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1 Division of Earth & Ocean Sciences, Duke University, Durham, NC 27708-0230, USA jkarson{at}eos.duke.edu
2 Danish Lithosphere Center, 10 Øster Voldgade, 1350 Copenhagen K, Denmark
The Tertiary East Greenland Volcanic Rifted Margin is characterized by massive magmatic construction that produced a distinctive crustal architecture including: (1) a thick pile of flood basalts continuing offshore as seismically imaged ‘seaward-dipping reflector sequences’; (2) an extensive margin-parallel mafic dyke swarm; and (3) shallow crustal gabbroic plutons and deeper crustal ‘underplated’ material. These igneous units developed in the framework of an asymmetrical, crustal-scale fold, or ‘flexure’, that accommodated major subsidence along the continent-ocean transition. Extensive exposures along the margin reveal that the flexure and associated igneous structures define rift segments separated by various types of structural discontinuities. First-order segments occur between major triple-rift junctions as at Kangerlussuaq. At an intermediate scale, second-order accommodation zones bound margin segments c. 100 km in length with long-lived structural and/or magmatic expressions. Third-order discontinuities, spaced at tens of kilometres, correspond to smaller accommodation zones at abrupt along-strike changes fault or magmatic structures. Outcrop-scale transfer and transform faults occur at still smaller scales. Some of the larger accommodation zones appear to be related to pre-existing Precambrian structures and may have helped localize relatively late, post-flexure alkalic intrusions. The style of segmentation provides a link between similar segmentation patterns in continental rifts and mid-ocean ridge spreading centres that persist long after continental separation.
