Gravity Survey at the Oates Coast during GANOVEX VIII

Report of the project:

GANOVEX – German Antarctic North Victoria Land Expedition

Logo GANOVEX 8 - German Antarctic North Victoria Land Expedition

Oates Coast Area

A regional gravity survey was conducted during the 1999/2000 Ganovex VIII/ ItaliAntartide XV - Expedition to the Oates Coast Area, Antarctica. 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 RES (Radio Echo Sounding) ice thickness measurements, performed simultaneously during the expedition, could be used for the evaluation of the data.

Topography Ganovex8 Area Source: BGR

Altogether 71 points were approached by helicopter and measured gravimetrically (thick pale dots on the topographic map to the left). The measurements were tied to stations with known absolute gravity values, which had been determined during previous GANOVEX expeditions to the area.

Free Air Anomaly Ganovex8 Area Source: BGR		Bouguer Anomaly Ganovex8 Area Source: BGR
Free Air anomaly map of the Oates Coast area. All existing gravity data from the expeditions GANOVEX IV to VIII (~310 points) have been used to produce this map. Their locations are plotted as small symbols. The prominent glaciers, above all Rennick, are excelled as strong negative anomalies. This is well understandable as they are representing enormous mass deficits due to the much lower densities of the ice (which is not corrected for in Free Air) and probably underlying sediments compared to the density of the bedrock.A remarkable, ample 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 in larger depth of some km while the cause of a very strong, isolated anomaly farther to the west seems to be superficial and characterized by a peak in the sub ice topography.		In the Bouguer anomaly map (above and 3D presentation below) one can observe 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, obviously step like around 158 /159°E and then once more around 155°. An explanation with a changing crustal thickness must still be checked by isostatic models. The large glaciers Rennick and Lillie remain strong negative anomalies also in Bouguer, where the mass deficits due to the lighter ice masses should be cancelled. This can be explained only partly with lighter sediments at the glaciers’ bases. The coincidence of the strong minimum east of the middle Lillie glacier with a large intrusive body indicated as belonging to the Admiralty Igneous Complex in the geological map is striking. It obviously possesses a reduced density, but increased magnetic susceptibility. As a strong positive anomaly, however, rises the block of the Bowers Mountains between the two glaciers mentioned.

Magnetic and Gravity Model Source: BGR		Bouguer Anomaly Ganovex8 Area Source: BGR