G E O L O G Y O F G R E E N L A N D S U R V E Y B U L L E T I N 1 8 1 · 1 9 9 9 Precambrian geology of the Disko Bugt region, West Greenland
Edited by Feiko Kalsbeek
GEOLOGICAL SURVEY OF DENMARK AND GREENLAND MINISTRY OF ENVIRONMENT AND ENERGY
1 Geology of Greenland Survey Bulletin 181
Keywords Age determinations, Archaean, Disko Bugt, economic geology, geological map, Proterozoic, structural geology, West Greenland.
Cover Unconformity between Archaean greenstones and Palaeoproterozoic metasedimentary rocks of the Anap nunâ Group on Qapiarfi it, north-east of Disko Bugt. The rocks of the Anap nunâ Group, to the right of the river, are here hardly deformed and at very low metamorphic grade. The lower part consists of a marble conglomerate and is overlain by dark sandstones and siltstones, within which sedimentary structures are well preserved. Photo: A.A. Garde.
Chief editor of this series: Peter R. Dawes Scientifi c editor of this volume: Feiko Kalsbeek Editorial secretaries: Esben W. Glendal and Birgit Eriksen Critical readers: P.R. Dawes (Denmark), B. Hageskov (Denmark), L.M. Larsen (Denmark), D.C. Rex (UK), H. Sørensen (Denmark), J. van Gool (Denmark), M. Whitehouse (Sweden), as well as intra-project reviewing. Graphic production and reproduction: Knud Gr@phic Consult, Odense, Denmark Manuscripts submitted: 29th December, 1997 Final versions approved: 26th March, 1999 Printed: 22nd July, 1999
ISBN 87-7871-063-4 ISSN 1397-1905
Geology of Greenland Survey Bulletin The series Geology of Greenland Survey Bulletin is a continuation of Bulletin Grønlands Geologiske Undersøgelse and incorporates Rapport Grønlands Geologiske Undersøgelse.
Citation of the name of this series It is recommended that the name of this series is cited in full, viz. Geology of Greenland Survey Bulletin If abbreviation of this volume is necessary the following form is suggested: Geology Greenland Surv. Bull. 181, 179 pp.
Available from Geological Survey of Denmark and Greenland Thoravej 8, DK-2400 Copenhagen NV, Denmark Phone: +45 38 14 20 00, fax: +45 38 14 20 50, e-mail: [email protected] or Geografforlaget ApS Fruerhøjvej 43, DK-5464 Brenderup, Denmark Phone: +45 63 44 16 83, fax: +45 63 44 16 97, e-mail: [email protected]
© Danmarks og Grønlands Geologiske Undersøgelse (GEUS), 1999
2 Contents
Preface ...... F. Kalsbeek 4
Precambrian geology of Nuussuaq and the area north-east of Disko Bugt, West Greenland ...... (For detailed table of contents, see page 6) ...... A.A. Garde and A. Steenfelt 6
Review of isotope data for Precambrian rocks from the Disko Bugt region, West Greenland ...... F. Kalsbeek and P.N. Taylor 41
SHRIMP U-Pb zircon ages for Archaean granitoid rocks, Ataa area, north-east Disko Bugt, West Greenland ...... A.P. Nutman and F. Kalsbeek 49
Proterozoic thermal activity in the Archaean basement of the Disko Bugt region and eastern Nuussuaq, West Greenland: evidence from K-Ar and 40 Ar-39Ar mineral age investigations ...... H. Rasmussen and P.M. Holm 55
Stratigraphy, structure and geochemistry of Archaean supracrustal rocks from Oqaatsut and Naajaat Qaqqaat, north-east Disko Bugt, West Greenland ...... H. Rasmussen and L.F. Pedersen 65
The Precambrian supracrustal rocks of Nunataq, north-east Disko Bugt, West Greenland ...... A.K. Higgins and N.J. Soper 79
An Archaean sill complex and associated supracrustal rocks, Arveprinsen Ejland, north-east Disko Bugt, West Greenland ...... B. Marshall and H.K. Schønwandt 87
The Archaean Atâ intrusive complex (Atâ tonalite), north-east Disko Bugt, West Greenland ...... F. Kalsbeek and L. Skjernaa 103
Albitised gneisses in the area between Paakitsoq and Kangerluarsuk, north-east Disko Bugt, West Greenland ...... M.J. Ryan and J.C. Escher 113
A gold-bearing volcanogenic-exhalative horizon in the Archaean(?) Saqqaq supracrustal rocks, Nuussuaq, West Greenland ...... A.A. Garde, B. Thomassen, T. Tukiainen and A. Steenfelt 119
Gold mineralisation at Eqi, north-east Disko Bugt, West Greenland ...... H. Stendal, C. Knudsen, M. Marker and B. Thomassen 129
Proterozoic tectonic overprinting of Archaean gneisses in Nuussuaq, West Greenland ...... A.A. Garde and A. Steenfelt 141
