A metamorphosed basic dyke swarm in the vicinity of Sarqarigsup nunâ (Ravns Storø area), Fiskenæsset, southern West Greenland

C.R.L Friend

doi:10.34194/rapggu.v73.7416

Abstract

Ancient dyke swarms have been used successfully as time markers throughout the Archaean of West Greenland, particularly in subdividing the early Archaean in the Godthåb region (McGregor, 1973). This paper describes a swarm of metamorphosed basic dykes which cut across the lithologicallayering and an early tectonic fabric in the Ravns Storø group of metavo1canic and plutonic rocks. Previously only sporadic occurrences of metamorphosed basic dykes have been noted in the Fiskenæsset region. The Sarqarigsup nuna swarm may thus have a significant part to play in the division of the events which have taken place in the area from the Frederikshåbs Isblink to Bjørnesund and perhaps even further north.

Highlights

Introduetion Ancient dyke swarms have been used successfully as time markers throughout the Archaean of West Greenland, in subdividing the early Archaean in the Godthåb region (McGregor, 1973)
Previous work The first description of the Ravns Storø area under the GGU mapping programme was by Windley (Windley et al, 1966), whose investigations were mainly concerned with the border relations of the metavolcanics and the gneisses
Sketch map of Sarqarigsup numl in the Ravns Storø area showing the iocation of lhe metamorpho ed dykes in relation to the boundary of the amphibolite bell

Summary

UmiarssuakulOp nunå

Layers containing recognisable pillow structures occur together with amphibolites which probably developed from more massive lavas. The dykes cut across the foliation and fold in the amphibolite They have suffered Jater deformation whieh varies in character aeeording to the angle at which they cut the foliation The. dyke tend to be eonspieuous as they are more massive and darker eoloured than the greyish amphibolites Greyish in colour and has a weak garbenschiefer texture It can be distinguished from the massive dark green metalavas which it cuts. Il bears a resemblance to the grey amphibolites whieh oeeur immediately north-west across the strike, from whieh it ean be distinguished by its more massive weathering. The metalavas show jointing at right angles to the foliation planes which are here parallel to the lithological layering. /iTrace of foliation ~ Metamorphosed dykes [TIJ Pegmatite n Deformed pillow lavas ru No exposure

Qagssikasaup nuna

Discussion