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.
Highlights
The petrology, structure and chronology of the Vatnahverfi area comprising ca. 300 sq. km SE of Igaliko fjord, Julianehåb district, S Greenland, is described
Today the area affords excellent pasture for numerous sheep belonging to Greenlandic farmers, Abel Kristiansen (Eqaluit), Henning Lund (Qanisartut) and Abel Christiansen (SØndre Igaliko) whose farmsteads are on sites originally occupied by the Nordic settlers, and to whom I am indebted for generous hospitality
On the shore of Igaliko fjord the Julianehåb granite (G2) and hornblende gabbro are cut by a number of small dykes and sheets of granodiorite that is in turn cut by dykes and sheets of the meladiorite - leucogranodiorite suite
Summary
In the terrain south of 1963 Camp IV and between Skygge Sø and Undir HØfda Elv the homogeneous biotite - hornblende gneisses are cut by numerous discordant, medium-dark grey, fine-grained, schistose amphibolite dykes. They are relatively straight, trend between northeast and east-northeast, and are mostly less than 50 cm wide but are up to 2 m in width. The granitisation is slight, it indicates that these are second period dykes Their primary structures are well preserved because of the lack of aggressivness of the surrounding gneisses during the Sanerutian reactivation, (cf DA2 dykes in the more aggressive Julianehåb granite). In thin sections this rock is found to consist essentially of calcic andesine (30% estimated), hypersthene (15%). olivine (15%), augite (15%), brown mica (10%). opaque oxide (5%) and two varieties of Julianehåb grani,e v gabbro V
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