Paleomagnetism of mafic dikes from the Avalon Peninsula, eastern Newfoundland
DOI:
https://doi.org/10.4138/1388Abstract
As part of a major study of the Avalon zone in eastern Newfoundland, we describe the palromagnetism of two series of dikes located in the Bauline and Colliers-Harbour Main areas, respectively. Detailed alternating field (AF) and thermal experiments performed on these dikes indicate that they are characterized by two significantly different mean directions of magnetization: SE++(D = 153°, I = +62*; K = 46, N = 12 sites) and SW (D = 217°, I = +58°, K = 58, N = 12 sites ) with corresponding paleopole positions at A (4°N, 34"U; dp,dm = 8", 10°) and C (2"N, 81°W; dp, dm = 6", 9'). Antipoles A and C are located in southerly latitudes, and a comparison with other poles of Avalonian rocks from New Brunswick, Nova Scotia and Newfoundland indicates a Silurian to Siluro-Devonian age for these dikes. Poles A and B are interpreted as representing rapid apparent polar wander with respect to eastern Newfoundland during Silurian time. Two components of magnetization, corresponding to two distinct geological events, are observed in the dikes investigated and this situation favours the following geological scenario for the evolution of the Avalon microcontinent: (a) intracratonic rift zone resulting in long-lived Late Hadrynian and Cambrian continental extension, (b) a very late phase of distension in separating miniplates during Silurian and Early Devonian time. RÉSUMÉ Dans le cadre d'une étude d'envergure de la zone d'Avalon menée dans l'est de Terre-Neuve, nous décrivons le paléomagnétisme de deux séries de dykes situées dans les régions de Bauline et de Colliers - Harbour Main respectivement. Des experiences détaillées de désaimantation par champ alternatif (CA) et par lavage thermique démontrent que deux directions moyennes de l'aimantation caractérisent les dykes: SE++(D = 153°, I = +62*; K = 46, N = 12 sites de prélèvement) et SO (D = 217°, I = +58°, K = 58, N = 12 sites de prélèvement) avec des paléopöles correspondants aux positions A (4°N, 34"U; dp,dm = 8", 10°) et C (2"N, 81°W; dp, dm = 6", 9'). Les antipôles A et C se situent à des latitudes méridionales et par comparaison avec d'autres pôles de roches avaloniennes du Nouveau-Brunswick, de la Nouvelle-Écosse et de Terre-Neuve, on attrlbue aux dykes un âge Silurien à Siluro-Dévonien. On interprète les pôles géomagnétiques A et B comme le résultat de displacements rapides du pôle par rapport avec l'est de Terre-Neuve durant le Silurien. On observe dans ces dykes deux composantes de magnétisation, correspondant à deux évènements géologiques distincts. Ceci suggère le scenario suivant pour expliquer l’évolution du microcontinent Avalon: (a) un rift intracratonique qui se traduit par une longue période d'extension continentale depuis l'Hadrynien tardif jusqu'au Cambrien; (b) du Silurien jusqu'au début du Dévonien, une phase tardive de distension lors de la séparation des miniplaques. [Traduit par le journal]Downloads
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