Elevated sub-ice thermal flux mapping using magnetotellurics considering the U.S. Great Basin as an analog

Phil Wannamaker1, Graham Hill2, John Stodt3, Virginie Maris1, Yasuo Ogawa4, Kate Selway5

1University Of Utah/Energy & Geoscience Institute, Salt Lake City, United States, 2University of Canterbury, Gateway Antarctica, Christchurch, New Zealand, 3Numeric Resources LLC, Salt Lake City, United States, 4Tokyo Institute of Technology, Volcanic Fluid Research Center, Tokyo, Japan, 5Macquarie University, Earth and Planetary Sciences, Sydney, Australia

Bedrock heat flux of Marie Byrd Land and much of the West Antarctic Ice Sheet has been conjectured to significantly exceed the global average of ~85 mWm-2, e.g. 100-200 mWm-2 or more, with implications for ice sheet stability. Advective affects may complicate shallow heat flow measurements and so deeper-seeking geophysical techniques may have a greater role in estimating crustal thermal state. The actively extensional U.S. Great Basin province has been considered a partial tectonic analog to West Antarctica although extension rates in the latter are generally much less. The magnetotelluric (MT) geophysical method has been widely applied in the Great Basin to understand province-scale down to geothermal prospect-scale thermal structure using electrical resistivity as a proxy. There, widespread zones of crustal magmatic underplating and fluid release over broad areas correlate with surface heat flow and volcanic occurrences, with depth to top of low resistivity approximating an isotherm. Spatially concentrated low-resistivity upwellings imply local upward convection and commonly connect into known high-temperature geothermal resource areas exhibiting magmatic-origin fluid fluxes. This has been the basis of significant recent research into greenfield reconnaissance for blind, high-enthalpy geothermal systems. Similar low-resistivity structures correlating with analogous magmatic and convective processes in West Antarctica have been revealed in recently published MT field campaigning there. Appropriately designed surveys have potential to constrain the magnitude and spatial variation of crustal geotherms including local hotter zones that could provide particularly high thermal input to the overlying ice sheets.

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