The palaeomagnetism of Cambro-Ordovician redbeds, the Erquy Spilite Series and the Tregastel-Ploumanac'h granite complex, Armorican Massif (France and the Channel Islands)

Abstract

Summary. In addition to a component (A) of recent origin, two NRM components are distinguished in the Cambro-Ordovician redbeds of the Armorican Massif. In most sites other than those from northern Brittany the oldest (C) is probably Silurian or early Devonian, and is mainly carried by specularite with high blocking temperatures. This component was variably overprinted by a Devonian or early Carboniferous component (B3) which was probably acquired as a viscous PTRM on uplift after burial, and is carried by hematite pigment with intermediate to high blocking temperatures. In the red succession of Plourivo-Brehec (northern Brittany) declination scatter of two intermediate to high blocking temperature components (B1 and B2) is consistent with clockwise rotation of the bulk of Europe during the late Carboniferous, implied independently by published European Carboniferous palaeomagnetic data. Stable NRM in the Erquy Spilite Series yields a palaeomagnetic pole at 344 E, 35 N (dp = 21, dm = 22), and was probably acquired during remagnetization following Late Precambrian or early Cambrian folding. This is consistent with a middle to late Cambrian age of remagnetization estimated by comparison with other poles of known age. A palaeomagnetic pole position at 332 E, 34 S (dp = 4, drn = 7) determined for the Hercynian Trbgastel-Ploumanac'h complex is consistent with other middle to late Carboniferous poles from elsewhere in Europe.