PRECAMBRIAN BASEMENT OF GREENLAND
Archaean and Palaeoproterozoic crustal evolution in central West Greenland

Jeroen van Gool, Adam Garde, Christian Knudsen, Sandra Piazolo (now at university of Stockholm), Julie Hollis, Kristine Thrane (now at the Danish Lithosphere Centre), with Stanislaw Mazur (University of Wroclaw, Poland), Ian Alsop (St. Andrews University, Scotland), James Connelly (University of Texas at Austin, USA), Mogens Marker (Geological Survey of Norway), Jean-François Moyen (Univ. Stellenbosch, RSA), Christopher Thomas (British Geological Survey), and five Master's students from Copenhagen, Lund, and Texas.

This project investigates the geology of the northern Nagssugtoqidian orogen, from Nordre Strømfjord to Jakobshavn Isfjord, in order to improve the understanding of the Precambrian tectonic evolution of the region and to provide a geological framework for the understanding of the development of mineral deposits in central West Greenland. The work is carried out concurrently with an evaluation of the mineral potential of the region by the Department of Economic Geology. Presently the project is in its final phase of publication of the results.

The project has the following aims: Reconstruction of the Palaeoproterozoic and Archaean geological evolution of the region Evaluation of the link to the Rinkian belt to the north Publication of 1:100 000 scale geological maps of the region

The northern Nagssugtoqidian orogen – scope and results
The region between Søndre Strømfjord and central Disko Bugt in central West Greenland is underlain predominantly by Archaean crust that was reworked during the Palaeoproterozoic Nagssugtoqidian orogeny. Previous research by the Danish Lithosphere Centre in the southern and central parts of the orogen firmly established the collisional nature of the Nagssugtoqidian orogeny. In the centre of the orogen, limited volumes of Palaeoproterozoic intrusive calc-alkaline rocks and supracrustal rocks were added to the crust in the orogenic cycle.

The new work in the northern part of the orogen was aimed at establishing to what extent this tectonic model could be extended northwards. It has long been recognised that there is a distinct difference between the main aspects of the Nagssugtoqidian orogen, with its predominant ENE fabric, and the Rinkian belt to the north, dominated by large fold structures and a division in distinct domains. Also the links between these two distinct belts were addressed, and associated field investigations were carried out in the Rinkian belt (link to Adam's page on Rinkian geology).

Mineralisations in the region are mainly found in supracrustal rocks, which occur in thin belts and represent only a small percentage of the exposed rocks. The research focussed predominantly on mapping and understanding these belts in terms of their age, depositional environment, geochemistry, structures, and metamorphic evolution.

The main results show that the Palaeoproterozoic overprint is substantially weaker in the northern part of the Nagssugtoqidian orogen than south of the Nordre Strømfjord shear zone, and only minor volumes of Palaeoproterozoic supracrustal rocks have been identified. The tectonic style varies and changes progressively from south to north, from a dominant ENE trend to a more fold dominated style. The region north of Nordre Strømfjord can also be divided into several small, but distinct domains.

Activities:
Four summers' fieldwork was carried out in 2000-2003 in the area between 67°30'N and 69°10'N. This involved mapping, data collection, and rock sampling for geochemistry, geochronology, structural geology and metamorphic petrology. About 25 persons from GEUS and several external institutes participated. The project's field activities in 2001 were presented on Danish television in a half hour's program in Danmarks Radio educational series. Laboratory work, data reduction and compilation are in the final stages. Four Master's theses have until now been completed. Three workshops with international participation were held in 2002, 2003 and 2004. Four 1:100 000 scale geological maps will be published (see overview map). The Ussuit map sheet (link to Ussuit map project) was printed in 2004, and the remaining three map sheets will follow in 2005 and 2006. A GEUS bulletin will be dedicated to the geology of central West Greenland and present some of the scientific results. Further results are intended for publication in international journals.

Key references: Garde, A.A., Hollis, J.A., Christiansen, M.S., Mazur, S. & van Gool, J.A.M. 2004: Low-pressure metamorphism during Archaean crustal growth: a low-strain zone in the northern Nagssugtoqidian orogen, West Greenland. Geological Survey of Denmark and Greenland Bulletin 4, Report of Survey activities 2003, 73–76.

Piazolo, S., Alsop, G.I., Møller Nielsen, B., & van Gool, J.A.M., 2004: The application of GIS to unravel patterns of deformation in high grade terrains: a case study of indentor tectonics from West Greenland. In: Alsop, G.I. and Holdsworth, R.E. (editors), Flow processes in Faults and shear zones. Geological Society (London) Special Publication 224, 63–78.

Stendal, H., Nielsen, B.M., Secher, K., & Steenfelt, A. 2004: Mineral resources of the Precambrian shield of central West Greenland (66° to 70°15'N), Part 2. Mineral occurrences. Danmarks og Grønlandsk Geologiske Undersøgelse Rapport 2004/20, 212 pp.

van Gool, J.A.M., Alsop, G.I., Árting, U.E., Garde, A.A., Knudsen, C., Krawiec, A.W., Mazur, S., Nygaard, J., Piazolo, S., Christopher, T.W., & Thrane, K. 2002: Precambrian geology of the northern Nagssugtoqidian orogen, West Greenland: mapping in the Kangaatsiaq area. Geology of Greenland Survey Bulletin 191, 13-23.

van Gool, J.A.M., Connelly, J.N., Marker, M. & Mengel, F.C. 2002: The Nagssugtoqidian Orogen of West Greenland: tectonic evolution and regional correlations from a West Greenland perspective. Canadian Journal of Earth Sciences 39, 665-686.