GRENVILLIAN BASEMENT AND A MAJOR UNCONFORMITY WITHIN THE CALEDONIDES OF NORDAUSTLANDET, SVALBARD

Variously deformed granites and migmatites underlie the Neoproterozoic successions of Nordaustlandet, Svalbard. New U-Pb zircon investigations of two types of intrusions from Lapponiahalvoya, northwestern Nordaustlandet, have yielded ages of 93 +/- 8 and Ma (Kontaktberget granite) and 961 +/- 17 Ma (Lapponiafj ellet granite), confirming previous, less precise multi-grain, Pb-Pb evidence of Grenvillian igneous activity. The Kontaktberget granite cuts metasediments (Brennevinsfjorden Group), that are tightly folded and are separated from overlying volcanic and volcaniclastic rocks (Kapp Hansteen Group) by a major discordance (the Botniahalvoya Unconformity). The latter has been mapped in northwestern Nordaustlandet and is inferred to exist in central areas between Vestfonna and Austfonna. The Kapp Hansteen Group, with associated intrusive quartz porphyries, are probably a late orogenic expression of the Grenvillian igneous activity. The lack of igneous rocks in the overlying Neoproterozoic succession (Murchisonfjorden Supergroup) suggests that the base of this major unit is also a significant unconformity. This new evidence emphasizes the importance of the belt of Grenvillian tectonothermal activity, referred to here as the Nordauslandet Orogeny, that reaches from the classical provinces of North America and southern Scandinavia, via the East Greenland Caledonides, into the high Arctic.