Magmatism and Eurekan deformation in the High Arctic Large Igneous Province: 40Ar-39Ar age of Kap Washington Group volcanics, North Greenland

摘要

The High Arctic Large Igneous Province is unusual on two counts: first, magmatism was prolonged and has been suggested to include an initial tholeiitic phase (130-80Ma) and a second alkaline phase (85-60Ma); second, it was subsequently deformed during the Eurekan Orogeny. New 40Ar-39Ar dating of alkaline volcanics from Kap Kane, part of the Kap Washington Group volcanics at the northern tip of Greenland, provides an emplacement age of 71.2±0.5Ma obtained from amphibole in lapilli tuffs, and a thermal resetting age of 49-47Ma obtained in feldspar and whole-rocks from trachyte flows. Patch perthite feldspars and coeval resetting of Rb-Sr isotopes by hydrothermal fluids provide further support for thermal overprinting. This thermal event is interpreted as a result of compressional tectonism of the Kap Cannon Thrust Zone in which older Palaeozoic metasediments were thrusted northwards over the Kap Washington Group volcanics. The formation of the tholeiitic suite (130-80. Ma) is linked to the opening of the Canada Basin and may involve mantle plume action. Formation of the alkaline suite (85-60. Ma) is attributed to continental rifting in the Lincoln Sea area linked to seafloor spreading in the Labrador Sea and the Baffin Bay, and to eastwards displacement of Greenland relative to North America. The alkaline suite, therefore, may be unrelated to the main tholeiitic phase of the High Arctic Large Igneous Province. The subsequent initiation of continental rifting and ensuing seafloor spreading in the Northeast Atlantic resulted in spreading and volcanism (61-25. Ma) on both sides of Greenland, pushing Greenland northwards relative to North America. The tectonic setting in the High Arctic thus changed from extensional to compressional and volcanic activity was terminated. Evaluation of plate kinematic models shows that the relative northwards movement of Greenland culminated in the Eocene, coinciding with thermal resetting. We conclude that compression in North Greenland peaked at 49-47. Ma and coincided with the Eurekan Orogeny in a belt across the Canadian Arctic Islands and western Svalbard.