Gravity Survey at the Oates Coast Area, East Antarctica, during the Joint German - Italian Expedition 1999/2000

G. Reitmayr¹, W. Korth², G. Caneva³ & F. Ferraccioli^3#

¹Bundesanstalt für Geowissenschaften und Rohstoffe, Stilleweg 2, 30655 Hannover - Germany
²Technische Fachhochschule Berlin, FB III, Luxemburger Str. 10, 13353 Berlin - Germany
³Dipartimento Territorio e Risorse, Sez.Geofisica, Università di Genova,  V.le Benedetto XV 5, 16132 Genova – Italy
^#now at: British Antarctic Survey, High Cross, Madingley Road, Cambridge CB3 0ET – United Kingdom

Received 8 November 2002; accepted in revised form 19 September 2003
 

Abstract - A regional gravimetric survey was conducted during the joint German-Italian (GANOVEX VIII – ItaliAntartide XV) expedition to the Oates Coast Area, Antarctica, in 1999/2000. Besides the actual determination of the force of gravity, precise values for the coordinates of each of the gravity stations were determined by differential GPS (Global Positioning System) measurements. The results of airborne ice thickness measurements using the RES (Radio Echo Sounding) method, which were conducted during the expedition as well, were used for the evaluation of the gravity data. Altogether 71 points were approached by helicopter and measured gravimetrically. The measurements were tied to stations with known absolute gravity values, which had been determined during previous GANOVEX expeditions to the area.
Besides the conventional corrections, the thickness of the ice was taken into account. The geographic coordinates and the calculated gravity values are given in tables. These results were added to the already existing data of former GANOVEX expeditions and finally the Free Air and Bouguer anomalies maps were generated (Figs. 2 & 3).
The Bouguer map shows the usual increase in gravity towards the coast due to the thinning of the earth’s crust. In addition, gravity increases clearly along the coast towards the west, sharply around 159/158°E and again, but more subdued around 155°. An explanation for the inferred changing crustal thickness associated with the gravity changes must still be consistent with isostatic models. The large Rennick Glacier and Lillie Glacier are associated with strong negative Bouguer anomalies, where the mass deficits due to the lighter ice masses should be canceled. This can be explained only partly by lighter sediments at the glaciers’ bases. The strong minimum east of the middle Lillie glacier coincides with a large intrusive body of lower density, but increased magnetic susceptibility. A strong positive anomaly, however, coincides the block of the Bowers Mountains that lies between the two glaciers mentioned earlier.
A distinct, large anomaly over the Matusevich glacier, which was discovered during the aeromagnetic survey, was also examined gravimetrically in more detail. The main anomaly has its cause probably at depth of some kms while the cause of a very strong, isolated anomaly farther to the west seems to be more superficial and characterized by a peak in the sub ice topography.


 

*Corresponding author (reitmayr@bgr.de)