U-Pb geochronology and REE geochemistry of the pulsed Cretaceous magmatism in High Arctic Canada: implications for lithospheric evolution and magma genesis

  • Author / Creator
    Dockman, David M
  • Cretaceous magmatism in the Sverdrup Basin of Arctic Canada consists of alkalic and tholeiitic phases that are widely considered to be part of the circum-Arctic High Arctic large igneous province (HALIP). The emplacement of large igneous provinces is commonly attributed to mantle plumes. However, recent studies have questioned the validity of a plume model for the HALIP, as well as questioned whether the younger magmatic phases of the province should be included as part of the same LIP. A paucity of U-Pb ages of mafic intrusions and robust Ar/Ar ages has hindered tectonomagmatic interpretations of this geographically remote province. This study presents new major- and trace-element geochemical data plus Sr-Nd isotope systematics for mafic intrusions and lavas collected from Ellesmere and Axel Heiberg Islands, accompanied by new U-Pb and Ar/Ar ages to better constrain the temporal evolution of the HALIP and the controls on its magma chemistry. After accounting for the effects of crustal contamination, Sr-Nd isotope systematics indicate that tholeiitic and alkalic magmas are derived from similar mantle sources, with no evidence for the input of enriched lithospheric mantle. Therefore, variations in REE geochemistry between the two magma types are interpreted as being primarily controlled by differences in the lithospheric ‘lid’ thickness. REE inversion modeling revealed a bimodal distribution in ‘lid’ thickness (65 ± 5 and 45 ± 4 km). Correlation of magma chemistry with regional structural analysis indicates that the production and emplacement of alkalic and tholeiitic magmas are spatially segregated by the tectonic domains of the Sverdrup Basin. Six U-Pb and four Ar/Ar ages obtained in the present study range from 122 ± 2 Ma to 78.5 ± 1.8 Ma, within the range of previously published results for the HALIP. The U-Pb ages are the first reported on mafic intrusive sheets on Axel Heiberg and Ellesmere Islands, including two coincident age determinations at ~117 Ma, which is an age that previous studies have yet to report. In addition, the discovery of a xenocrystic zircon, within a diabase intrusive, that crystallized from a mafic melt at 184.6 ± 1.8 Ma documents the first reported evidence of Jurassic magmatism in the Sverdrup Basin. These new age results, combined with all modern (post-2000) published ages, detail a >50 Myr duration of magma emplacement that occurred in at least three pulses, around 122 Ma, 95 Ma, and 81 Ma, with gaps of 21 and 6 Myr between pulses. We suggest that the ~122 Ma pulse, which is exclusively tholeiitic, may be primarily plume-generated and should be correlated to the other circum-Arctic tholeiites within the HALIP. However, in the younger magmatism, the contemporaneous production of alkalic and tholeiitic magmas, their spatial distribution, and the periodicity of the last two pulses (~95 and 81 Ma) indicate that alternating modes of edge-driven mantle convection (EDC) might be the primary control on magma genesis. A distal plume could intensify EDC magma production, but the influence of a mantle plume on the ~95 and 81 Ma pulses would be secondary to EDC and thus these younger magmas should not be considered part of the HALIP.

  • Subjects / Keywords
  • Graduation date
    Fall 2016
  • Type of Item
  • Degree
    Master of Science
  • DOI
  • License
    This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.