The Egersund dykes (SW Norway): A robust Early Ediacaran (Vendian) palaeomagnetic pole from Baltica

Abstract

Palaeomagnetic data for Baltica in the Late Precambrian are highly ambiguous, and have therefore, given rise to different interpretations concerning the need to explain Varangerian glaciations through snowball Earth conditions. We present new palaeomagnetic data from the 616 ± 3 Ma (U-Pb) Egersund dykes in SW Norway, which yield a palaeolatitude of 53° + 16°/-13° for the studied location. This would indicate that the Baltica plate spanned latitudes between 50° and 75° S in the Early Ediacaran. The pole position (31°N, 44°E, dp/dm = 15/17) confirms earlier studies, but the primary nature of the remanence is now supported by two positive contact tests. A new 40Ar/39Ar biotite age of 600 ± 10 Ma from one of the dykes suggests that remanence acquisition in the dykes took place between 600 and 616 Ma. The Egersund palaeomagnetic data demonstrate that Baltica was located at relatively high latitudes at the time of the Varangerian glaciations. Additional palaeomagnetic sites in the Rogaland Igneous Complex yield a pole position (46°S, 238°E, dp/dm = 17/19) that confirms previous studies. The age of this remanence has traditionally been quoted as c. 930 Ma based on U-Pb ages from the complex. However, previous 40Ar/39Ar hornblende ages of around 870 Ma are now supported by a new 40Ar/39 biotite age of 869 ± 14 Ma obtained from a noritic dyke, and we argue that this represents an uplift/cooling age which better represents the age of the remanence in SW Norway. © 2006 The Authors Journal compilation © 2006 RAS.