Abstract
As part of the GGU activity in the Disko Bugt region, central West Greenland (Kalsbeek, 1989), the authors carried out helicopter-supported geological reconnaissance mapping and stream sediment sampling for geochemical mapping in the area between Jakobshavn Isfjord and Qarajaq Isfjord (fig. 1). A considerable part of the season was spent in the eastern part of the Nûgssuaq peninsula, partly to complete the stream sediment sampling initiated in 1986 (see Steenfelt, 1988) and also because previous geological field work in eastern Nûgssuaq was very limited. The existing geological map at a Rapp. Grønlands geol. Unders. 145. 16-20 (1989) scale of 1:500 000 covering Nûgssuaq is almost entirely based on interpretation of aerial photographs. During the field work large occurrences of hitherto unknown anorthosite/gabbro rocks and supracrustal sequences were discovered in the gneiss terrain. Both the anorthosite/gabbro and supracrustal units appear to be tectonically interleaved with strongly foliated, flat-Iying or shallowly south-dipping orthogneisses, which themselves contain numerous shear zones suggesting substantial subhorizontal movements.
Highlights
Escher, A. & Bum, M. 1967: Stratigraphy and structural development of the Precambrian rocks in the area north-east of Disko Bugt, West Greenland
M. & Knudsen, C. 1989: Middle Proterozoic ultramafic lamprophyre dykes in the Archaean of the Ata area, central West Greenland
Wc consider that all the anorthosite/leucogabbro ocCllrrCl1Ces and associated gabbroic and ultrabasic rocks at Nllgssuaq, as well as lIle anorthosite/leucogabbro occurrenec at Drygalski Halvø, may represent disrupted parts of a large Archaean layercd intrusion comparable lo (he Fiskenæsset Complex af southern West Greenland (Myers, 1985)
Summary
The largest occurrence (c. 25 km in area) on Nugssuaq consists of massive snowball-type anorthositel leucogabbro with associated medium-grained anorthosite, leucogabbro, hornblende gabbro and ultrabasic rocks, and is well exposed on the steep sides of an ice-capped mountain c. 7 km west of Boye Sø (a, fig. 1; fig. 3). Gabbro and ultrahasic rocks bclonging to the Boye Sø anorthosite eomplex extend to the soulh-east, perhaps all the way 10 the soutll coast af Nugssuaq. Wc consider that all the anorthosite/leucogabbro ocCllrrCl1Ces and associated gabbroic and ultrabasic rocks at Nllgssuaq, as well as lIle anorthosite/leucogabbro occurrenec at Drygalski Halvø, may represent disrupted parts of a large Archaean layercd intrusion comparable lo (he Fiskenæsset Complex af southern West Greenland (Myers, 1985). The distribution af these rocks, as known at present. In addition to the regional survey a number of sediment samples were collected in the small streams draining the Boye Sø anorthosite complex, and these will be analysed for the platinum group elements
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