International Geologiical Congress - Oslo 2008

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AAN-01 Antarctic geodynamic evolution and paleogeography

 

Uncovering the West Antarctic Rift System with recent aerogeophysical data over Ellsworth Land

 

Fausto Ferraccioli, British Antarctic Survey (United Kingdom)
Tom Jordan, British Antarctic Survey (United Kingdom)
Jack Holt, University of Texas at Austin (United States)
Don Blankenship, University of Texas at Austin (United States)
Theresa Diehl, University of Texas at Austin (United States)
David Vaughan, British Antarctic Survey (United Kingdom)
Hugh Corr, British Antarctic Survey (United Kingdom)
 

 

The West Antarctic Rift System (WARS) is one of the major geodynamic elements of the Antarctic plate. The WARS is often envisaged as extending for over 3000 km from the Ross Sea region to the base of the Antarctic Peninsula, and is flanked, on the East Antarctic side, by the impressive Transantarctic Mountains. The crustal structure and tectonic evolution of the Ross Sea segment of the WARS is quite well-understood due to extensive seismic and potential field investigations, coupled with drilling. Since the 90's significant progress has been made in tracing the WARS beneath the central part of the West Antarctic Ice Sheet (WAIS), due to a combination of geophysical investigations including seismic refraction, magnetotelluric, seismological and aerogeophysical observations. The Amundsen Sea Embayment (ASE) sector of the WARS, has however remained so far poorly known due to the lack of comparable geophysical exploration. Yet, this is a key region to investigate geological boundary conditions for the WAIS, because this part of the WAIS is highly dynamic today, and is potentially unstable.

We present some results from a major collaborative effort between the British Antarctic Survey and the University of Texas to explore the ASE region. Over 100,000 line-km of new aerogeophysical data, including airborne radar, aeromagnetic and airborne gravity were collected as part of this collaboration. The airborne radar datasets provide a significantly improved picture of the subglacial topography, including basins, such as the prominent Byrd Subglacial Basin, the Bentley Subglacial Trench, and the trench beneath Pine Island Glacier. The highlands areas, including the Hudson Mountains, the Sinuous Ridge, the Ellsworth Mountains, and volcanoes of the Marie Byrd block are also imaged.

The new potential field data uncovers the WARS over Ellsworth Land. New aeromagnetic images, including vertical derivative, tilt derivative, maximum horizontal gradient of pseudo-gravity, and Euler Deconvolution maps, trace tectonic structures associated with several rift basins. These basins were highly magmatic in the Cenozoic west of 97W, in contrast to a much more weakly magmatic segment of the rift further to the east. Major crustal boundaries between the Marie Byrd Land block, the WARS and the Ellsworth Mountains rift flank are now imaged.

Modelling of airborne gravity data reveals both broad and narrow regions of thinned continental crust and allows an estimation of lithospheric rigidities to be derived. We propose a multi-stage rifting model for this part of the WARS and suggest that rifting and coupled magmatic processes induced elevated heat-flow beneath this sector of the WAIS. Subglacial sedimentary basins are also revealed by our aeromagnetic and isostatic residual gravity data. These basins provide a geological template for enhanced glacial flow, in particular over the Byrd Subglacial Basin region.

 

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