U-Pb zircon age of a dolerite dyke from near Hamningberg,Varanger Peninsula, North Norway, and its regional significance

Abstract

A dolerite dyke cutting very low-grade metasedimentary rocks of the Løkvik- fjellet Group near Hamningberg, NE Varanger Peninsula, Finnmark, has yielded a U-Pb zircon upper intercept age of 567,1 +30\/23 Ma. This ENE-WSW-trending dyke, and others of comparable field character, petrography and geochemistry in this northeastern part of Varanger, have previously given Late Devonian\/Early Carboniferous, K-Ar whole-rock ages. Accepting 567 Ma as the approximate age of intrusion, the K-Ar dates are considered to reflect a thermal resetting associ- ated with either a late-Scandian pulse or a slightly later, regional crustal extension and rifting event known from borehole data in the Barents Sea. A Late Devonian thermal overprint has also affected comparable dolerite dykes on the nearby Rybachi Peninsula of Northwest Russia.