Deformation at the southern boundary of the late Archaean Atâ tonalite and the extent of Proterozoic reworking of the Disko terrane, West Greenland ...... J. Grocott and S.C. Davies 155
Early Proterozoic thrust tectonics east of Ataa Sund, north-east Disko Bugt, West Greenland ...... J.C. Escher, M.J. Ryan and M. Marker 171
3 Preface
Between 1988 and 1992 the Geological Survey of major aim of the Project was to obtain more infor- Greenland (GGU) launched a number of expeditions mation on the development of the onshore part of to the Disko Bugt region in central West Greenland the late Phanerozoic West Greenland Basin, which is (Fig. 1), the ‘Disko Bugt Project’ (Kalsbeek 1989, 1990; parti-cularly relevant to the hydrocarbon potential of Kalsbeek & Christiansen 1992; Christiansen 1993). The the basin. aim of this project was threefold. Firstly, it was impor- This volume reports on the Precambrian geology tant to enhance the general geological knowledge of of the region. Work was centred on the area around the region, especially the eastern (Precambrian) parts the abandoned settlement Ataa (Fig. 2), where many being rather poorly known. Secondly, reconnaissance mineral showings had been recorded within Archaean studies by Kryolitselskabet Øresund A/S in the 1970s supracrustal rocks. Although this area was visited by and early 1980s and follow up investigations by GGU various geologists in the 19th and in the beginning of had revealed mineral showings with Cu, Zn, Au and the 20th century, the fi rst detailed geological map was Ag, which required further investigation. The third made by Escher & Burri (1967; this paper also sum- marises earlier work). These authors, however, were unable to distinguish the Archaean supracrustal rocks from the early Proterozoic metasedimentary sequences which were later shown to occur in the area (Fig. 2),
Nuussuaq essentially because routine radiometric age determina- tions were not then available. Moreover, the hypothesis of massive alteration of rocks by ‘granitisation’ proc- esses was adhered to by many geologists working in Greenland at that time, which heavily infl uenced the interpretations (and, to some extent, the map) of these authors. Therefore, although the map of Escher & Burri • (1967) was useful during the Disko Bugt Project, new fi eld studies were necessary. The Disko Bugt Project was thus inaugurated and a base camp was erected at Ataa, from which fi eld work in the Precambrian basement was carried out in 1988, 1989 and 1991. The work was carried out in close co- operation with the Geological Institute of the University of Copenhagen; several staff members took part in the mapping, and fi ve students wrote their Danish (cand. scient.) theses on various aspects of the Precambrian geology of the region. Results of the fi eld investigations have earlier been documented by the 1:250 000 geological map ‘Precam- brian Geology between Qarajaq Isfjord and Jakobshavn Isfjord, West Greenland’ (Garde 1994), and a sheet in the
Cretaceous–Tertiary basin Survey’s 1:100 000 series Geological map of Greenland, Ataa 69 V.3 Nord (Escher 1995). The 1:250 000 map Precambrian basement sheet is included with this volume. The present volume contains 14 papers describing Fig. 1. The Disko Bugt region with the Precambrian basement in the east and the onshore part of the Cretaceous–Tertiary various aspects of the Precambrian geology of the Disko West Greenland Basin in the west. The fi gure also shows the Bugt region. The fi rst paper presents a broad overview outline of the 1:250 000 geological map (Garde 1994) enclosed of the geology of Nuussuaq and the area north-east with this volume. of Disko Bugt (Fig. 1), and serves as an introduction
4 Geology of Greenland Survey Bulletin 181, 4–5 (1999) © GEUS 1999 For several reasons publication of this volume has Nuussuaq been much delayed. Anticipated papers on regional 71˚00´ aspects of the mineral potential of the region and on Torsukattak Anap geophysical investigations carried out during the fi eld Nunaa INLAND ICE work have not materialised, but may be published at a later date.
