PRECAMBRIAN BASEMENT OF GREENLAND
The Ketilidian orogen in South Greenland

Adam A. Garde, with Agnete Steenfelt and Henrik Stendal (Department of Economic Geology)[links]. Currently active international collaborators are O. Eklund (Univ. Turku, Finland) J. Grocott (Kingston Univ., UK), K.J.W. McCaffrey (Univ. Durham, UK), M.A. Hamilton (Univ. Toronto, Canada).

The Palaeoproterozoic Ketilidian orogen forms the southernmost part of Greenland. This part of Greenland is a gold province, and the fore arc of the Ketilidian orogen hosts the only current Greenlandic mine, namely the Nalunaq gold mine in Kirkespirdalen, which opened in 2003. The excellently exposed orogen is a prime example of juvenile magmatic accretion of new continental crust and also hosts primitive basaltic rocks and a major rapakivi suite.

Scope of recent activities and results
Two map sheets (scale 1:100 000) from the central and eastern parts of the Ketilidian orogen were produced in the late 1990s during an evaluation of the economic potential by the Department of Economic Geology and an international research group. This work supplemented much older maps from the southern and western parts of the orogen, which were produced during the Survey's first systematic regional survey in Greenland in the 1960s. The research group also established a modern plate-tectonic interpretation of the orogen. In addition, a new gold prospect was discovered at Kangerluluk on the east coast, with a geological setting that has much in common with the Nalunaq deposit. The most recent research by GEUS and an international research group highlights the tectonic, magmatic and geochronological evolution in the north-western and eastern parts of the orogen, and the orogenic setting of the Ketilidian rapakivi granites. These studies have been supported by the Carlsberg Foundation, the Danish Natural Science Research Council and the British NERC. A geological excursion for 13 senior geologists and nine PhD students from Nordic and Baltic countries was carried out in August-September 2004 with two local boats, M/S Søkongen and M/S Kissavik. The excursion was led by A.A. Garde from GEUS and M.A. Hamilton, Univ. Toronto, Canada, and was sponsored by the Nordic science network NorFA.

A short outline of the Ketilidian orogen
The Ketilidian orogen is one of several Palaeoproterozoic orogens in West Greenland including Inglefield Land in northernmost West Greenland and the collisional Rinkian-Nagssugtoqidian system in central-northern West Greenland [to links til Nag + Rinkian]. These all resulted from overall N-S shortening with progressive younging towards the south. The Ketilidian orogen correlates westward with the Makkovik system in eastern Labrador, whereas the linkage with the Palaeoproterozoic belts in Scandinavia remains uncertain.

The Ketilidian orogen was accreted to the southern margin of the Archaean craton about 1.8 Ga ago in a transpressive convergent setting with subduction from the south. The Border zone in the north-west comprises sedimentary rocks deposited on the Archaean craton, overlain by rift-related pillow lavas and sills with primitive, tholeiitic chemistry. The central part of the orogen consists of a major, juvenile calc-alkaline arc (Julianehåb batholith), which was also the source of voluminous fore arc deposits. These are mainly immature arkoses and turbidites, which crop out at the southern tip of Greenland. The proximal part of the fore arc also comprises andesitic to basic volcanic rocks, which contain several gold mineralisations aside from the Nalunaq mine. The Ketilidian orogen also hosts a prominent suite of late-orogenic rapakivi granites and related mafic intrusions.

Recent publications
Garde, A.A., Chadwick, B., Grocott, J., Hamilton, M.A. McCaffrey, K.J.W. & Swager, C.P. 2002: Mid-crustal partitioning and attachment during oblique convergence in an arc system, Palaeoproterozoic Ketilidian orogen, southern Greenland. Journal of the Geological Society (London) 159, 247-261. Garde, A.A., Hamilton, M.A., Chadwick, B., Grocott, J. & McCaffrey, K.J.W. 2002: The Ketilidian orogen of South Greenland: geochronology, tectonics, magmatism, and forearc accretion during Palaeoproterozoic oblique convergence. Canadian Journal of Earth Science 39, 765-793. McCaffrey, K.J.W., Grocott, J., Garde, A.A. & Hamilton, M.A. 2004: Attachment formation during partitioning of oblique convergence in the Ketilidian orogen, South Greenland. In Grocott, J., McCaffrey, K.J.W., Taylor, G. & Tikoff, B. (eds.): Vertical coupling and decoupling in the lithosphere. Geological Society, London, Special Publications 227, 231–247. Stendal, H., Frei, R., Hamilton, M.A. & Mueller, W.U. 2001: The Palaeoproterozoic Kangerluluk gold-copper mineralization (southeast Greenland): Pb and Nd isotopic constraints on its timing and genesis. Mineralium Deposita 36 , 177-188.