Rb/Sr age of the Kap Washington Group, North Greenland, and its geotectonic implications

Abstract

The Kap Washington Group is a bedded suite of rhyolitic lavas and tuffs that forms the northernmost rock province of Greenland (Dawes & Soper, 1973). The volcanic group borders on the north the Palaeozoic North Greenland fold belt from which it is separated by the southerly-dipping Kap Cannon thrust (fig. 38). K/Ar whole-rock age determinations of 34.9±5.3 m.y. and 32.3±3.2. m.y. on somewhat mylonitised lava samples were earlier regarded as giving an approximate minimum age of vo1canic consolidation and a maximum age of the Kap Cannon thrusting (Dawes & Soper, 1971). This note reports on Rb/Sr isotopic work that dates the Kap Washington Group, the five samples proeessed suggesting an age of about 63 m.y. Thus the general age of extrusion and con olidation of the vo!canie pile is eonsidered to be earlie t Tertiary.