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Palaeozoic palaeomagnetic studies, in the Welsh Basin-recent advances

Published online by Cambridge University Press:  01 May 2009

J. E. T. Channell ,
C. McCabe ,
T. H. Torsvik ,
A. Trench  and
N. H. Woodcock
J. E. T. Channell
Affiliation:
Department of Geology, University of Florida, Gainesville, FL 32611, USA
C. McCabe
Affiliation:
Department of Geology and Geophysics, Louisiana State University, Baton Rouge, LA 70803, USA
T. H. Torsvik
Affiliation:
Geological Survey of Norway, P. B. 3006 Lade, N-7002 Trondheim, Norway
A. Trench
Affiliation:
Department of Geology, University of Western Australia, Nedlands, Perth, WA 6009, Australia
N. H. Woodcock
Affiliation:
Department of Earth Sciences, University of Cambridge, Cambridge, CB2 3EQ, U.K.
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Abstract

In the last two years, new palaeomagnetic data from Wales have resulted in radical revision of the Ordovician palaeogeography of Eastern Avalonia, part of the southern margin of the Iapetus Ocean. Combined with Palaeozoic palaeomagnetic data from Laurentia and Gondwana, these data suggest that Eastern Avalonia was a peri-Gondwanide high latitude continental fragment during at least part of Ordovician time, with a palaeolatitude of about 62° S and 51° S in Arenig and Llanvirn time, respectively. This implies a latitudinal width of the early Ordovician Iapetus Ocean between Eastern Avalonia and Laurentia of at least 30°. Geological evidence for the proximity of Eastern Avalonia and Laurentia suggests that the intervening Iapetus Ocean closed during Silurian time, from late Llandovery to early Ludlow. Recent palaeolatitude data from the Iapetus bordering continents are consistent with closure by middle to late Silurian time. New pre-Acadian early Devonian palaeomagnetic data from the Old Red Sandstone places the Welsh Basin at about 17° S, consistent with a palaeogeography in which Laurentia, Baltica, Avalonia, Armorica, and possibly Gondwana, were part of a single supercontinent. Pervasive late Carboniferous/early Permian remagnetization affects the Welsh Basin. The remagnetization is probably associated with fluids emanating from the Variscan thrust front. We do not observe remagnetization associated with Acadian orogeny and the remagnetizations, which have been studied in more detail in North America, appear to be a unique feature of the Variscan-Hercynian-Alleghenian orogeny.

Type
Articles
Information
Geological Magazine , Volume 129 , Issue 5 , September 1992 , pp. 533 - 542
Copyright
Copyright © Cambridge University Press 1992

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