Integrating Gravity, Magnetic, and Magnetotelluric Data Over Devon Ice Cap, Canadian Arctic, to Investigate the Subglacial Geology

Abstract

The subglacial geology beneath Devon Ice Cap (DIC) is not well understood. An airborne radar study published in 2018 suggested the presence of a hypersaline, subglacial lake beneath DIC where geologic modeling suggested that the source of the brine was an underlying evaporite-rich sedimentary unit. However recent surface based seismic and electromagnetic data have revealed the absence of subglacial water beneath the center of DIC. Continued studies of this subglacial environment require knowledge of the sediments and bedrock beneath the ice. In this study we combine previously published geology and geothermal studies with new surface-based magnetotelluric, airborne gravity and aeromagnetic data, to investigate the subglacial geology under DIC. The integrated results show that beneath the center of DIC there is likely a frozen sedimentary unit (3,000–6,000 Ωm) overlying unfrozen crystalline basement rocks of the Canadian shield (400–2,000 Ωm), at depths of 1,500 m–2,000 m. This agrees with recent studies of ice dynamics on DIC, where glacier velocities are low (<20 m a⁻¹), within the interior regions of DIC implying the ice is dominantly frozen to the bed. Furthermore, relatively low-density sedimentary rocks (∼2.2 g/cm³) are the likely cause of the gravity low (−50 to −70 mgal) observed in the northeast of the ice cap and could have implications for future ice dynamics.