Paleomagnetism and rock magnetism of Early Silurian Dunn Point volcanics, Avalon Zone, Nova Scotia

Séguin, Maurice K.; Rao, K. V.; Deutsch, E. R.

doi:10.1016/0031-9201(87)90091-4

Cited by 8 publications

(4 citation statements)

References 27 publications

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“…(2) The suggestion that results from the Dunn Point Formation volcanics are unreliable because of a 'controversial age of magnetization' relative to folding is misleading. 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.…”

Section: Implications For a P P A R E N T Polar W A N D E Rmentioning

confidence: 99%

Early Silurian palaeolatitude of the Springdale Group redbeds of central Newfoundland: a palaeomagnetic determination with a remanence anisotropy test for inclination error

Hodych

Buchan

1994

Geophysical Journal International

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S U M M A R YWe studied the palaeomagnetism of red fine-grained sandstones and coarse siltstones of the early Silurian Springdale Group of central Newfoundland. At 10 sites, a high blocking temperature characteristic remanence carried by haematite was isolated. This remanence is shown to predate probable early Devonian folding. Anti-parallel north-and south-directed remanences through a 100 m section of redbeds and a positive conglomerate test on haematite-bearing volcanic clasts suggest absence of remagnetization. Inverting the south-directed sites and unfolding yields a characteristic remanence with a mean declination of 23.6" and a mean inclination of -14.2" (myg5 = 7.3", k = 45.4). The inclination corresponds to a probable early Silurian palaeolatitude of 7"s f 4". We find no significant difference between early Silurian palaeolatitudes for central Newfoundland north and south of the Red Indian Line suture, and conclude that the part of the Iapetus Ocean across the suture had narrowed to less than about 5" by the early Silurian. This is consistent with palaeomagnetic results from Britain and Ireland that suggest no more than a narrow Iapetus at low palaeolatitude by the early Silurian.We also tested whether we have underestimated palaeolatitude because of sediment compaction reducing remanence inclination from that of the early Silurian field. We measured anisotropy of the isothermal remanence (IRM) acquisition for one specimen from each stable site, finding that a field of 200 to 800 rnT applied at 45" to bedding produced an isothermal remanence oriented on average at 42" to bedding. Theory then predicts that sediment compaction caused less than 2" average inclination shallowing in the Springdale Group redbeds, and less than a 1" underestimation of palaeolatitude.

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Section: Implications For a P P A R E N T Polar W A N D E Rmentioning

confidence: 99%

Early Silurian palaeolatitude of the Springdale Group redbeds of central Newfoundland: a palaeomagnetic determination with a remanence anisotropy test for inclination error

Hodych

Buchan

1994

Geophysical Journal International

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“…From West (North American) Avalonia, the only Ordovician or Silurian palaeomagnetic results that are published in full and that have been interpreted to pre‐date folding are those from the steeply dipping Dunn Point Formation volcanics of Nova Scotia. Early studies by Van der Voo & Johnson (1985) and Seguin, Rao & Deutsch (1987) yielded conflicting fold tests, with the former reporting a positive test and the latter an inconclusive test. In a later more detailed re‐study of the Dunn Point volcanics, Johnson & Van der Voo (1990) obtained a positive fold test, suggesting that the remanence pre‐dates Devonian folding.…”

Section: Introductionmentioning

confidence: 99%

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

Hodych¹,

Buchan

1998

Geophys. J. Int.

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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.

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“…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.…”

Section: Implications For a P P A R E N T Polar W A N D E Rmentioning

confidence: 99%

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

Stamatakos

Voo

Pluijm

et al. 1994

Geophysical Journal International

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S U M M A R YRecent palaeomagnetic results from coeval Silurian sedimentary and volcanic rocks of Newfoundland yield contradictory results, with shallow characteristic directions recorded by the redbeds and steeper characteristic directions recorded by the volcanics. In their recent paper on the Springdale Group redbed, Hodych & Buchan (1994a) argue that the redbed magnetization is more reliable based on a fold test, dual-polarity magnetization, conglomerate test and an IRM acquisition experiment specifically designed to test for compaction or inclination error. Accordingly, these authors dismiss the volcanic results as well as the Silurian reference poles for Laurentia, citing possible remagnetization or other complications. However, we argue that the IRM experiments of Hodych & Buchan (1994a) are flawed and do not necessarily resolve the question of inclination error. Moreover, we point out that the conglomerate test is incomplete and that the proposed tectonic reconstruction based solely on the redbed magnetization implies a unique tectonic scenario that is incompatible with out present understanding of Silurian palaeogeography.

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Paleomagnetism and rock magnetism of Early Silurian Dunn Point volcanics, Avalon Zone, Nova Scotia

Cited by 8 publications

References 27 publications

Early Silurian palaeolatitude of the Springdale Group redbeds of central Newfoundland: a palaeomagnetic determination with a remanence anisotropy test for inclination error

Early Silurian palaeolatitude of the Springdale Group redbeds of central Newfoundland: a palaeomagnetic determination with a remanence anisotropy test for inclination error

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

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

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