• Ataa Acknowledgements
Arveprinsen I gratefully acknowledge the help of colleagues within Ejland and outside GEUS for careful reviews of papers. I thank Ataa Sund Stuart Watt for generous help and advise with the tech- nical editing of this volume. 69˚30´ 10 km 51˚00´ 50˚00´
Archaean migmatitic gneisses References Atâ tonalite Christiansen, F.G. 1993: Disko Bugt Project 1992, West Greenland. Archaean supracrustal rocks Rapport Grønlands Geologiske Undersøgelse 159, 47–52. Proterozoic supracrustal rocks Escher, A. & Burri, M. 1967: Stratigraphy and structural devel- opment of the Precambrian rocks in the area north-east of Homogeneous tonalitic orthogneiss Disko Bugt, West Greenland. Rapport Grønlands Geologiske Undersøgelse 13, 28 pp. Fig. 2. Geological sketch map of the Ataa area north-east of Escher, J.C. 1995: Geological map of Greenland, 1:100 000, Ataa Disko Bugt. 69 V.3 Nord. Copenhagen: Geological Survey of Greenland. Garde, A.A. 1994: Precambrian geology between Qarajaq Isfjord and Jakobshavn Isfjord, West Greenland, 1:250 000. Copen- to the following contributions and as a description of hagen: Geological Survey of Greenland. Kalsbeek, F. 1989: GGU’s expedition in the Disko Bugt area, 1988. the 1:250 000 map of Garde (1994). This is followed Rapport Grønlands Geologiske Undersøgelse 145, 14–16. by three papers with geochronological data, dealing Kalsbeek, F. 1990: Disko Bugt Project, central West Greenland. with the original formation age of the rocks and with Rapport Grønlands Geologiske Undersøgelse 148, 21–24. the age(s) of later metamorphism. It is shown that, Kalsbeek, F. & Christiansen, F.G. 1992: Disko Bugt Project 1991, although most rocks in the Disko Bugt region were West Greenland. Rapport Grønlands Geologiske Undersøgelse formed during the late Archaean, early Proterozoic 155, 36–41. overprinting has been intense. The next fi ve papers describe lithostratigraphic units in the Ataa area, with Feiko Kalsbeek emphasis on the Archaean supracrustal rocks. The latter are much better preserved here than is generally the case elsewhere in Greenland, and show many similari- ties with the greenstone belts which occur, for example, in the Canadian Shield. Next follow two papers which describe the gold min- eralisation locally associated with Archaean supracrustal sequences; interestingly, the setting of the gold min- eralisation at the two localities is very different. The fi nal three papers deal with the structural evolution of the region. Although it is often diffi cult to distinguish between Archaean and early Proterozoic structures, it is evident that early Proterozoic tectonism has had a major impact on the present-day structural grain of large parts of the Disko Bugt region.
5 Precambrian geology of Nuussuaq and the area north-east of Disko Bugt, West Green- land ...... A.A. Garde and A. Steenfelt...... 6
Contents: Descriptions of lithological units on the 1:250 000 scale map ...... 10 Archaean gneisses north of Torsukattak ...... 10 Nuussuaq gneisses ...... 10 Gneisses on Nunataq ...... 12 Archaean supracrustal rocks along the coasts of Torsukattak and in the Ataa domain ...... 12 Saqqaq supracrustal rocks ...... 13 Itilliarsuk supracrustal rocks ...... 14 Western occurrence, around Itilliarsuk ...... 14 Eastern occurrence, Qeqertaarsuk and Inussuk ...... 16 Nunataq ...... 17 Correlation of the Archaean supracrustal rocks north of Torsukattak ...... 17 Arveprinsen-Eqi supracrustal rocks, south of Torsukattak ...... 18 Oqaatsut ...... 19 Arveprinsen Ejland ...... 19 Anap Nunaa ...... 20 Qingaarsuaq ...... 20 Eqi and Maniitsoq ...... 21 Correlation of the Archaean supracrustal rocks south of Torsukattak ...... 22 Comparison between the Archaean supracrustal rocks north and south of Torsukattak . 22 Boye Sø anorthosite complex ...... 22 Other occurrences of anorthosite and related rocks on Nuussuaq ...... 24 Archaean rocks south of Torsukattak ...... 24 Atâ tonalite ...... 24 Gneisses and supracrustal rocks in the Rodebay domain ...... 25 Rodebay granodiorite ...... 25 Late granitoid rocks ...... 26 Nunatarsuaq domain ...... 26 Nunatarsuaq supracrustal rocks ...... 26 Proterozoic platform sediments and intrusive rocks ...... 29 Anap nunâ Group ...... 29 Proterozoic marble on northern Nuussuaq ...... 30 Basic dykes and sills ...... 31 Albitisation ...... 32 Lamprophyres and lamproites ...... 32 Structural and metamorphic evolution ...... 33 Nuussuaq domain ...... 34 Evidence for Proterozoic deformation in Nuussuaq and on Nunataq ...... 34 Shear zones in southern Nuussuaq and the boundary between the Nuussuaq and Ataa domains ...... 35 Ataa domain ...... 35 Proterozoic deformation in the Ataa domain ...... 35 Rodebay domain ...... 36 Nunatarsuaq domain ...... 37 Concluding remarks ...... 37 Acknowledgements ...... 38 References ...... 38
