The bedrock Geology of Vatnahverfi, Julianehåb district, South Greenland

Abstract

The petrology, structure and chronology of the Vatnahverfi area comprising ca. 300 sq. km SE of Igaliko fjord, Julianehåb district, S Greenland, is described. All the rocks are of Precambrian age and belong to the Ketilidian, Kuanitic, Sanerutian and Gardar periods. The Ketilidian period is represented by a migmatite complex comprising various biotite and hornblende gneisses showing relict supracrustal structures and intermingled with foliated granites. The complex belongs to the lower amphibolite facies. Mapping combined with stereographic structural analysis shows that the complex was initially folded about NE-trending B1 axes and subsequently on vertical to NW-trending B2 axes. The Kuanitic period was a hiatus in the plutonism and is represented by the intrusion of discordant dolerite and microdiorite dykes and hornblende gabbro (appinitic) plutons. Renewed plutonism during the Sanerutian period caused local reactivation of the Julianehåb granite as is indicated by fragmentation and, granitisation of the older basic bodies. Discordant amphibolite dykes and sheets, including a net-veined meladiorite - leucogranodiorite suite, were subsequently intruded under synplutonic conditions. A discordant batholith and satellitic sheets of biotite adamellite were emplaced towards the close of the Sanerutian period. The subsequent Gardar period is represented by faulting, mineralisation and the intrusion of various generations of dolerite, trachyte and alkali trachyte dykes.