravetown Group in eastern Newfoundland (24°± 5°S, Pisarevsky et al 2011) and the Caldecote volcanics in England (27°± 6°S, Vizan et al 2003) indicate that Avalonia was situated at low latitudes. 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).…”