J. Kienle, T. F. Redfield* and A. M. Goodliffe (Geophysical Institute, University of Alaska Fairbanks, Fairbanks, AK 99775-0800 USA)
* Currently at Dept. Geology, Arizona State University, Tempe, AZ., 85287-1404, USA
During 1988/89, a gravity study of the Transantarctic Mountains was conducted by the University of Alaska as part of the fifth German Antarctic North Victoria Land Expedition (GANOVEX V). The purpose of the expedition was to study the tectonics and origin of the Transantarctic Mountains in North Victoria Land. To this end, the geophysics group acquired 120 gravity data points in the Mt. Melbourne Quadrangle and in the lower Rennick Glacier region. All measurements were placed on bedrock, and the majority were located with the Global Positioning satellite navigation System (GPS). All stations were fully terrain corrected. In addition, corrections for the gravitational effects of glacier ice were estimated at each station from two- and three-dimensional gravity models of plausible ice-rock interfaces.
The completed Bouguer anomaly gravity map of the Mt. Melbourne Quadrangle reveals a strong negative gravity gradient of about 2 mGal/km from Terra Nova Bay towards the Transantarctic Mountains. The gravity field changes from about +20 mGal near the coast to approximately -150 mGal at the crest of the Transantarctic Mountains. The Bouguer gravity map of the Rennick Glacier area and Oates Coast between the Rennick and Matusevich Glaciers shows a change from the pronounced gravity gradient associated with the Transantarctic Mountain front. Long-wavelength, complicated regional gravity patterns, including two pronounced gravity lows, lie over the coast and the northern end of the USARP Mountains.
We speculate that the transition from a well-behaved regional Bouguer gravity gradient within the Mt. Melbourne Quadrangle to the less ordered patterns of the north coast is related to the presence of the Rennick Graben. The Graben might represent a failed rift zone between Antarctica and Australia. Alternatively, the lack of an obvious regional gravity gradient at the north coast might be associated with fundamental deep crustal or mantle mass deficiencies within the Rennick Graben at the northern end of the Ross Sea rifting zone. More data should be gathered along the coast and between the two study sites to improve resolution and interpretation.