The Eskolabreen Formation is the lowermost unit within the tectonostratigraphic pile of the Caledonian Hecla Hoek succession of Ny Friesland, Svalbard, and is exposed in the core of the Atomfjella Antiform. It is composed of strongly deformed and banded migmatitic gneisses and amphibolites, and intercalated granitic gneisses. U-Pb dating of prismatic zircons from a band of muscovite-biotite gneiss yields a poorly defined upper intercept age of ca. 1770 Ma. Zircons from two nearby samples of granitic gneiss yield a pooled upper intercept age of 1766 ± lO Ma, interpreted to date the intrusion of the granite. A lower intercept age for these zircons at 404 ± 8 Ma, and a similar U-Pb titanite age, record the age of Caledonian metamorphism in Ny Friesland. The results agree with U-Pb zircon and titanite ages recorded from the overlying Bangenhuk granitoids, and emphasize the importance of the ca. 1.7-1.8 Ga tectonothermal event within the intercalated basement units of the Ny Friesland Caledonides.

A. N. Larionov, Laboratory for Isotope Geochemistry, Geological Institute, Kola Science Center, 14 Fersman Street, Apatity 184 200, Russia;
Å. Johansson, Laboratory for Isotope Geology, Swedish Museum of Natural History, Box 50 007, S-104 05 Stockholm, Sweden;
A. M. Tebenkov & A. N. Sirotkin, Polar Marine Geological Expedition (Spitsbergen Division), 24 Pobeda Street, Lamonosov 189 610, Russia.