40Ar-39Ar and U-Pb dating of Cretaceous continental rift-related magmatism on the northeast Canadian Arctic margin

Cretaceous igneous rocks related to the Canadian part of the High Arctic Large Igneous Province (HALIP) were investigated geochronologically using the U-Pb and Ar-Ar methods. The study focused on the predominantly alkaline bimodal Wootton Intrusive (WIC) and Hansen Point Volcanic complexes (HPVC) at northwest Ellesmere Island. Outcrops of these igneous suites form two parallel NE-SW striking chains and are tectonically controlled by pre-existing fault zones (Mitchell Point and Emma Fiord fault zones). Gabbro, granite and quartz syenite of the WIC yielded identical U-Pb zircon and in part titanite ages with a weighted mean of 92.1 +/- 0.1 Ma whereas the weighted mean U-Pb zircon age of three microgranites is 92.7 +/- 0.3 Ma. These dates indicate a very short time span for intrusion of the WIC of probably less than 1 Ma. The main interval for the emplacement of the HPVC is bracketed by Ar-Ar feldspar and whole-rock ages of 83 +/- 2 Ma to 77 +/- 4 Ma without significant age differences between the two chains. Tholeiitic mafic dykes cutting Proterozoic to early Palaeozoic metamorphic rocks in the vicinity of the HPVC yielded a wide range of Ar-Ar whole-rock ages (c. 122 to 94 Ma). These rocks can be temporally and geochemically correlated with the basalts of the Isachsen and Strand Fiord formations of the Sverdrup Basin. The Ar-Ar whole-rock age of 101 +/- 6 Ma of a basalt from Mokka Fiord, eastern Axel Heiberg Island, fits also to the late Albian to early Cenomanian stratigraphic age of the Strand Fiord Formation. Ar-Ar ages of 49 and 46 Ma for two HPVC-type rhyolites from northeast Wootton Peninsula are interpreted to date hydrothermal overprint of older volcanics, associated with a reactivation of the Mitchell Point Fault Zone in the Eocene.