6 Geology of Greenland Survey Bulletin 181, 6–40 (1999) © GEUS 1999 Precambrian geology of Nuussuaq and the area north-east of Disko Bugt, West Greenland
Adam A. Garde and Agnete Steenfelt
The Precambrian terrain of eastern Nuussuaq and north-east Disko Bugt largely consists of late Archaean (c. 2800 Ma) orthogneisses, intercalated with units of strongly deformed Archaean supracrustal rocks. The latter are up to several kilometres wide and comprise both metavol- canic and metasedimentary rocks within which local occurrences of gold have been found. In central Nuussuaq a layered complex of anorthosite, leucogabbro, gabbro and ultramafi c rocks is tectonically intercalated with Archaean orthogneisses, and an intrusive complex of Archaean tonalites and trondhjemites, largely unaffected by Archaean and Proterozoic deformation, occurs in the area north-east of Disko Bugt. Here an up to c. 3.5 km thick sequence of early Proterozoic shallow marine clastic sediments and minor marble unconformably overlies Archaean rocks. Several suites of basic dykes are present, and dykes and small plugs of ultramafi c lamprophyre and lamproite (age c. 1750 Ma) are common in the central part of the region. Most of the region was overprinted by early Proterozoic deformation and metamorphism. Prominent Proterozoic fl at-lying ductile shear zones with north- or north-westward movement of the hanging wall are overprinted by open folds.
Geological Survey of Denmark and Greenland, Thoravej 8, DK-2400 Copenhagen NV, Denmark. E-mail: [email protected].
Keywords: anorthosite, Archaean rocks, Disko Bugt, Nuussuaq, Proterozoic deformation, Prot- erozoic rocks, West Greenland
This paper describes the Precambrian geological evolu- terrain, an active continental margin, and a high-grade tion of the Disko Bugt – Nuussuaq region (Fig. 1). It is gneiss-amphibolite terrain. In addition, a Proterozoic based on fi eld work by the former Geological Survey setting with platform sedimentation and basic and of Greenland (GGU) and the Geological Institute, lamproitic magmatic activity is present in the central University of Copenhagen, in 1988, 1989 and 1991 part of the region. during the Disko Bugt Project (Kalsbeek 1989, 1990; A small number of isotopic age determinations has Kalsbeek & Christiansen 1992). The account also serves been carried out (Kalsbeek et al. 1988; Kalsbeek & as a description of the geological map at scale 1:250 000 Taylor 1999, Nutman & Kalsbeek 1999 and Rasmus- (Garde 1994) enclosed in the present volume, and in sen & Holm 1999, all in this volume), but most of the the course of the geological description reference is tentative distinctions made in this account between made to the main lithological and structural units on Archaean and Proterozoic rocks and structures are this map. inferred from fi eld observations. In particular it has Precambrian basement is exposed in the eastern part been diffi cult to separate Archaean and Proterozoic of Nuussuaq and on the mainland north-east of Disko deformation events. Bugt (Fig. 1). There are both Archaean and Proterozoic The present account is primarily based on informa- rocks, and most of the region has been exposed to tion gathered by the authors during reconnaissance both Archaean and Proterozoic phases of deforma- mapping, but it also relies heavily on more detailed tion. Several geotectonic settings are recognised in work in the central part of the region by the other the region: an Archaean low-grade granite-greenstone participants in the Project, see the 1:100 000 geological
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