Abstract

Northern Baffin Island is intersected by spectacular swarms of predominantly northwesterly trending diabase dykes. Cross-cutting relationships, K–Ar ages, and paleomagnetic contact tests indicate that these dykes represent at least two major episodes of Hadrynian igneous activity. The Borden dykes were emplaced during the earlier of these episodes. They are about 950 Ma old and have a paleomagnetic pole position of 153.3°E, 26.7°S, δm = 8.6e, δp = 6.1°. The later episode saw the emplacement of the previously defined Franklin dykes, which are about 750 Ma old. The newly defined Borden pole lies at the southern extremity of the Grenville Loop and has an age consistent with poles of similar position that were derived from rocks of the Grenville Province.All of the dykes probably reflect tension acting in an east-northeast–west-southwest direction. The directions of thick northwest trending dykes, which form a considerable angle to that expected from east-northeast tension, are thought to have been controlled by earlier (circa 1200 Ma) fractures of the Borden fault zones. The two main surges of magma may coincide with two -periods of Hadrynian uplift in the Boothia Peninsula area to the west.

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