Thermal Regimes and Architecture of the Crust and Upper Mantle 
Inferred from Electrical Conductivity Investigations

Philip E. Wannamaker1, John A. Stodt1, Louise Pellerin1, and Steven L. Olsen2
1University of Utah, Energy & Geoscience Institute, 423 Wakara Way, Ste 300, Salt Lake City, 
UT, 84108, U.S.A., pewanna@egi.utah.edu; 2RedRock Analog Design, 1218 E Emerson Ave., 
Salt Lake City, UT, 84105

Deformation of the continents is heterogeneous and reflects the interplay between force and 
strength. Variations of strength in both brittle and ductile regimes have fluid content and thermal 
contrasts as primary controls. These physical properties and other geochemical fluxes can be 
mapped according to their electrical conductivity using electromagnetic (EM) survey methods, 
specifically magnetotellurics (MT). Constraints on crust/mantle composition and thermal history 
narrow the possible physical states and fluid compositions inferred from imaged geophysical 
structure. Geochemical flow paths implied from geophysical structure can provide insight to 
fluid/magma conduits and ore deposition. Other mechanisms of high conductivity such as 
graphite can be discriminated according to macro-scale textures and external constraints on 
temperature and oxidation state. Experiences in classic tectonic environments world-wide 
including the Antarctic interior demonstrate the potential of deep conductivity surveying. MT 
wavefields have distinct resolving kernels and provide complementary information about 
geochemical and geophysical state of the crust and upper mantle. In the context of the proposed 
Earthscope program, MT stations are to be collocated with the passive seismometers of the 
USArray Bigfoot array with an average station spacing of about 70 km. There should be merit in 
considering a similar deployment style for lithospheric investigations in Antarctica, which would 
have additional payoff for magnetospheric current studies. 
     Two successful deployments of deep conductivity profiling within the Antarctic interior using 
the MT method took place in the 1990's. Novel developments in electrode preamp design were 
required to overcome the high contact impedance (up to 2 M-ohm) at the electrode-firn interface 
for the electric field component. The first profile deployment took place out of the central West 
Antarctica (CWA) camp in concert with seismic and potential field studies to assess the thermal 
regime there in extended West Antarctica. High crustal and upper mantle resistivities were 
imaged which are consistent with extension that is long inactive or amagmatic. The second MT 
experiment took place across the South Pole Station area to assess crustal structure and thermal 
regime in this high-standing area of East Antarctica. A conductive sedimentary section, possibly 
the Beacon Supergroup, immediately under the 3 km ice sheet was inferred, which showed 
pronouced lateral variations in thickness reminiscent of horst-graben structure. The lower crust 
and upper mantle also are of high conductivity, which appears uniform over at least the 54 km 
profile length. This suggests an enhanced thermal regime for the South Pole region that may be 
influenced by plume processes implied in other studies. A strong, crustal-scale conductor 
running parallel to the acquired profile, and normal to the trend of the Trans Antarctic Mountains 
(TAM), also is imaged suggesting a fossil suture zone containing graphitized metasediments or 
perhaps sulfides.