DORMANT STATE OF RIFTING BELOW THE BYRD SUBGLACIAL BASIN, WEST ANTARCTICA, IMPLIED BY MAGNETOTELLURIC (MT) PROFILING

During the 1994-1995 austral summer field season, we collected twelve, high-quality MT soundings over the Byrd Subglacial Basin of central W est Antarctica (82 degrees 36' S lat., 118 degrees 14' W long. approx. ) in the period range 0.01 s to 400 s. Ten equispaced sites in a 54 km profile cross regional aeromagnetic trends and complement seismic ref lection and refraction results collected by others. Our purposes were to prove such measurements were feasible over the 2 km thick interior ice sheet, and to show from deep electrical resistivity whether the By rd Basin comprises an active rift environment. The difficult acquisiti on of electric field data on ice was overcome using a custom electrome ter system, with preamplifiers located at the electrode sites to buffe r the high contact impedances of the ice as close to the source as pos sible. Two-dimensional modeling of the profile shows that resistivity of the deep crust anti upper mantle is about 2000-3000 ohm-m to 100 la n depth or more. This is much higher than observed in active extension al regimes, suggesting that the current state of rifting, at least in this part of central West Antarctica, is dormant.