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Geological Society, London, Special Publications; 2004; v. 227; p. 231-248;
DOI: 10.1144/GSL.SP.2004.227.01.12
© 2004 Geological Society of London

Orogenic Examples

Attachment formation during partitioning of oblique convergence in the Ketilidian orogen, south Greenland

K. J. W. McCaffrey1, J. Grocott2, A. A. Garde3 & M. A. Hamilton4,*

1 Department of Earth Sciences, University of Durham, Durham, DH1 3LE, UK
2 Earth Sciences and Geography, Kingston University, Kingston upon Thames, Surrey, KT1 2EE, UK
3 GEUS, OsterVolgade 10, 1350 Copenhagen K, Denmark
4 Geological Survey of Canada, 601 Booth Street, Ottawa, ON, K1A 0E8 Canada
* Department of Geology, Earth Sciences, University of Toronto, 22 Russell St, Torono, ON, M5S 3B1, Canada

Subhorizontal attachment zones provide coupling between lithospheric layers in orogenic belts. A mid-crustal attachment zone is exposed in the Palaeoproterozoic Ketilidian orogen, south Greenland, which formed as a result of north-directed oblique convergence at a cordilleran-type margin. Rifting (c. 2.1 Ga) and compressional deformation and magmatism (> 1850 Ma) on the continental margin was followed by an extended sinistral transpression from 1850 to 1730 Ma now separated into three episodes or peaks of activity. The first episode was focused on the back-arc region and was followed by the main arc construction phase during which transpression was partitioned into strike-slip and contraction components. Despite the longevity of this active margin system, individual tectonic events took place rapidly, e.g. development of fore-arc D1-D3 and accompanying high-temperature, low-pressure metamorphism took place over c. 12 Ma. We explain the fore-arc and batholith evolution by the upward migration of an underlying attachment structure through the upper crustal partitioned blocks. This migration may be attributed to an increase in the geothermal gradient accompanied by, or followed by, exhumation of the mid-crust. The partially molten, hence weak, attachment zone solidified and strengthened during cooling before emplacement of the post-orogenic rapakivi suite during the third distinct phase of mild sinistral transpression.